^0rtl|  Carolina  ^tate 
^niUersttg 


^l{is  book  itiae  preatnteb  bg 


Elizabeth  Stone 


Digitized  by  tine  Internet  Archive 

in  2009  with  funding  from 

NCSU  Libraries 


http://www.archive.org/details/textbookofveterOOsiss 


A  TEXT-BOOK 


of 


VETERINARY  ANATOMY 


SEPTIMUS   SISSON,  S.B.,  V.S. 

PROFESSOR    OF    COMPAPATIVK     ANATOAW     IN    OHRi    STATE     UMVEPSITV.    COLUiWBUS.   OHIO 
MEMBEl'    OF    THE    AMERICAN     AS5(.)C1AT10N    OF    ANATOMISTS 


WITH   588   ILLUSTRATIONS 
MANY  IN  COLORS 


I'HII.ADEIJ'HIA    AND.  LONDON 

W.  B.  SAUNDERS   COMPANY 

1910 


Coi'YRionr,  1910,  by  W.  B.  Saunders  Co.mpanv 


KATHERINE  OLDHAM  SISSON 

IN    GRATEFUL    RECOGXITIOX    OF    COXSFANT 

INSPIRATION    AND    ENCOURAGEMENT 

THIS    BOOK    IS    DEDICATED 

Bv  THE  Author 


PREFACE 

The  lack  of  a  modern  and  well-illustrated  book  on  the  structure  of  the  jjrinci- 
pal  domestic  animals  has  been  acutely  felt  for  a  long  time  Ijy  teachers,  students, 
and  practitioners  of  veterinary  medicine.  The  work  here  offered  is  the  expression 
of  a  desire  to  close  this  gaj)  in  our  literature. 

The  study  of  frozen  sections  and  of  material  which  has  l)een  hardened  by  intra- 
vascular injection  of  formalin  has  profoundly  modified  our  views  concerning  the 
natural  shajie  of  many  of  the  viscera  and  has  rendered  possible  much  greater  pre- 
cision in  topographic  statements.  The  experience  of  the  author  during  the  last 
ten  years,  in  which  almost  all  of  the  material  used  for  dissection  and  for  frozen 
sections  in  the  anatomical  laboratory  of  this  University  has  been  hardened  with 
formalin,  has  demonstrated  that  many  of  the  current  descriptions  of  the  organs  in 
animals  contain  the  same  sort  of  errors  as  those  which  prevailed  in  regard  to  similar 
structures  in  man  previous  to  the  adoption  of  modern  methods  of  preparation. 

While  the  method  of  treatment  of  the  subject  is  essentially  systematic,  topog- 
raphy is  not  by  any  means  neglected  either  in  text  or  illustrations;  it  is  hoped  that, 
this  will  render  the  book  of  value  to  the  student  in  his  clinical  courses  and  to 
the  practitioner.  Embryological  and  histological  data  have  been  almost  entirely 
excluded,  since  it  was  desired  to  offer  a  text-book  of  convenient  size  for  the  student 
and  a  work  of  ready  reference  for  the  ])ractitioner.  It  is  believed  that  the  use  of 
black  tjTie  for  the  names  of  important  structures  and  of  small  print  for  certain 
details  or  matter  of  secondary  importance  will  prove  useful  in  this  respect. 

Veterinary  anatomical  nomenclature  is  at  present  quite  chaotic  in  English- 
speaking  countries.  In  this  work  an  attempt  is  made  to  eliminate  some  terms 
which  do  not  appear  to  the  author  to  fulfil  any  useful  purpose,  and  others  which  are 
clearly  erroneous  or  otherwise  undesirable.  In  manj^  cases  the  terms  agreed  upon 
by  the  Congresses  at  Baden  and  Stuttgart  are  adopted  either  in  the  original  Latin 
or  in  anglicized  form;  otherwise  these  terms  are  added  in  parenthesis.  The 
author  favors  the  substantial  adoption  of  this  terminology,  l)ut  considered  it 
desirable  to  offer  a  sort  of  transitional  stage  at  present. 

The  original  illustrations  are  chiefly  reprodvictions  of  photographs,  many  of 
wiiich  were  taken  by  Air.  F.  H.  Haskett.  The  preparation  of  the  pictures  for 
reproduction  was  carried  out  by  Messrs.  J.  V.  Alteneder  and  W.  J.  Xorris.  The 
author  takes  pleasure  in  expressing  his  appreciation  of  the  care  and  skill  exercised 
by  these  gentlemen  in  this  often  difficult  task. 

The  author  is  under  great  obligation  to  Professors  Ellenberger  and  Baum  in 
Dresden,  to  Professor  Schmultz  in  Berlin,  and  to  their  publishers  for  permission  to 
use  or  to  copy  figures  from  their  most  excellent  works.  Their  generositj'  in  tliis 
matter  has  made  it  possil)le  to  supply  this  text  with  a  larger  number  of  high-class 
illustrations  than  is  to  be  found  in  anj'  other.  A  few  figures  have  Ijeen  taken  from 
other  sources,  and  proper  credit  has  Ijeen  given  in  each  case. 

For  checking  over  certain  data  and  for  assistance  in  the  correction  of  the  ])roofs 
the  author  is  much  indebted  to  his  associate,  Dr.  F.  B.  Hadley. 

The  author  desires  to  express  his  high  appreciation  of  the  determination  and 
constant  effort  of  the  jjublishers  to  do  all  in  their  power  to  render  the  book  worthy 
of  favorable  reception  by  the  profession  for  whom  it  is  intended. 

Ohio  State  University,  Columbus,  Ohio  SEPTIMUS  SiSSOX. 

September,  1910 


CONTENTS 


IXTKODUCTIOX 

OSTEOLOGY  page 

The  Skeleton 19 

Structure  of  Bones 20 

Development  and  Growth  of  Bone 22 

Composition  ami  Physical  Properties  of  r()n(              : 23 

Descriptive  Terms 23 

The  Vertebral  Column 24 

The  Rihs  and  Costal  Cartilages 25 

Costal  Cartilages '21) 

The  Sternum 26 

The  Thorax 27 

The  Skull 27 

Bones  of  the  Thoracic  Limb 27 

Bones  of  the  Pelvic  Limb 29 

Skeleton  of  the  Horse 31 

Vertebral  Column 31 

Ribs 43 

Sternum 4.5 

Bones  of  the  Skull 47 

Cranium 47 

Face 57 

The  Skull  as  a  Whole 65 

The  Cranial  Cavity 69 

The  Xasal  Cavity 71 

The  Paranasal  Sinuses 72 

Bones  of  the  Thoracic  Limb 74 

Bones  of  the  Pelvic  Limb "2 

Ski:leton  of  the  Ox 112 

Vertebral  Column 112 

Ribs 114 

Sternum 115 

Bones  of  the  Skull 115 

The  Skull  as  a  Whole 123 

Bones  of  the  Thoracic  Limb 1-7 

Bones  of  the  Pelvic  Limb I'^l 

Skeleton  of  the  Pig 


136 


138 
139 
139 


Vertebral  Cohmin 1''6 

Ribs 

Sternum 

Bones  of  the  Skull 

The  Skull  as  a  Whole 1*4 

Bones  of  the  Thoracic  Limb 146 

Bones  of  the  Pelvic  Limb 148 

Skeleton  of  the  Dou '  _ 

Vertebral  Column ^^^ 


Rib: 


153 


12 


PAGE 

Sternum ^^^ 

Bones  of  the  Skull '-^3 

The  Skull  as  a  Whole ^^^ 

Hones  of  the  Thoracic  Liml).  .  '"-' 

Hones  of  the  Pelvic  Liml) "'•'' 


AKTHROLOCn' 


SVNARTHIJOSKS. 


lti'.» 


DlAHTHKOSES '  ~" 

AmI'IIIAHTHHOSES '  '  - 

AuTicri.ATioNs  OP  tub;  House '  '- 

Joints  and  Liframents  of  the  Vertebra- '  ''- 
Atlanto-o(•(•ipital  Articulation '''■ 

Costo-vertebral  Articulations I '  ' 

C'osto-choiKlral  Articulations 1 '  ^ 

f 'hondro-sternal  Articulations .  ^  '^ 

Sternal  Joints  ami  Ligament;  .  ''"^ 

Articulations  of  the  Skull '"•> 

Articulations  of  the  Thoracic  Limb.    .  1^" 

Articulations  of  the  Pelvic  Limb !'•" 

AiiTiciLATiONs  OK  TiiK  Ox.  Pk;.  AND  Doii  -D:! 


THE  MUSCrLAK  SYSTEM— MYOLOCY 

TnK  Mfsci.Es  AND  Accessory  Strt'ctires  I'll 

FaSCI.K    AND    MlSCI.ES    OF    THE    HORSE '-'13 

Panniculus  carnosus 213 

Fascia"  and  Muscles  of  the  Head -13 

Kascia'  and  Muscles  of  the  Xcck 224 

Fascia'  and  Muscles  of  the  Hack  and  Loins  23") 

Fascia'  and  Muscles  of  the  Tail 23S 

Muscles  of  the  Thorax 240 

Muscles  of  the  Abdomen 24."i 

Muscles  of  the  Thoracic  Limb 2.")() 

Fascia-  and  Muscles  of  the  Pelvic  Limb  27:i 

Muscles  ok  the  Ox.  2(t.") 

Muscles  ok  the  Pig  311 

Mi'SCLES   OK   THE    D()(i  31S 


1)I( 

SPLA\(HN()1>()GY- 

FESTIVE    SVSTE.M    OF    THE    IIoRSE 

The  Mouth 

The  Tonjiue 

The  Teeth 

-TH]'; 

dk; 

I'lSTHE 

SYSTh 

:m 

330 
330 

335 

33S 

The  Salivary  Cdands 

The  Pharvnx 

34ti 
34S 

The  O'".sophaf;us 

The  .\l)doiiiinal  Cavity.  . 
The  Peritoneum. . . 
The  Pelvic  Cavity 

The  Stomach 

The  Snii.ll  Intestine 
The  Large  hitcsliiK 
The   Pani'ieas 
The  Liver. 
The  Spleen . 
The  Peritoneum 

3o0 
352 
353 

354 

357 

3()0 
3()3 
371 
373 
377 
379 

CONTEXTS  13 

Digestive  System  or  the  Ox 3,S2 

Digestive  System  of  the  Sheep 40,-, 

Digestive  System  of  the  Pig 410 

Digestive  System  of  the  Dog 423 

THE  RESPIRATOKV  SYSTEM 

Respikatory  System  of  the  Horse 436 

The  Nasal  Cavity.  436 

Tlio  Larynx 44O 

The  Trachea .  448 

Tlie  Bronchi 4.50 

The  Thoracic  Cavity 4.i0 

Tlie  Pleura 451 

The  Lungs 4.'):j 

The  Thyroid  Gland  of  the  Horse 457 

The  Thymts  of  the  Horse 458 

Respiratory  System  of  the  Ox 458 

Respiratory"  System  of  the  Pig  . .                                     464 

Respiratory-  Sy'stem  of  the  Dog                                        466 


THE  uri)(;exital  system 

L'rixary  Organs  of  the  Horse 469 

The  Kidneys 469 

The  Ureters 47") 

The  Urinary  Bladch'r  47o 

The  Adrenal  Bodies 477 

Urinary  Organs  of  the  Ox  47s 

Urinary  Organs  of  the  Pic.  4S1 

Urinary  Organs  of  the  Dog  48o 


THE  MALE  GENITAL  ORGANS 

^L\LE  Genital  Organs  of  the  Horse....  48o 

The  Testicles 485 

The  Scrotum 487 

The  ^■as  Deferens.  488 

The  Spermatic  Conl  489 

The  Tunica  Yaginali.^  489 

Descent  of  the  Testicles.  .  490 

The  YesicuUf  Seminales . .  491 

The  Prostate 493 

The  Uterds  Masculinus 493 

The  Bulbo-urethral  Glands  493 

Tlie  Penis 494 

The  Prepuce 496 

Male  Genital  Organs  of  the  Ox  -iOO 

Male  Genital  Organs  of  the  Pk;  ■)04 

Male  Genital  Organs  of  the  Do(;  506 


THE  FEMALE  GENITAL  ORGANS 

Genital  Organs  of  the  Mai;e 508 

The  Ovaries ''08 

The  Uterine  or  Fallopian  Tubes -'H 

The  Uterus 'H 

The  Vagina -i  1 4 


14  CONTENTS 

PtGE 

The  Vulva 514 

Tin-  I'lrlhra 515 

The  Mammary  Glaiuls 516 

Genital  Organs  of  the  Cow 517 

Genital  Okgans  of  the  Sow 521 

Genital  Ougans  of  the  Bitch 522 


ANGIOLOGY 

The  Organs  of  CiRriLATioN 524 

Ulood-vascvlar  System  of  the  Horse 525 

The  Pericardium 525 

The  Heart 526 

The  Pulmonary  Artery 535 

The  Systemic  Arteries 535 

The  Coronary  Arteries 537 

The  BracliiocephaHc  Trunk  or  Anterior  Aorta 537 

Arteries  of  the  Thoracic  Limb 556 

Branches  of  the  Thoracic  Aorta 565 

Branches  of  the  Abdominal  Aorta 566 

Arteries  of  the  Pelvic  Linib  578 

The  Veins 585 

The  Pulmonary  \'eins 585 

The  Systemic  Veins 585 

The  Anterior  Vena  Cava  and  its  Tributaries 586 

The  Posterior  Vena  Ca\a  and  its  Tributaries 595 

The  Lymphatic  System 599 

Lymphatic  System  of  the  Horse tiOO 

The  Lymph  (Jlands  and  Vessels  of  the  Head  and  Neck 1501 

The  Lymph  Glanils  and  Vessels  of  the  Thorax 603 

The  Lymph  Glands  and  Vessels  of  the  Abdomen  and  Pelvis 604 

The  Lymph  Glands  an<l  Vessels  of  the  Thoracic  Limb 605 

The  Lymph  tilands  and  Vessels  of  the  Pelvic  Limb 606 

The  Foetal  Circulation 606 

Blood-vascclar  System  of  the  Ox 608 

The  Pericardium  and  Heart 608 

The  Arteries (iOO 

The  \'eins 621 

Lymphatic  System  of  the  Ox (i23 

ClRCl'LATORY    SvSTEM    OF  THE    PlG 626 

The  Pericardium  and  Heart 626 

The  Arteries (327 

The  Veins 630 

Lymphatic  System  of  the  Pig. .  .  630 

CiRciLATOUY  System  of  the  Dog.  1332 

The  Pericardium  and  Heart (532 

The  Arteries 633 

The  Veins (341 

Lymphatic  System  of  the  Dog.  .  (543 


XKITIOLOGY.— THE  NERVOUS  SYSTEiM 

General  Considerations ^\_^_^ 

Nervous  System  of  the  House (j4j^ 

The  Spinal  Cord ....  g4g 

The  Brain 

The  Cranial  Xerves 


652 

67(i 


The  Spinal  Nerves. .  (31).) 


CONTENTS  15 

PAGE 

Sympathetic  Nervous  System  of  the  Horse 710 

Nervous  System  of  the  Ox 715 

Nervous  System  of  the  Pig 720 

Nervous  System  of  the  Dog 724 


.ESTHESIOLOGY 

The  Sense  Organs  and  Skin  of  the  Horse 734 

The  Eye 734 

Tlie  Ear 747 

Tho  Skin Tlil 

The  Olfactory  and  Gustatory  Apparatus 772 

The  Sense  Organs  and  Skin  of  the  Ox 772 

The  Sense  Organs  and  Integument  of  the  Pig 777 

The  Sense  Organs  and  Integument  of  the  Dog 779 


In-dex 783 


VETERINARY  ANATOMY 


INTRODUCTION 

Anatomy  is  the  branch  of  biological  science  which  deals  with  the  form  and 
structure  of  organisms,  both  animal  and  vegetal.  It  is  therefore  in  close  correlation 
with  physiology,  which  treats  of  the  functions  of  the  body. 

Etymologically  the  word  "anatomy"  signifies  the  cutting  apart  or  disassociat- 
ing of  parts  of  the  body.  In  the  earlier  phases  of  its  development  anatomy  was 
necessarily  a  purely  descriptive  science,  based  on  such  observations  as  were  possible 
with  the  unaided  eye  and  simple  dissecting  instruments — the  .scalpel,  forceps,  and 
the  like.  At  this  time,  therefore,  the  term  adequately  expressed  the  nature  of  the 
subject.  But  as  the  scope  of  the  science  extended  and  the  body  of  anatomical 
knowledge  grew,  subdivisions  became  necessary  and  new  terms  were  introduced  to 
designate  special  fields  and  methods  of  work.  With  the  introduction  of  the  mi- 
croscope and  its  accessories  it  became  possilile  to  study  the  finer  details  of  structure 
and  minute  organisms  hitherto  unknown,  and  this  field  of  inquiry  rapidly  developed 
into  the  science  of  microscopic  anatomy  or  histology  as  conventionally  distinguished 
from  gross  or  macroscopic  anatomy.  In  the  same  way  the  study  of  the  changes 
which  organisms  undergo  during  their  development  soon  attained  sufficient  im- 
portance to  be  regarded  on  practical  grounds  as  a  separate  branch  known  as 
embryology. 

This  term  is  usually  limited  in  its  application  to  the  earher  phases  of  development  during 
which  the  ti.ssues  and  organs  are  formed.  The  term  ontogeny  is  used  to  designate  the  entire 
development  of  the  individual.  The  ancestral  history  or  phylogeny  of  the  species  is  constituted 
by  the  evolutionary  changes  which  it  has  undergone  as  disclosed  by  the  geological  record. 

Comparative  anatomy  is  the  description  and  comparison  of  the  structure  of 
animals,  and  forms  the  basis  for  their  classification.  By  this  means — including 
extinct  forms  in  the  scope  of  inquiry — it  has  been  possiljle  to  show  the  genetic 
relationship  of  various  groups  of  animals  and  to  elucidate  the  significance  of  many 
facts  of  structure  which  are  otherwise  quite  obscure.  The  deductions  concerning 
the  general  laws  of  form  and  structure  derived  from  comparative  anatomical 
studies  constitute  the  science  of  morphology  or  philosophical  anatomy.  The 
morphologist,  however,  deals  only  ^vith  such  anatomical  details  as  are  necessary 
to  form  a  basis  for  his  generalizations.  The  anatomical  knowledge  required  in  the 
practice  of  medicine  and  surgery  is  evidently  of  a  different  character  and  must 
include  many  details  which  are  of  no  particular  interest  to  the  morphologist. 

Special  anatomy  is  the  description  of  the  structure  of  a  single  type  or  species, 
e.  g.,  anthropotomy,  hippotomy. 

Veterinary  anatomy  is  the  branch  which  deals  with  the  form  and  structure  of 
the  principal  domesticated  animals.  It  is  usuallj'  pursued  with  regard  to  pro- 
fessional requirements,  and  is  therefore  largely  descriptive  in  character.  As  a 
matter  of  convenience  the  horse  is  generally  selected  as  the  tj'pe  to  be  studied  in 
detail  and  to  form  a  basis  for  comparison  of  the  more  essential  differential  characters 
in  the  other  animals. 

Two  chief  methods  of  stud}-  are  employed — the  systematic  and  the  topo- 
graphic. In  the  former  the  body  is  regarded  as  consisting  of  sjstems  of  organs  or 
2  17 


18  VETERINARY    ANATOMY 

apparatus  which  are  similar  in  origin  and  structure  and  are  associated  in  the  per- 
formance of  certain  functions.     The  divisions  of  systematic  anatomy  are: 

1.  Osteology 

2.  Arthrology 

3.  Myology 

4.  Splanchnology 

(1)  Digestive  System 

(2)  Respiratory  System 

(3)  Urogenital  System 

(a)  Urinary  Organs 
(6)  Genital  Organs 

5.  Angiology 

6.  Neurology 

7.  .fcthesiology 

(1)  Sense  Organs 

(2)  Common  Integument. 

The  term  topographic  anatomy  designates  the  methods  by  which  the  relative 
positions  of  the  various  jiarts  of  tiie  body  are  accurately  determined.  It  presup- 
poses a  fair  working  knowledge  of  sj'stematic  anatomy. 

Descriptive  Terms. — In  order  to  indicate  precisely  the  position  and  direction 
of  parts  of  the  body,  certain  descriptive  terms  are  employed,  and  must  be  under- 
stood at  the  outset.  In  the  explanation  of  these  terms  it  is  assumed  here  that 
they  apply  to  a  quadruped  such  as  the  horse  in  the  ordinary  standing  position. 
The  surface  directed  toward  the  plane  of  support  (the  ground)  is  termed  inferior 
or  ventral,  and  the  opposite  surface  is  superior  or  dorsal;  the  relations  of  parts  in 
this  direction  are  named  accordingly.  The  longitudinal  median  plane  divides  the 
body  into  similar  halves.  A  structure  or  surface  which  is  nearer  than  another  to 
the  median  plane  is  internal  or  medial  to  it,  and  an  object  or  surface  which  is  further 
than  another  from  the  median  plane  is  external  or  lateral  to  it.  Planes  parallel 
to  the  median  plane  are  sagittal.  Transverse  or  segmental  jilanes  cut  the  long  axis 
of  the  body  perpendicular  to  the  median  plane,  or  an  t)rgan  or  limb  at  right  angles 
to  its  long  axis.  A  frontal  plane  is  perpendicular  to  the  median  and  transverse 
planes.  The  head  end  of  the  body  is  termed  anterior,  cephalic,  or  cranial ;  and  the 
tail  cm!  posterior  or  caudal;  relations  of  structures  with  regard  to  the  longitudinal 
axis  of  the  body  are  designated  accorilingly.  Certain  terms  are  used  in  a  special 
sense  as  applied  to  the  limbs.  Proximal  and  distal  express  relative  distances  of 
parts  from  the  axis  of  the  body.  The  anterior  face  of  the  thoracic  limb  from  the 
elbow  downward  is  also  termed  dorsal,  and  the  opposite  face  volar.  In  the  corre- 
sponding part  of  the  pelvic  limb  the  terms  are  dorsal  and  plantar  respectively.  In 
the  same  regions  radial  and  ulnar  (thoracic  limb),  tibial  and  fibular  (pelvic  limb), 
may  be  used  to  designate  that  side  of  the  extremity  on  which  the  corresponding 
bone  is  situated;  they  are  therefore  equivalent  respectively  to  internal  or  medial 
and  external  or  lateral  in  the  animals  with  which  we  are  concerned. 

It  is  evifirntly  advantapeous  to  employ  terms  which  are  as  far  as  possible  independent  of 
the  position  of  the  body  in  space  and  capable  of  general  application,  c.  g.,  dorsal,  ventral,  proximal, 
etc.  It  is  also  d('siral)le  that  the  terms  internal  and  external  he  reserved  to  indicate  relations  of 
depth  in  ca\-ities  or  organs,  and  medial  and  lateral  to  designate  relations  to  the  median  plane. 
Such  terms  are  coming  into  more  extensi\e  use  in  human  and  veterinary  anatomy,  but  the  older 
nomenclature  is  very  firmly  established  and  cannot  well  be  discarded  at  once  and  entirely. 


OSTEOLOGY 

THE  SKELETON 
The  term  skeleton  is  applietl  to  the  framework  of  hard  structures  which  sup- 
ports and  protects  the  soft  tissues  of  animals.     In  the  descriptive  anatomy  of  the 
higher  animals  it  is  usually  restricted  to  the  bones  and  cartilages,  although  the 
ligaments  which  bind  these  together  might  well  be  included. 

In  zoology  the  term  is  used  in  a  much  more  comprehensive  sense,  and  includes  all  the  harder 
supporting  and  protecting  structures.  When  the  latter  are  situated  externally,  they  form  an 
exoskeleton,  derived  from  the  ectoderm.  Examples  of  this  are  the  shells  and  chitinous  coverings 
of  many  invertebrates,  the  scales  of  fishes,  the  shields  of  turtles,  and  the  feathers,  hair,  and  hoofs 
of  the  higher  vertebrates.  The  endoskeleton  (with  which  we  have  to  deal  at  present)  is  embedded 
in  the  soft  tissues.  It  is  derived  chiefly  from  the  mesoderm,  but  includes  the  notochord  or  primi- 
tive axial  skeleton,  which  is  of  entodermal  origin. 

The  skeleton  may  be  divided  primarily  into  three  parts:  (1)  axial;  (2)  appen- 
dicular;  (3)  splanchnic. 

The  axial  skeleton  compri.ses  the  vertebral  column,  ribs,  .sternum,  and  skull. 

The  appendicular  skeleton  includes  the  bones  of  the  limbs. 

The  splanchnic  skeleton  consists  of  certain  bones  developed  in  the  substance 
of  some  of  the  viscera  or  soft  organs,  e.  g..  the  os  penis  of  the  dog  and  the  os  cordis  of 
the  ox. 

The  number  of  the  bones  of  the  skeleton  of  an  animal  varies  with  age,  owing 
to  the  fusion  during  gro^i^h  of  skeletal  elements  which  are  separate  m  the  foetus 
or  the  young  subject.  Even  in  adults  of  the  same  species  numerical  variations 
occiu-,  e.  g.,  the  tarsus  of  the  horse  may  consist  of  six  or  seven  bones,  and  the  carpus 
of  seven  or  eight ;  in  all  the  domestic  mammals  the  nimiber  of  cocc\-geal  vertebrae 
varies  considerably. 

The  bones  are  commonly  divided  into  four  classes  according  to  their  shape 
and  function. 

(1)  Long  bones  (Ossa  longa)  are  typically  of  elongated  cylindrical  form  with 
enlarged  extremities.  They  occur  in  the  Umbs,  where  they  act  as  supporting 
columns  and  as  levers.  The  cylindrical  part,  termed  the  shaft  or  body  (Corpus), 
is  tubular,  and  incloses  the  medullary  cavity,  which  contains  the  medulla  or 
marrow. 

(2)  Flat  bones  lOssa  plana)  arc  expanded  in  two  directions.  They  furnish 
sufficient  area  for  the  attachment  of  muscles  and  afford  protection  to  the  organs 
which  they  cover. 

(3)  Short  bones  (Ossa  brevia),  such  as  those  of  the  carpus  and  tarsus,  present 
somewhat  similar  dimensions  in  length,  breadth,  and  thickness.  Their  chief  func- 
tion appears  to  be  that  of  diffusing  concu.ssion.  Sesamoid  bones,  which  are 
developed  in  the  capsules  of  some  joints  or  in  tendons,  may  be  included  in  this 
group.     They  diminish  friction  or  change  the  direction  of  tendons. 

(4)  Irregular  bones.  This  group  would  include  bones  of  irregular  shape, 
such  as  the  vertebrae  and  the  bones  of  the  cranial  base;  they  are  median  and 
unpaired.  Their  functions  are  various  and  not  so  clearh'  specialized  as  those  of 
the  preceding  classes. 

This  classification  is  not  entirely  satisfactory;  some  bones,  e.  3.,  the  ribs,  are  not  clearly 
provided  for,  and  others  might  be  variously  placed. 

19 


20 


OSTEOLOGY 


STRUCTURE  OF  BONES' 

Bones  consist  chiefly  of  bone  tissue,  but  considered  as  organs  they  present 
also  an  enveloi)in}i  membrane,  termed  the  periosteum,  the  medulla  or  marrow, 
vessels,  and  nerves. 

The  architecture  of  bone  can  be  studied  best  by  means  of  longitudinal  and 
cross-sections.  These  show  that  the  bone  consists  of  an  external  shell  of  dense 
compact  substance,  within  which  is  the  more  loosely  arranged  spongy  substance. 


Fic.  1. — Krontal  SncTioN  or  L/ rgk  Mktatahsai.  Fk;.  2. — Sagittal  Section  of  I.argk  Metatarsal 

Bone  of  Horse,  Posterior  Part.  Bone  of  Horse. 

S.C.,  Compact  substance;    S.s.,  spong.v  substance;    C.tn.,  mcdullar.v  civitv;    F.n..  nutrient  foramen.     .Note  the 
greater  tliickncss  of  the  compact  substance  of  the  inner  and  anterior  parts  of  the  shaft. 


In  typical  long  boiivs  the  siiaft  is  hollowed  to  form  tlie  medullary  cavity  (Cavum 
medullare). 

The  compact  substance  (Substantia  compacta)  differs  greatly  in  thickness  in 
various  situations,  in  conformity  witli  the  stresses  and  strains  to  which  the  bone  is 
subjected.  In  the  long  bones  it  is  thickest  in  the  middle  part  of  the  shaft  and  thins 
out  toward  the  extremities.  On  the  latter  the  layer  is  very  thin,  and  is  especially 
dense  and  smooth  on  joint  .surfaces. 

'  Only  the  gross  stnirtiire  is  discussed  liere.  For  the  microscopic  structvir(>  reference  is  to 
be  made  to  histoIoRical  works. 


STRUCTURE    OF    BONES  21 

The  spongy  substance  (Substantia  spongiosa)  consists  of  delicate  bony  plates 
and  spicules  which  run  in  various  directions  and  intercross.  These  plates  are 
definitely  arranged  with  regard  to  mechanical  requirements,  so  that  systems  of 
pressure  and  tension  plates  can  be  recognized,  in  conformity  with  the  lines  of  pres- 
sure and  the  pull  of  tendons  and  ligaments  respectively.  The  intervals  (marrow 
spaces)  between  the  plates  are  occuiDied  by  marrow.  The  spongy  substance  forms 
the  bulk  of  short  bones  and  of  the  extremities  of  long  bones;  in  the  latter  it  is  not 
confined  to  the  ends,  but  extends  a  variable  distance  along  the  shaft  also.  Some 
bones  (Ossa  pneumatica)  contain  air-spaces  or  sinuses  within  the  compact  sub- 
stance instead  of  spongy  bone  and  marrow.  In  certain  situations  the  two  compact 
layers  of  flat  bones  are  not  separated  by  spongy  bone,  but  fuse  with  each  other; 
in  some  cases  of  this  kind  the  bone  is  so  thin  as  to  be  translucent,  or  may  even 
undergo  absorption,  producing  an  actual  deficiency. 

The  flat  bones  of  the  cranial  vault  and  sides  are  composed  of  an  outer  layer  of 
ordinary  compact  substance,  an  inner  laj'er  of  very  dense  bone,  the  tabula  vitrea, 
and  between  these  a  variable  amount  of  spongy  bone,  here  termed  diploe. 

The  periosteum  is  the  membrane  which  invests  the  outer  surface  of  bone, 
except  where  it  is  covered  with  cartilage.  It  consists  of  an  outer  protective  fibrous 
layer,  and  an  inner  cellular  osteogenic  layer.  During  active  growth  the  osteogenic 
layer  is  well  developed,  but  later  it  becomes  much  reduced.  The  fibrous  layer 
varies  much  in  thickness,  being  in  general  thickest  in  exposed  situations.  The 
adhesion  of  the  periosteum  to  the  bone  also  differs  greatly  in  various  places;  it 
is  usually  very  thin  and  easily  detached  where  it  is  thickly  covered  with  muscular 
tissue  which  has  little  or  no  attachment.  The  degree  of  vascularity  conforms  to 
the  activity  of  the  periosteum. 

The  marrow  (Medulla  ossium)  occupies  the  interstices  of  the  spongy  bone  and 
the  medullary  cavity  of  the  long  bones.  There  are  two  varieties  in  the  adult — 
red  and  yellow.  In  the  young  subject  there  is  only  red  marrow  (Medulla  ossium 
rubra),  but  later  this  is  replaced  in  the  medullary  cavity  l)y  yellow  marrow  (Medulla 
ossium  flava).  The  red  marrow  contains  several  types  of  characteristic  cells  and 
is  a  blood-forming  substance,  while  the  yellow  is  practically  ordinary  adipose  tissue. 

Since  yellow  marrow  is  formed  by  regressive  changes  in  red  marrow,  including  fatty  infiltra- 
tion and  degeneration  of  the  characteristic  cells,  we  find  transitional  forms  or  stages  in  the  process. 
In  aged  or  badly  nourished  subjects  the  marrow  may  undergo  gelatinous  degeneration,  resulting 
in  the  formation  of  gelatinous  marrow. 

Vessels  and  Nerves. — It  is  customary  to  recognize  two  sets  of  arteries — the 
periosteal  and  the  medullary.  The  former  ramify  in  the  periosteum  and  give  off 
innumerable  small  branches  which  enter  minute  openings  (Volkmann's  canals)  on 
the  surface  and  reach  the  Haversian  canals  of  the  compact  substance.  Other 
branches  enter  the  extremities  of  the  long  bones  and  supply  the  .spongy  bone  and 
marrow  in  them.  In  the  case  of  the  larger  bones — and  especially  the  long  bones — 
the  large  medullary  or  nutrient  artery  enters  at  the  so-called  nutrient  foramen 
(Foramen  nutricium),  passes  in  a  canal  (Canalis  nutricius)  through  the  comjjact 
substance,  and  ramifies  in  the  marrow;  its  branches  anastomose  with  the  central 
branches  of  the  periosteal  set.  The  larger  veins  of  the  spongy  bone  do  not,  as  a 
rule,  accompany  the  arteries,  but  emerge  chiefly  near  the  articular  surfaces.  Within 
the  bone  they  are  destitute  of  valves. 

The  lymph-vessels  form  perivascular  channels  in  the  periosteum  and  the 
Haversian  canals  of  the  compact  substance.  Lymph-spaces  exist  at  the  peri]ihery 
of  the  marrow. 

The  nerves  appear  to  be  distributed  chiefly  to  the  blood-vessels.  Special 
nerve-endings  (Vater-Pacini  corpuscles)  in  the  periosteum  are  to  be  regarded  as 
sensory,  and  prolaably  are  concerned  in  mediating  the  muscle  sense  (Kopsch). 


22 


OSTEOLOGY 


DEVELOPMENT  AND  GROWTH  OF  BONE ' 

The  priiiiitivp  embryonal  skeloton  consists  of  cartilaKO  and  fibrous  tissue,  in 
which  the  l)ones  develop.  The  process  is  termed  ossification  or  osteogenesis,  and 
is  effected  essentially  by  bone-producing  cells,  calletl  osteoblasts.  It  is  customary, 
therefore,  to  desijiiiate  as  membrane  bones  those  which  are  developed  in  fibrous 
tissue,  and  as  cartilage  bones  those  which  are  preformed  in  cartilage.  The  princi- 
pal membrane  bones  are  those  of  the  roof  and  sides  of  the  cranium  and  most  of  the 
bones  of  the  face.  The  cartilage  bones  comprise,  tlierefore,  most  of  the  skeleton. 
Correspondingly  we  distinguish  intramembranous  and  endochondral  ossification. 

In  intramembranous  develoiiment  the  ])ro('ess  begins  at  a  definite  center  of 
ossification  where  the  cells  (osteoblasts)  surround  themselves  with  a  deposit  of 
bone.  The  process  extends  from  this  center  to  the 
periphery  of  the  future  bone,  thus  producing  a  net- 
work of  bony  trabeculae.  The  trabeculse  rapidly 
thicken  and  coalesce,  forming  a  bony  plate  which 
is  separated  from  the  adjacent  bones  by  persistent 
fibrous  tissue.  The  superficial  part  of  the  original 
tissue  becomes  periosteum,  and  on  the  deep  face  of 
this  successive  layers  of  periosteal  bone  are  formed 
by  osteoblasts  until  the  bone  attains  its  definitive 
thickness. 

In  endochondral  ossification  the  process  is  funda- 
mentally the  same,  but  not  quite  so  simple.  Osteo- 
blasts emigrate  from  the  deep  face  of  the  perichon- 
drium or  primitive  periosteum  into  the  cartilage  and 
cau.se  calcification  of  the  matrix  or  ground-substance 
of  the  latter.  Vessels  extend  into  the  calcifying  area, 
the  cartilage  cells  shrink  and  disappear,  forming 
primary  marrow  cavities  which  are  occupied  b^'  pro- 
cesses of  the  osteogenic  tissue.  There  is  thus  formed 
a  sort  of  scaffolding  of  calcareous  trabeculse  on  which 
the  bone  is  constructed  l)y  the  osteoblasts.  At  the 
same  time  perichondral  bone  is  formed  by  the  osteo- 
blasts of  the  primitive  periosteum.  The  calcified 
cartilage  is  broken  do-mi  and  absorbed  through  the 
agency  of  large  cells  called  osteoclasts,  and  is  re- 
placed by  bone  deposited  by  the  osteoblasts.  The 
osteoclasts  also  cause  alisorption  of  the  primitive 
bone,  producing  the  marrow  cavities;  thus  in  the 
case  of  the  long  bones  the  primitive  central  spongy 
bone  is  largely  absorbed  to  form  the  medullary  cavity 
of  the  shaft,  and  persists  chiefly  in  the  extremities. 
Destruction  of  the  central  part  and  formation  of  subperiosteal  bone  continue  until 
the  shaft  of  the  bone  has  completed  its  growth. 

A  typical  long  bone  is  developed  from  three  primary  centers  of  ossification, 
one  for  the  diaphysis  or  shaft  and  one  for  each  epiphyses  or  extremity.  Many 
bones  have  secondary  centers  from  which  jirocesses  or  apophyses  develop. 

The  foregoing  outline  accounts  for  the  growth  of  bones  except  in  regard  to 
length.  Increase  in  length  may  be  explained  briefly  as  follows:  Provision  for  con- 
tinued o.s.sification  at  either  end  of  the  diaphysis  is  made  by  a  layer  of  actively 
growing  cartilage— the  epiphyseal  cartilage— which  intervenes  between  the  diaph- 

'Only  a  brief  gpneral  statement  of  osteogenesis  can  be  made  here;  details  must  be  sought 
in  cmbryologiral  literature. 


—Left  Femur  of  Young  Pig, 
ExTKRNAi,  View,  to  .Show  Di- 
vision OF  A  Long  Bonk  into 
Shaft  («)  and  Extremities. 
Proximal  extremity  consists  of 
two   parts,   head    (/i)    and   trochanter 
major   {t.   m.),    which   have    separate 
centers  of  ossification.     Distal  extrem- 
ity consists  of  trochlea  (/)  and  condyles 
(c):     e.l.,  epiphyseal    cartilages;    8/., 
supracondyloid  fossa. 


CHEMICAL    COMPOSITION    OF    BONE — DESCRIPTIVE   TERMS  23 

ysis  and  the  epiphj-sis.  It  is  evident  that  so  long  as  this  cartilage  persists  and 
grows,  new  bone  may  continue  to  be  formed  at  its  expense,  and  increase  of  length 
is  possible.  When  the  epiphyseal  cartilage  ceases  to  grow,  it  undergoes  ossifica- 
tion, the  bone  is  consolidated,  and  no  further  increase  in  length  is  possible.  This 
fusion  takes  place  at  fairly  definite  periods  in  the  various  bones,  and  it  is  of  value 
to  know  the  usual  times  at  which  it  occurs  in  the  larger  bones  of  the  limbs  at  least. 

After  the  bones  have  reached  their  full  size,  the  periosteum  becomes  relatively  reduced  and 
inactive  so  far  as  its  osteogenic  layer  is  concerned;  the  bone-forming  function  may  be  stimulated 
by  various  causes,  as  is  well  seen  in  the  healing  of  fractures  and  the  occurrence  of  bony  enlarge- 
ments. 

CHEMICAL  COMPOSITION  OF  BONE 
Dried  bone  consists  of  organic  and  inorganic  matter  in  the  ratio  of  1  :  2 
approximately.  The  animal  matter  gives  toughness  and  elasticity,  the  mineral 
matter  hardness,  to  the  bone  tissue.  Removal  of  the  organic  matter  by  heat  does 
not  change  the  general  form  of  a  bone,  but  reduces  the  weight  by  about  one-third, 
and  makes  it  ver.y  fragile.  Conversely,  decalcification,  while  not  affecting  the  form 
and  size  of  the  bone,  renders  it  soft  and  pliable.  The  animal  matter  when  boiled 
>-ields  gelatin.  The  following  table  represents  the  composition  in  lOU  parts  of  ox 
bone  of  average  quality : 

Gelatin 33.30 

Phosphate  of  Ume 57.35 

Carbonate  of  lime 3.85 

Phosphate  of  magnesia 2.05 

Carbonate  and  chlorid  of  sodium 3.45 

100.00 

PHYSICAL  PROPERTIES  OF  BONE 
Fresh  dead  bone  has  a  yellowish-white  color;  when  macerated  or  boiled  and 
bleached,  it  is  white.  The  specific  gravity  of  fresh  compact  bone  is  a  little  over 
1.93.  It  is  very  hard  and  resistant  to  pressure;  a  .5-milIimeter  cube  of  compact 
bone  of  the  ox  will  resist  pressure  up  to  852  pounds,  if  the  pressure  be  applied  in 
the  line  of  the  lamellae  (Rauber).  Its  tensile  strength  is  estimated  to  be  nearly 
twdce  that  of  oak. 

DESCRIPTIVE  TERMS 

The  surfaces  of  the  bones  present  a  great  variety  of  eminences  and  depressions, 
as  well  as  perforations.  The  prominences  and  cavities  may  be  articular,  or  non- 
articular,  furnishing  attachment  to  muscles,  tendons,  ligaments  or  fascia.  A 
number  of  descriptive  terms  are  used  to  designate  these  features,  and  the  following 
are  some  of  those  in  general  use: 

Process  (Processus)  is  a  general  term  for  a  prominence. 

A  tuberosity  (Tuber,  Tuberositas)  is  a  large,  rounded  projection;  a  tubercle 
(Tuberculum)  is  a  smaller  one. 

The  term  trochanter  is  appUed  to  a  few  prominences,  e.  g.,  the  trochanters  of 
the  femur. 

A  spine  (Spina)  or  spinous  process  (Processus  spinosus)  is  a  pointed  projection. 

A  crest  (Crista)  is  a  sharp  ridge. 

A  line  i  Linea)  is  a  very  small  ridge. 

A  head  (Caput)  is  a  rounded  articular  enlargement  at  the  end  of  a  bone; 
it  may  be  joined  to  the  shaft  by  a  constricted  part,  the  neck  (Collum). 

A  condyle  (Condylus)  is  an  articular  eminence  which  is  somewhat  cylindrical; 
a  non-articular  projection  in  connection  with  a  condyle  may  be  termed  an  epi- 
condyle. 


24 


OSTEOLOOY 


A  trochlea  is  a  puUc^y-likc  articular  mass. 

A  glenoid  cavity  (("avitas  glenoiilalis)  is  a  shallow  articular  depression,  and  a 
cotyloid  cavity  or  acetabulum  is  a  deeper  one. 

The  term  facet  is  eonmionly  applied  to  articular  surfaces  of  small  extent, 
especially  when  they  are  not  strongly  concave  or  convex. 

The  terms  fossa,  fovea,  groove  or  sulcus,  and  impression  are  applied  to  various 
forms  of  depressions. 

\  foramen  is  a  perforation  for  the  transmission  of  vessels,  nerves,  etc. 

A  sinus  nr  antrum  is  an  air-cavity. 

Other  terms,  such  as  canal,  fissure,  notch,  etc.,  require  no  explanation.' 


VERTEBRAL  COLUMN 
The  vertebral  column  (Columna  vertel)ralis)  is  the  fundamental  part  of  the 
skeleton.     It  consists    of  a  chain  of  median,    unpaired,    irregular    bones  which 
extends  from  the  skull  to  the  end  of  the  tail.     In  the  adult  certain  vertebrae  have 

become  fused  to  form  a  single  bony  mass 
with  which  the  pelvic  girdle  articulates. 
Vertebra?  so  fused  are  termed  fixed  or 
"false"  vertebrae  (Vertebrae  immoliiles),  as 
distinguished  from  the  movable  or  "true" 
vertebrae  (\'ertebrff  mobiles). 

The  column  is  subdivided  for  descrip- 
tion into  five  regions,  which  are  named  ac- 
cording to  the  part  of  the  body  in  which 
they  are  placed.  Thus  the  vertebrae  are 
designated  as  cervical,  thoracic  (or  dorsal), 
lumbar,  sacral,  and  coccygeal  or  caudal 
(Vertebra;  cervicales,  thoracales,  lumbales, 
sacrales,  coccygea?).  The  number  of  verte- 
brae in  a  given  species  is  fairly  constant  in 
each  region  except  the  last,  so  that  the  ver- 
tebral formula  may  be  expressed  (for  the 
horse,  for  example)  as  follows: 
C,T„L„S,Cy„_,, 
The  vertebrae  in  a  given  region  have 
special  characters  by  which  they  may  be 
distinguished  from  those  of  other  regions,  and  individual  vertebrae  have  characters 
which  are  more  or  less  clearly  recognizable.  All  typical  vertebrae  have  a  common 
plan  of  structure,  which  nnist  first  be  understood.  The  parts  of  which  a  vertebra 
consists  arc  the  body  or  centrum,  the  arch,  and  the  processes. 

The  body  (Cor])us  vertebra^  is  the  more  or  less  cylindrical  mass  on  which  the 
other  parts  are  constructed.  The  anterior  and  po.sterior  extremities  of  the  body 
are  attached  to  the  adjacent  vertebra'  by  intervertebral  fibro-cartilages,  and  are 
usually  convex  and  concave  respectively.  The  dorsal  surface  is  flattened  and  enters 
into  the  formation  of  the  vertebral  canal,  while  the  ventral  aspect  is  rounded 
laterally,  and  is  in  relation  to  various  muscles  and  viscera.  In  the  thoracic  region 
the  body  presents  two  pairs  of  demifacets  (Fovete  costales)  at  the  extremities  for 
articulation  with  the  heads  of  two  pairs  of  ribs. 

The  arch  (.\rcus  vertebra-)  is  constructed  on  the  dorsal  aspect  of  the  body. 
It  consists  originally  of  two  lateral  halves,  each  of  which  is  considered  to  consist 
of  a  pedicle  and  a  lamina.     The  pedicles  form  the  lateral  parts  of  the  arch,  and  are 

'  As  mi(ilit  1)0  expected  from  the  history  of  .iniitoniy,  a  good  many  of  these  terms  are  more  or 
less  interchangeable;   furthermore,  a  given  skeletal  feature  m:iy  differgreatly  in  various  species. 


To  illustrate  plan  of  structun 


Jaeef 


>F  Horse. 
rtebra;. 


THE    RIBS  25 

cut  into  in  front  and  beliind  by  tiie  vertebral  notches  (Incisura  vortebralis  cranialis, 
caudalis).  The  notches  of  two  adjacent  vertebra?  form  intervertebral  foramina 
for  the  passage  of  the  spinal  nerves  and  vessels;  in  some  vertcliru',  however,  these 
are  complete  foramina  instead  of  notches.  The  laminje  are  plates  which  complete 
the  arch  dorsallj',  uniting  with  each  other  medially  at  the  root  of  the  spinous 
process. 

The  body  and  the  arch  form  a  bony  ring  which  incloses  the  vertebral  foramen 
(Foramen  vertebrale);  the  series  of  vertebral  rings,  together  with  the  ligaments 
which  unite  them,  inclose  the  vertebral  canal  (Canalis  vertebralis),  which  con- 
tains the  spinal  cord  and  its  coverings  and  vessels. 

The  articular  processes,  two  anterior  and  two  posterior  (Processus  articulares 
craniales.  cautlales),  project  from  the  borders  of  the  arch  on  either  side.  They 
present  joint  surfaces  adapted  to  those  of  adjacent  vertebrs,  and  the  remaining 
surface  is  roughened  for  muscular  and  ligamentous  attachment. 

The  spinous  process  (Processus  spinosus)  is  single,  and  projects  dorsally  from 
the  middle  of  the  arch.  It  varies  greatly  in  form,  size,  and  direction  in  different 
vertebrse.     It  furnishes  attachment  to  muscles  and  ligaments. 

The  transverse  processes  (Processus  transversi)  are  two  in  number  and  project 
laterally  from  the  side  of  the  arch,  or  from  the  junction  of  the  arch  and  body. 
In  the  thoracic  region  each  has  a  facet  for  articulation  with  the  tubercle  of  a  rib 
(Fovea  costalis  transversalis).  They  also  give  attachment  to  muscles  and  liga- 
ments. 

Some  vertebrae  have  also  a  ventral  or  haemal  spine. 

Mammillary  processes  (Processus  mammillares)  are  found  in  most  animals  on 
the  last  thoracic  and  anterior  lumbar  vertebrae  between  the  transverse  and  anterior 
articular  processes  or  on  the  latter. 

Accessory  processes  (Processus  accessorii),  when  present,  are  situated  between 
the  transverse  and  posterior  articular  processes. 

Development. — The  vertebrae  are  developed  by  ossification  in  the  cartilage 
which  surrounds  the  notochord  and  forms  the  sides  of  the  neural  canal.  There  are 
three  primary  centers  of  ossification,  one  for  the  bodj-  and  one  for  each  side  of  the 
arch.  Secondary  centers  appear  later  for  the  summit  of  the  spinous  process 
(except  in  the  cervical  region),  the  extremities  of  the  transverse  processes,  and  the 
thin  epiphj'seal  plates  at  the  extremities  of  the  body. 

Sometimes  there  are  at  first  two  centers  for  the  body  which  soon  fuse.  The  process  of  ossifi- 
cation extends  from  the  lateral  centers  to  form  not  onlj-  the  corresponding  part  of  the  arch,  but 
also  the  processes  and  a  part  of  the  body  next  to  the  root  of  the  arch  (Radix  arcus).  In  the  horse 
and  ox  the  body  and  arch  are  usually  fused  at  birth,  but  the  epiphyses  do  not  fuse  till  growth  is 
complete.  In  the  pig,  sheep,  and  dog  the  body  and  arch  are  united  at  birth  by  cartilage  (.neuro- 
central  sjTichondrosis),  but  fuse  in  the  first  few  months. 


THE  RIBS 

The  ribs  (Costae)  are  elongated  curved  bones  which  form  the  skeleton  of  the 
lateral  thoracic  walls.  They  are  arranged  serially  in  pairs  which  usually  corre- 
spond in  number  to  the  thoracic  vertebrae.  Each  articulates  dorsally  with  the  spine 
and  is  continued  ventrally  by  a  costal  cartilage.  Those  which  articulate  with  the 
sternum  by  means  of  their  cartilages  are  termed  sternal  or  "true"  ribs  (Co.stae 
sternales  s.  verae);  the  remainder  are  asternal  or  "false"  ribs  (Costae  asternales  s. 
spuriac).  Ribs  at  the  end  of  the  series  which  have  their  ventral  ends  free  in  the 
abdominal  wall  are  named  floating  ribs  (Costae  fluctuantes).  The  intervals  be- 
tween the  ribs  are  termed  intercostal  spaces  (Spatia  intercostalia). 

A  typical  rib'  consists  of  a  shaft  and  two  extremities.    The  shaft  (Corpus  costae) 

'The  term  is  employed  here,  as  is  usual  in  descriptive  anatomy,  to  designate  only  the  bony 
part  of  the  rib  (Os  costale) ;   morphologically  it  includes  the  cartilaginous  part  also. 


26  OSTEOLOGY 

is  l)aiul-likc  and  varies  much  in  l(>ngtli,  lircadth,  and  curvature.  In  the  case  of 
some  ribs  tlie  curvature  is  not  uniform,  but  is  most  accentuated  at  a  certain  point, 
termed  the  angle  of  the  rib  (Aiifjulus  costa>);  this  occurs  at  a  variable  distance 
from  the  vertcl)ral  end,  and  is  usually  marked  by  a  rough  ridge.  The  direction 
also  varies;  the  first  rib  is  almost  vertical,  while  the  remainder  slope  liackward 
in  increasing  degree.  The  external  surface  is  convex,  and  the  internal  flattened 
from  etige  to  etlge;  on  the  latter,  close  to  the  posterior  border,  is  the  costal  groove 
(Sulcus  costalis),  which  fades  out  vcntrally.  It  contains  the  intercostal  vein. 
The  anterior  and  posterior  borders  ari'  thin  and  sharp  on  some  ribs,  rounded  on 
others. 

The  vertebral  extremity  (Extremitas  vertebralis)  consists  of  the  head,  neck, 
and  tubercle.  The  head  (Capitulum  costa;)  is  the  actual  end  of  the  rib,  and  is 
rounded  and  .somewhat  enlarged.  It  presents  two  facets  (Fades  articularis  capituli 
costa")  for  articulation  with  the  bodies  of  two  adjacent  thoracic  vertebrae;  these 
surfaces  are  separated  by  a  groove  in  which  the  conjugal  ligament  is  attached. 
The  neck  (CoUum  costip)  joins  the  head  to  the  shaft.  It  varies  in  length  and 
diameter.  Its  outer  surface  is  rough,  its  inner  smooth.  The  tubercle  (Tuberculum 
costa;)  projects  backward  at  the  junction  of  the  neck  and  shaft.  It  has  a  facet 
(Facies  articularis  tuberculi  costa?)  for  articulation  with  the  transverse  process  of 
the  posterior  vertebra  of  the  two  with  which  the  head  articulates.  The  tubercle 
grailually  approaches  the  head  in  the  posterior  ribs,  and  eventually  fuses  with  it. 

The  sternal  extremity  (Extremitas  sternalis)  is  commonly  slightly  enlarged, 
and  has  a  rough  depression  in  which  the  co.stal  cartilage  is  embedded. 

Development.  —The  ribs  are  ossified  in  cartilage  from  three  centers — one  each 
for  the  shaft  (and  sternal  end),  head,  and  tubercle;  the  third  center  does  not  occur 
in  the  last  two  rilw. 

THE  COSTAL  CARTILAGES 
These  (Cartilagines  costales)  are  bars  of  hyaline  cartilage  which  continue  the 
ribs.     Those  of  the  sternal  ribs  articulate  with  the  sternum,  while  the  remainder 
overlap  and  are  attached  to  each  other  to  form  the  costal  arch  (Arcus  costalis). 

THE  STERNUM 

The  sternum  or  breast-bone  is  a  median  segmental  bone  which  completes  the 
skeleton  of  tlie  thorax  ventrally,  ami  articulates  with  the  cartilages  of  the  sternal 
ribs  laterally.  It  consists  of  six  to  eight  bony  segments  (Sternebne)  connected  by 
intervening  cartilage  in  the  young  subject.  Its  form  varies  with  that  of  the  thorax 
in  general  and  with  the  development  of  the  clavicles  in  animals  in  which  they  arc 
present.  Its  anterior  extremity,  the  manubrium  stemi  or  presternum,  is  specially 
affected  by  the  latter  factor,  being  l)road  and  strong  when  the  clavicles  are  well 
developed  and  articulate  Avith  it  (as  in  man),  relatively  small  and  laterally  com- 
pre.s.sed  when  they  are  absent  (as  in  the  horse)  or  rudimentary  (as  in  the  dog). 
The  cartilages  of  the  first  pair  of  ribs  articulate  with  it.  The  body  or  mesostemum 
(Corpus  sterni)  presents  laterally,  at  the  junction  of  the  segments,  concave  facets 
(Incisunr  costales)  for  articulation  with  the  cartilages  of  the  .sternal  ribs.  The 
posterior  extremity  or  metastemum  presents  tiie  xiphoid  (or  ensiform)  cartilage 
(Processus  xiphoiihnis) ;  tliis  is  thin  and  plate-like,  as  in  the  horse  and  ox,  or  narrow 
and  short,  as  in  the  jiig  and  dog. 

Development.— The  cartilaginous  sternum  is  formed  by  the  fusion  medially 
of  two  lateral  bars  which  unite  the  ventral  ends  of  the  first  eight  or  nine  costal 
cartilages,  anil  is  primitively  unsegmented.  The  manubrium  ossifies  from  a  single 
center,  but  the  centers  for  the  other  .segments  appear  to  be  primitively  paired. 
The  sternum  never  becomes  completely  ossified;    details  in  regard  to  persisting 


THE    THORAX — THE    BOXES    OF   THE    THOKACIC    LIMB  27 

cartilage  will  be  given  in  the  special  descriptions.  The  layer  of  compact  tissue  is 
for  the  greater  part  very  thin  and  the  spongy  substance  is  open-meshed  and  very 
vascular. 

THE  THORAX 

The  skeleton  of  the  thorax  comprises  the  thoracic  vertebra?  dorsally,  the  ribs 
and  their  cartilages  laterally,  antl  the  sternum  ventrally.  The  thoracic  cavity 
(Cavum  thoracis)  resembles  in  shape  an  irregular  truncated  cone;  it  is  compressed 
laterally,  especially  in  front,  and  the  dorsal  wall  or  roof  is  much  longer  than  the 
ventral  wall  or  floor.  The  anterior  aperture  (Apertura  thoracis  cranialis)  is 
bounded  by  the  first  thoracic  vertebra  dorsally,  the  first  pair  of  riljs  and  their 
cartilages  laterally,  and  the  manubrium  sterni  ventrally.  The  posterior  aperture 
(Apertura  thoracis  caudalis)  is  bounded  by  the  last  thoracic  vertebra,  the  last 
pair  of  ribs,  the  costal  arches,  and  the  anterior  part  of  the  xiphoid  cartilage. 

It  may  be  noted  here  that  the  diaphragm  (which  forms  the  partition  between  the  thoracic 
and  abdominal  cavitie.s)  does  not  follow  the  costal  arches  in  its  posterior  attachment,  so  that  the 
posterior  ribs  enter  also  into  the  formation  of  the  abdominal  wall. 


THE   SKULL 

The  term  skull  is  usually  understood  to  include  all  of  the  bones  of  the  head. 
The  head  consists  of  the  cranium  and  the  face,  and  it  is  therefore  convenient  to 
divide  the  bones  into  cranial  and  facial  groups. 

The  cranial  bones  (Ossa  cranii)  inclose  the  brain  with  its  membranes  and 
vessels  and  the  essential  organs  of  hearing.  They  concur  with  the  facial  bones  in 
forming  the  orbital  and  nasal  cavities,  in  which  the  peripheral  organs  of  sight  and 
of  smell  are  situated. 

The  facial  bones  (Ossa  faciei)  form  the  skeleton  of  the  oral  and  nasal  cavities, 
and  also  support  the  larynx  and  the  root  of  the  tongue. 

Most  of  the  bones  of  the  skull  are  flat  bones,  developed  in  membrane;  those 
of  the  cranial  base  may  be  clas.sed  as  irregular,  and  are  cartilage  bones.  Only 
two  form  permanent  movable  joints  with  other  parts  of  the  skull.  The  mandible 
or  lower  jaw-bone  forms  diarthrodial  joints  with  the  temporal  bones,  and  the  hyoid 
bone  is  attached  to  the  latter  by  bars  of  cartilage.  The  other  bones  form  immov- 
able joints,  most  of  which  disappear  with  age. 

In  order  to  study  the  separate  bones,  skulls  of  young  subjects  are  necessary,  since  later  most 
of  the  Unes  of  demarcation  become  effaced.  The  relations  of  each  bone  to  its  surroundings  should 
be  specially  noted,  since  the  final  object  is  to  understand  the  skull  as  a  whole.  In  the  descriptions 
which  follow  the  skull  is  considered  with  its  long  axis  horizontal,  and  that  of  the  horse  will  serve 
as  a  type. 

THE  BONES  OF  THE  THORACIC  LIMB 

The  thoracic  limb  consists  of  four  chief  segments,  viz.,  the  shoulder  girdle, 
the  arm,  the  forearm,  and  the  forefoot  or  manus. 

The  shoulder  girdle  (Cingulum  extremitatis  thoracicae),  when  fully  developed, 
consists  of  three  bones — the  scapula  or  shoulder-blade,  the  coracoid,  and  the 
clavicle  or  collar-bone.  In  the  domesticated  mammals  only  the  scapula,  a  large, 
flat  bone,  is  well  developed,  and  the  small  coracoid  element  has  fused  with  it,  while 
the  clavicle  is  either  absent  or  is  a  small  rudiment  embedded  in  the  mastoido- 
humeralis  muscle.  There  is  therefore  no  articulation  of  the  shoulder  mth  the 
axial  skeleton. 

The  shoulder  girdle  is  fully  developed  in  birds  and  the  lower  mammals  (monotremata).  In 
the  higher  mammals  the  coracoid  is  reduced  to  the  coracoid  process  of  the  scapula,  and  the  develop- 
ment of  the  cla\-icle  is  in  conformity  with  the  function  of  the  limb.     Thus  in  typical  quadrupeds, 


28  OSTEOLOGY 

such  as  the  horse  and  ox,  in  which  the  forcliniljs  arc  used  only  for  support  and  locomotion,  the 
clavicle  is  absent.  Other  animals  which  use  these  limbs  for  Rrasprng,  burrowinK,  climbing,  etc. 
(c.<7.,man,  apes,  moles),  have  well-developed  clavicle.s  which  connect  the  scapula  withthesternum. 

The  ann  (Brarliiiim)  contains  a  single  long  bone,  the  humerus  or  arm  hone. 

In  the  forearm  (Antihracliiuni)  are  two  long  hones,  the  radius  and  ulna. 
These  vary  in  relative  size  anil  mobility.  In  the  horse  and  ox  the  two  bones  are 
fused,  and  tiie  lower  i)art  of  the  limb  is  fixed  in  the  position  of  pronation.  The 
radius  is  plaeed  in  front  and  supports  the  weight.  The  ulna  is  well  developed  only 
in  its  upper  part,  which  forms  a  lever  for  the  extensor  muscles  of  the  elbow.  In 
the  pig  the  ulna  is  the  larger  and  longer  of  the  two  bones,  but  is  closely  attached  to 
the  back  of  the  ratlins.  In  the  dog  the  ulna  is  also  w-cll  developed  and  a  small 
amount  of  movement  is  possible  between  the  two  bones. 

The  forefoot  or  hand  (Manus)  consists  of  three  subdivisions,  viz.,  the  carpus, 
metacarpus,  and  digit  or  digits. 

The  carpus,  popularly-  termed  the  "knee"  in  animals,  and  homologous  with 
the  wrist  of  man,  contains  a  group  of  short  bones  (Ossa  carpi).  These  are  typically 
eight  in  number  and  are  arranged  in  two  transverse  rows — a  proximal  or  anti- 
braciiial,  and  a  tlistal  or  metacarpal.  The  bones  of  the  proximal  row.  named  from 
the  radial  to  the  ulnar  side  (/.  e.,  from  within  outward),  are  the  radial,  intermediate, 
ulnar,  and  accessory  carpal  bones.  The  bones  of  the  di.^tal  row  are  designated 
numerically,  in  the  same  direction,  as  first,  second,  third,  and  fourth  carpal  bones. 

This  nomenclature,  introduced  by  Gegenbaur,  and  now  used  largely  by  comparative  anat- 
omists, seems  decidedly  preferable  to  the  variety  of  terms  borrowed  from  human  anatomy  and 
based  on  the  form  of  the  bones  in  man.  The  following  table  of  synonyms  in  common  use  is  ap- 
pended for  comparison.     The  Latin  terms  and  abbreviated  notations  are  given  in  parenthesis. 

Radial  (Os  carpi  radiale,  Cr) Scaphoid 

Internu'iliate  (Os  carpi  intermedium,  Ci) Semilunar 

Ulnar  (Os  carpi  ulnarc,  Cu) Cuneiform 

.Acces.sory  (Os  carpi  accessorium,  Ca) Pisiform 

rir.'^t  carpal  (Os  carpale  primum,  CI) Trapezium 

Second  carp;d  (Os  I'arpale  secundum,  C2) Trapezoid 

Third  carpal  (Os  carpale  tertium,  C3) Os  magnum 

P'ourth  carpal  (Os  carpale  quartum,  C4) Unciform 

The  central  carpal  bone  (Os  carpi  centrale)  is  omitted,  since  it  is  not  a  separate  clement  in 
the  animals  under  consideration  here. 

The  metacarpus  contains  typically  five  metacarpal  bones  (Ossa  metacarpalia 
I-V),  one  for  each  digit;  the.y  arc  long  bones  and  are  designated  numerically  from 
within  outward.  This  arrangement  occurs  in  the  dog,  although  the  first  meta- 
carpal is  much  smaller  than  the  others,  and  the  second  and  fifth  are  somewhat 
reduced.  Further  reduction  has  taken  place  in  the  other  animals,  resulting  in 
the  perissodactyl  and  artioilactyl  forms.  In  the  hor.se  the  first  and  fifth  metacarpals 
are  absent,  the  third  is  the  large  supporting  metacarpal  bone  and  carries  the  single 
digit,  while  the  seconil  and  fourth  arc  much  reduced.  In  artiodactyls  (e.  g.,  ox, 
sheep,  pig)  the  third  and  fourth  are  the  chief  metacarpals  and  carry  the  well 
developed  digits;  they  are  fused  in  the  ox  and  sheep.  The  others  are  variously 
reduced  or  absent  as  noted  in  the  specitil  descriptions  to  follow. 

The  fossil  remains  of  the  ancestors  of  the  existing  Kquida'  illustrate  in  a  most  complete  man- 
ner the  reduction  which  has  occurred  in  this  respect.  The  earliest  known  ancestor  of  the  horse, 
Eohippus  or  Ilyracolherium  of  the  Lower  Eocene,  had  four  well  developed  metacarpal  bones, 
each  of  which  carried  a  digit;  the  first  metacarpal  bone  was  small.  Eleven  intermediate  stages 
show  the  gradu.al  evolution  of  the  race  from  this  primitive  animal,  which  was  about  the  size  of 
the  domestic  cat.     There  is  reason  to  belie\e  that  earlier  forms  had  five  digits. 

The  digits  fDigiti  manus)  are  homologous  with  the  fingers  of  man,  and  are 
typically  five  in  niunber.  They  are  designated  numerically  from  the  radial  to 
the  ulnar  side,  in  correspondence  with  the  metacarpus.  The  full  number  is  present 
in  the  dog.     In  the  ox  and  pig  the  third  and  fourth  are  well  developed  and  support 


THE    BONE.S    OF    THE    PELVIC    LIMB  29 

the  weight,  while  the  second  and  fifth  are  reduced.  The  existing  horse  has  a  single 
digit,  the  third  of  his  polythictyl  ancestors.  Tlie  skeleton  of  each  fully  developed 
digit  consists  of  three  phalanges  and  certain  sesamoid  bones.  The  first  or  proximal 
phalanx  (Phalanx  prima)  articulates  with  the  corresponding  metacarpal  bone  above 
and  with  the  second  or  middle  phalanx  (Phalanx  secunda)  below.  The  third 
or  distal  phalanx  (Phalanx  tertia)  is  inclos<>d  in  the  hoof  or  claw,  and  is  modified  to 
conform  to  the  latter.  The  sesamoid  bones  (Ossa  sesamoidea)  are  develo])ed 
along  the  course  of  the  flexor  tendons  or  in  the  joint  capsules.  Two  proximal 
sesamoids  (Ossa  sesamoidea  phalangis  primiB)  occur  at  the  flexor  side  of  the  meta- 
carpo-phalangeal  joint  and  form  a  pulley  for  the  flexor  tendon.  The  distal 
sesamoids  (Ossa  sesamoidea  phalangis  tertiae)  are  similarly  placed  between  the 
deep  flexor  tendon  and  the  joint  between  the  second  and  third  phalanx;  they  are 
absent  in  the  dog,  which  has  a  small  sesamoid  on  the  extensor  side  of  the  meta- 
carpo-phalangeal  joints,  and  often  at  the  proximal  interphalangeal  joint  also. 

Numerous  cases  are  recorded  of  the  occurrence  of  supernumerary  digits  (hyperdactylism) 
in  the  horse  and  other  animals.  In  some  pigs,  on  the  other  hand,  the  two  chief  digits  are  fused, 
and  the  condition  appears  to  be  inherited. 


THE  BONES  OF  THE  PELVIC  LIMB 

The  pelvic  limb,  like  the  thoracic,  consists  of  four  segments,  viz.,  the  pelvic 
girdle,  thigh,  leg,  and  the  hind  foot  or  pes;  the  last  is  subdivided  into  tarsus, 
metatarsus,  and  digits. 

The  pelvic  girdle  (Cingulum  extremitatis  pelvinse)  consists  of  the  os  coxae  or 
hip  bone,  which  joins  its  fellow  of  the  opposite  side  ventrally  at  the  symphysis 
pelvis,  and  articulates  very  firmly  with  the  sacrum  dorsally.  The  two  coxal  bones, 
together  with  the  sacrum  and  the  first  two  or  three  coccygeal  vertebrae,  constitute 
the  bony  pelvis.  The  os  coxje  consists  originally  of  three  flat  bones,  the  ilium, 
ischium,  and  pubis,  which  meet  at  the  acetabulum,  a  large  cotyloid  cavity  that 
articulates  with  the  head  of  the  femur.  The.se  three  parts  are  fused  before  growth 
is  complete,  but  are  considered  separately  for  convenience  of  description.  The 
ilium  (Os  ilium)  is  situated  in  the  lateral  wall  of  the  pelvis,  the  pubis  (Os  pubis)  in 
the  anterior  part,  and  the  ischium  (Os  ischii)  in  the  posterior  part  of  the  ventral 
wall. 

The  thigh  (Femur),  like  the  arm,  contains  a  single  large,  long  bone,  the  femur 
or  thigh  bone  (Os  femoris).  This  articulates  with  the  acetabulum  above  and  the 
tibia  and  patella  below. 

The  skeleton  of  the  leg  (Crus)  comprises  three  bones  (Ossa  cruris),  viz.,  the 
tibia,  fibula,  and  patella.  The  tibia  is  a  large  prismatic  long  bone  which  supports 
the  weight,  and  articulates  below  with  the  tibial  tarsal  bone.  The  fibula  is  situated 
along  the  outer  border  of  the  tibia,  from  which  it  is  separated  by  the  interosseous 
space  of  the  leg.  It  is  much  more  slender  than  the  tibia  and  does  not  articulate 
with  the  femur.  In  the  pig  and  dog  it  has  a  complete  shaft  and  two  extremities, 
but  in  the  horse  and  ox  it  is  much  reduced  and  otherwise  modified.  The  patella 
or  "knee-cap"  is  a  short  bone  which  articulates  with  the  trochlea  of  the  distal  end 
of  the  femur;  it  is  to  be  regarded  as  a  large  sesamoid  bone  intercalated  in  the  tendon 
of  the  quadriceps  femoris  muscle. 

The  tarsus  or  "  hock  "  consists  of  a  group  of  short  bones  (Ossa  tarsi)  numbering 
five  to  seven  in  the  different  animals.  The  proximal  or  crural  row  consists  of  two 
bones,  the  tibial  and  fibular  tarsals ;  the  former  is  situated  at  the  inner  or  tibial 
side,  and  has  a  trochlea  for  articulation  with  the  distal  end  of  the  tibia;  the  latter, 
situated  externally,  has  a  process,  the  tuber  calcis,  which  projects  upward  and 
backward  and  constitutes  a  lever  for  the  muscles  which  extend  the  hock  joint.  The 
distal  or  metatarsal  row  consists  of  four  bones  when  seven  tarsal  elements  are 


30 


OSTEOLOGY 


present,  as  in  the  pifj;  and  dog.     They  are  best  designated  niiiiu'ticaliy  as  first  tarsal, 
second  tarsal,  etc.     The  central  tarsal  is  interposed  between  the  rows. 

The  prccciiinK  terms  are  anplicizcil  abbreviations  of  those  introdueed  by  Oegenbaur  into 
comparative  anatomy.     The  Latin  names  and  synonyms  are  given  in  the  following  table. 

Til>ial  (Os  tarsi  tibialc,  Tt.) Astragahis  or  Talus 

Fibular  (Os  tarsi  filnilare,  Tf.) Calcaneus  or  Os  calcis 

Central  (Os  tarsi  rentrale,  Te.) Seaphoid  or  Navicular 

First  Tarsal  (Os  tarsale  primum,  Tl) First  or  internal  cuneiform 

Second  Tarsal  (Os  tarsale  .secundum,  T2) Second  or  middle  cuneiform 

Third  Tarsal  (<)s  tarsale  tertium,  T3) Third  or  external  cuneiform 

Fourth  Tarsal  (Os  tarsale  (luartuin,  T4) Cuboid. 

The  metatarsal  and  digital  bones  resemble  in  general  those  of  the  corresponding 
regions  of  the  thoracic  limb;  the  differential  features  will  be  noted  in  the  special 
descriptions. 


Fio.  .5.— Skeleton  of  Hobsk.  with  Odtline  of  Tontocr  of  Tiont. 

v.,r.,hr».''V/^"^',V"i'""'?u'""";'  "'■'"''"'•  '"■•  '■"•'"  """■'"='<'  ^""■''™:  '■■''■■  ""venteenth  thoracic 
vertebra.  /./.  first  lumbar  vertebra;  B.L..  s..«h  lumbar  vertebra;  K.  .sacrum;  /.«..  first  corcvgeal  vertebra- 
/«..S..H..xtee„th  coccygeal  vertebra;  ff./e.,  si.vth  rib;  e.K..  costal  cartilage; /«.«.,  last  rib;  1,  scapula;  I',  cartilage 
fi  7.Tn',  7  "'""',  -T^'-  ^  ^'""""''  ••'  """■""'  •■P'™"''vle  of  humerus;  5,  external  tuberosity  of  humerus; 
™     n   ZriV;  ;i"^  "•^'^"^^    lO.crv..:    11.  accessory  carpal  hone;    12,  meta: 

7    s^hium-    8    ent  rTf,T^  ,„  ;  "'^"'  '■"""'"''■  "•  "'"'"^   '«■  •«'•  ^•^•"''•■''  ■'"''  '°"'™"'  -"'"-^  of  '»"">: 

■    ■     bi-Tham     "r  ■    '»•""■,  "".'•"  ""'^"'   27,  trochanter  minor;    28.  trochanter  tertius;    20.  patella 

UnerElcnblr^  •'  »"  rr\  ';'''"^  "^^  "'"""■  22.  tarsus:  24.  tuber  calcis;  25.  metatarsus;  26.  digit 
tAiier  tllcnbergcr-Baum,  Auat.  for  Kiiuatler.)  "■»". 


THE  SKELETON  OF  THE  HORSE 


31 


THE  SKELETON  OF  THE  HORSE 

The  skeleton  of  the  horse  consists  of  205  bones,  as  shown  in  the  following  table. 

Vertebral  column 54 

Ribs 36 

Sternum 1 

Skull  (including  auditory  ossicles) 34 

Thoracic  limbs 40 

Pehic  limbs 40 

205 

In  this  enumeration  the  average  number  of  coccygeal  vertebra-  is  taken  to  be  IS,  the  tem- 
poral and  OS  coxfe  are  not  divided  into  parts,  the  usual  number  of  carpal  and  tarsal  elements  is 
taken,  and  the  sesamoids  are  included. 


The   Vertebral  Column 
The  vertebral  formula  of  the  horse  is  C^Tj^LgSjCy^^ 


a>^ 


"Anterior  articu- 
lar process  of 
axis 


l" Anterior  part  of 

transverse  pro- 
cess 
Posterior  part  of 
transverse  pro- 
cess 
Dorsal  crest 


^  Posterior  articu- 
lar process 


Anterior   articu- 
lar process 


Fig.  6. — Cervicil  Vehtebr.e  of  Hohse. 
DoRS.^L  View.  (After  Schmaltz, 
Atlas  d.  .\nat.  d.  Pferdes.) 


Fossa  atlantis 


Basi-occipital 
Orri pilal  condyle 
I'(iraiiia.s-loid    (sti/l- 
oid)  process 


:^ERVICAL   VeRTEBR.E    OF    HoRSE,   VENTRAL  ViEW.      (After 

Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


32  THE  SKELETON  OF  THE  HORSE 

THE  CERVICAL  VERTEBRA 
These  are  quadrangular,  massive,  and  longer  than  the  vertebrae  of  other  regions; 
they  decrease  in  length  from  the  second  to  the  last.     The  third,  fourth,  and  fifth 
are  typical,  and  have  the  following  characters: 

1.  The  bodies  are  long  as  compared  with  those  of  other  vertebra^.  Each 
presents  a  median  ventral  spine  or  crest,  which  becomes  more  prominent  as  it  is 
traced  backward,  and  is  tubercuhite  at  its  posterior  end.  The  lateral  aspect  is 
concave.  The  dorsal  surface  has  a  flat  central  area  which  is  narrow  in  the  middle 
of  the  vertebra',  and  wide  at  either  end;  it  gives  attachment  to  the  superior  com- 
mon ligament.  On  either  side  of  this  area  is  a  groove  which  lodges  the  longitudinal 
spinal  vein.  These  lateral  grooves  are  connected  at  the  middle  of  the  surface  Ijy 
a  transverse  furrow,  in  which  there  are  several  foramina  through  which  veins 
emerge  from  the  spongy  sub.stance  of  the  body.  The  anterior  extremity  presents 
a  head  which  lias  an  oval  articular  surface,  strongly  convex,  and  wider  above  than 
below.    The  posterior  extremity  is  larger  and  has  a  nearly  circular  cotyloid  cavity. 

2.  The  arches  are  large  and  strong.     They  are  perforated  on  either  side  by  a 


ArticuUiT  processes 
Anterior  arliculnr  process^ 


TninisriTse  process 


Articular  cavity 


Facet  for  tubercle  of  first  rib 
Facets  for  head  of  first  rib 
Fio.  8.— Last  CKRVirAi,  an-i.  Fms^T  TnORAcir  Vkhtebr,*:  ok  Horsk,  Lateral  View,      (.\fter  Schmaltz,  Atla.«  d. 

Anat.  d.  Ptcrdes.) 

foramen  which  communicates  with  the  foramen  transversarium.     The  vertebral 
notches  are  large. 

3.  The  articular  processes  are  large.  Their  articular  surfaces  are  extensive, 
oval  m  outline,  and  slightly  concave;  the  anterior  ones  are  directed  upward  and 
mward,  the  posterior  downward  and  outward.  The  remaining  surface  is  mainly 
roughened  for  ligamentous  and  nmscular  attachment.  A  crest  connects  the 
articular  processes  of  the  same  side  on  the  fourth  and  fifth;  on  the  third  it  does  not 
reach  the  anterior  process. 

4.  The  transverse  processes  are  large  and  plate-like.  Each  arises  by  two 
roots,  one  from  tli,.  arch  and  one  from  the  body;  between  these  is  the  foramen 
transversarium,  through  which  the  vertebral  artery  passes.  The  process  divides 
externally  mto  anterior  and  posterior  branches,  which  are  thickened  and  rough  for 
muscular  attachment. 

5.  The  spinous  process  is  represented  by  a  crest  (Crista  spinosa),  which 
widens  behmd,  and  is  connected  by  ridges  with  the  posterior  articular  processes. 

The  sixth  cervical  vertebra  has  the  following  distinctive  features:  It  is  shorter 
and  wid.-r  than  the  fifth.     The  arch  is  large,  especially  posteriorly.     The  posterior 


THE    ATLAS 


33 


articular  processes  are  shorter,  thicker  and  further  apart;  they  are  connected  with 
the  anterior  ones  by  a  thick  ridge.  The  spinous  process  is  less  riuliniontary;  it 
is  half  an  inch  or  more  (ca.  1.5  cm.)  in  height.  The  transverse  processes  iiave 
three  branches;  the  third  part  is  a  thick,  ahnost  sagittal  plate,  which  form.s  with 
its  fellow  and  the  body  a  wide  ventral  groove  on  the  posterior  part  of  the  vertebra; 
the  other  branches  correspond  to  those  of  the  typical  vertebnc,  but  are  short  and 
thicker.  The  foramen  transversarium  i.s  large;  below  its  posterior  end  is  a  fossa. 
The  ventral  crest  is  small  and  is  less  prominent  posteriorly. 

Tlie  third  branch  of  the  transverse  process  and  the  fossa  are  sometimes  alisent  on  one  side. 

The  seventh  cervical  vertebra  is  readily  distinguished  by  the  following  charac- 
ters: It  is  shorter  and  wider  than  the  others.  The  body  is  flattened  dor.so-ventrally 
and  wide,  especially  behind;  here  it  has  a  demifacet  on  either  side  for  articulation 
with  part  of  the  head  of  the  first  rib.  The  arch  and  its  notches  are  large.  The 
anterior  articular  processes  are  wider  and  longer  than  the  jjostcrior  pair.  The 
spinous  process  is  an  inch  or  more  (ca.  3  cm.)  in  height.  The  transverse  process 
is  unilivided,  and  has  no  foramen  transversarium.  The  ventral  crest  is  replaced 
by  a  pair  of  tubercles. 

In  some  specimens  a  large  foramen  transversarium  is  present  on  one  side  or  (rarely)  on 
both. 


Foramen 
Iransver- 
sarium        Ventral 
areh 


atlantis 


[G.    9. — .\tlas    of    Horse,    .\nterior    \\v.\ 
(.\fter  Schmaltz,  .\tlas  d.  .\Dat.  d.  Pferdes.) 


Ventral  tubercle 


Fig.    10. — Atlas  of   Horse.   Posterior  View 
Schmaltz,  .\tlas  d.  .\nat.  d.  Pferdes.) 


The  Atlas 

This  vertebra  is  decidedly  atypical  in  form  and  structure.  The  body  and 
spinous  process  are  absent.  It  has  the  form  of  a  strong  ring,  from  which  two 
curved  plates,  the  wings,  project  laterally.  The  ring  incloses  a  very  largo  vertebral 
foramen,  and  consists  of  two  lateral  masses  connected  by  dorsal  and  ventral  arches. 

The  lateral  masses  (Massse  laterales)  present  two  deep  oval  anterior  articular 
cavities  (Fovete  articulares  craniales)  which  receive  the  occipital  condyles;  they  are 
separated  by  a  «ade  notch  above  and  a  narrow  one  below.  The  outer  margin  is  also 
notched,  and  a  triangular  non-articular  depression  cuts  into  the  inner  part  of  each 
cavity.  The  posterior  articular  surfaces  (Facies  articulares  caudales)  are  some- 
what saddle-shaped;  the>-  are  confluent  on  the  ventral  arch  below,  but  are  widely 
separated  above,  and  do  not  conform  in  shape  to  the  corresponding  surfaces  of  the 
axis. 

The  dorsal  arch  (Arcus  dorsalis)  presents  a  median  dorsal  tubercle  (Tubercu- 
lum  dorsale)  and  is  concave  below.  It  is  perforated  on  either  side  near  its  anterior 
margin  by  the  intervertebral  foramen.  The  anterior  border  is  deeply  notched,  and 
the  posterior  is  thin  and  concave. 

The  ventral  arch  (Arcus  ventralis)  is  thicker,  narrower,  and  less  curved  than 
3 


34 


THK    SKELETON    OK    THE    HORSE 


tlic  dorsal.  On  its  lower  surface  is  the  ventral  tubercle  (Tuhorculum  ventrale), 
into  which  the  terminal  tendon  of  the  longus  colli  muscle  is  inserted.  The  upper 
face  has  po.-iteriorly  a  transversely  concave  articular  surface  (Fovea  dentis),  on 
which  the  dens  or  odontoid  jiroccss  of  the  axis  rests.  In  front  of  this  is  a  transverse 
rough  excavation  for  the  attachment  of  the  odontoid  ligament. 

The  wings  ( Ahe)  are  modified  transverse  processes.  They  arc  extensive  curved 
plates  which  project  outward,  downward,  and  backward  from  the  lateral  masses. 
The  dorsal  surface  is  concave.  Between  the  ventral  aspect  of  the  wing  and  the 
lateral  mass  is  a  cavity,  the  fossa  atlantis;  in  this  there  is  a  foramen  which  opens 
into  the  vertebral  canal.  The  border  is  thick  and  rough.  Two  foramina  perforate 
each  wing.  The  anterior  one.  the  foramen  alare,  is  connected  with  tlie  interverte- 
bral foramen  by  a  short  groove.     Tiie  pc^sterior  one  is  the  foramen  transversarium. 

Development. — The  atlas  o.ssifies  from  three  or  four  centers,  one  or  two  for 
the  ventral  arch,  and  one  on  either  side  for  each  lateral  mass,  wing,  and  half  of  the 
dorsal  arch.  At  Ijirtli  the  bone  consists  of  three  pieces — the  ventral  arch  and  two 
lateral  parts,  which  arc  separated  by  a  layer  of  cartilage  in  the  dorsal  median  line. 
These  parts  are  usually  fused  at  about  six  months. 


Axis 


I  iilcrverlibrdl  for. 
I  l^osl.  artic.  process 
j  Ant.  arlic.  process 
Dorsal  crest 


^mamen        ForaiZt         I'll'rrrrlebral 

trnnsrersarium         >"•""""       Foramen 

IrdHst'ir.sdriiim 
Veidrid  crest 

Ventral  crest 

Fig.  11.— Fibst  Three  Cervical  Vebtebr.e  of  IIor.se.  Lateral  View,     (.\fter  Schmaltz,  .\tlas  .1     \nat    d 

Pferdes.) 

The  Axis 
The  axis  (Epistropheus)  is  the  longest  of  the  vertebra>,  and  is  characterized 
by  the  presence  of  the  odontoid  process,  which  projects  from  the  anterior  part  of 
the  body.  '  ' 

The  body  has  a  median  ventral  crest  wiiich  terminates  in  a  tubercle  behind. 
The  anterior  extremity  presents  centrally  the  odontoid  process  (Dens);  this  has  a 
convex  articular  surface  ventrally  for  articulation  witli  the  ventral  arch  of  the  atlas 
and  two  rough  depressions  for  the  attachment  of  the  odontoid  ligament  dor^ally' 
I'lankmg  this  on  either  sule  are  the  modified  anterior  articular  processes,  which 
have  saddle-shapetl  articular  surfaces  confluent  below  with  that  of  the  dens  The 
posterior  extremity  has  the  usual  cavity. 

Th(>  arch  presents  in  the  young  sul)ject  a  notch  on  each  side  of  its  anterior 
border;  this  is  converte.l  into  a  foramen  by  a  ligament  which  usually  ossifies  later. 
1  he  posterior  border  has  the  usual  notches. 

Tli(>  posterior  articular  processes  are  typical. 

The  transverse  processes  are  small,^  single,  and  proi(>ct  backward  The 
roramen  transversarium  is  small. 

Thr  spinous  process  is  very  large  and  strong.  Its  free  border  is  rough,  thickens 
posteriorly,  and  is  continued  to  the  articular  processes  bv  two  ridges  The  lateral 
surfaces  are  concave  and  rough  for  muscular  attachment 


THE    THOHACIC    VERTEUR.K 


35 


Development. — The  axis  has  six  or  seven  centers  of  ossification.  In  aiklition 
to  the  usual  five,  one  or  two  appear  for  the  dens,  which  is  regarded  as  the  displaced 
body  of  the  atlas.  A  nucleus  belli  nd  the  dens,  which  remains  distinct  to  three  or 
four  years  of  age,  is  considered  by  Lesbre  to  be  the  head  of  the  axis. 


Occipital  crest 


Median  crest 


PanimiiMiiiil  process^  L 


Dorsal  arch  of  atlas 


Anterior  articular  process  nj  axis 


I nterrertebral  foramen  i^      in 

i 

Foramen  transversarium 

Post,  articular  processes 
Ant.  articular  processes 

Transverse  process 
Dorsal  crest  — 


Foramen  transversarium 
Post,  articular  processes 

Fig.  12. — Occipital  Bo.ve  and  First  Three  Ckrvical  Vf.htebh.e  of  Horse,  Dorsal  View.     (After  Schmaltz, 
.Atlas  d.  .\nat.  d.  Hfenles.) 


THE  THORAQC  VERTEBRA 
These  (Vertebne  thoracales)  are  usually  eighteen  in  number  in  the  horse,  but 
there  are  sometimes  nineteen,  rarely  seventeen.     As  regional  characters  we  note 
the  surfaces  for  articulation  with  the  ribs  and  the  length  and  form  of  the  spinous 


36 


THE    SKELETON    OF   THE    HORSE 


processes.     Those  in  the  middle  of  the  series  are  the  most  t3'pical  and  present  the 
following  features: 

1.  The  bodies  are  short  and  constricted  in  the  middle.  The  ends  are  expanded 
and  have  articular  surfaces  which  are  not  strongly  curved.  On  the  upper  part  of 
each  side  are  anterior  and  posterior  costal  facets  (Fovea  costalis  cranialis,  cau- 
dalis),  which,  with  those  of  adjacent  vertebrae,  form  sockets  for  the  heads  of 
the  ribs. 

2.  The  arches  are  small.  Their  posterior  notches  are  relatively  large  and  arc 
often  converted  into  rdrainiiia. 

3.  The  articular  processes  are  small.     Tiie  anterior  jmir  are  in  fact  represented 


Anterior  nrliriilar  process 


Facet  for  head  of 


Posterior  artieulnr  process 
Transi'crse  processes 


Faci'ls  for  tubercles  of  ribs 


'tiects  for  heads  of  ribs 
Intirnrtilirdl  foramina 


Facet  fur  tubercle  of  rib 


.ric  Vkrtebr.*:  of  Ho 
d.  .\nat.  d.  Pferdes.) 


(After  Schmaltz,  Atlas 


only  by  two  oval  facets  on  the  anterior  part  of  the  laminae  which  face  almost  directly 
upward.  The  jiosterior  pair  spring  from  the  base  of  the  spinous  process;  their 
facets  face  almost  directly  dowiiward. 

4.  The  transverse  processes  are  short,  thick,  and  tuberous  at  the  free  end. 
Each  has  a  facet  (Fovea  transversaria)  for  articulation  with  the  tuberosity  of  the 
rib  which  has  the  same  .serial  number. 

5.  The  spinous  process  is  large,  narrow,  and  sK)pes  upward  and  Ijackward. 
The  anterior  border  is  thin,  the  posterior  wider  and  furrowed.  The  summit  is 
expanded  and  rough. 

The  first  thoracic  vertebra  is  easily  recognized  by  the  following  specific  charac- 
ters:  The  body  is  wide  and  flattened  dorso-vcntrally.     In  front  it  has  a  head  like 


THE    THORACIC    VERTEBRjE 


37 


the  cervical  vertebra\  and  behind  a  cavity  somewhat  deeper  than  any  other  thoracic 
vertebra.  Two  costal  facets  are  found  on  either  side,  and  a  well-marked  spine 
ventrally.  The  arch  is  large  and  strong,  and  has  large  notches.  The  articular 
processes  are  much  larger  than  those  of  other  thoracic  verteljra^  and  resemble  a 
good  deal  those  of  the  seventh  cervical  in  form.  The  transverse  processes  are 
short  and  thick,  and  each  has  on  its  ventral  aspect  a  large  concave  facet  for  articu- 
lation with  the  tubercle  of  the  first  rib.  The  spinous  process  is  curved  backward 
and  tapers  to  a  point.  Its  length  is  usually  about  three  or  four  inches  (ca.  8  to 
10  cm.).  It  may  be  mistaken  at  first  glance  for  the  last  cervical,  but  is 
promptly  identified  by  the  three  costal  facets  on  each  side  and  the  length  of 
the  spine. 

The  last  thoracic  vertebra  is  distinguished  by  the  absence  of  the  posterior  pair 
of  costal  facets,  and  the  confluence  of  the  anterior  pair 
with  those  on  the  transver.se  processes. 

The  serial  position  of  others  may  be  determined  at 
least  approximately  by  the  following  data:  (1)  The 
bodies  gradually  diminish  in  length  and  width  to  the 
middle  of  the  region  and  then  increase  slightly.  Their 
costal  facets  become  smaller  and  less  concave  from  first 
to  last.  The  ventral  crest  is  distinct  on  three  or  four 
vertebrse  at  either  end  of  the  region.  (2)  The  transverse 
processes  diminish  in  size  and  are  placed  lower  down 


Spine  — 


Facet  for  head 

"^"^  Body       of  rib        ^ 

Fig.  14. — Third  Thohacic  ^'ERTKBR.K  avd  I'pi 
OF  Rib  of  Horse,  .\nterior  View. 
Schmaltz.  Atlas  d.  .\nat.  d.  Pferdes.) 


Facets  , 
heads  of  ribs 

Fig.   15. — Lowe 
Schmaltz 


'ciilnr  rarity 
of  body 


Horse,    Posterior    View. 
.\tlas  d.  .\nat.  d.  Pferdes.) 


as  they  are  traced  backward.  Their  costal  facets  become  smaller  and  lower 
in  position;  on  the  last  (and  sometimes  on  its  predecessor  also)  it  fuses  with 
the  costal  facet  of  the  body.  The  upper  non-articular  part  of  the  process 
gradually  becomes  more  sharply  defined,  and  in  the  last  four  or  five  separates  to 
form  the  mammillary  process.  (3)  The  spinous  processes  increase  in  length  to 
the  third  and  fourth,  and  then  gradually  diminish  to  the  fifteenth,  beyond  which 
they  have  about  the  same  length.  The  backward  inclination  is  most  pronounced 
in  the  second,  the  sixteenth  is  vertical,  and  the  last  two  are  directed  a  little  forward. 
The  longest  spines  (i.  e.,  those  of  the  withers)  are  the  thickest  and  have  expanded 
summits  which  remain  more  or  less  cartilaginous;  the  others  are  more  plate-like, 
and  are  surmounted  by  a  thick  lip.  The  second  spine  is  more  than  twice  as  large 
as  the  first.  The  summits  of  the  fourth  and  fifth  usually  form  the  highest  point 
of  the  withers. 

Development.— There  are  six  or  seven  centers,  three  for  the  body,  two  for 
the  arch,  and  one  for  the  spinous  process;  some  of  the  latter  have  an  additional 
center  for  the  summit. 


38 


THE    SKELKTON    OF   THE    HORSE 


THE  LUMBAR  VERTEBRAE 
TIk"  lumbar  vertebrae  (N'ertchni'  lunil)al('s)  are  usually  six  hi  number  in  the 
horse.     They  arc  cliaractcrized  by  the  size  and  form  of  their  transverse  processes. 
The  bodies  of  the  first  three  are  triangular  on  cross-section,  and  present  a 


Spine 
A nUrior  arliciilar  processes 

■imsrcrse  process 

Transrcrse  process 
Facet  far  head  of  lirsl 


Fio.  16. — First  THORAric  Vertebra  an-d  Upper    Part  of   First  Rib   of  Horse,   .\n'terior   View.     (After 
Schmaltz,  .Vtlas  d.  .\nat.  d.  Pferdes.) 

distinct  ventral  crest.  From  the  fourth  backward  they  i)ecome  wider  and  flatter 
and  the  ventral  crest  fades  out. 

The  arches  of  the  first  two  or  three  are  about  equal  in  size  and  similar  to  that 
of  the  last  thoracic;  from  the  fourth  they  decrease  noticeably  in  breadth  and  height. 

The  anterior  articular  processes  are  fused  with  the  mammillary  processes,  and 


MammiUary  processes 


Facet  for  head  of  rib 
Facet  for  tubercle  of  rib 
liderrerle 


'oslcrior  iniiciilnr  processes 


Ilciid  of  rib 


Fi.;.   17.  — Last  Two  Tii 


on\ric  ANB  l-'i 


.IBAR    VeH 

I  d.  .\nnt. 


(.\ftcr  Schmaltz 


present  superiorly  concave  surfaces  for  articulation  with  the  posterior  pair  of  the 
precediiiK  vertebra.  The  posterior  articular  processes  project  distinctly  from  the 
arch  at  the  ba,se  of  the  si)inous  i)n)cess,  and  have  vent  rally  convex  articular  sur- 
faces, which  fit  into  the  grooved  surfaces  of  the  anterior  ])air  of  the  next  vertebra. 
The  transverse  processes  are  large  plates,  flattened  dorso-ventrallv,  which 
project  outward  ami   usually  curve  slightly  downward;    their  length  increases  to 


THE    SACRUM  39 

the  third  and  fourth,  and  then  diminishes  to  the  last,  which  is  the  shortest.  The 
first  one  or  two  usually  curve  somewhat  backwartl,  the  last  two  decidedly  forward. 
Those  of  the  fifth  have  an  oval  concave  facet  on  the  inner  part  of  the  posterior  border 
for  articulation  with  the  sixth  process;  the  latter  has  a  corresponding  convex  facet 
on  the  anterior  border,  and  a  larger  concave  surface  on  the  posterior  border  for 
articulation  with  the  wing  of  the  sacrum.  Sometimes  the  fifth  process  has  a  small 
surface  for  articulation  with  the  fourth.  The  inner  part  of  the  sixth  process  is 
thick,  the  outer  part  thinner,  narrower,  and  curved  forward.  The  inner  part  of 
the  fifth  is  also  somewhat  thickened. 

The  spinous  processes  resemlilc  those  of  the  last  two  thoracic  vertebra;. 
They  are  usually  about  equal  in  height,  but  minor  differences  are  common,  and  the 
width  diminishes  in  the  last  three. 

Development. — This  is  similar  to  that  of  the  thoracic  vertebra^.  The  extremi- 
ties of  the  transverse  processes  remain  cartilaginous  for  some  time  after  ossification 
is  otherwise  complete. 

The  transverse  processes  of  this  region  are  considered  equivalent  to  the  proper  transverse 
process  +  the  costal  element,  and  hence  the  distinctive  term  processus  lateralis  (s.  costarius) 
has  been  proposed.  The  occurrence  of  a  lumbar  rib  in  connection  with  the  transverse  process  of 
the  first  lumbar  is  not  rare.     Reduction  of  the  number  to  five  has  been  observed  frequently,  and 


Ma  m  III  illfi  rij  processes 
Aiiteriar  articular  prac 


Transverse 
process 


Ventral  spine     N^I^LjP^   Body 
Fig.  is. — .Skcoxd  Lumbar  Vp:rtebra  of  Horse,  Anterior  View.     (After  Schmaltz,  .\tla.-5  d.  .\nat.  d.  Pferden.) 

may  or  may  not  be  compensated  by  an  aflditional  thoracic  \-ertebra.  This  variation  is  not  more 
common  in  certain  races  as  Sanson  and  others  have  maintained.  \  erj'  few  cases  are  recorded  of 
seven  lumbar  vertebra? — especially  with  the  normal  thoracic  number.  An  anomalous  vertebra 
with  mixed  thoracic  and  lumbar  characters  sometimes  occurs  at  the  junction  of  the  two  regions. 


THE  SACRUM 

The  sacrum  (Os  .sacrum)  is  formed  by  the  fusion  of  five  vertebrje  usually,  and 
is  conveniently  described  as  a  single  bone.  It  is  triangular  in  form  and  is  wedged 
in  between  the  ilia,  with  which  it  articulates  very  firmly  on  each  side.  Its  long 
axis  is  gently  curved,  and  slightly  oblique,  so  that  the  posterior  end  is  a  little  higher 
than  the  anterior.     It  presents  two  surfaces,  two  borders,  a  base,  and  an  apex. 

The  dorsal  surface  presents  centrally  the  five  sacral  spines,  which  are  directed 
upward  and  backward,  and  have  (with  the  exception  of  the  first)  tuberous  summits 
which  are  sometimes  bifid. 

The  first  spine  is  relatively  thin  and  narrow,  and  is  not  so  high  as  the  internal  angle  of  the 
ilium.  The  second  is  the  longest,  and  the  height  diminishes  rapidly  to  the  last.  The  bases  of  the 
spines  are  often  fused  in  old  subjects. 

On  either  side  of  the  spines  is  a  groove,  in  which  are  the  four  dorsal  sacral 


40 


THE    SKELETON    OF   THE    HOESE 


foramina  (Foramina  sacralia  dorsalia);  the  dorsal  branches  of  the  sacral  nerves 
enierKc  through  tlu'in. 

The  ventral  or  pelvic  surface  (Facies  pelvina)  is  concave  in  its  length,  wide  in 
front,  narrow  behind.  It  is  marked  by  four  more  or  less  distinct  transverse  lines 
(Linea'  transversir),  which  indicate  the  demarcation  of  the  bodies  of  the  vertebrtr. 
At  the  ends  of  these  lines  are  the  ventral  sacral  foramina  (Foramina  sacralia 
ventralia),  which  are  larger  than  the  dorsal  series  and  diminish  in  size  from  first 
to  last;   they  transmit  the  ventral  divisions  of  the  sacral  nerves. 

The  tlorsal  and  ventral  foramina  communicate  with  the  sacral  canal  and  are 
together  eciuivalent  to  the  usual  intervertebral  foramina. 


2   C     2'       1' 


Fio.  19. — Sacbi-m  of  Horse,  Dobso-latf.hal  View. 
r,  Body  of  first  sacral  vertebra;    .1.  arch  of  first  vertebra;    Ca.  sacral  canal;   P.s.  1-5   .sacriil  .-pines-    Pt 
»in«p.  of  sacrum;    I.  1',  surfaces  for  articulation  with  transverse  processes  of  last  lumbar  vertebra-    /■'  a     auricul-i'r 
rs[!',T   -:-''''7'="'»'-»™'=«f»«'-   3-C,  dorsal  sacral  foramina;    7,  in.erarcuate  space;   S,  lateral  border";   A,  apex 


The  lateral  borders  are  rough,  thick  in  front,  thin  Ijehiiul. 

The  base  (Basis  (j.ssis  .sacri)  is  directed  forward,  and  is  relatively  very  wide 
It  presents  centrally  the  body  of  the  first  sacral  segment,  which  is  wide  transversely 
Hattened  dor.so-ventrally,  and  has  a  rounded  .surface  which  articulates  with  the 
last  lumbar  vertebra  through  the  medium  of  an  intervertebral  fibro-cartilage 
\r  ' Ti  .  '^-'^'■.g'"  I'rojects  slightly,  forming  the  promontory  (Promontorium). 
Above  the  body  is  the  entrance  to  the  sacral  canal,  flanked  by  a  pair  of  articular 
processes,  which  project  upward  and  forward  from  the  arch",  and  have  concave 
sur  a.vs  internally  for  articulation  with  those  of  the  last  lumbar  vertebra.  On 
with  ,7''',"^/  '''■'^'',  '^  ^  «'""°^1'  "«t''h  which  is  converted  into  a  foramen  bv  apposition 
with  the  last  lumbar.     1  he  lateral  parts  of  the  base,  the  wings  or  al*  (Ala-  sacrales), 


THE    COCCYGEAL    VERTEBRiE  41 

are  strong  prismatic  masses  with  pointed  ends,  which  result  from  the  fusion  of  the 
first  with  part  of  the  second  transverse  process.  Each  has  in  front  a  large,  oval, 
slightly  convex  surface  for  articulation  with  the  transverse  process  of  the  last  lum- 
bar. Posteriorly  there  is  an  elongated  oval  area  which  faces  upward,  backward, 
and  outward.  This  is  the  auricular  surface  (Facies  auricularis),  which  articulates 
with  the  ilium;  it  is  slightly  concave  in  its  length,  and  somewhat  rough  and  irregu- 
lar. The  rest  of  the  dorsal  surface  of  the  wing  is  roughened  for  ligamentous  attach- 
ment, while  the  ventral  surface  is  smooth. 

The  apex  (.\pex  ossis  sacri)  is  the  posterior  aspect  of  the  last  sacral  vertebra 
and  is  ciuite  small.  It  presents  the  elliptical  flattened  surface  of  the  body,  above 
which  is  the  triangular  posterior  opening  of  the  sacral  canal,  surmounted  by  the 
last  sacral  spine.  There  is  a  pair  of  narrow  notches  between  the  arch  and  body, 
above  which  rudiments  of  articular  processes  may  occur. 

The  name  sacral  canal  (Canalis  sacralis)  is  applied  to  that  part  of  the  vertebral 
canal  which  traverses  the  sacrum.  Its  anterior  part  is  large  and  has  the  form  of 
a  triangle  \^-ith  the  angles  rounded  off;  its  width  is  about  twice  its  height.  Traced 
backward  it  is  seen  to  diminish  in  size  rapidly,  and  the  po.sterior  opening  is  quite 
small  and  triangular. 

The  term  lateral  part  (Pars  lateralis)  designates  the  portion  external  to  the 
foramina,  which  results  from  the  fusion  of  the  transverse  processes. 


Spine 


Vertebral  canal 


Body  Posterior  end  of  body 


Fig.    20. — First    Coccvghal    Vertebra    of    Horse,        Fig.    21. — First    Coccygeal    Vertebra    of    Horse, 
Left  View.     (After  Schmaltz,  Atlas  d.  Aoat.  Dorsal  View,     (.\fter  Schmaltz,  Atlas  d.  .\nat. 

d.  Pferdes.)  d.  Pferdes.) 

Development. — The  several  sacral  vertebrte  ossify  in  the  t^-pical  manner. 
Separate  centers  for  costal  elements  in  the  lateral  parts  have  not  yet  been  found  in 
the  domesticated  animals.  Fusion  begins  in  front,  and  is  usually  not  complete 
behind  till  near  adult  age.  The  lateral  parts  unite  before  the  bodies.  It  is  rather 
curious  that  the  epiphyseal  plates  of  adjacent  segments  unite  with  each  other  before 
they  fuse  with  the  main  portion  of  the  bodies. 


THE  COCCYGEAL  VERTEBRA 
These  (Vertebrae  coccygeal)  vary  considerably  in  number,  but  eighteen  maj' 
be  taken  as  an  average.  From  first  to  last  they  become  reduced  in  size  and,  with 
the  exception  of  a  few  at  the  beginning  of  the  series,  consist  of  bocUes  only.  The 
first  three  have  bodies  which  are  somewhat  flattened  dorso-ventrally,  constricted 
in  the  middle,  and  have  at  the  ends  slightlj-  convex,  elliptical,  articular  surfaces. 
The  ventral  surface  has  a  median  groove  for  the  coccj'geal  arterj-.  The  arch  is 
small  and  triangular;  it  is  formed  of  two  fiat  plates  which  are  prolonged  to  form  a 
short  spinous  process  with  a  thickened  and  often  double  summit.  The  anterior 
notches  are  absent.  Functional  articular  processes  are  not  present,  but  small 
rudiments  of  the  anterior  pair  commonly  occur.  The  transverse  processes  are 
relatively  large  plates  which  project  horizontally  outward.  Further  back  the  arch 
becomes  incomplete,  open  above,  and  soon  disappears;    the  transverse  processes 


42  THE  SKELETON  OF  THE  HORSE 

gradually  fade  out,  and  the  vertebra?  are  reduced  to  cylindrical  rods  of  diminishing 
size.     The  last  one  has  a  pointed  end. 

Variations.— The  number  is  said  by  good  observers  to  vary  lietween  fourteen  and  twenty- 
one.  In  old  age  the  fii-st  is  often  fused  with  the  sacrum,  and  sometunes  with  the  second.  Ihe 
arch  of  the  third  may  be  open. 

THE  VERTEBRAL  COLUMN  AS  A  WHOLE 

In  the  mid-dorsal  line  is  the  series  of  spinous  processes,  which  are  low  ridges 
in  the  cervical  region  with  the  exception  of  the  .-second  and  seventh,  reach  their 
maximum  height  at  the  fourth  and  fifth  tlioracic  vertebra?,  and  diminish  to  the 
fifteenth  or  sixteenth  thoracic.  Behinil  this  they  are  about  equal  in  height  as  far 
as  the  last  lumbar  and  first  sacral,  which  arc  somewhat  lower.  The  second  sacral 
spine  is  about  as  high  as  the  middle  lumbar;  behind  this  they  diminish  rather 
rapidly  in  height  and  fade  out  about  the  third  coccygeal.  Their  inclination  back- 
ward is  most  tlecided  at  the  second  thoracic,  diminishes  from  the  sixth  or  seventh 
to  the  fifteenth  or  sixteenth,  which  is  vertical  and  is  termed  the  anticlinal  or 
diaphragmatic  vertebra.  Behind  this  they  are  inclined  a  little  forward  until  tlie 
sacrum  is  nachetl;  here  there  is  an  abrupt  change  to  the  backward  inclination,  so 
that  a  considerable  interspinous  angle  is  formed. 

On  either  .side  of  the  spinous  processes  is  a  vertebral  groove  which  contains  the 
deep  nmscles  of  the  spine.  The  floor  of  the  groove  is  formed  by  the  lamina?  and 
articular  processes.     It  is  wide  in  the  neck  and  narrows  progressively  in  the  back. 

Viewed  from  the  side,  the  column  presents  a  series  of  curves.  When  the  head 
and  neck  are  in  the  ordinary  neutral  position,  the  anterior  part  of  the  cervical  spine 
forms  a  gentle  curve,  concave  ventrally.  The  posterior  cervical  and  first  thoracic 
vertebra?  form  a  more  pronounced  curve  in  the  opposite  direction.  At  the  junction 
of  the  cervical  and  thoracic  regions  there  is  a  marked  change  of  direction,  forming  a 
ventral  ])rojection  or  angle.  At  the  second  thoracic  vertebra  a  gentle  curve,  con- 
cave ventrallj',  begins.  This  is  continued  to  the  lumbo-sacral  junction,  where 
there  is  a  change  of  direction,  and  hence  a  promontory.  The  sacrum  has  a  variable, 
but  never  very  pronounced,  ventral  concave  curvature,  which  is  continued  in  a 
much  accentuated  form  in  the  coccygeal  region.  It  may  be  remarked  that  a  line 
through  the  summits  of  the  spines  does  not  correspond  to  these  curves  formed  bj- 
the  bodies. 

The  vertebral  canal,  of  cour.se,  corresponds  in  curvature  to  the  bodies.  Its 
caliber  varies  greatly  at  different  i)oints.  The  greatest  diameter  (ca.  5  cm.)  is  in 
the  atlas,  where  it  contains  the  dens  of  the  axis  in  addition  to  the  spinal  cord,  and 
provision  must  be  made  for  extensive  movement.  It  is  very  much  smaller  in  tlie 
axis  (ca.  2..5  cm.  wide,  3  cm.  high).  It  widens  con.sidcrably  at  the  junction  of  the 
cervical  and  thoracic  regions  to  accommodate  the  cervical  enlargement  of  the  spinal 
cord.  Beyond  this  it  diminishes,  and  is  smaller  in  the  middle  of  the  back  than  at 
any  preceding  point;  this  is  correlated  with  the  small  size  of  the  spinal  cord  and  the 
very  limited  movement  of  the  spine.  At  the  middle  of  the  lumbar  region  it  again 
widens  consitlerably  to  contain  the  lumbar  enlargement  of  the  spinal  cord.  The 
caliber  diminishes  very  rapidly  from  the  second  sacral  segment  liackward,  and  the 
canal  cea.ses  to  l)e  complete  at  the  fourth  coccygeal  vertebra. 

The  articular  processes  are  very  large  and  wide  apart  in  the  neck,  greatly 
reduced  and  much  closer  together  in  the  back,  larger  and  interlocking  in  the  lumba- 
region. 

The  transverse  processes  arc  large  and  outstanding  in  the  neck,  where  they 
form  the  outer  boundary  of  a  ventral  groove  occupied  by  the  longus  colli  muscle. 
In  the  back  they  are  short  and  stout,  and  are  characterized  by  the  facets  for  the 
tubercles  of  tlie  ribs.     On  the  first  thoracic  vertebra  this  facet  is  large,  deeply  con- 


THE    RIBS  43 

cave,  and  situated  alnio.st  directly  outward  from  the  cavity  for  the  head  of  tiie  rib; 
traced  backward  it  becoine.s  smaller  and  flatter,  and  gradually-  comes  to  lie  behind 
the  cavity  for  the  head  of  the  rib,  with  which  it  is  fused  on  the  last  and  often  also  on 
the  next  to  the  last  thoracic  vertebra.  The  processes  in  the  lumbar  region  have  a 
characteristic  elongated  plate-like  form.  In  the  sacral  region  they  are  fused  to 
form  the  wings  and  lateral  parts  of  the  sacrum.  In  the  coccygeal  region  they  are 
at  first  of  considerable  size  relatively,  but  undergo  rapid  reduction,  and  disappear 
at  the  fifth  or  sixth  vertebra. 

The  cavities  for  the  heads  of  the  ribs  diminish  progressively  in  size  and  depth 
from  first  to  last. 

The  mammillary  processes  are  usually  distinct  on  the  fourteenth  to  the  .seven- 
teenth thoracic  vertebriP.  In  front  of  these  they  blend  with  the  transverse,  behind 
with  the  anterior  articular  processes. 

The  length  of  the  vertebral  column  (including  the  intervertebral  fibro-cartilages)  in  a  hor.sc 
of  medium  size  is  about  260  to  265  cm.  (ca.  8  feet  8  inches  to  8  feet  10  inches).  The  relative  lengths 
of  the  various  regions  appear  to  vary  most  in  the  neck  and  back. 

The  table  below  gives  the  measurements  in  centimeters  in  a  trotting  stallion  of  medium  size 
and  in  an  adult  Percheron  stallion.     The  percentages  are  in  round  numbers. 


1 

60.0 

22.7% 
37.2% 
12.0% 

7.6% 
20.5% 

74.0 
100.0 
36.5 
22.5 
58.0 

25.4% 

Thoracic 

Lumbar 

Sacral 

9S.0 
31.5 
20.0 
.^4  0 

34.4% 

12.5% 

7.7% 

20.0% 

263.5 

100.0 

291.0 

100.0 

The  Ribs 

There  are  usually  eighteen  pairs  of  ribs  in  the  horse,  but  a  nineteenth  rib  on 
one  side  or  both  is  not  at  all  rare.  Eight  are  sternal  or  "true"  ribs,  the  remainder 
asternal  or  "false."  Ribs  from  different  parts  of  the  series  vary  much  in  length, 
curvature,  and  other  characters.  We  will  therefore  consider  as  a  type  a  rib  from 
the  middle  of  the  series  first,  and  afterward  note  the  chief  serial  differences  A 
t3rpical  rib  has  the  following  characters: 

The  shaft  or  body  (Corpus  costae)  is  elongated,  relatively  very  narrow,  and 
strongly  curved;  the  curvature  is  most  pronounced  in  the  dorsal  third,  and  the 
ventral  part  is  twisted  and  inclined  inward,  so  that  when  a  rib  is  laid  with  its  outer 
surface  on  the  table,  the  ventral  end  is  raised.  The  external  surface  is  convex  in 
its  length  and  also  transversely;  its  anterior  ])art  is,  however,  grooved  longitudin- 
ally. A  distinct  angle,  ('.  e.,  a  point  at  which  the  curve  of  the  rib  changes  rather 
suddenly,  as  in  man,  can  scarcely  be  said  to  exist  in  the  horse.  The  term  is  often 
applied,  however,  to  a  corresponding  rough  elevation  which  gives  attachment  to  the 
ilio-costalis  muscle;  it  is  most  distinct  on  the  fourth  to  the  eighth  inclusive.  The 
internal  surface  is  smooth,  concave  in  its  length,  and  rounded  from  side  to  side; 
the  costal  groove,  situated  posteriorly,  is  very  distinct  above  and  fades  out  about 
the  middle.     The  anterior  border  is  concave,  the  posterior  convex. 

The  vertebral  extremity  (Extremitas  vertebralis)  consists  of  the  head,  neck, 
and  tubercle.  The  head  (Capitulum  costa>)  has  an  articular  surface  (Fades 
articularis  capituli  costa>),  composed  of  two  convex  facets,  anterior  and  posterior, 
separated  by  a  groove  for  the  attachment  of  the  conjugal  ligament.  It  articulates 
with  the  cavity  formed  by  facets  on  the  bodies  of  two  adjacent  thoracic  vertebrae 


44 


THE    SKELETON    OF   THE    HORSE 


Tubercle 


and  the  intcrvcrtpbral  filjro-cartilage.  The  neck  (Collum  costse)  is  roughened 
above  and  in  front.  Tlie  tubercle  (Tul)ercuhnn  cost;e)  is  placed  above  and  behind 
the  junction  of  neck  and  shaft;  it  has  a  small  surface  (Fades  articularis  tuberculi 
costa;)  for  articulation  with  the  transverse  process  of  the  corresponding  thoracic 
vertebra. 

The  sternal  extremity  (Extreniitas  sternalis)  is  somewhat  expanded,  and  is 
continued  by  the  costal  cartilage. 

The  first  rib  is  easily  distinguished.  It  is  the  shortest  and  least  curved.  At 
the  lower  jiait  of  the  anterior  border  there  is  a  smooth  impression  where  the  brachial 
vein  curves  around  it;    above  this   is  usually  the  scalene  tubercle.     The  costal 

groove  is  absent.  The  head  is  large  and 
has  two  facets  of  unequal  extent  which 
meet  at  an  acute  angle  in  front ;  the  smaller 
one  faces  forward  and  articulates  with  the 
last  cervical  vertebra;  the  larger  one  is 
flirected  inward  and  articulates  with  the 
first  thoracic  vertebra.  The  neck  is  thick 
and  very  short.  The  tubercle  is  larger  than 
that  of  any  other  rib  and  has  an  extensive 
articular  surface  which  is  convex  in  its 
length.  The  sternal  end  is  larger  than  that 
of  any  other  rib;  it  is  thick  and  very  wide, 
and  is  turned  a  little  forward. 

The  last  rib  is  the  most  slender  and 
regularly  curved.  It  is  usually  but  little 
longer  than  the  second.  The  facet  on  the 
tubercle  is  confluent  with  that  of  the  head. 
(This  feature,  however,  is  usual  on  the 
seventeenth  also,  and  not  rare  on  the  six- 
teenth.) 

The  serial  position  of  the  other  ribs  may 
l)e  determined  approximately  by  the  follow- 
ing considerations:  The  length  increases 
from  the  first  to  the  tenth  and  eleventh 
and  then  diminishes.  The  width  increases 
somewhat  to  tlie  sixth  and  then  diminishes. 
The  anterior  border  is  thin  and  sharp  from 
tlie  second  to  the  eighth,  and  behind  this 
becomes  thick  and  rounded.  The  external 
groove  is  distinct  on  the  fourth  to  the  eighth 
inclusive.  The  curvature  increases  in  de- 
gree rapidly  from  the  first  to  the  seventh, 
remains  about  the  same  to  the  sixteenth,  and 
then  decreases  very  noticeably.  In  regard 
to  florso-ventral  direction,  the  first  rib  inclines  a  little  forward,  the  second  is  about 
vertical,  wliile  behind  this  tliey  slope  backward  in  increasing  degree,  so  that  a 
plane  tangent  to  tlie  ventral  ends  of  the  last  pair  cuts  the  tliird  lumbar  vertebra. 
The  head  and  tubercle  (hminish  in  size  from  first  to  last.  Their  relative  positions 
change  in  that  tlie  tubercle  of  the  first  rib  lies  almost  directly  outward  from  the 
heatl,  while  further  back  it  gradually  comes  to  lie  behind  it.  The  neck  is  longest 
on  the  l()ngest  rilis,  and  is  absent  on  the  last  two  or  three.  A  costo-transverse 
foramen  is  foniied  between  the  neck  and  the  transverse  process. 

Development.— The  ribs  ossify  in  cartilage  from  three  centers,  one  each  for  the 
shaft,  head,  and  tubercle;    the  third  center  is  absent  in  some  of  the  posterior  ribs. 


Fio.  22. — LkktSkvknth  RinoF  Horse.  Antero- 
KXTKHNAL  ViEW.  (After  Schmaltz,  Atlas 
<1.  Anat.  d.  Pfenles.) 


THE    COSTAL    CARTILA(iES — THE    STERNUM  45 

Variations. — A  nineteenth  rib  on  one  side  or  both  is  not  rare.  It  is  usually  imperfectly 
developed  and  quite  variable.  In  some  cases  it  is  a  mere  strip  of  cartilaKe  connrcted  by  licament 
with  the  first  lumbar  transverse  process;  in  other  cases  it  is  (issifie<i,  and  may  lie  fused  with  the 
process;  in  others  again  it  is  connected  with  an  additional  presacral  vertebra  which  may  be 
thoracic  or  lumbar  or  ambiguous  in  character,  it  is  commonly  floating,  but  may  be  attached  to 
the  eighteenth.     Reduction  in  number  is  uncommon.     Fusion  of  adjacent  ribs  sometimes  occurs. 


THE  COSTAL  CARTILAGES 
The  first  costal  cartilage  is  an  inch  or  more  (2.5  to  3  cm.)  in  length.  The  upper 
part  is  very  wide  and  thick.  The  sternal  end  is  small.  The  two  articulate  with 
each  other  as  well  as  with  the  sternum.  The  cartilages  of  the  other  sternal  ribs 
increase  progressively  in  length  and  become  more  rounded.  The  sternal  end  is 
expanded  and  has  an  elliptical  convex  facet  for  articulation  with  the  sternum.  The 
cartilages  of  the  asternal  ribs  are  long,  slender,  and  pointed.     The  ninth  is  the 

Ir  CariniJ'orni  cartilage 

Ventral  hor  tcr •jH^ 

Costal  cartilages  -^ II       /  y^-- Ribs 


"^^^       ^sJLm'  ^-^ 

Xiphoid  cartilage 

Fig.  23.— Sternum  .a.nd  Costal  C.4Rtil.\gks  of    Horse,  Vextr.il  View.     (After  Ellenberger-Baum,    Anat.  f. 

Kunstler.) 

longest,  and  is  very  finnly  attached  to  the  eighth;  behind  this  they  diminish  pro- 
gressively in  size,  and  are  attached  to  each  other  by  elastic  tissue.  Except  in  the 
case  of  the  first,  the  cartilage  does  not  continue  the  direction  of  the  rib,  but  forms 
with  the  latter  an  angle  which  is  open  in  front,  and  decreases  in  obtuseness  from 
second  to  last. 

More  or  less  extensive  ossification  is  to  be  regarded  as  a  normal  occurrence, 
especially  in  the  cartilages  of  the  sternal  ribs. 

The  Sternum 

The  sternum  of  the  horse  is  shaped  somewhat  like  a  canoe;  it  is  compressed 
laterally,  except  in  its  posterior  part,  which  is  flattened  dorso-ventrally.  It  is 
inclined  obliquely  so  that  the  posterior  end  is  about  six  to  eight  inches  (15  to  20 
cm.)  lower  than  the  anterior. 

The  dorsal  surface  has  the  form  of  a  very  narrow  isosceles  triangle  with  the 
apex  in  front.     It  is  concave  longitudinally,  flattened  transversely. 

The  lateral  surfaces  are  convex  above,  slightly  conca^-e  below,  and  dimmish 
in  extent  behind.  Each  presents  on  its  upper  part  seven  articular  cavities  (Foveae 
costales),  which  receive  the  sternal  ends  of  the  second  to  the  eighth  costal  cartilages 
inclusive.     These  cavities  are  situated  in  series  at  the  intersternebral  junctions. 


46 


THE    SKELETON    OK    THE    HORSE 


The  first  four  arc  elliptical  in  outline  with  the  Ions  diameter  vortical,  and  are  sep- 
arated i)y  considerable  regular  intervals.  The  others  are  ]irogrcssivcly  smaller, 
more  circular,  and  closer  together.  The  area  below  these  cavities  gives  attachment 
to  the  pectoral  muscles. 


Fir,.  24. — Stkrntm  ok  Hor.<i-,.  Latkrai.  Vu.w. 
Tho  sternebrtr  are  ilesiKiiateil  by  Kciman  numpials  ami  the  costal  facets  by  ordinary  figures. 


First  rib 


The  dorso-lateral  borders  separate  the  dorsal  and  lateral  surfaces.     They  give 
attachincnt  to  tho  lateral  branches  of  tho  sternal  ligament. 

Tho  ventral  border  forms  the  prominent  kool-like  crest  of  the  sternum  (Crista 
sterni)  which  may  i)o  felt  in  tho  living  animal;    it  fades  out  behind. 

The     anterior     extremity    or     manubrium 

L  sterni'    can    be    distinctly    felt    in    the    central 

furrow  of  the  l)reast.     It   consists  of  a  laterally 
(■()m])rosso(l  cartilaginous  prolongation,  commonly 
called  the  cariniform  cartilage.    Its  lateral  surfaces 
')  are  flat  and  furnish  attachment  to  muscles  of  the 

l)roast  and  nock.  The  ventral  border  is  rounded, 
anil  is  continued  backward  on  the  body  of  the 
1)0110.  The  dorsal  border  is  concave  and  has  an 
articular  cavity  for  tho  first  pair  of  costal  cartil- 
ages. 

The  posterior  extremity  is  formed  by  the 
xiphoid  or  ensiform  cartilage  (Processus  xiphoi- 
dous).  This  is  a  thin  ])lato,  connected  in  front 
with  the  last  bony  segment  by  a  relatively  thick, 
narrow  neck,  and  expanding  in  nearly  circular 
form  behind  and  laterally.  Its  dorsal  surface  is 
concave,  and  gives  attachment  to  the  diaphragm. 
The  vtmtral  surface  is  convex.  Tho  free  margin 
is  very  thin. 

Development. — At  birth  the  sternum  of  the 
hor.se  consists  of  seven  bony  segments  or  sternebra? 
united  by  intor.stornoliral  cartilages.  The  last  two 
sttTnobnp  fuse  in  the  second  month,  but  the 
others  do  not  usually  unite  completely  oven  in 
old  age.  The  sternebra"  consist  of  very  vascular 
spongy  bone  cover(>(l  by  a  very  thin  layer  of  com- 
pact substance.  The  adult  sternum  thus  con- 
sists to  a  very  considerable  extent  of  persisting 
cartilage,  viz.,  the  interstornobral  cartilages,  tho  ventral  keel,  and  the  extremities; 
in  old  ago  these  undergo  partial  ossification. 

'Tlip  manubrium  .storni  of  man  is  cciuivalcnt,  slrictlv  speaking,  to  the  cariniform  faitilage 
+  I  lie  first  osijeous  segment  of  the  horse. 


Fig.  25.— .An 

WAX    O 


KRIOR    APKRTl'RK    OF    THO 

HoRKK.     (.\fter  .Schmaltz 
.\nat.  .1.  Pfenles.) 


THE    THORAX — THE    OCCIPITAL    BONE 


47 


THE  THORAX 

The  bony  thorax  of  tlie  horse  is  reinarkal)ly  compressed  laterally  in  its  anterior 
part,  but  widens  greatly  behind.  The  anterior  aperture  is  oval  and  very  narrow- 
below;  in  a  horse  of  medium  size  its  greatest  width  is  about  4  inclies  (10  cm.),  and 
its  height  7  to  8  inches  (ca.  18  to  20  cm.).  The  ventral  wall  or  floor  is  about  Hi 
inches  (40  cm.)  long,  and  the  dorsal  wall  or  roof  aliout  38  to  40  inches  (05  to  100 
cm.)  long.  The  height  from  the  last  segment  of  the  sternum  to  the  seventh  or 
eighth  thoracic  vertebra  is  about  twice  that  of  the  anterior  aperture ;  this  is  due  to 
the  obliquity  and  divergence  of  the  roof  and  floor.  The  greatest  width  of  the  pos- 
terior aperture  is  about  20  to  24  inches  (50  to  60  cm.).  The  intercostal  spaces 
increase  in  width  from  the  first  to  the  seventh  or  eighth,  and  then  diminish.  Their 
average  width  is  about  l'^  to  1.^  2  inches  (3  to  3.5  cm.). 


The  Bones  of  the  Skull 
(a)  bones  of  the  cranium 

The  bones  of  the  cranium  (Ossa  cranii)  are  the  Occipital.  Sphenoid,  Ethmoid, 
Interparietal,  Parietal,  Frontal,  and  Temporal.  The  first  four  are  single,  the  others 
paired. 


OcciiJttdl  rci 
Occipital  ciiiiilyl 


^\^Sii  priuicci  [fital 


Exliriial  auditory  iiiealus 

atinoid  cavity  of  squamous  temporal 
y  Parietal 

Orbital  wing  of  sphenoid 
ff  !)(i  ^  Frontal  crest 

Frontal  born 


Vascular  iini.ression 


Fig.  26.— Skull,  Atlas,  axd  .\xis  of  Horse,  Lateral  View. 
8,  Bmlv  of  mandible;  28',  horizontal  (molar)  part  of  ramus;  30,  vertical  part  of  ramus;  9,  zygomatic 
process  of  squamous  temporal;  U.  coronoid  process  of  mandible;  12,  supraorbital  process;  1.3".  paramastoid 
(styloid)  process  of  occipital;  19,  orbit;  20,  malar  bone;  21,  lacrimal  bone;  22,  nasal  bone;  2.3,  prema.xilla; 
23',  nasal  process  of  premaxilla;  25,  29,  canine  teeth;  26,  maxilla;  27,  facial  crest;  31,  coiitl.vie  of  inandible; 
32,  atlas;   33.  axis;  x.  wing  of  atlas;  e.  naso-maxillary 


(.\fter  EUenberger-Baum,  .\nal.  fiir  Kilnstler.) 


The  Occipital  Bone 
The  occipital  bone  (Os  occipitale)  is  situated  at  the  posterior  part  of  the  cra- 
nium, of  which  it  forms  the  posterior  wall  and  part  of  the  ventral  wall  or  base.' 
'The  long  a.xi.s  of  the  skull  is  considered  to  be  horizontal  in  these  descriptions. 


48 


THK    SKELETON    OF   THE    JIORSE 


Its  lower  part  is  perforated  centrally  by  a  large,  almost  circular  opening,  the 
foramen  magnum  (Foramen  occipitale  magnum),  at  which  the  brain  and  spinal 
cord  join.  The  foramen  is  bounded  laterally  and  dorsally  by  the  lateral  parts  of 
the  bone,  and  ventrally  by  the  basilar  part  or  process.  Aliove  the  lateral  parts- 
hut  not  entering  into  the  formation  of  the  foramen  magnum— is  the  squamous  part. 

The  lateral  parts  (Partes  laterales)  bear  the  occipital  condyles  (Condyli 
occii)itales),  whicii  articulate  with  the  atlas.  The  condyles  are  obliquely  placed, 
wide  apart  dorsally,  and  separated  by  a  small  interval  ventrally.  The  articular 
surface  is  curved  so  sharply  in  the  dorso-ventral  direction  as  to  form  a  blunt  ridge 


Occipilal  crest 
Upper  border  of 
Foramen  magnum   - 

Hypoglossal  foramen "• 

For.  lacerum  poslerius 

Slylo-masloid  foramen  — 

Ilyoid  process ^ 

Muscular  process  .. 

For.  lacerum  anterius  -"/j 
Tubercles  at  spheno- 
occipital junction 

Alar  foramen  -4- 

Plerygoid  process 
of  sphenoid 
Pterygoid  bont 

Vomer  (nice)  ._ 
Pterygoid  process  of 
pidate  bone 
Palate  bone  (perpen- 
dicular part) 
Alveolar  tuberosity 

Posterior  narcs  . 
Lust  molar  tooth  - 


^[edian  crest  for  Ug.  nuchce 
Occipital  condyle 
ParamaMoid  process 
Condyloid  fossa 
Mastoid  process 
Bidhi  ossca 

Postglcnoid  /iroccss 

Glenoid  caiity 

Temporrd  condyle 
Zygomiilir  process 
Ittfratemporal  fossa 

Zygomatic  process  of 
malar 

Pterygo-palatine  fossa 
Maxillary  hiatus 
-  MaTillary  tuberosity 
Facial  crest 
Hamulus  of  pterygoid 
Vomer 

Palate  lione  (horizon- 
tal part) 
Ant.  palatine  foramen 

Palatine  groove 

Palatine  process  of 
maxilla 

Fir..  27.— LisK  Drawing  ov  Posterior  Half  of  Base  of  Skui.i.  of  Horse,  Without  Mandiih.e.     (Ke.v  to 

Fig.  28.) 
1.  Inrisiir.i  carolica;    2.  incisura  ovali.s;    3,  incisura  ^pinosa;    4,  external  orifice  of  paricto-tcmporal  canal; 
S.  Eustachian  canal;    fi,  iictro-tympanic  fiiaure;    7.  external  auditory  canal;    8,  hyoiil  proces,s;    9,  Vidian  groove; 
10.  supraorbital  procew;    .1.  basilar  part  of  occipital;    B,  body  of  .sphenoid;    C,  temporal  wing  of  sphenoid;    D, 
squamous  temporal  bone;   E.  petrous  temporal  bone;   /•',  orbital  part  of  frontal  bone. 


externally.  The  cranial  surface  is  concave  and  smooth.  External  to  the  condyle  is 
the  paramastoid  or  styloid  process  (Processus  jugularis),  a  strong  flattened  bar  of 
bone  which  projects  downward  and  liackward;  its  external  surface  is  convex  and 
roughened  for  muscular  attachment.  Between  the  root  of  this  process  and  the 
condyle  is  a  smooth  deiire.ssion,  the  condyloid  fossa  (Fossa  condyloidea  inferior); 
in  this  is  the  hypoglossal  foramen  (Foramen  hyi)oglossi),  which  transmits  the  nerve 
of  like  name. 

The  basilar  part  or  process  (Pars  basilaris)  is  a  strong,  somewhat  prismatic 
bar  which  extends  forward  from  the  ventral  margin  of  the  foramen  magnum.     It 


THE    OCCIPITAL    BONE 


49 


is  inuch  narrower  in  front  tlian  behind.  The  ventral  surface  is  rounded.  The 
cranial  surface  is  concave  and  smooth;  its  posterior  part  supports  the  medulla, 
and  its  anterior  part  has  a  shallow  cavity  on  which  the  pons  rests.  The  lateral 
borders  are  thin  and  sharji,  and  form  the  inner  margin  of  the  foramen  lacerum 
(Foramen  lacerum  et  jugulare).     The  anterior  end  has,  in  the  young  subject,  a 


'  V 


The  skuU  is  inclined  sliglitly.     (Notation  on  liey  fig.  27 


semicircular,  flat,  pitted  surface  which  is  attached  to  the  body  of  the  sphenoid  bone 
by  a  layer  of  cartilage;  in  the  adult  there  is  complete  fusion.  On  the  ventral  aspect 
of  the  junction  are  tubercles  for  the  attachment  of  the  ventral  straight  muscles  of 
the  head. 

The  squamous  part  (Squama  occipitalis)  is  the  somewhat  quadrilateral  mass 
4 


50  THE  SKELETON  OF  THE  HORSE 

situated  ahovo  the  lateral  portions,  from  which  it  remains  distinct  til!  the  second 
year  The  outer  surface  is  crossed  by  a  very  prominent  ridge,  the  occipital  crest; 
the  middle  part  of  this  is  thick,  transverse  in  direction,  and  forms  the  highest  point 
of  the  skull  when  the  head  is  in  the  ordinary  position;  laterally  it  becomes  thinner 
and  runs  downward  and  forward  to  join  the  temporal  crest.'  The  crest  divides 
the  surface  into  two  verv  unequal  parts;  the  small  anterior  area  (Planum  parietale) 
presents  a  median  rid-je  which  is  the  posterior  part  of  the  external  sagittal  crest; 
the  lar're  area  below  Ihe  crest  (Planum  nuchale)  also  has  a  central  eminence,  the 
external  occipital  protuberance,  on  the  sides  of  which  the  funicular  part  of  the 
ligamentum  nucha-  is  attached.  The  internal  surface  is  concave  and  presents  a 
deep  central  depression  and  two  shallower  lateral  ones  which  adapt  it  to  the  surface 
of  the  cerebellum. 

The  occipital  bone  is  connected  by  suture  with  the  interparietal,  two  parietals, 
and  two  temporals,  and  by  synchondrosis  With  the  sphenoid;  the  condyles  articu- 
late with  the  atlas. 

Development.— The  occipital  ossifies  in  cartilage  from  four  centers,  and  con- 
sists at  birth  of  four  pieces  as  described  above.'  The  lateral  parts  unite  with  the 
basilar  at  three  to  four  months,  and  with  the  squama  in  the  second  year,  when  the 
bone  is  consolidated. 

The  parieto-oecipital  suture  and  the  spheno-occipital  synchondrosis  are  ob- 
literated about  the  fifth  year  usually.  The  temporo-occipital  suture  partially 
ossifies  in  old  subjects. 

The  Sphenoid  Bone 

The  sphenoid  bone  (Os  sphenoidale)  is  situated  in  the  base  of  the  cranium,  its 
central  pari  lying  in  front  of  the  basilar  part  of  the  occipital.  It  consists  of  a  cen- 
tral part,  the  l)ody,  two  pairs  of  wings,  and  two  pterygoid  processes. 

The  body  (Corpus)  is  a  cylindrical  bar,  flattened  dorso-ventrally,  and  wider 
in  front  than  behind.  Its  ventral  surface  (Facies  externa)  is  convex  in  the  trans- 
verse direction:  and  its  anterior  part  is  concealed  to  a  large  exient  In-  the  vomer 
and  pterygoid  bones.  The  cerebral  surface  (Facies  cerebralis)  presents  the  fol- 
lowing features:  (1)  In  front  is  a  raised,  flattened  part  which  is  subdivided  by  a 
median  elevation  into  two  slightly  concave  lateral  areas;  this  part  ha.s  a  posterior, 
thin,  free  margin  (Limbus  sphenoidalis),  which  overlies  the  entrance  to  the  optic 
foramina.  (2)  .Just  behind  this  and  at  a  lower  level  is  a  smooth  transverse  de- 
pression, the  optic  groove  (Sulcus  chiasiiudis),  on  which  the  optic  chia.sma  rests. 
(3)  From  each  end  of  tiiis  groove  the  optic  foramen  passes  forward  and  outward  to 
terminate  in  the  po.sterior  part  of  the  orbital  fossa.'  (4)  Near  the  posterior  end 
is  a  central  depression,  the  hypophyseal  or  pituitary  fossa  (Fossa  hypophysea), 
which  loilges  the  hypojihysis  cerebri  or  pituitary  body.  On  each  side  of  this  is  an 
ill-defined  groove  for  the  internal  carotid  artery  and  the  cavernous  sinus.  The  an- 
terior end  is  exi)anded,  and  is  excavated  to  form  the  sphenoidal  sinuses.  These 
cavities  extend  back  a.s  far  as  the  optic  groove,  and  are  usually  continuous  in  front 
with  the  cavities  in  the  vertical  parts  of  the  palate  bones:  they  are  separated  by  a 
complete  septum  which  is  not  always  median.^     The  posterior  end  is  flat  and  is 

'  The  oooipital  crest  of  this  description  i.s  equivalent  to  the  external  occipital  protuberance 
and  superior  nuchal  Hne  of  man.  \  curved  line  a  little  lower  down,  which  is  continued  on  the 
paraniiistoid  process,  represents  the  inferior  nuchal  Une  of  man. 

'Other  terms  for  these  parts  are  basioccipital  (basilar  part),  exoccipitals  (lateral  parts), 
and  supraoccipital  (squamous  part).  It  sliould  lie  noted,  however,  that  the  lines  between  the 
tuisioccipital  and  exoccipitals  pa,ss  through  tlie  lower  part  of  the  condyles. 

'  This  foramen  miglit  well  be  called  a  canal,  since  it  is  an  inch  or  more  in  length. 

*  The  cavity  so  formed  may  be  termed  the  sphenopalatine  sinus.  The  sphenoidal  sinus  maj- 
be  a  separate  cavity  which  communicates  only  with  the  ventral  ethmoidal  meatuses;  this  arrange- 
ment exists  in  about  a  lliird  of  tlic  cases,  according  to  PauUi. 


THE    SPHENOID    BONE  51 

joined  to  the  basilar  part  of  the  occipital;  at  the  lino  of  junction  there  is 
dorsally  a  transverse  elevation,  the  spheno-occipital  crest  (Crista  spheno- 
occipitalis). 

The  orbital  wings  (Ake  orbitales)  curve  upward  and  somewhat  outward  from 
the  sides  of  the  lioily  of  the  pre-sphenoid.  Their  inner  or  cerebral  surfaces  are 
concave,  and  are  marked  by  digital  impressions  (Impressiones  digitat;e)  for  the  gyri 
of  the  cerebrum.  The  external  surface  is  convex  and  is  largely  concealed  by  the 
overlapping  temporal  wing  and  the  sciuamous  temporal  and  frontal  bones;  a 
narrow  part  of  it  (Facies  orliitalis)  is  uncovered  on  the  innei-  wail  of  the  orbital 
cavity  at  the  sphenoidal  notch  of  the  frontal  bone.  The  dorsal  border  unites  with 
the  frontal  bone  at  the  spheno-frontal  suture.  The  anterior  border  joins  the  eth- 
moid at  the  spheno-ethmoidal  suture;  at  its  lower  part  it  concuis  with  the  frontal  in 
the  formation  of  the  ethmoidal  (or  internal  orbital)  foramen.  The  posterior  border 
is  overlapped  by  the  temporal  wing  and  the  squamous  temporal.  The  root  of  the 
wing  is  perforated  by  the  optic  foramen.  Immediately  below  and  behind  the  latter 
(i.  e.,  beneath  the  root)  is  the  foramen  lacerum  orbitale  or  orbital  fissure.  Below 
this,  and  separated  from  it  usually  by  a  thin  plate,  is  a  larger  opening,  the  foramen 
rotundum,  which  is  bounded  externally  by  the  root  of  the  pterygoid  process.  Be- 
hintl  these  foramina  is  the  pterygoid  crest  (Crista  pterygoidea),  which  is  continued 
downward  and  forward  on  the  iDterygoid  process;  on  its  upper  part  may  l)e  foimd 
the  small  and  inconstant  trochlear  (or  pathetic)  foramen.  Just  behind  the  crest 
is  the  temporal  foramen  (For.  alare  parvum),  through  which  the  anterior  deep 
temporal  artery  emerges  from  the  alar  canal  of  the  pterygoid  process. 

The  temporal  wings  (Alis  temporales)  extend  outward  and  somewhat  upward 
from  the  body  of  the  post-sphenoid;  they  are  irregularly  quadrilateral  in  outline. 
The  external  surface  (Facies  temporalis)  enters  into  the  formation  of  the  infra- 
temporal fossa,  and  bears  the  pterygoid  process  on  its  anterior  part;  at  the  junction 
with  the  body  there  is  a  small  groove  for  the  pterygoid  nerve.  The  internal 
surface  (Facies  cerebralis)  presents,  at  the  junction  with  the  body,  two  longitudinal 
grooves  (Sulci  nervorum).  The  outer  groove  is  the  larger,  and  leads  forward  to 
the  foramen  rotundum;  it  contains  the  maxillary  nerve.  The  inner  groove  con- 
ducts to  the  orbital  fissure,  and  contains  the  third,  sixth,  and  ophthalmic  nerves. 
The  outer  groove  is  bounded  externally  by  a  thin  overhanging  crest,  on  which  is  a 
small  groove  for  the  fourth  nerve.  The  remainder  of  the  surface  is  concave  and 
supports  the  pyriform  lobe  of  the  brain.  The  dorsal  border  joins  the  squamous 
temporal  at  the  spheno-squamous  suture.  The  anterior  border  joins  the  orbital 
wing.  The  posterior  border  forms  the  anterior  boundary  of  the  foramen  lacerum; 
it  presents  three  notches,  which  are  (from  within  outward)  the  carotid,  oval,  and 
spinous  (Incisura  carotica,  ovalis,  spinosa).  The  angle  of  junction  of  the  dorsal 
and  posterior  borders  articulates  with  the  parietal  bone. 

The  pterygoid  processes  (Processus  pterygoidei)  arise  from  the  temporal  wings 
and  the  body.  They  project  downward  and  forward,  and  curve  outward  at  the 
lower  part.  The  root  is  perforated  by  the  alar  canal  (Canalis  alaris),'  which 
transmits  the  internal  maxillary  artery.  From  this  canal  a  liranch  leads  upward 
and  forward  to  open  at  the  temporal  foramen.  The  external  surface  is  concave,  and 
is  marked  by  lines  for  muscular  attachment.  The  internal  surface  is  largely  con- 
cealed by  the  overlapping  palate  and  pterygoid  bones,  with  which  it  concurs  in  the 
formation  of  the  pterygoid  or  Vidian  canal. 

Development. — Tlie  sphenoid  is  ossified  in  cartilage,  and  consists  in  early  life 
of  two  distinct  parts,  the  pre-sphenoid  and  post-sphenoid.  The  former  develops 
from  two  centers,  one  in  each  wing ;  the  latter  has  three  centers,  one  for  the  body 
and  one  for  each  wing.  The  pterygoid  processes  ossify  from  the  centers  of  the 
temporal  wings. 

'  This  is  also  called  the  subsphenoidal  canal  or  pterygoid  foramen. 


52 


THE    SKELETON    OF   THE    HOHSE 


Variation  — Tlio  dorsal  bor.icr  of  the  orbital  wing  may  come  to  the  surface  through  a 
defect  hi  the  frontal  bone  at  the  place  whore  the  horn  process  is  situated  in  annuals  which  have 
frontal  horns. 

The  Ethmoid  Bone 
The  ethmoid  (Os  ethinoidalc)  is  sitiuitod  in  front  of  the  body  and  orbital  wings 
of  the  sphenoid.  It  projects  forward  between  the  orbital  plates  of  the  frontal 
bones  and  enters  into  the  formation  of  the  cranial,  nasal,  and  paranasal  cavities.' 
It  consists  of  four  parts— the  criliriforin  plate,  two  lateral  masses,  and  the  per- 
pendicular plate. 

The  cribriform  plate  (Lamina  cribrosa)  is  a  sieve-like  partition  lietween  the 
cranial  and  nasal  cavities.  Its  margin  joins  the  orbital  wings  of  the  sphenoid 
laterally,  and  the  cranial  plate  of  the  frontal  bones  dorsally.  Its  cranial  surface 
is  divided  into  two  parts  by  a  median  ridge,  the  crista 
gain,  which  is  the  intracranial  portion  of  the  perpendicu- 
lar plate.  Each  half  forms  a  deep  oval  cavity,  the  eth- 
moidal or  olfactory  fossa,  which  lodges  the  olfactory  bulb. 
The  plate  is  perforated  by  numerous  small  foramina  for 
the  passage  of  the  olfactory  nerve  filaments,  and  on 
either  side  is  the  much  larger  ethmoidal  foramen.  The 
nasal  surface  is  convex,  and  has  the  lateral  masses 
attached  to  it. 

The  lateral  masses  or  labyrinth  project  forward  from 
the  cribriform  plate  into  the  jwsterior  part  of  the  nasal 
cavity,  which  they  nearly  fill.  Each  mass  is  somewhat 
conical  in  shape,  with  the  base  attached  to  half  of  the 
cribriform  plate.  The  inner  surface  is  separated  by  a 
narrow  space  from  the  perpendicular  plate.  The  outer 
surface  is  convex  and  faces  chiefly  into  the  frontal  and 
maxillary  sinuses,  but  is  attached  behind  to  the  inner  wall 
of  the  orbital  cavity;  it  is  covered  by  a  very  thin  layer  of 
bone,  the  lamina  papyracea.  The  mass  consists  of  a  large 
number  of  delicate,  scroll-like  plates  of  bone,  termed 
ethmo-turbinals  or  ethmoidal  cells.  These  are  attached 
to  the  lamina  papyracea,  and  are  separated  by  narrow 
intervals  termed  ethmoidal  meatuses,  which  communicate  with  the  na.sal  cavity. 
In  the  living  aiiinuil  the  ethuio-turliinals  are  covered  with  mucous  membrane. 

The  lateral  ma-ss  is  a  very  complex  structure,  the  arrangement  of  which  may  be  studied  on 
crass-sections  of  decalcified  specimens  with  the  mucous  membrane  retained.  Each  mass  consists 
of  six  turbinals  which  extend  almost  to  the  perpendicular  plate  and  are  termed  endoturbinals. 
These  diminish  in  size  from  above  downward;  the  largest  is  attached  to  the  nasal  lione,  and  is 
hence  usually  called  the  n;iso-turbinal  or  superior  turbinal;  the  second  is  much  .smaller,  and  is  very 
conuiionly  termed  the  great  ethmoid  cell,  lietween  the  endoturbinals  are  twenty-one  small 
ectoturbinals,  and  all  arc  beset  with  secondary  and  tertiary  coiled  lamella;. 

The  perpendicular  plate  or  mesethmoid  (Lamina  perpendicularis)  is  median, 
and  forms  the  posterior  part  of  the  septum  nasi.  Its  lateral  surfaces  are  nearly 
plane,  but  are  marked  below  by  some  <irooves  and  ridges;  they  are  covered  by  the 
nasal  mucous  membrane.  Tlie  anterior  border  is  irregular  and  is  continuous  with 
the  .septal  cartilage.  The  posterior  border  projects  into  the  cranial  cavity  as  a 
ridge,  the  crista  galli.  The  dorsal  border  joins  the  frontal  bones  at  their  line  of 
junction— the  frontal  suture.  Tlic  ventral  border  is  received  into  the  groove  of 
the  vomer. 

Development.— The  ethmoid  develojis  in  cartilage  from  five  centers,  two  for 

'  On  account  of  its  deep  situation,  and  the  fact  that  it  cannot  be  separated  from  its  surround- 
ings, the  ethmoid  must  be  studied  by  means  of  appropriate  sagittal  and  transverse  sections  of  the 
skull. 


Fig.  29. — Cross-bkction  or 
Latkrai.  Ma88  of 
Ethmoid     Bo.vk    of 

HoK«E. 


THE    INTERPARIETAL    BONE 


53 


each  lateral  mass,  and  one  for  the  perpendicular  plate;  from  the  latter  ossification 
extends  into  the  cribriform  plate.  At  birth  the  perpendicular  and  cribriform  plates 
are  entirely  cartilaginous.  By  the  time  ossification  is  complete  the  ethmoid  has 
unitetl  with  surrounding  bones  to  such  an  extent  that  it  cannot  be  separated  intact 
for  study. 

Occipital  crest 

Supraocci  irital 


Tetiiporul  crest 


Zygomnlic  process 

Supraorbital  foramen 

Orbit 


Malar  bum::       -  ,       2H 

\ 
Facial  crests     , 


Infraorbital  foramen ^v  -  'f 


Nasal  process  of  premaxilla 


Canine  tooth 
Foramen  incisinim 


2i 

Fig.  30. — Skull  of  Horse,  Dorsal  View. 
12,  Supraorbital  process;    14,  parietal    bone;    14',  external  sagittal  crest 
crest;    21,  lacrimal  bone;    22,  nasal  bone;    26,  maxilla;    24,  incisor  teeth 
Kiinstler.) 


Coronoid  jTrocess 


5,  frontal  bone;    15',  frontal 
(After  EUenberger-Baum,  Anat.  fiir 


The  Interparietal  Bone 

This  bone  (Os  interparietale)  is  centrally  placed  between  the  squamous  part 
of  the  occipital  and  the  parietal  bones.  It  is  usually  described  a.s  a  single  bone, 
although  it  ossifies  from  two  chief  lateral  centers,  and  is  sometimes  distinctly 
paired  in  skulls  of  young  foals. 

The   external    surface    (Facies   externa)    is    quadrilateral   and    is   flat   and 


54  THE  SKELETON  OF  THE  HORSE 

smootl.  in  tlH-  very  y.mnK  foal:   lat.-r  it   presents  the  median  external  sagittal 

""'"^^Thr  internal  surface  ( Facies  eereijralis)  presents  tlie  internal  occipital  pro- 
tuberance, a  thn.-si.l..,l  i,r..cess  which  projects  downward  ami  lorward  int..  the 
cranial  cavity  l)etween  the  cerebral  hemispheres  and  the  cerebellum:  it  lias  three 
concave  surfaces  and   three  sharp   borders   which   form   part    ot    the   tentorium 

osseum.  ,  j.     r  ±i  •    *  i 

The  posterior  border  is  thick:  it  joins  the  sciuamous  part  of  the  occipital 

bone.     Tiie  lateral  and  anterior  borders  are  united  by  suture  with  the  parietal 

bones.  ,  i  ■  r  i   i       i 

Development- Tlie  iuterparic^tal  ossihes  m  membrane  from  two  chiet  lateral 
centers.'  It  fuses  first  with  the  i^arictals,  somewhat  later  with  the  occipital,  but 
the  period  at  which  this  union  takes  place  is  quite  variable. 

The  Parietal  Bones 
The  two  parietal  bones  (Ossa  parietalia)  form  the  greater  part  of  the  roof  of 
the  cranium:   they  unite  in  the  median  line,  forming  the  sagittal  suture.    Each  is 
fiuadrilateral  in  outline  and  has  two  surfaces  and  four  borders. 

The  external  surface  (Facies  parietalis)  is  convex,  and  is  marked  by  a  more  or 
less  prominent  curved  line,  the  external  sagittal  crest;  this  is  median  in  its  posterior 
part,  and  is  continuous  with  the  crest  of  like  name  on  the  occipital  Ijone;  in  front 
it  curves  outward  and  is  continuous  with  the  frontal  crest.  The  surface  external  to 
the  crest  (Planum  tcmporale)  enters  into  the  formation  of  the  temporal  fossa,  and 
is  roughened  for  the  attachment  of  the  temporal  muscle. 

The  internal  nr  cerebral  surface  (Facies  cerebralis)  is  concave.  It  presents 
numerous  digital  impressions  (Impressiones  digitatir)  which  correspond  to  the  gyri 
of  the  cerebrum.  There  are  also  furrows  (Sulci  ^asculosi)  for  the  meningeal  arte- 
ries. Along  the  inner  border  there  is  a  sagittal  groove  (Sulcus  sagittalis)  for  the 
superior  longitudinal  sinus. 

The  anterior  border  joins  the  frontal  bone  at  the  parieto-frontal  suture  (Sutura 
coronalis). 

The  posterior  border  meets  the  occijjital  bone  at  the  parieto-occipital  suture 
(Sutura  lambd()i(l(>a).  Below  this  junction  it  curves  inward  and  concurs  with  the 
temporal  bone  in  the  formation  of  the  parie to-temporal  canal  (Meatus  temporalis). 
A  transverse  groove  (Sulcus  transversus)  connects  thi.-^  canal  with  the  sagittal 
sulcus. 

The  internal  border  is  thick  and  serrated.  It  joins  its  fellow  at  the  sagittal 
suture,  and  (in  the  young  subject)  meets  the  interparietal  at  the  interparietal  suture. 
The  line  of  junction  is  marked  internally  In-  th(>  internal  sagittal  crest  (Crista 
sagittalis  interna). 

The  external  border  is  beveled  and  is  overla])])e(l  by  the  sciuamous  temporal 
bone,  forming  the  paricto-temporal  suture  (Sutura  jiarieto-sciuamosa).  The  angle 
of  junction  of  the  external  and  ])osterior  borders  articulates  wath  the  posterior 
angle  of  the  tein|)oral  wing  of  the  splienoid. 

Development.  Ivich  jiarietal  l.one  ossifies  in  membrane  from  a  single  center. 
In  the  young  foal  the  central  part  of  the  bone  is  much  more  convex  than  in  the 
adult  anil  forms  a  iirominence  similar  to  the  pronounced  tuber  parietale  of  the 
young  child;  the  external  sagittal  crest  is  not  present,  and  the  external  surface  is 
smooth. 

The  sagitliil  suture  is  usually  dosed  at  four  years,  the  parieto-oceipital  at  five  years,  and  the 
paricto-temporal  at  twelve  to  fifteen  yeans. 

'  AeeordinR  to  Martin,  tliere  are  originally  four  eenters,  two  anterior  and  two  posterior 
(smaller)  ones,  wliieli  fuse  in  a  variable  manner. 


THE  FRONTAL  BONES — THE  TEMPORAL  BONES  55 

The  Frontal  Bones 

The  frontal  bones  (Ossa  frontalia)  are  situated  on  the  limits  of  the  cranium 
and  face,  lietwccii  the  parietals  behind  and  the  nasal  bones  in  front.  Each  is 
irregularly  (luadrilaterah  and  consists  of  frontal,  orbital,  and  temporal  parts. 

The  frontal  part  (Pars  naso-frontalis)  forms  the  basis  of  the  forehead.  Its 
external  surface  (Facies  frontalis)  is  nearly  flat,  anil  is  smooth  and  subcutaneous; 
it  is  sejiarated  from  the  temporal  part  by  the  external  frontal  crest  (Crista  frontalis 
externa).  At  the  junction  with  the  orbital  part  the  supraorbital  or  zygomatic 
process  (Proc.  zygomaticus)  curves  outward  and  downward  to  join  the  z>goiiiatic 
arch.  The  process  partially  separates  the  orbit  from  the  temporal  fos.sa;  its  root 
is  perforated  by  the  supraorbital  foramen,  or  presents  instead  a  notch  on  its  anterior 
border;  its  upper  surface  is  convex,  while  the  lower  or  orbital  surface  is  concave 
and  smooth,  forming  a  sliallow  fossa  for  the  lacrimal  gland  (Fossa  glandulse  lacri- 
malis).  The  internal  surface  enters  into  the  formation  of  the  cranial  cavity  and 
the  frontal  sinus.  The  cranial  .surface  presents  digital  impressions  for  the  cerebral 
gyri.  The  two  plates  of  the  bone  separate  and  diverge  in  front,  and  thus  inclose 
a  large  air-space  which  is  part  of  the  frontal  sinus.  The  cranial  plate  curves  down- 
ward and  articulates  with  the  cribriform  plate  of  the  ethmoid  bone;  the  facial  plate 
extends  forward  and  joins  the  nasal  and  lacrimal  bones. 

The  orbital  part  (Pars  orbitalis)  forms  the  major  part  of  the  inner  wall  of  the 
orbital  cavity.  It  is  separated  from  the  frontal  ]iart  l)y  a  prominent  ridge  which  is 
part  of  the  orbital  margin.  Its  external  or  orbital  surface  is  concave  and  smooth, 
and  presents  superiorly  a  small  depression  (Fovea  trochlearis),  which  is  bridged 
by  a  small  bar  of  cartilage,  around  which  the  superior  oblique  muscle  of  the  eye  is 
reflected.  The  lower  border  concurs  with  the  orljital  mng  of  the  sphenoid  in  the 
formation  of  the  ethmoidal  or  internal  oi'bital  foramen.  The  internal  surface  faces 
into  the  frontal  sinus  and  gives  attachment  to  the  lateral  mass  of  the  ethmoid. 

The  temporal  part  is  separated  from  the  orbital  part  by  the  deep  sphenoidal 
notch  (Incisura  sphenoidalis),  which  is  occupied  by  the  orliital  wing  of  the  sphenoitl. 
Its  external  surface  forms  part  of  the  inner  wall  of  the  temporal  fossa.  The 
internal  surface  is  largely  covered  Ijy  the  orl^ital  -ning  of  the  sphenoid  in  the  young 
subject,  but  later  forms  part  of  the  wall  of  the  frontal  sinus. 

The  principal  connections  of  the  frontal  bone  are  as  follows:  (1)  The  inner  border  joins  its 
fellow  at  the  frontal  suture.  ('2)  The  anterior  border  meets  the  na.sal  and  lacrimal  at  the  naso- 
frontal and  fronto-lacrimal  sutures.  (.3)  Laterally  it  forms  the  spheno-frontal  suture  with  the 
orbital  wing  of  the  sphenoid,  and  also  joins  the  palate  bone  and  maxilla.  (4)  Posteriorly  it 
meets  the  parietal  at  the  parieto-frontal  (or  coronal)  suture,  and  articulates  below  this  with  the 
squamous  temporal,  (.i)  The  extremity  of  the  supraorbital  process  unites  with  the  zygomatic 
process  of  the  temporal  Ijone. 

Development. — Each  ossifies  in  membrane  from  one  center  which  appears  in 
the  root  of  the  supraorbital  process.  In  the  new-born  foal  there  is  a  slit  between 
the  cranial  plate  and  the  orbital  and  temporal  plates  which  receives  the  cartilagin- 
ous margin  of  the  orbital  wing  of  the  sphenoid. 

The  Temporal  Bones 

The  temporal  bone  (Os  temporale)  forms  the  greater  part  of  the  lateral  wall 
of  the  cranium.  It  is  situated  between  the  occipital  behind,  the  parietal  above, 
the  frontal  in  front,  and  the  sphenoid  below.  It  consists  of  two  distinct  parts, 
squamous  and  petrous. 

1 .  The  squamous  temporal  (Squama  temporalis)  is  a  shell-like  plate  which  has 
two  surfaces  and  four  borders. 

The  internal  surface  ( Facies  cerebralis)  is  largely  overlapped  by  the  surround- 
ing bones,  but  its  central  part  is  free  and  presents  digital  impressions  and  vascular 
grooves. 


56  THE  SKELETON  OF  THE  HORSE 

The  external  surface  (Facies  temporalis)  is  convex,  and  enters  into  the  forma- 
tion of  the  temporal  fossa.  From  its  lower  part  there  springs  the  zygomatic 
process  (Processus  zygomatieus),  which  forms  the  external  boundary  of  the  tem- 
poral fossa.  It  is  at  first  directed  outward,  and  is  wide  and  flattened  dorso-ven- 
trally.  It  then  turns  forward,  becomes  narrower,  and  is  twisted  so  that  its  surfaces 
are  internal  anil  external.  Its  anterior  end  is  pointed  and  joins  the  zygomatic 
process  of  the  malar  bone,  with  which  it  forms  the  zygomatic  arch  (Arcus  zygo- 
matieus). The  narrow  anterior  ])art  has  a  convex  outer  surface  and  a  concave 
inner  one.  Its  ui)per  bonier  has  a  rough  area  for  articulation  with  the  supraorbital 
process  of  the  frontal.  Its  lower  border  is  wide  and  rough.  The  wide  posterior 
part  presents  on  its  ventral  face  a  surface  for  articulation  with  the  condyle  of  the 
mandible.  This  surface  consists  of  a  transversely  elongated  condyle  (Tuberculum 
articulare),  behind  which  is  the  glenoid  fossa  (Fossa  mandibularis).  The  fossa  is 
limiteil  behind  by  the  post-glenoid  process,  the  anterior  surface  of  which  is  articu- 
lar. Behind  this  process  is  a  fossa  in  which  is  the  external  opening  of  the  parieto- 
temporal canal.  The  dorsal  .surface  is  concave  and  forms  the  outer  boundary  of 
the  temporal  fo.ssa.  The  superior  border  is  sinuous  and  is  continuous  behind  with 
the  temporal  crest. 

The  posterior  process  (Processus  posterior)  s])rings  from  the  posterior  part  of 
the  squama.  Its  external  surface  is  crossed  by  the  temporal  crest,  which  forms 
here  the  outer  limit  of  the  temporal  fossa.  The  internal  surface  forms  the  outer 
boundary  of  the  parieto-temporal  canal,  and  is  elsewhere  applied  to  the  petrous 
portion.  It  diviiles  into  two  branches,  upper  and  lower;  the  upper  branch  unites 
with  the  occipital  bone,  while  the  lower  one  curves  downward  l)ehind  the  external 
autlitory  process  and  overlaps  the  mastoid  process. 

The  superior  border  of  the  squamous  temporal  articulates  with  the  parietal, 
forming  the  parieto-temporal  suture.  The  inferior  border  joins  the  temporal  wing 
of  the  sphenoid  at  the  spheno-squamous  suture.  The  anterior  border  unites  with 
the  frontal  bone,  and  tiie  posterior  with  the  parietal. 

2.  The  petrous  temporal  (Os  ix'trosum)  is  placed  between  the  occipital  behind 
and  the  parietal  in  front,  and  is  largely  overlapped  externally  by  the  squamous 
temporal.     It  has  the  form  of  a  four-sided  pyramid,  the  base  of  which  is  ventral. 

The  external  surface  is  mainly  concealed  by  the  seiuanunis  temporal,  Init  two 
features  are  visible.  A  short  tube  of  bone,  the  external  auditory  process,  protrudes 
from  the  lowest  part  through  the  notch  of  the  .squamous  temporal.  The  process  is 
directed  outwartl,  upward,  and  a  little  forward.  It  gives  attachment  to  the  annular 
cartilage  of  the  ear.  Its  lumen,  the  external  auditory  meatus  (Meatus  acusticus 
extcrnus),  conducts  to  the  cavity  of  the  middle  ear  (tympanum)  in  the  dry  skull, 
but  is  separated  from  it  by  the  tympanic  membrane  in  the  natural  state.  The 
mastoid  process  |)rojects  ventrally  in  the  interval  lietween  the  posterior  process 
of  the  siiuamous  temi)oral  and  the  root  of  the  paramastoid  (or  styloid)  process  of 
the  occijiital  bone;  its  outer  surface  is  crossed  by  a  curved  groove  which  leads  to 
the  parieto-temporal  canal. 

The  internal  surface  faces  into  the  cerebellar  fossa  of  the  cranium.  It  is  con- 
cave and  sii til  l)iit  irregular.     In  its  lower  part  is  the  entrance  to  a  short  canal, 

the  internal  auditory  meatus,  which  transmits  the  seventh  and  eighth  cranial  nerves. 

Tlic  fun. Ins  .)f  till,  meatus  is  divided  liy  a  orost  into  a  superior  and  an  inferior  fossa.  In  the 
superior  one  is  the  oriKin  of  the  facial  canal,  wliicli  eurves  through  the  bone  and  opens  exter- 
nally at  the  stylo-ni;usloid  foramen;  it  transmits  the  faeial  (seventh  cranial)  nerve.  The  in- 
ferior fossa  presents  small  foramina  for  (he  passage  of  filjers  of  the  auditory  (eiehth  cranial) 
nerve.  .    v    a  / 

Behind  the  meatus  and  near  the  posterior  margin  of  the  surface  is  the  slit-like 
opening  of  the  aquicductus  vestibuli,  covered  by  a  scale  of  bone.  Below  this  is  a 
narrow  fissure,  the  orifice  of  the  aquaeductus  cochleae. 


BONES    OF   THK    FACE  57 

Tlif  anterior  surface  looks  upward  and  forwartl.  The  outer  part  articulates 
with  the  jjarietal  bone  ami  the  inner  part  faces  into  the  cerebral  fossa  of  the  cranium. 
A  sharp  bortler,  the  petrosal  crest  (Crista  petrosa),  separates  this  surface  from  the 
inner  one. 

The  posterior  surface  joins  the  lateral  part  of  the  occipital  bone. 

The  base  forms  the  outer  l^oundary  of  the  foramen  lacerum  basis  cranii.  It 
is  very  irreoular  and  presents  a  number  of  important  features.  The  hyoid  process 
is  a  short  rod  which  projects  downward  and  forward  below  the  base  of  the  external 
auditory  process,  inclosed  in  a  bony  tul>e:  it  is  connected  by  a  bar  of  cartilage  with 
the  hyoiil  bone.  The  stylo-mastoid  foramen  is  situated  lietween  the  root  of  the 
hyoid  process  and  the  mastoid  process;  it  is  the  external  opening  of  the  facial  canal, 
through  which  the  facial  nerve  emerges.  The  bulla  ossea  is  a  considerable  emi- 
nence situated  centrally:  it  is  thin-walled  and  incloses  a  cavity  which  is  part  of  the 
tympanum.  The  muscular  process'  is  a  sharp  spine  which  projects  downward 
and  forwanl  from  the  anterior  part  of  the  base;  it  gives  origin  to  the  tensor  and 
levator  palati  muscles.  External  to  the  root  of  the  preceding  is  the  small  petro- 
tympanic or  Glaserian  fissure  (Fissura  petro-tympanica)  for  the  passage  of  the 
chorda  tympani  nerve.  The  osseous  Eustachian  tube  is  a  semicanal  at  the  inner 
side  of  the  root  of  the  muscular  process;  it  leads  to  the  tympanum.  At  the  inner 
side  of  the  preceding  is  the  slit-like  orifice  of  the  petrosal  canal,  which  communicates 
with  the  facial  canal. 

The  apex  projects  upward  and  backward  lietween  the  squamous  temporal  and 
the  occipital  Ijone. 

Development. — The  petrous  temporal  may  be  regarded  as  consisting  of  petro- 
mastoid  and  tympanic  parts.  The  latter  includes  the  external  auditory  process, 
the  bulla  ossea,  and  the  muscular  process;  it  is  developed  in  membrane.  The 
petro-mastoid  is  developed  in  the  cartilaginous  ear  capsule.  Its  petrous  part 
consists  of  very  dense  bone  which  contains  the  labyrinth  or  internal  ear  and  forms 
the  inner  wall  of  the  tympanum. 

The  parieto-temporal  canal  (Meatus  temporalis)  is  a  continuation  of  the  trans- 
verse groove  which  extends  outward  from  the  base  of  the  tentorium  Oisseum.  It 
is  directed  downward,  forward,  and  somewhat  outward,  and  opens  externally  in 
front  of  the  root  of  the  auditory  process.  It  is  bounded  by  the  squamous  temporal 
externally,  the  petrous  behind,  and  the  parietal  in  front  and  internally.  Several 
foramina  open  from  it  into  the  temporal  fossa.  It  contains  a  large  vein  (A'ena 
cerebralis  dorsalis),  the  continuation  of  the  transverse  sinus  of  the  dura  mater. 

The  foramen  lacerum  basis  cranii  (Foramen  lacerum  et  jugulare)  is  a  large 
irregular  opening  in  the  cranial  ba.se,  bounded  internally  by  the  basilar  part  of  the 
occipital  bone,  externally  by  the  petrous  temporal,  and  in  front  by  the  temporal 
wing  of  the  sphenoid.  It  consists  of  a  large  anterior  part  (Foramen  lacerum  an- 
terius),  and  a  narrow  posterior  part  (Foramen  lacerum  posterius  s.  jugulare). 
It  transmits  the  internal  carotid  artery,  the  middle  meningeal  artery,  the  mandi- 
bular, ninth,  tenth,  and  eleventh  cranial  nerves,  and  the  inferior  cerebral  vein. 

In  the  fresh  state  the  foramen  is  occupied  by  a  dense  fibrous  membrane  which  is  perforated 
by  apertures  for  the  various  structures  transmitted.  Thus  there  are  three  opemngs  m  front  for 
the  internal  carotid  artery,  the  mandibular  nen'e,  and  the  middle  memngeal  artery;  thp.-^c  arc 
(from  within  outward)  the  foramen  caroticum,  ovale,  spinosum. 

(Bi  BONES  OF  THE  FACE 

The  bones  of  the  face  (Ossa  faciei)  are  the  Maxilla,  Premaxilla,  Palatine, 
Pterygoid,  Nasal,  Lacrimal,  Malar,  Superior  Turbinal,  Inferior  Turbinal,  ^  omer, 
Mandible,  and  Hyoid.     The  last  three  are  single,  the  others  paired. 

>  This  is  commonly  termed  the  styloid  process.  It  is  not  the  homologue  of  the  styloid  process 
of  man. 


58  THE  SKELETON  OF  THE  HORSE 

The  Maxillae 

Tlio  maxillae  arc  the  principal  bones  of  the  upper  jaw  and  carry  the  upper 
cheek  teetli.  They  arc  situated  on  the  lateral  aspect  of  the  face,  and  articulate 
with  almost  all  of  the  facial  bones  and  the  frontal  and  temporal  also.  For  descrip- 
tion each  may  be  dividcti  into  a  body  and  two  processes. 

The  body  (Corpus  iiiaxilhcl  i)ri'scnts  two  surfaces,  two  borders,  and  two  ex- 
tremities. Tlic  external  or  facial  surface  (Facies  lateralis)  is  somewhat  concave 
in  front  and  convex  behind.  On  its  i)osterior  part  is  a  horizontal  ridge,  the  facial 
or  zygomatic  crest  (Crista  facialis);  in  a  skull  of  medium  size  its  anterior  end  is 
about  an  incii  and  a  half  (3  to  4  cm.)  above  the  third  or  fourth  cheek  tooth,  and  it 
is  continued  behind  liy  a  corresponding  ridge  on  the  malar  bone.  About  two  inches 
(5  cm.)  above;  an<l  a  little  in  front  of  the  anterior  end  of  the  crest  is  the  infra- 
orbital foramen  (Foramen  infraorbitale) ;  this  is  the  external  opening  of  the  infra- 
orbital canal. 

In  the  young  lior.si>  llic  anterior  part  of  tlic  surface  is  convex  over  the  enibetUletl  parts  of  the 
teeth.     AJi  the  latter  are  extruded  the  surface  flattens  and  becomes  concave  in  old  subjects. 

The  internal  or  nasal  surface  (Facies  nasalis)  is  concave  dorso-ventrally;  it 
forms  the  greater  i)art  of  the  lateral  wall  of  the  nasal  cavity.  Its  upper  part  is 
crossetl  obli(iuel\-  forward  and  downwarti  by  the  shallow  lacrimal  groove  (Sulcus 
lacrimalis),  which  contains  the  naso-lacrimal  duct;  in  the  adult  the  posterior  part 
of  the  groove  is  converted  into  a  canal,  which  is  continuous  wdth  that  on  the  inner 
surface  of  the  lacrimal  bone.  Below  the  groove  is  the  inferior  turbinal  crest 
(Crista  conchalis  inferior),  to  which  the  inferior  turbinal  bone  is  attached.  Lower 
down  and  parallel  with  the  turbinal  crest  is  the  palatine  process,  which  projects 
inward  like  a  shelf.  Behind  this  the  surface  is  rough  for  articulation  with  the  palate 
bone;  this  area  is  crossed  liy  a  gr()()\-e  which  concurs  with  a  furrow  on  the  palate 
bone  in  the  formation  of  the  palatine  canal.  The  posterior  part  of  the  bone  is 
excavated  to  form  part  of  the  maxillary  sinus. 

The  superior  border  is  irregular  antl  scaly.  Its  anterior  part  is  grooved  and 
its  posterior  part  beveled  for  articulation  witli  the  nasal  process  of  the  premaxilla 
anil  the  nasal  and  lacrimal  Imnes. 

The  inferior  or  alveolar  border  (Processus  alveolaris)  is  thick,  and  presents  six 
large  cavities,  tlu^  alveoli,  for  the  cheek  teeth.  I'he  alveoli  are  separated  by  tran.s- 
verse  interalveolar  septa.  There  is  often  a  small  alveolus  for  the  first  premolar 
("wolf  tooth")  close  to  the  first  large  one.  iMirther  forward  the  border  is  narrow 
and  forms  part  of  the  interdental  or  interalveolar  space  (Margo  interalvcolaris). 
Behind  the  last  alveolus  is  a  rough  area,  the  alveolar  tuberosity. 

The  anterior  extremity  is  pointed.  It  joins  the  iiremaxilla,  and  forms  with  it 
the  alveolus  for  the  canine  tooth. 

The  posterior  extremity  forms  a  rounded  prominence,  the  maxillary  tuberosity 
(Tuber  ntaxillarc).  Internal  to  the  tuberosity  is  a  deep  cavity,  the  maxillary 
hiatus,  in  which  are  three  foramina.  The  upper  one,  tlie  maxillary  foramen,  leads 
into  the  infraorbital  canal.  The  lower  one,  the  posterior  palatine  foramen,  is  the 
entrance  to  the  palatine  canal.  Tlie  spheno-palatine  foramen  perforates  the  inner 
wall  of  the  hiatus  and  opens  into  the  nasal  cavity. 

The  zygomatic  or  temporal  process  (Processus  temporalis)  projects  backward 
above  and  external  to  the  tuberosity;  it  is  overlapped  by  the  corresponding  part 
of  the  malar  and  also  articulates  with  the  zygomatic  process  of  the  temporal.  A 
small  curved  plate  extends  inward  from  it  and  joins  the  frontal  and  palate  bones, 
forming  part  of  tlw  floor  of  the  oH)it. 

The  palatine  process  (Processus  palatinus)  is  a  plate  which  projects  horizon- 
tally inward  from  the  lower  part  of  the  inner  surface  of  the  body.    It  forms  the 


THE    1>REMAX1LL^ 


59 


greater  part  of  the  basis  of  the  hard  palate.     Its  superior  (jr  nasal  surface  is 

smooth  and  concave  transversely;   on  its  anterior  part,  close  to  the  inner  border, 

is  a  shallow  groove  in  which  the  organ  of  Jacobson  is  situated.     The  inferior  or 

palatine  surface  is  slightly  concave  from  side  to  side,  and  presents  along  its  outer 

liart  the  palatine  groove  (Sulcus  palatinus).     The  groove  is  a  continuation  of  the 

palatine  canal,  and  contains  the  palatine  artery  and  nerve.     The  internal  border 

unites  with  its  fellow  to  form  the 

median  palatine  suture;    its  nasal 

aspect  bears  the  nasal  crest,  which 

forms,  with  that  of  the  opposite 

process,  a  groove  for  the  vomer. 

The  posterior  border  unites  with 

the  horizontal  part  of  the  palate 

bone  at   the   transverse   palatine 

suture. 

The  infraorbital  or  superior 
dental  canal  extends  almost  hori- 
zontally from  the  maxillary  fora- 
men to  the  infraorbital  foramen. 
It  is  placed  at  the  upper  edge  of 
the  inner  plate  of  the  maxilla, 
and  traverses  the  maxillary  sinus. 
Near  the  infraorbital  foramen  it 
gives  off  a  small  canal  (Canalis 
alveolaris  incisivus)  which  lies 
above  the  roots  of  the  premolars 
and  extends  also  into  the  pre- 
maxilla,  carrying  vessels  and 
nerves  to  the  teeth  there. 

Development. — The  maxilla 
ossifies  in  memljrane  below  and 
external  to  the  cartilaginous  nasal 
capsule.  It  has  one  chief  center 
and  a  supplementary  one  in  the 
region  of  the  deciduous  canine 
tooth  (Martin). 

The  Premaxillae 

The  premaxillae  (Ossa  incis- 
iva)  form  the  anterior  part  of  the 
upper  jaw  and  carry  the  incisor 
teeth.  Each  consists  of  a  body 
and  two  processes,  nasal  and  pala- 
tine. 

The  body  is  the  thick  an- 
terior part  which  carries  the  in- 
cisor teeth.  Its  labial  or  superior 
surface  is  convex  and  smooth,  and 
is  related  to  the  upper  lip.     The 

palatine  or  inferior  surface  is  concave  and  presents  a  foramen  a  little  behind  its 
middle.'  Tlie  internal  surface  is  rough,  and  joins  the  opposite  hone;  it  is  marked 
by  a  curved  groove,  which  forms  with  that  on  the  opposed  surface,  the  incisive 

'  This  foramen  is  somewhat  variable  in  position,  but  is  commonly  opposite  the  comer  in- 
cisor.    Smaller  inconstant  foramina  are  often  present. 


-Upper  Ja 


Half 


OF  Horse  About  Four 
Years  Old,  Ventral  View. 
1.  1.  Po.sterior  nares;  2.  vomer;  3,  horizontal  p.irt  of 
palate  bone;  4,  anterior  palatine  foramen;  .5,  palatine  groove; 
6.  transverse  palatine  suture;  7,  median  palatine  suture;  8. 
palate  process  of  maxilla;  9,  palate  process  of  premaxilla;  10, 
foramen  incisivum;  11,  malar  bone;  12,  maxilla;  1.3.  anterior 
end  of  facial  crest;  14.  interalveolar  space;  1.  1-3.  incLsor 
teeth;  C.  canine  tooth;  PI.  first  premolar  or  "wolf"  tooth. 


60  THE  SKELETON-  OF  THE  HORSE 

foramen  { Foramen  iiK-i.sivuiii).  The  alveolar  border  (Limbus  alveolaris)  separates 
the  ijahitiiio  aiul  lal)ial  surfaces;  it  is  curved  and  thick,  and  presents  three  alveoH 
for  the  incisor  teeth;  behind  the  third  alveolus  it  is  rounded  and  free,  forming  part 
of  the  interalveolar  space. 

Tlie  nasal  process  (Processus  nasalis)  projects  baclvward  and  uinvard  from  the 
bodv,  forming  Iicre  the  lateral  wall  of  the  nasal  cavity.  The  two  surfaces,  facial 
and  nasal,  are  smooth  and  rounded.  The  superior  border  is  free,  thick,  and  smooth. 
The  inferior  border  is  dentated  and  joins  the  maxilla;  at  its  anterior  end  it  forms 
witii  the  latter  the  alveolus  for  the  permanent  canine  tooth.'  The  posterior 
extremity  fits  into  the  interval  between  the  nasal  bone  and  the  maxilla. 

The  palatine  process  (Processus  palatinus)  is  a  thin  plate  which  forms  the  an- 
terior i)art  of  the  basis  of  the  hard  palate.  Its  nasal  or  superior  surface  has  a 
longitudinal  ridge  which  forms  with  that  of  the  other  side  a  groove  for  the  septal 
cartilage.  Tiie  palatine  or  inferior  surface  is  flat.  The  internal  border  is  serrated 
and  meets  its  fellow  at  the  median  palatine  suture.  The  external  border  is  seji- 
arated  from  the  maxilla  and  the  nasal  process  by  the  palatine  cleft  (Fissura  pala- 
tina).  The  posterior  extremity  fits  into  the  interval  between  the  vomer  and  the 
palatine  process  of  tiie  maxilla. 

Development. — The  i)remaxilla  ossifies  from  a  single  center.  Fusion  of  the 
two  Ijones  is  complete  at  the  end  of  the  third  or  the  beginning  of  the  fourth  year. 

The  Palatine  Bones 

The  palatine  bones  (O.ssa  palatina)  are  situated  on  either  side  of  the  posterior 
nares,  and  form  the  posterior  margin  of  the  hard  palate.  Each  is  twisted  so  as  to 
form  a  horizontal  and  a  perpendicular  part. 

The  horizontal  part  (Pars  horizontalis)  is  a  narrow  ])late  which  forms  the  ]ios- 
terior  part  of  tlie  iianl  palate.  It  presents  smooth  nasal  antl  palatine  surfaces. 
The  internal  border  meets  its  fellow  at  the  median  jialatinc  suture,  on  the  nasal 
aspect  (if  which  is  tiie  nasal  crest.  The  anterior  border  joins  the  palate  process  of 
the  maxilla  at  tiie  transverse  palatine  suture,  and  forms  with  it  the  anterior  pala- 
tine foramen.  The  posterior  border  is  concave  and  free;  it  gives  attachment  to 
the  aponeurosis  of  the  soft  palate. 

The  perpendicular  part  (Pars  perpendicularis)  is  more  extensive  and  forms  the 
outer  boundary  of  tlie  posterior  nares.  The  nasal  or  internal  surface  is  in  the 
greater  part  of  its  extent  concave  and  smooth ;  it  is  marked  by  a  narrow  rough  area 
to  which  the  pterygoid  bone  is  attached.  Below  this  the  bone  curves  outward, 
forming  the  pterygoid  process.  The  maxillary  or  external  surface  (Facies  max- 
illaris)  presents  three  areas  for  consideration.  The  largest  articulates  with  the 
maxilla;  it  is  rough  ami  is  crossed  by  a  groove  which  enters  into  the  formation  of 
tiic  iiahitine  canal.  Behind  this  is  a  smooth  part  which  assists  in  forming  the 
pterygo-palatine  fossa.  The  rough  area  below  this  is  overlap])ed  by  the  jiterygoid 
])r(i((ss  of  the  spiieiioid  bone.  The  superior  border  is  jierforated  by  the  spheno- 
palatine foramen.  Behind  the  foramen  tlie  two  i)lates  of  the  bone  separate  to 
inclose  part  of  the  spheno-palatine  sinus.  The  inner  plate  curves  inward  to  articu- 
late with  the  vomer.  Tiie  outer  i)late  joins  the  maxilla  anil  frontal  anil  the  orbital 
wing  of  the  spiienoid. 

Development. — The  palatine  bone  ossifies  in  membrane  from  a  single  center. 

The  Pterygoid  Bones 

The  pterygoid  bones  (Ossa  ptcrygoidea)  are  narrow,  thin,  bent  plates,  situated 

on  either  side  of  tjic  |)osterior  nares.     Each  has  two  surfaces  and  two  extremities. 

The  internal  surface  is  smooth,  and  forms  part  of  the  boundary  of  the  posterior 

nares.     The  external  smface  articulates  with  the  palatine,  vomer,  and  sphenoid, 

'  The  alveolus  for  the  temporary  canine  is  commonly  formed  in  the  maxilla  alone. 


THE    NASAL    BONES — THE    LACRIMAL    BOXES  61 

concurrinp;  with  the  hist  in  the  formatiiMi  of  the  pterygoid  or  Vidian  canal.  The 
anterior  extremity  is  free,  turned  slightly  outward,  and  forms  the  hamulus,  a  pulley 
around  which  the  tendon  of  the  tensor  palati  muscle  is  reflected. 

Development. — The  pterygoid  ossifies  in  membrane  from  a  single  center. 

The  Nasal  Bones 

The  nasal  bones  (0,ssa  nasalia)  are  situated  in  front  of  the  frontal  bones  and 
form  the  greater  part  of  the  roof  of  the  nasal  cavity.  They  have  an  elongated 
triangular  outline,  wide  behind,  pointed  in  front.  Each  presents  two  surfaces,  two 
borders,  a  base,  and  an  apex. 

The  external  or  facial  surface  is  smooth  and  is  convex  transversely:  the 
profile  contour  is  usually  slightly  wavy,  with  a  depression  about  its  middle  and  a 
variably  prominent  area  in  front. 

The  internal  or  nasal  surface  is  smooth  and  concave  from  side  to  .side.  About 
in  its  middle  it  jiresents  the  superior  turbinal  crest  (Crista  conchalis  dorsalis), 
which  is  parallel  with  the  inner  border,  and  has  the  superior  turbinal  bone  attached 
to  it.  Most  of  this  surface  faces  into  the  nasal  cavity,  but  its  posterior  part  enters 
into  the  formation  of  the  frontal  sinus;  the  latter  area  is  marked  off  by  an  oblique 
ridge. 

The  internal  border  is  straight,  and  meets  the  opposite  bone  at  the  nasal  suture. 

The  external  border  is  irregular.  Its  anterior  third  is  free  and  concurs  with 
the  nasal  process  in  forming  the  naso-maxillary  notch  (Incisura  naso-maxillaris). 
Behind  this  it  is  scaly  for  articulation  with  tlie  end  of  the  nasal  process,  the  maxilla, 
and  the  lacrimal,  forming  the  naso-maxillary  and  naso-lacrimal  sutures. 

The  base  or  posterior  end  is  lieveled  and  overlaps  the  frontal  bone,  forming  the 
naso-frontal  suture. 

The  apex  is  pointed  and  thin. 

Development. — Each  nasal  bone  ossifies  in  membrane  from  a  single  center. 
The  nasal  suture  does  not  close  completely  even  in  old  age.  In  some  cases  the  two 
plates  separate  to  inclose  a  small  air-space  in  the  posterior  part. 

The  Lacrimal  Bones 

The  lacrimal  bones  (Ossa  lacrimalia)  are  situated  at  the  anterior  part  of  the 
orbit,  and  extend  forward  on  the  face  to  the  posterior  border  of  the  maxilla.  Each 
presents  three  surfaces  and  a  circumference. 

The  external  aspect  is  clearly  divided  into  orbital  and  facial  parts  by  the  orbital 
margin.  The  orbital  surface  (Fades  orbitalis)  is  triangular  in  outline,  smooth  and 
concave;  it  forms  part  of  the  inner  and  front  wall  of  the  orbit.  Near  the  orbital 
margin  it  presents  a  funnel-like  fossa  for  the  lacrimal  sac  (Fossa  sacci  lacrimalis), 
which  is  the  entrance  to  the  osseous  lacrimal  canal.  Behind  this  is  a  depression  in 
which  the  inferior  oblique  muscle  of  the  eye  takes  origin.  The  facial  surface 
(Facies  facialis)  is  more  extensive,  and  has  the  form  of  an  irregular  pentagon. 
It  is  slightl}'  convex  and  smooth  in  the  foal,  flattened  in  the  adult.  It  usually 
bears  the  small  lacrimal  tubercle,  situated  nearly  an  inch  (ca.  2  cm.)  from  the 
orbital  margin. 

The  nasal  or  internal  surface  (Facies  nasalis)  faces  into  the  frontal  and  ma.x- 
illary  sinuses.  It  is  concave  antl  very  irregular,  and  is  crossed  almo.st  horizontally 
by  the  osseous  lacrimal  canal  (Canalis  lacrimalis  osseus). 

The  orbital  margin  (^Margo  orbitalis)  is  concave,  rough  above,  smooth  below. 

The  circumference  articulates  above  with  the  frontal  and  nasal  bones,  below 
with  the  malar  and  maxilla,  in  front  with  the  maxilla,  and  behind  with  the  frontal. 
The  various  sutures  so  formed  are  designated  by  combinations  of  the  names  of  the 
bones. 

Development. — Each  ossifies  in  membrane  from  a  single  center. 


62  the  skeleton  of  the  horse 

The  Malar  Bones 

The  malar  or  zygomatic  bones  (Ossa  zygomatica)  arc  placed  between  the  lac- 
rimal above  and  tlic  maxilla  Itelow  and  in  front.  Each  is  irregularly  triangular  in 
ouUine  and  jin-sents  three  surfaces,  three  borders,  a  base,  and  an  apex. 

The  facial  surface  is  smooth,  slightly  convex,  wide  in  front,  and  narrow  behind. 
At  its  lower  part  it  ])resents  the  facial  or  zygomatic  crest,  which  is  continuous  in 
front  with  the  similar  ridge  on  the  maxilla  and  behind  with  the  zygomatic  process  of 
the  temporal:  the  crest  is  rough  below,  where  the  masseter  muscle  is  attached  to  it. 

Tlie  orbital  surface  is  separated  from  the  facial  surface  by  the  concave  orbital 
margin.  It  is  concave  ami  smootli,  and  forms  part  of  the  lower  and  front  wall  of 
the  orbit. 

The  nasal  surface  is  concave  and  faces  into  the  maxillary  sinus.  In  the  young 
foal  a  considcraiilc  part  of  it  articulates  with  the  maxilla. 

The  superior  border  articvilates  with  the  lacrimal  chiefly,  but  to  a  small  extent 
behind  with  the  maxilla  also. 

The  inferior  border  and  the  base  articulate  with  the  maxilla. 

The  apex  is  beveled  above  and  is  overlapped  bj-  the  zygomatic  process  of  the 
temporal  bone. 

Development. — Each  ossifies  in  niemlirane  from  one  or  two  centers. 

The  Turbinal  Bones 

The.se  (Ossa  turbinata)  are  delicate,  scroll-like  bones,  four  in  nund)er,  which 
are  attached  to  the  lateral  walls  of  the  nasal  cavity.  They  project  into  the  cavity 
and  greatly  tliniinish  its  extent.  Each  is  composed  of  a  very  thin  lamina,  cribriform 
in  many  places,  and  covered  on  both  sides  with  mucous  membrane  in  the  fresh 
state.     They  are  arranged  in  two  jiairs,  superior  and  inferior. 

The  superior  or  naso-turbinal  (Concha  tlorsalis)'  is  somewhat  cylindrical  in 
form,  small  at  its  anterior  ]iart,  ami  flattened  transversely.  It  is  attached  to  the  tur- 
binal crest  of  the  nasal  tjonc  and  the  nasal  plate  of  the  frontal  bone.  The  anterior 
part  is  rolled  like  a  scroll  one  and  a  half  times,  thus  inclosing  a  cavity  which  com- 
municates with  the  middle  meatus  nasi.  The  arrangement  is  best  seen  on  a  cross- 
section  (Fig.  37) .  The  posterior  part  is  not  rolled,  but  its  lower  border  is  attached  to 
the  lateral  nasal  wall,  thus  helping  to  inclose  a  large  space  which  is  part  of  the  fron- 
tal sinus.  This  cavity  is  separated  from  that  of  the  scroll-like  part  by  a  transverse 
septum.  The  internal  surface  is  flattened,  and  is  separated  from  the  septum  nasi 
by  a  narrow  interval,  the  common  meatus  (Meatus  nasi  communis).  Another 
narrow  passage,  the  superior  meatus  (.Meatus  nasi  superior),  separates  the  upper 
surface  from  the  roof  of  the  nasal  ca\ity.  The  space  between  the  lower  surface 
and  the  inferior  turbinal  is  the  middle  meatus  (Meatus  nasi  medius).  The  anterior 
extremity  is  prolonged  toward  the  nostril  by  two  small  bars  of  cartilage. 

Tlie  inferior  or  maxillo-turbinal  bone  (Concha  ventralis)  is  shorter  and  smaller 
posteriorly  than  the  upptT  one.  It  is  attached  to  the  inferior  turbinal  crest,  and 
consists,  like  the  upper  one,  of  an  anterior  coiled  and  a  posterior  uncoiled  portion. 

To  expros.s  l)rieflv  the  mode  of  coiling  of  tho  two  bone.s  of  tho  samp  side  wo  may  sav  that 
they  are  rolled  toward  the  septum  and  each  other. 

The  inferior  and  posterior  borders  of  the  posterior  part  are  attached  to  the 
maxilla,  thus  helping  to  inclose  a  cavity  which  is  part  of  the  maxillarv  sinus.  The 
lower  .-surface  is  separated  from  the  floor  of  the  nasal  cavitv  by  the  inferior  meatus 
(Meatus  nasi  inferior),  which  is  much  larger  than  the  other  nasal  passages.  The 
anterior  extremity  is  prolonged  to  the  nostril  by  a  curved  bar  of  cartilage. 

Development.— Each  ossifies  in  cartilage  from  a  single  center. 
'  This  bone  is  really  a  greatly  developed  first  ethmo-turbiiial. 


the  vomer — the  mandible  63 

The  Vomer 

The  vomer  is  a  median  unpaired  bone,  which  assists  in  forming  the  lower  part 
of  the  septum  nasi.  It  is  composed  of  a  thin  lamina  which  is  hent  (except  in  its 
posterior  part)  so  as  to  form  a  narrow  groove  (Sulcus  sei)ti  narium),in  wliich  the 
lower  part  of  the  perpendicular  ])late  of  the  ethmoid  bone  and  the  septal  cartilage 
are  received.  The  lateral  surfaces,  right  and  left,  are  highest  near  the  posterior 
end  and  diminish  gradually  to  the  anterior  end;  they  are  slightly  convex  dorso- 
\'entrall\-,  and  are  covered  by  the  nasal  mucous  membrane  during  life.  The  in- 
ferior border  is  thin  and  free  in  its  posterior  third,  and  divides  the  posterior  nares 
into  right  and  left  halves;  in  the  remainder  of  its  extent  it  is  wider  and  is  attached 
to  the  nasal  crest.  The  anterior  extremity  lies  above  the  ends  of  the  palatine  jiro- 
cesses  of  the  prcmaxillse.  The  posterior  extremity  consists  of  two  wings  (Ahe 
vomeris)  which  extend  outward  below  tlie  body  of  the  pre-sphenoid;  posteriorly 
they  form  a  notch  (Incisura  vomeris),  and  laterally  join  the  palate  and  pterygoid 
bones. 

Development. — The  vomer  is  primitively  double,  and  ossifies  from  a  center  on 
either  side  in  the  membrane  covering  the  cartilaginous  septum  nasi;  the  two  laminaj 
then  fuse  below  and  form  a  groove. 

The  Mandible 

The  mandible  or  inferior  maxilla  (Mandibula)  is  the  largest  and  the  only 
movable  bone  of  the  face.  The  two  halves  of  which  it  consists  at  birth  unite  during 
the  second  or  third  month,  and  it  is  usually  described  as  a  single  bone.  It  carries 
the  lower  teeth,  and  articulates  by  its  condyles  with  the  squamous  temporal  on 
either  side.     It  consists  of  a  body  and  two  rami.' 

The  body  (Corpus  mandibulse)  is  the  thick  anterior  part  which  bears  the  incisor 
teeth.  It  presents  two  surfaces  and  a  border.  The  lingual  or  superior  surface 
(Facies  lingualis)  is  smooth  and  slightly  concave;  dm'ing  life  it  is  covered  by  mucous 
membrane,  and  the  tip  of  the  tongue  overlies  it.  The  labial  or  mental  surface 
(Facies  mentalis)  is  convex  and  is  related  to  the  lower  lip.  It  is  marked  by  a  metlian 
furrow  which  indicates  the  position  of  the  primitive  symphysis  maiidibula\  The 
curved  alveolar  border  (Limbus  alveolaris)  jiresents  six  alveoli  for  the  incisor  teeth, 
and  a  little  further  liack  two  alveoli  for  the  canine  teeth  in  the  male;  in  the  mare 
the  latter  are  usually  absent  or  small. 

The  rami  (Rami  mandibulse)  extenil  backward  from  the  body  and  diverge 
to  inclose  the  submaxillary  space  (Spatium  mandibulare).  Each  ramus  is 
bent  so  as  to  consist  of  a  horizontal  part  (Pars  molaris)  which  bears  the  lower 
cheek  teeth,  and  a  vertical  part  (Ramus  mandibulse)  which  is  expanded  and 
furnishes  attachment  to  powerful  muscles;  the  term  angle  is  applied  to  the  most 
prominent  part  of  the  curve.  The  ramus  presents  two  surfaces,  two  borders,  and 
two  extremities.  The  external  surface  is  smooth  and  slightly  convex  from  edge 
to  edge  on  the  horizontal  part;  at  the  junction  with  the  body  it  presents  the  mental 
foramen  (Foramen  mentale),  which  is  the  external  opening  of  the  mandibular  or 
inferior  dental  canal.  On  the  vertical  part  it  is  somewhat  concave  and  presents  a 
number  of  rough  lines  for  the  attachment  of  the  masseter  muscle.  The  internal 
surface  of  the  horizontal  part  is  smooth,  and  presents  a  shallow  longitudinal  tle- 
pression  in  its  middle;  above  this  there  is  often  a  faint  mylo-hyoid  line  for  the  at- 
tachment of  the  muscle  of  like  name.  At  the  lower  part  of  the  junction  with  the 
body  there  is  a  small  fossa  for  the  attachment  of  the  genio-hyoid  and  genio-glossus 
muscles.     On  the  vertical  part  the  surface  is  concave,  and  is  marked  in  its  lower  and 

'  In  the  Stuttgart  Xomenclator  Anatomicus  (S.  N.  A.)  the  body  (Corpus)  is  the  part  which 
bears  the  teeth,  and  is  divided  into  a  pars  incisiva  and  a  pars  molaris.  The  ramus  is  the  rest 
of  the  bone. 


64  THE  SKELETON  OF  THE  HORSE 

posterior  part  Ijy  rough  lines  for  the  attachment  of  the  internal  pterygoid  muscle. 
In  front  of  its  middle  is  the  mandibular  or  inferior  maxillary  foramen  ( Foramen 
mandibulare),  which  is  the  posterior  orifice  of  the  mandibular  or  inferior  dental 
canal  (Canalis  mandibulae).  The  canal  curves  downward  and  passes  forward 
below  the  cheek  teeth,  opening  externally  at  the  mental  foramen;  it  is  continued 
into  the  body  of  the  bone  as  a  small  canal  (Canalis  alvcolaris  incisivus),  which 
carries  the  vessels  and  nerves  to  the  incisor  teeth.  Tlie  superior  or  alveolar  border 
forms  anteriorly  part  of  the  interalveolar  space;  here  it  is  thin,  liehind  this  it  is 
thick  and  is  excavated  by  six  alveoli  for  the  lower  cheek  teeth.  Beliind  the  last 
alveolus  it  curves  sharply  upward  and  is  narrow  and  rough.  In  the  young  foal 
there  is  commonly  a  small  alveolus  for  the  vestige  of  the  first  premolar  ("wolf 
tooth")  close  to  the  first  large  one.  The  inferior  border  of  the  horizontal  part  is 
nearly  straight;  it  is  thick  and  rounded  in  the  young  horse,  becoming  narrower  and 
sharp  in  old  subjects.  At  its  posterior  part  there  is  a  smooth  impression  (Incisura 
vasorum)  where  the  facial  vessels  and  parotid  duct  turn  round  the  bone.  Behind 
this  point  the  lioriler  curves  sharply  upward,  forming  the  angle  (Angulus  mandi- 
buhe);  this  part  is  thick  and  has  two  roughened  lii)s,  internal  and  external,  sep- 
arated by  a  considerable  intermediate  space;  near  tlie  condyle  it  becomes  narrower. 
The  anterior  extremity  joins  the  l)ody.  The  superior  extremity  comprises  the 
coronoid  process  in  front  and  the  condyle  l)eliin(i,  tlie  two  being  s(>]iarated  by  the 
sigmoid  notch  (Incisura  niandibuhe),  through  which  the  nerve  to  the  masseter 
muscle  passes.  The  coronoid  process  (Processus  coronoideus)  is  thin  transversely 
and  curved  slightly  inward  and  backward.  It  projects  upward  in  the  temporal 
fo.ssa,  and  furnishes  insertion  to  the  temporal  muscle.  The  condyle  (Capitulum 
mandiljulaj)  lies  at  a  much  lower  level  than  the  end  of  the  coronoid  process.  It  is 
elongated  transversely  and  articulates  with  the  squamous  temporal  through  the 
medium  of  an  articular  disc.  The  part  below  the  condyle  is  usually  termed  the 
neck  (Colluin  mandibuhc);  on  its  antero-internal  part  is  a  depression  (Fovea 
pterygoidea)  for  the  attachment  of  the  external  pterygoid  muscle.  The  middle  of 
the  vertical  part  of  the  ramus  consi.sts  to  a  large  extent  of  a  single  plate  of  compact 
substance  which  may  be  so  thin  in  places  as  to  be  translucent. 

Development.— The  mandible  develops  from  two  chief  centers  in  the  connec- 
tive ti.ssue  which  overlies  the  paired  Meckel's  cartilages.  At  birth  it  consists  of 
two  symmetrical  halves  which  meet  at  a  median  symphy.sis.  Fusion  usually  occurs 
in  the  second  or  third  month. 

Age  changes.— Thcsp  are  associatpil  largely  i\-ith  the  prowth  and  later  with  the  reduction 
of  the  teetli.  In  the  yoiinf;  horse,  m  which  the  teeth  are  large  and  are  in  great  part  embedded 
in  the  bone,  the  body  is  thick  and  .strongly  curved,  and  the  horizontal  part  of  the  lanuis  is  also 
11  T^''^'''  "■'^  ''^'^*''  '"'''  '"^""U''"''  from  the  bone,  the  body  becomes  flattened  and  narrower, 
and  the  horizontal  part  of  the  ramus  is  thinner,  especially  in  its  lower  part:  the  angle  and  the 
impression  in  front  of  it  arc  more  pronounced. 

The  Hyoid  Bone 

The  hyoid  bone  (Os  hyoideum)  is  situated  chiefly  between  the  vertical  parts 
of  the  rami  of  the  mandilile,  but  its  upper  part  extends  somewhat  further  back. 
It  IS  attached  to  the  petrous  temporal  bones  by  rods  of  cartilage,  and  supports  the 
root  of  the  tongue,  the  pharynx,  and  larynx.  It  consists  of  a  bodv,  a  lingual  process, 
and  three  pairs  of  cornua. 

The  body  or  basihyoid  (Basis  ossishyoidei)  is  a  short  transverse  bar,  compressed 
dorso- vent  rally.  The  ui)per  surface  is  concave  and  smooth  in  its  middle,  and  pre- 
sent.s  at  each  end  a  convex  facet  or  tubercle  for  articulation  with  the  small  cornu. 
The  lower  surface  is  slightly  roughened  for  muscular  attachment.  The  anterior 
border  carries  medially  the  lingual  process.  The  posterior  border  is  concave  and 
smooth  in  its  middle,  and  carries  on  either  side  the  thyroid  cornu.     The  body,  the 


THE    SKULL   AS    A    WHOLE 


G5 


lingual  process,  anil  the  thyroid  processes  are  fused  together,  and  may  be  compared 
to  a  spur  or  a  fork  with  a  very  short  handle. 

The  lingual  process  (Processus  lingualis)  projects  forward  medially  from  the 
body,  and  is  embeilded  in  the  root  of  the  tongue  during  life.  It  is  compre.s.sed 
laterally  and  has  a  blunt-pointed  free  end.  The  lateral  surfaces  are  slightly  con- 
cave.    The  upper  border  is  narrow,  the  lower  thick  and  irregular. 

The  thyroid  comua  or  thyrohyoids  (t'ornua  laryngea)'  extend  backward  and 
upwaril  from  the  lateral  parts  of  the  body.  They  are  compressed  laterally  (except 
at  their  junction  with  the  body),  and  their  posterior  ends  are  connected  with  the 
anterior  comua  of  the  th>Toid  cartilage  of  the  larynx. 

The  small  comua  or  keratohyoids  (C'ornua  minora)  are  short  rods  which  are 
directed  upward  and  forward  from  either  end  of  the  upper  surface  of  the  body. 
Each  is  somewhat  constricted  in  its  middle  part  and  has  slightly  enlarged  ends. 
The  lower  end  has  a  small  concave  facet  which  articulates  with  the  body.  The 
upper  end  articulates  with  the  great  cornu,  or  with  the  middle  cornvi  when  present. 

The  great  comua  or  stylohyoids  are  much  the  largest  parts  of  the  bone.  They 
are  directed  upward  and  backward, 
and  are  connected  above  with  the 
base  of  the  petrous  temporal  bones. 
Each  is  a  thin  plate,  seven  or  eight 
inches  (ca.  18  to  20  cm.)  long,  which 
is  slightly  curved  in  its  length,  so 
that  the  external  surface  is  concave 
and  smooth.  The  internal  surface 
is  convex  and  smooth.  The  borders 
are  thin.  The  upper  extremity  is 
large  and  forms  two  angles;  the 
upper  angle  is  connected  by  a  rod 
of  cartilage  with  the  hyoid  process 
of  the  petrous  temporal  bone;  the 
lower  angle  is  somewhat  thickened 
and  rough  for  muscular  attachment. 
The  lower  extremity  is  small,  and 
articulates  with  the  small  or  the 
middle  cornu. 

Tlie  middle  comua  or  epihyoids 
are  small  wedge-shaped  pieces  or 
nodules    interposed     between    the 

small  and  great  cornua.     They  are  usually  transitory,  and  unite  with  the  great 
cornua  in  the  ailult. 

Development. — The  hyoid  ossifies  in  the  cartilages  of  the  second  and  third 
visceral  arches.  Each  part  has  a  separate  center,  except  the  lingual  process,  which 
ossifies  bv  extension  from  the  body.     The  latter  has  primarily  two  centers  (:Martin). 


Fig.  32. — Hvoid  Boxe  of  Horse,  Viewed  from  the  Side 
AND  Somewhat  from  i.v  Front. 
a.  Body;  b,  lingual  process;  c,  thyroid  cornu;  c',  car- 
tilage of  c;  d.  small  cornu;  e,  middle  cornu;  /,  great  cornu; 
/'.  muscular  angle  of  great  cornu;  f/.  cartilage  of  great  cornu. 
(EUenberger-Baum,  .\nat.  d.  Haustiere.) 


THE  SKULL  AS  A  WHOLE 
The  skull  of  the  hor.se  has  the  form  of  a  long  four-sided  pyramid,  the  base  of 
which  is  posterior.  It  is  convenient  to  exclude  the  mandible  and  hyoid  from  present 
consideration.  The  division  between  the  cranium  (Cranium  cerebrale)  and  the  face 
(Cranium  viscerale)  may  be  indicated  approximately  by  a  transverse  plane  through 
the  anterior  margins  of  the  orbits. 

The  superior  or  frontal  surface  (Norma  frontalis)  is  formed  by  the  upper  part 
of  the  occipital,  the  interparietal,  parietal,  frontal,  and  nasal  bones.     It  may  be 
1  These  correspond  to  the  great  comua  of  man. 
5 


66 


THE   SKELETON    OF   THE    HORSE 


divided  into  parietal,  frontal,  nasal,  and  premaxiUary  regions.  The  panetal  region 
extends  from  the  occipital  crest  t.)  the  parieto-frontal  or  coronal  suture.  It  is 
marked  mediallv  l.v  the  external  sagittal  crest,  which  bifurcates  ui  front,  the 
branches  becomin}-;  continuous  with  the  frontal  crests.  The  latter  curve  outward 
to'the  root  of  the  supraorl)ital  process.  The  frontal  region  is  the  widest  part  of 
the  surface  and  is  smooth  and  almost  flat.  It  is  bounded  in  front  by  the  naso- 
frontal suture.     On  either  side  of  it  is  the  root  of  the  supraorbital  process,  pierced 


Fiii 


33. — Cranial  and  Obbitai.  Regions  of  Skull  of  Horse,  Lateral  View.     The  Zvcomatic  .\rch 
Sfl'RAORBlTAL  PROCESSES  Have  Been  S.awn  Off. 


1,  Occipital  condyle;  2,  condyloid  fossa;  3.  paramasloid  or  styloid  process;  .J,  occipital  crest;  5,  external 
ocri|iilal  protuberance;  6,  external  auditory  meatus;  7.  mastoid  process;  8,  hyoid  process;  9.  stylomastoid  fora- 
men; 10,  muscular  process;  11,  foramen  lacerum  anterius;  12,  postglenoid  process;  13,  glenoid  cavit.\-;  14,  tem- 
poral condyle;  15,  Vidian  groove;  16,  alar  canal  of  pterygoid  i)rocess  indicated  by  arrow;  17,  temporal  foramen; 
IS,  ethmoidal  foramen;  19,  optic  foramen;  20,  foramen  lacerum  orbitale;  21,  maxillary  foramen;  22,  spheno- 
palatine foramen;  2,'J.  posterior  palatine  foramen;  24,  supraorbital  foramen  (o])ened):  25,  lacrimal  fossa;  26, 
ilepression  for  origin  of  obliquus  oculi  inferior;  27.  facial  crest;  28,  maxinar.v  tuberosit.v;  29,  alveolar  tuberosity; 
oO,  hamulus  of  pterygoid  bone;  S.o.,  supraoccipital;  P,  parietal;  .S,  scitiamoiis  temporal;  B.o.,  basioccipital; 
B.f..  basisphenoid;  .1.?..  temi>oral  wing  of  sphenoid;  .4. o.,  orbital  wing  of  sphenoid:  /*/. p. .  pterj-goid  process  of 
-phenoid;  P.p.,  perpendicular  part  of  palate  bone;  F.F'.  facial  and  orbital  i>arts  of  frontal  bone;  L.L',  orbital 
and  facial  parts  of  lacrimal  bone;  .U,  facial  jiart  of  malar  bone;  ^t.r..  maxilla;  a.  parieto-occipital  suture;  b, 
parielo-temporal  or  squamous  suture;  c.d,  spheno-squamous  suture;  c,  palato-frontal  suture;  /,  fronto-lacrimal 
suture. 


by  the  supraorbital  foramen.  The  nasal  region  is  convex  from  side  to  side,  wide 
behind,  narrow  in  front.  Its  ])rofile  is  in  some  cases  nearly  straight;  in  others  it 
is  undulating,  with  a  variably  marked  depression  about  its  middle  and  at  the  an- 
terior end.  The  premaxiUary  region  presents  the  osseous  nasal  aperture  ( Apcrtura 
nasalis  ossea)  and  the  foramen  incisivum. 

The  lateral  surface  ( Norma  lateralis)  may  l)e  diviiled  into  cranial,  ortiital,  and 
maxillary  or  preorbital  regions. 


THE    SKULL   AS   A   WHOLE  67 

The  cranial  region  jiresonts  the  temporal  fossa,  the  zygomatic  arch,  and  the 
outer  part  of  the  petrous  temporal  hone. 

The  temporal  fossa  is  l)oumled  internally  by  the  sagittal  and  frontal  crests, 
externally  by  the  temporal  crest  and  the  zygomatic  arch,  and  behind  by  the  occipital 
crest.  Its  upper  and  middle  parts  are  rough  for  the  attachmtuit  of  the  temporal 
muscle.  In  its  lower  posterior  part  are  several  foramina  which  communicate  with 
the  parieto-temporal  canal.     The  fossa  is  continuous  in  front  with  the  orbital  cavity. 

The  zygomatic  arch  is  formed  by  the  zygomatic  processes  of  the  temporal, 
malar,  and  maxilla.  Its  ventral  face  presents  the  condyle  and  glenoid  cavity  for 
articulation  with  the  lower  jaw,  through  the  medium  of  the  articular  tlisc.  Behind 
the  glenoid  cavity  is  the  post-glenoid  process. 

The  external  auditory  process  projects  outward  through  a  deep  notch  in  the 
lower  margin  of  the  s(iuamous  temporal  below  the  temporal  crest.  A  little 
further  back  is  the  mastoid  process,  crossed  in  its  upper  part  by  a  groove  for  the 
mastoid  artery. 

The  orbital  region  comprises  the  orbit  and  the  pterygo-palatine  fossa. 

The  orbit  is  a  cavity  which  incloses  the  eyeball,  with  the  muscles,  vessels,  and 
nerves  associated  with  it.  It  is  not  separated  in  the  skeleton  from  the  temporal 
fossa.  The  long  axis  of  the  cavity,  taken  from  the  optic  foramen  to  the  middle  of 
the  inlet,  is  directed  forward,  outward,  and  slightly  upward.  The  inner  wall 
(Paries  medialis)  is  complete  and  extensive.  It  is  concave  and  smooth,  and  is 
formed  by  the  frontal  and  lacrimal  and  the  orbital  wing  of  the  sphenoid.  In  its 
extreme  anterior  part  is  the  fo.ssa  for  the  lacrimal  sac.  Behind  this  is  a  small  de- 
pression in  which  the  inferior  oblique  muscle  of  the  eye  arises;  here  the  i)late  which 
separates  the  orbit  from  the  maxillary  sinus  is  very  thin.  The  upper  wall  (Paries 
superior)  is  formed  by  the  frontal  and  to  a  small  extent  by  the  lacrimal  bone.  It 
presents  the  supraorbital  foramen,  which  perforates  the  root  of  the  supraorbital 
process.  The  lower  wall  (Paries  inferior)  is  very  incomplete,  and  is  formed  by  the 
malar,  the  zygomatic  process  of  the  temporal,  and  to  a  small  extent  by  the  maxilla. 
The  external  boundary  (Paries  lateralis)  is  the  supraorbital  process.  At  the  ex- 
treme posterior  part  is  the  orbital  group  of  foramina.  Four  are  situated  in  front 
of  the  pterygoid  crest.  Of  these,  the  uppermo.st  is  the  ethmoidal  or  internal 
orbital  foramen,  which  transmits  the  ethmoidal  vessels  and  nerve.  The  optic 
foramen  is  situated  a  little  lower  and  further  back;  it  transmits  the  optic  nerve. 
Immediately  below  the  optic  is  the  foramen  lacerum  orbitale,  which  transmits  the 
ophthalmic,  third,  sixth,  and  sometimes  the  fourth  nerve;  commonly  there  is  a 
very  small  trochlear  or  pathetic  foramen  in  the  crest  for  the  last  named  nerve. 
The  foramen  rotundum  is  below  the  foramen  lacerum,  from  which  it  is  separated 
by  a  thin  plate;  it  transmits  the  superior  maxillary  nerve.  The  alar  canal  opens 
in  common  \vith  the  foramen  rotundum,  and  the  anterior  opening  of  the  pterygoid 
or  Vidian  canal  is  also  found  here.  The  temporal  foramen  (For.  alare  parvum)  is 
just  behind  the  pterygoid  crest  and  on  a  level  with  the  foramen  lacerum.  It  is 
the  upper  opening  of  a  canal  which  leads  from  the  alar  canal,  and  through  it  the 
anterior  deep  temporal  artery  emerges.  The  inlet  of  the  orbital  cavity  (Aditus 
orbitiB)  is  circumscribed  by  a  complete  bony  ring,  which  is  nearly  circidar.  Its 
antero-inferior  part  (Margo  infraorbitalis)  is  smooth  and  rounded;  the  remainder 
(Margo  supraorbitalis)  is  rough  and  irregularly  notchctl.  During  life  the  cavity  is 
completed  by  the  periorbita  or  ocular  sheath,  a  conical  fibrous  membrane,  the  apex 
of  which  is  attached  around  the  optic  foramen. 

Below  the  orbital  cavity  is  the  pterygo-palatine  fossa.  Its  wall  is  formed  by 
the  pterygoid  process,  the  perpendicular  part  of  the  palate  bone,  and  the  tuber 
maxillare.  Its  deep  anterior  part  ( maxillary  hiatus)  contains  three  foramina.  The 
upper  one,  the  maxillary  foramen,  is  the  entrance  to  the  infraorliital  canal,  which 
transmits  the  infraorl)ital  nerve  and  ves.sels.     The  spheno-palatine  foramen  trans- 


(J8  THK    SKELETON    OF   THE    HORSE 

mits  vosscls  ami  nerves  of  like  name  to  the  nasal  cavity.  The  lower  foramen,  the 
posterior  palatine,  transmits  the  palatine  artery  and  nerve  to  the  palatine  canal. 
The  upper  part  of  the  fossa  is  smooth,  and  is  crossed  by  the  internal  maxillary 
artery  and  the  maxillary  nerve.  The  lower  part  is  chiefly  roughened  for  the  attach- 
ment of  the  internal  pterysroid  muscle,  but  is  crossed  in  front  by  a  smooth  groove 
in  which  the  jialatinc  vein  lies. 

The  maxillary  or  preorbital  region  is  formed  chiefly  by  the  maxilla,  but  also  by 
the  premaxilla,  and  the  facial  parts  of  the  lacrimal  and  malar  bones.  Its  contour 
is  approximately  triangular,  the  base  being  posterior.  It  offers  two  principal 
features.  The  facial  crest  extends  forward  from  the  lower  margin  of  the  orbit, 
and  ends  abruptl>-  at  a  i)()int  about  an  inch  and  a  half  (3  to  4  cm.)  above  the  third 
or  fourth  cheek  tooth;'  its  inferior  aspect  is  rough  for  the  attachment  of  the  masse- 
ter  muscle.  The  infraorbital  foramen  is  situated  in  a  transverse  plane  about  an 
inch  (ca.  2  to  3  cm.)  in  front  of  lli(>  end  of  the  crest  and  about  two  inches  (5  cm.) 
above  it.  The  foramen  opens  forward,  and  through  it  the  infraorbital  artery  and 
nerve  emerge.  The  surface  over  the  premolar  teeth  varies  greatly  with  age,  in 
conformity  with  the  size  of  the  embedded  parts  of  the  teeth.  In  the  young  horse 
the  surface  here  is  strongly  convex,  the  outer  plate  of  bone  is  thin  and  even  defective 
.sometimes  in  places,  and  the  form  of  the  teeth  is  indicated  by  eminences  (Juga 
alveolaria).  In  the  old  animal  the  surface  is  concave  on  account  of  the  extrusion 
of  the  teeth  from  the  l)one.  The  downward  curve  of  the  premaxilla  is  pronounced 
in  the  young  subject,  very  slight  in  the  aged. 

The  inferior  or  basal  surface  (Norma  basalis),  exclusive  of  the  mandible, 
consi-sts  of  cranial,  guttural,  and  palatine  regions. 

The  cranial  region  (Basis  cranii  externa)  extends  forward  to  the  vomer  and 
pterygoid  iiroccsscs  (Fig.  2S).  At  its  posterior  end  is  the  foramen  magnum,  flanked 
i)y  the  occipital  condyles.  External  to  the  latter  is  the  condyloid  fossa,  in  which 
is  tlu"  hypoglossal  foramen,  which  transmits  the  hypoglossal  nerve  and  the  con- 
dyloid artery  and  vein.  Further  outward  are  the  paramastoid  or  styloid  proc- 
esses (Processus  jugulares)  of  the  occipital  bone.  Extending  forward  centrally  is 
a  i)rismatic  bar,  formed  l)y  the  basilar  part  of  the  occipital  and  the  body  of  the 
sphenoid  bone;  at  the  junction  of  these  parts  are  tubercles  for  the  attach- 
ment of  the  ventral  straight  muscles  of  the  head.  On  either  side  of  the  basilar 
part  of  the  occipital  is  the  foramen  lacerum  basis  cranii,  bounded  externally  by 
the  ba.se  of  the  petrous  tein])oral  bone.  In  front  of  these  the  region  becomes  very 
wide  on  account  of  the  lateral  extension  of  the  zygomatic  processes,  bearing  on  the 
ventral  aspect  the  condyle  and  glenoid  cavity  for  articulation  with  the  mandible. 
Beyonil  this  the  process  turns  forward  and  joins  the  zygomatic  process  of  the  malar, 
completing  the  zygomatic  arch  and  the  surface  for  the  attachment  of  the  masseter 
muscle.  On  cither  side  of  the  body  of  the  sphenoid  is  the  infratemporal  fossa, 
formed  by  the  temjiora!  wing  ;uid  the  root  of  the  pterygoid  process  of  the  sphenoid 
bone.  It  is  bounded  in  front  by  the  pterygoid  crest,  which  separates  it  from  the 
orbit  and  the  ])terygo-palatine  fossa.  In  it  is  the  pterygoid  or  alar  foramen,  which 
transmits  the  internal  maxillary  artery.  A  little  lo^^er  is  the  entrance  to  the  ptery- 
goid (\'idian)  canal. 

The  guttural  region  presents  the  pharyngeal  orifice  of  the  nasal  cavity.  This  is 
ellii)tical  and  is  ilivided  in  its  depth  medially  by  the  vomer  into  two  posterior 
nares  or  choanae.  It  is  bounded  in  front  and  laterally  l)y  the  palate  and  pterygoid 
ijones.  Ix'hind  by  the  vomer.  It  is  flanked  by  tiie  hamular  jn-ocess  of  the  i)terygoid 
bones.  The  plane  of  the  opening  is  nearly  horizontal,  and  the  length  is  about 
twice  the  width. 

The  palatine  region  comprises  a  little  more  than  half  of  the  entire  length 

'  This  relation  vario,';  with  aRc;  in  the  young  hor.se  the  third  tooth,  in  the  old  subject  the 
fourth,  lies  below  the  end  of  the  cre.st. 


THE    CRANIAL    CAVITY 


69 


of  the  base  of  the  skull  (Fig.  31).  The  hard  palate  (Palatum  durum)  is 
concave  from  side  to  side,  and  in  its  length  also  in  the  anterior  part.  It 
is  formed  by  the  palatine  processes  of  the  preinaxilhe  and  maxilhn,  and  the 
horizontal  parts  of  the  palate  bones.  It  is  circumscribed  in  front  and 
laterally  by  the  superior  alveolar  arch,  in  which  the  upper  teeth  are  im- 
planted. The  interalveolar  space  (Margo  intcralveolaris)  is  that  part  of  the  arch 
in  which  alveoli  are  not  present.  Behind  the  last  alveolus  is  the  alveolar 
tuberosity,  and  internal  to  this  is  a  groove  for  the  palatine  vein.  In  the  middle 
line  is  the  median  palatine  suture  (Sutura  palatina  mediana).  In  the  line  of  the 
suture,  a  little  behind  the  central  incisors,  is  the  foramen  incisivum,  through  which 
the  palato-labial  artery  passes.  On  either  side,  parallel  with  the  alveolar  part  of 
the  maxilla,  is  the  palatine  groove  (Sulcus  palatinus),  which  contains  the  ])alatine 
vessels  and  nerve.  It  is  con- 
tinuous at  the  anterior  pala-  ^2' 
tine  foramen  with  the  palatine 
canal,  which  is  situated  be- 
tween the  maxilla  and  the  pal- 
ate bone.  The  palatine  cleft 
(Fissura  palatina)  is  the  nar- 
row interval  along  the  outer 
margin  of  the  palatine  process 
of  the  premaxilla;  it  is  closed 
in  the  fresh  state  by  cartilage. 
Scattered  along  each  side  of 
the  palate  are  several  vascular 
foramina.  The  transverse 
palatine  suture  (Sutura  pala- 
tina transversa)  is  about  half 
an  inch  from  the  posterior  bor- 
der. The  latter  is  in  a  plane 
through  the  last  molar  teeth, 
and  is  concave  antt  free. 

The  posterior  or  nuchal 
surface  (\orma  occipitalis)  is 
formed  by  the  occipital  bone. 
It  is  trapezoidal  in  outline, 
wider  below  than  above,  con- 
cave dorso-ventrally,  convex 
transversely.  It  is  separated 
from  the  superior  surface  by 
the  occipital  crest,  and  from 
the  lateral  surfaces  by  the  superior  curved  lines  (Linea?  nucha>  superiores).  Below 
the  crest  are  two  rough  areas  for  the  attachment  of  the  complexus  muscles.  A  little 
lower  is  a  central  eminence  on  the  sides  of  which  the  ligamentum  nucluc  is  attached. 
At  the  lowest  part  centrally  is  the  foramen  magnum,  at  which  the  brain  and  spinal 
cord  meet;  this  is  bounded  laterally  by  the  occipital  condyles,  which  are  flanked  by 
the  paramastoid  or  styloid  processes  (Processus  jugulares). 

The  apex  of  the  skull  is  formed  by  the  bodies  of  the  premaxilla-  and  mandible, 
carrying  the  incisor  teeth. 


Fio.  34. — Craniai.  Cavity  of  Horse  as  Seen  on  Sagittal  Sec- 
tion' OF  Skull. 
O.  Frontal  sinus;  r,  sphenoidal  sinus;  (,  cerebral  compartment 
of  cranium;  1-3,  ridges  (juga)  corresponding  to  fissures  of  lateral 
surface  of  cerebrum:  4,  groove  for  middle  cerebral  artery;  5,  en- 
trance to  for.  lacerum  orbitale;  6,  entrance  to  optic  foramen;  7,  S, 
grooves  on  sphenoid  bone;  9.  incisura  spinosa;  9',  groove  for  middle 
meningeal  artery;  10,  fossa  for  pyriform  lobe  of  cerebrum;  11, 
incisura  ovalis;  12,  incisura  carotica;  13,  internal  auditory  meatus; 
14,  foramen  lacerum  basis  cranii;  15,  hypoglossal  foramen;  16, 
petrous  temporal;  17,  orifice  of  aqua^ductus  vestibuli;  18,  orifice 
of  aquEeductus  cochleie;  19,  foramen  magnum;  20,  petrosal  crest; 
21,  two  plates  of  frontal  bone;  22,  .supraoccipital;  23,  basioccipital; 
24,  tentorium  osseum;  25,  body  of  sphenoid.  (.After  Ellenberger- 
Baum,  Top.  Anat.  d.  Pferdes.) 


THE  CRANIAL  CAVITY 
This  cavity  incloses  the  brain,  with  its  membranes  and  vessels, 
small,  and  is  ovoiil  in  shape. 


It  is  relatively 


70 


THE    SKF.LETON    OF   THE    HORSE 


The  superior  wall  or  roof  (Calvaria)  is  formed  by  the  supraoccipital,  inter- 
parietal, parietal,  and  frontal  hones.  In  the  middle  line  is  the  internal  sagittal 
crest,  wiiich  joins  the  crista  galli  in  front,  and  furnishes  attachment  to  the  falx 
cerel)ri.  Posteriorly  the  crest  is  continued  liy  the  sharj)  anterior  margin  of  the 
tentorium  osseum,  which  projects  downward  and  forward  into  the  cavity,  and  gives 
attachment  to  the  tentorivnn  ccrehclh  by  its  sharp  lateral  edges.  Behind  this  the 
roof  is  groovetl  centrally  for  the  mitldle  lobe  or  vermis  of  the  cerebellum.  Trans- 
verse grooves  pass  from  the  base 
of  the  tentorium  osseum  to  the 
parieto-temporal  canals.  The 
anterior  part  of  the  roof  is  hol- 
lowed by  the  frontal  sinus.  The 
occipital  part  is  verj-  thick  and 
strong. 

The  lateral  walls  are  formed 
by  the  occipital,  parietal,  tem- 
poral, and  frontal  bones,  and  in 
part  by  the  orbital  wings  of  the 
sphenoid.  Each  is  crossed  ob- 
liquely by  the  petrosal  crest, 
which  concurs  with  the  project- 
ing margin  of  the  parietal  bone 
and  the  tentorium  osseum  in 
dividing  the  cavity  into  cerebral 
and  cerebellar  compartments. 
Behind  the  crest  is  a  depression 
for  the  lateral  lobe  (hemisphere) 
of  the  cerebellum.  Below  this 
are  the  internal  auditory  meatus 
and  the  openings  of  the  aquae- 
ductus  vestibuli  and  aquaeductus 
cochlea^ 

The  roof  and  lateral  walls 
are  marked  by  digital  impres- 
sions and  vascular  grooves. 

The  inferior  wall  or  floor 
(Basis  cranii  interna)  may  l)e 
regarded  as  forming  three  fossa>. 
The  anterior  fossa  (Fossa  cranii 
anterior)  supports  the  frontal  and 
olfactory  parts  of  the  cerebrum. 
It  is  formed  chiefly  by  the  pre- 
sphenoid,  and  lies  at  a  higher 
level  than  the  middle  fossa.  In 
front  the  fossa  i.s  divided  medi- 
ally by  the  crista  galli,  lateral  to 
•which  are  the  deeji  ethmoidal  or 
olfactory  fossae  for  tlie  olfactorv 
lobes.  Ihe  ethmoidal  or  internal  orbital  foramen  perforates  the  cranial  wall 
at  the  outer  side  of  these  fossa.  Further  back  the  central  part  of  the  surface 
IS  slightly  elevated,  and  is  flanked  by  shallow  depressions  which  support  the  ol- 
factoo-  peduncles.  Po.steriorly  is  a  bony  shelf  which  covers  the  entrance  to  the 
optic  foranuna  ;  the  edge  of  this  shelf  and  the  posterior  borders  of  the  orbital  wings 
of  the  si)henoid  may  be  taken  as  the  line  of  demarcation  between  the  anterior  and 


Fig.  3.'). — Fi.oon  of  Cramai.  Tavitv  or  Hobsf. 

The  roots  of  the  cranial  nerves  are  shown  on  the  left  side 
and  are  (lej^ijcnated  by  number.  /.  .\nterior  cranial  fossa;  //. 
middle  cranial  fossa;  ///,  po,sterior  cranial  fossa;  a,  ethmoitlai 
fossa:  b,  ethmoidal  foramen:  c,  foramen  for  nasal  branch  of 
ophthalmic  artery:  d,  orbital  wing  of  sphenoid  bone;  e.  optic 
fo.Hsa;  /.  sella  turcica:  g,  spheno-occipital  crest;  li,  h' ,  dotted  line 
indicatinK  contour  of  pituitary  body;  h",  slight  elevation  repre- 
senting dorsum  selisc:  i,  k,  grooves  for  nerves  and  cavernous 
sinus;  /,  ilepression  for  pyriform  lobe  of  cerebrum;  m,  groove 
for  middle  meningeal  artery;  n,  depression  for  pons;  o.  foramen 
iaccrum  anterius;  p,  foramen  lacerum  posterius;  q,  incisura 
carotica;  <;',  incisura  ovalis;  (i",  incisura  spinosa;  r,  depression 
for  medulla  oblongata:  ».  hypoglossal  foramen:  (,  internal  audi- 
tory meatus;  u,  foramen  magnum;  r.  frontal  sinus;  w,  zygomatic 
process  of  tetnporal  bone;  x,  .section  of  |)etrous  temporal:  y, 
section  of  occipital  bone:  j,  crista  galli;  1,  1',  1",  dotted  lines 
indicating  position  of  olfactory  tracts  and  peduncle,  (.\fter 
Ellenberger-Haum,  Top.  .Vnat.  il,  I'fcrdes.) 


THE    NASAL    CAVITY 


71 


middle  fossse.  The  middle  fossa  (Fossa  craiiii  media)  is  the  widest  part  of  the 
cavity.  It  extends  l)ackward  to  the  internal  spheno-occipital  and  petrosal  crests, 
thus  corresponding  to  the  post -sphenoid.  In  its  middle  is  a  small  fossa,  the  sella 
turcica,  in  which  the  pituitary  body,  or  hypophysis  cerebri,  is  situated.  On  either 
side  are  two  grooves  for  nerves;  the  inner  one  transmits  the  ophthalmic,  third, 
and  sixth  nerves  to  the  foramen  lacerum  orbitale;  the  outer  one  leads  to  the  foramen 
rotuntlum,  and  lodges  the  maxillary  nerve.  External  to  the  grooves  is  a  depression 
for  the  pyriform  lobe  of  the  cerebrum.  The  posterior  fossa  ( Fossa  cranii  posterior) 
corresponds  to  the  basilar  part  of  the  occipital  bone.  It  contains  the  medulla, 
pons,  and  cerebellum.  In  front  is  a  median  depression  (Fossa  pontis)  for  the  pons. 
The  surface  behind  this  is  concave  transverseh'  and  slopes  gently  dowmwartl  to  the 
foramen  magnum;  it  supports  the  medulla.  On  either  side  are  the  foramen 
lacerum  basis  cranii  and  the  hypoglossal  foramen. 

The  anterior  or  nasal  wall  is  formed  l)y  the  cribriform  plate  of  the  ethmoid, 
which  separates  the  cranium  from  the  nasal  cavnt}-.  It  is  perforated  by  numerous 
foramina  for  the  passage  of  the  olfactorj-  nerve-bundles. 


Fig.  .36. — Median-  Sncnox  of  Skull  of  Horse  Without  the  M.\.vdiblc. 
The  septum  nasi  is  removed,  but  the  mucous  membrane  on  the  turbinal  bones  is  retained.  a,  a',  Superior 
turbinal  bone,  dotted  line  indicating  Umit  between  anterior  coiled  part  and  posterior  uncoiled  part;  6,  6',  superior 
turbinal  folds,  inclosing  bars  of  cartilage;  c.  fold  of  mucous  membrane  formed  by  union  of  b  and  b';  d,  d'.  anterior 
coiled  and  posterior  uncoiled  part  of  inferior  turbinal.  dotted  line  indicating  septum  between  them;  e,  /.  inferior 
turbinal  folds,  former  (alar  fold)  inclosing  bar  of  cartilage;  ff,  h,  t,  superior,  middle,  inferior  meatus;  o,  o',  frontal 
sinus;  partial  septum  between  o  and  o';  y.  nasal  part  of  frontal  sinus  (nasal  sinus);  r,  lateral  mass  of  ethmoid 
bone;  s,  sphenoidal  sinus;  t,  cranial  cavity;  u,  opening  made  in  superior  turbinal  bone  at  point  where  drainage 
of  frontal  sinus  may  be  obtained,     (.\fter  Eilenberger,  in  Leisering's  .\tlaa.) 


THE  NASAL  CAVITY 
The  nasal  cavity  (Cavum  nasi)  is  a  longitudinal  passage  which  exiends  through 
the  upper  part  of  the  face.  It  is  divided  into  right  and  left  halves  by  a  median 
septimi  nasi.  The  lateral  walls  are  formed  by  the  maxilla,  premaxilla,  and  the 
perpendicular  part  of  the  palate  liones.  Attached  to  them  are  the  turbinal  bones, 
which  subdivide  each  nasal  fossa  into  three  meatuses  (Meatus  nasi).  This  wall 
is  crossed  obliquely  by  the  canal  and  groove  for  the  naso-lacrimal  duct,  and  its 
posterior  part  is  perforated  by  the  spheno-palatine  foramen.  The  superior  wall 
or  roof  is  formed  by  the  frontal  and  nasal  bones.  It  is  concave  from  side  to  sitle, 
and  nearly  straight  longitudinally,  except  in  the  posterior  part,  where  it  curves 
dowmward.  It  presents  a  median  elevation,  the  nasal  crest.  The  inferior  wall 
or  floor  is  formed  by  the  palatine  processes  of  the  premaxillae  and  maxilhe,  and  the 
horizontal  parts  of  the  palate  bones.  It  is  ^^^der  but  considerably  shorter  than  the 
roof.  It  is  concave  transversely,  and  nearly  horizontal  from  before  backward, 
except  in  the  posterior  third,  where  there  is  a  slight  declivity.  The  anterior  part 
presents  a  median  groove  for  the  cartilaginous  septum,  and  a  furrow  for  the  organ 
of  Jacobson  on  either  side.  On  either  side  of  the  palatine  processes  of  the  premax- 
illae is  the  palatine  cleft. 


72  THE  SKELETON  OF  THE  HORSE 

Tlio  septum  nasi  is  incomplete  in  the  macerated  skull.  It  is  formed  by  the 
perpendicular  plate  of  the  ethmoid  behind,  and  the  vomer  below.  In  the  fresh 
state  it  is  completeil  bv  a  plate  of  cartilage. 

The  superior  meatus  (.Meatus  nasi  superior)  is  a  narrow  passage  between  the 
roof  and  the  superior  turbinal  bone.  It  ends  at  the  cribriform  plate  of  the  ethmoid. 
The  middle  meatus  (Meatus  nasi  medius)  is  the  space  between  the  two  turbmal 
bones.  In  its  posterior  part  is  the  very  narrow  opening  into  the  maxillary  smus. 
The  inferior  meatus  (Meatus  nasi  inferior)  is  the  channel  along  the  floor  which  is 
overhung  by  the  inferior  turbinal  bone.  It  is  much  the  largest  and  is  the  direct 
path  i)etween  the  anterior  and  posterior  nares. 

The  external  aperture  is  bounded  by  the  nasal  bones  and  the  premaxilla;. 


Fid.  37. — Crosr-skction  of  Nasal  Rkcion  of  Skull 
OF  Horsk;  thk  Skction  Passks  Through 
THK    .\ntkrior   End    of   thk    Facial   Crest, 

A.ND   BkTWKKN   THE    ThIRO   AND    FoURTH   ChEEK 

Teeth. 

a,  Superior,  h,  inferior  tiirhitiul  bone;  c,  d,  cavi- 
ties of  a  ami  b;  e,  common  meatus;  /.  i;,  h,  s\iperior, 
middle,  inferior  meatus;  i',  k,  passages  to  cavities  of 
turbinal  boiie-s;  /,  naso-lacrimal  duct;  m,  infraorbital 
canal;  n,  anterior  end  of  maxillary  sinus;  o,  septal 
cartilage.     (After  Kllenberger,  in  Lcisering's  .\tla.'i.) 


Flo.  .SR. — Cross-section  of  Nasal  Region  of  .Skull 
OF  Horse;    the  Section  is  Cct  About  Half- 
way between  the  Orbit  and  the  Anterior 
End   of   the    Facial  Crest,  and  P.\sses  be- 
tween the  Fifth  and  Sixth  Cheek  Teeth. 
a,  Superior,  b,  inferior  turbinal  bone;    c,  d,  cavi- 
ties of  a  and  b\    e,  common  meatus;    /,  superior,  (?, 
middle,   h,   inferior   meatus;     (',   placed    over   ridge  in 
maxillary  sinus;    k,  communication  between  outer  and 
inner    (turbinal)    part    of    maxillary    sinus;     /,    naso- 
maxillary opening;    m,  naso-lacrimal  canal;    n,  infra- 
orbital canal,     (.\fter  EUenberger,  in  Leisering's  Atlas.) 


The  posterior  extremity  or  fundus  is  sejiarated  from  the  cranial  cavity  by  the 
cribriform  i)late  of  the  ethiiioid,  and  is  largely  occupied  by  the  lateral  masses  of 
that  bone. 


THE  PARANASAL  SINUSES 

Connected  directly  or  indirectly  with  the  nasal  cavity,  of  which  they  are  diver- 
ticula, are  four  pairs  of  air-sinuses  (Sinus  paranasales),  viz.,  maxillary,  frontal, 
spheno-palatine,  and  ethmoidal. 

The  maxillary  sinus  (Sinus  maxillaris)  is  the  largest.  Its  external  wall  is 
formed  by  tlie  maxilla,  the  lacrimal,  and  the  malar.  It  is  bounded  internally  by 
the  maxilla,  the  inferior  turbinal,  and  the  lateral  mass  of  the  ethmoid  bone.  It 
extends  backward  to  a  transverse  plane  in  front  of  the  root  of  the  supraorbital 
process,  and  its  anterior  limit  is  indicated  a])proximately  by  a  line  dra\vn  from  the 
anterior  end  of  the  facial  crest  to  the  infraorbital  foramcm.  Its  upper  boundary 
corresponds  to  a  line  drawn  backward  from  the  .supraorbital  foramen  parallel  to 
the  facial  crest.  The  floor  is  forineil  by  the  alveolar  i)art  of  the  maxilla;  it  is  very 
irregular  and  is  crossed  by  bony  plates  running  in  various  directions.     The  last 


THE    PARANASAL    SINUSES  73 

three  cheek  teeth  project  up  into  the  cavity  to  an  extent  which  varies  with  age; 
they  are  covered  by  a  thin  plate  of  bone.  The  cavity  is  divided  into  anterior  and 
posterior  parts  by  an  obHque  septum.  The  outer  margin  of  the  septum  is  commonly 
about  one  and  a  half  to  two  inches  (ca.  3.5  to  5  cm.)  from  the  anterior  end  of  the 
facial  crest ;  from  here  it  is  directed  inward,  backward,  and  upward.  The  upper 
part  of  the  septum  (formed  by  the  posterior  end  of  the  inferior  turbinal  bone)  is 
verj'  delicate  and  usually  cribriform. 

The  position  of  the  septum  is  quite  variable.  It  is  not  rare  to  find  it  further  forward,  and 
in  some  eases  it  is  further  back  than  is  stated  above.  In  the  recent  state,  j.  c,  when  covered  by 
the  mucous  membrane  on  both  surfaces,  it  is  nearly  always  complete,  but  in  very  exceptional 
cases  there  is  an  opening  of  variable  size  in  the  upper  part. 

The  anterior  compartment,  often  called  the  inferior  maxillary  sinus,  is  partially 
divided  by  the  infraorbital  canal  into  an  external  maxillary  part  and  an  internal 
smaller  turbinal  part.  The  latter  communicates  with  the  middle  meatus  l)y  a  very 
narrow  slit  situated  at  its  highest  part.  The  posterior  compartment,  often  called 
the  superior  maxillary  sinus,  is  also  crossed  by  the  infraorbital  canal,  internal  to 
which  it  opens  freely  into  the  spheno-palatinc  sinus.     It  comnumicates  dorsally 


Fig.  39. — .Skcll  of  Horpf:.  Lateral  View  without  Mandibi.k.     Thf.  SixrPFP  are  Opened  rp. 

a.  Posterior  part,  b  and  c.  anterior  part  of  frontal  sinus;  d,  roof  of  superior  meatus:  c.  lateral  ma-ss  of  eth- 
moid bone:  /,  /'.  naso-Iacrimal  duct,  exposed  in  its  posterior  part:  ».  h,  posterior  and  anterior  compartments 
of  maxiUarj-  sinus  (also  designated  as  superior  and  inferior  maxillary  sinuses);  i'.  septum  between  »  and  h;  k. 
lower  limit  of  upper  thin  and  partly  membranous  portion  of  septum;  h  infraorbital  canal:  m,  turbinal  part  of 
maxillary  sinus:  n.  bullous  prominence  of  inferior  turbinal:  o,  orbit;  p.  infraorbital  foramen:  q,  continuation 
of  infraorbital  canal  to  premaxilla:    r,  limit  of  maxillary  sinus,     (.\fter  EUenberger,  in  Leiseriug's  Atlas.) 

with  the  frontal  sinus  through  the  large  oval  fronto-maxiUary  opening,  situated  at 
the  level  of  the  osseous  lacrimal  canal  and  the  corresponding  part  of  the  inner  wall 
of  the  orbit;  the  orifice  is  commonly  aljout  one  and  a  half  to  two  inches  (ca.  4  to 
.5  cm.)  long  and  an  inch  or  more  (2  to  3  cm. )  wide.  Just  in  front  of  this,  and  covered 
by  a  thin  plate,  is  the  narrow  naso-maxillary  fissure  (Aditus  naso-maxillaris),  by 
which  the  sinus  opens  into  the  posterior  part  of  the  middle  meatus. 

The  foregoing  statements  refer  to  the  arrangement  in  the  average  adult  animal.  In  the 
foal  the  ca^^ty  (with  the  exception  of  its  turbinal  part)  is  largely  occupied  by  the  developing 
teeth.  In  horses  five  to  six  vears  of  age  the  maxillary  part  of  the  sinus  is  still  filled  up  to  a  large 
degree  by  the  embedded  parts  of  the  teeth.  As  the  teeth  are  extruded  to  compensate  the  wear, 
more  and  more  of  the  cavitv  becomes  free,  until  in  old  age  only  the  short  roots  project  up  in  the 
floor,  covered  by  a  layer  of"  bone.  Other  facts  in  thi.s  connection  will  be  given  in  the  description 
of  the  teeth.  In  exceptional  ca-ses  the  posterior  part  of  the  inferior  turbinal  is  sniallcr  than 
usual  and  leaves  a  considerable  intenal,  through  which  the  maxillary  sinus  communicates  with 
the  nasal  cavity. 

The  frontal  sinus  fSinus  concho-frontalis)  consists  of  frontal  and  turbinal  parts. 
The  frontal  part  is  l)ounded  chiefly  by  the  two  plates  of  the  frontal  bone,  but  its 
floor  is  formed  in  part  by  the  lateral  mass  of  the  ethmoid.     It  extends  fon^-ard  to  a 


74 


THE    SKELETON    OF   THE    HORSE 


plane  tlirough  the  anterior  margins  of  the  orbits,  backward  to  one  through  the  tem- 
poral condyles,  and  outward  into  the  root  of  the  supraorbital  process.  It  is  separ- 
ated from  the  sinus  of  the  opposite  side  by  a 
complete  septum.  It  is  partially  subdivided  by 
a  number  of  bony  jilates.  The  turbinal  ]3art  is 
situated  in  the  posterior  part  of  the  superior  tur- 
binal bone,  roofed  in  by  the  nasal  and  lacrimal 
bones.  It  extends  forward  to  a  transverse  plane 
about  half-way  between  the  anterior  margin  of 
the  orbit  and  the  end  of  the  facial  crest.  Be- 
hind it  is  in  free  communication  with  the 
frontal  part  over  the  lateral  mass  of  the  eth- 
moid. It  is  separated  from  the  nasal  cavity 
by  the  thin  turbinal  plate.  The  frontal  and 
maxillary  sinuses  communicate  through  the 
large  opening  describeil  above. 

The  spheno-palatine  sinus  (Sinus  sjiheno- 
palatinus)  consists  of  two  parts  which  communi- 
cate under  the  lateral  mass  of  the  ethmoid. 
The  sphenoidal  (posterior)  part  is  excavated  in 
the  bod}^  of  the  pre-sphenoid.  The  palatine  (an- 
terior) part  is  between  the  two  plates  of  the  per- 
pendicular part  of  the  palate  bone,  under  the 
lateral  mass  of  the  ethmoid;  it  communicates 
freely  with  the  maxillary  sinus.  The  septum 
between  the  right  and  left  sinuses  is  not  usually 
median  in  the  sphenoidal  part. 

In  about  onp-third  of  the  cases  (according  to  Paulli) 
the  splicnoidal  and  palatine  parts  are  separated  by  a  trans- 
verse septum,  and  the  sphenoidal  part  then  communicates 
only  with  the  lower  ethmoidal  meatuses. 

The  term  ethmoidal  sinus  is  often  ajiplied 
to  the  cavity  of  the  largest  ethmo-turbinal.  It 
communicates  with  the  maxillarv  sinus. 


Fio.  40.— RKti.i.  OK  HonsR,  D0R.1A1.  View, 
wiTit  S1NU8KA  Exi'OSKD  By  Re- 
moval OK  THE  Outer  Plate  ok 
Bone. 

J,  Frontal  bone:  3.  nasal  bone;  3, 
lacrimal  bone;  4,  maxilla;  a,  po.stenor 
part  of  frontal  sinus;  a',  middle  part  of 
frontal  sinus;  6,  anterior  (turoinal)  part  of 
frontal  sinus;  r.  lateral  mu»n  of  ethmoid 
bone;  d,  roof  of  superior  meatus;  e,  fronto- 
maxillar)'  openinK;  /.  naso-inuxillury  open- 
ing below  plate  which  forms  the  anterior 
margin  of  c;  ff.  h,  posterior  un<l  anterior 
compartments  of  maxillary  sinus — often 
called  the  superior  and  inferior  maxillary 
sinuses;  i,  septum  between  0  and  h;  k, 
orbit;  /,  point  at  which  superior  turbinal 
bone  may  be  perforated  to  obtain  drainaKe 
into  na«al  cavity.  (,\fter  EllenberKer,  in 
l.eisering's  .\tlas.) 

bone,  where  it  gradually  subside 
and  in  great  part  subcutaneous 


The  Bones  of  the  Thoracic  Limb 
the  scapula 

The  scapula  is  a  flat  bone,  situated  on  the 
anterior  part  of  the  lateral  wall  of  the  thorax, 
and  extending  obliquely  from  the  vertebral  end 
of  the  seventh  or  eighth  rib  to  the  sternal  end  of 
the  first  rib.  It  is  curved  slightly  and  slopes 
outward  in  adaptation  to  the  form  of  the 
thoracic  wall.  It  is  triangular  in  outline,  and 
has  two  surfaces,  three  borders,  and  three 
angles. 

The   external   surface   or   dorsum   (Facies 

lateralis  s.   dorsalis)  is  divided  into  two  fosste 

by   the   spine    (S])ina   scapulae),  which   extends 

from    the  vertebral  border  to  the  nock  of   the 

The  free  edge  of  the  spine  is  thick,  rough, 

A  little  above  its  middle  is  a  variable  promi- 


THE    SCAPULA 


75 


nence,  the  tubercle  of  the  spine  (Tuber  spince),  to  which  the  trapezius  muscle 
is  attached.  The  supraspinous  fossa  (Fossa  supraspinata)  is  situated  in  front  of 
the  spine,  and  the  infraspinous  fossa  (Fossa  infraspinata)  behind  it.  The  former 
is  much  the  smaller  of  the  two;  it  is  smooth  and  is  occupied  by  the  supraspinatus 
muscle.  The  infraspinous  fossa  lodges  the  infraspinatus  nmscle;  it  is  wide  and 
smooth  in  its  upper  part,  narrower  below,  where  it  is  marked  by  several  rough  lines 
for  the  attachment  of  the  teres  minor  muscle;  near  the  neck  is  the  nutrient  foramen, 
and  a  little  lower  is  a  vascular  groove. 

The  costal  surface  or  venter  (Facies  costalis)  is  hollowed  in  its  lengtli  by  the 


-t  {la  ^  e 


Cervical  angie  ■ 


Supraspinous  fossa  — -^ 

Anterior  border — \^ 
Tubercle  of  spine 


Neck 


Tuberosity 


Fig.  41. — Left  Scap 


Infraspinous  fossa 
Vascular  groove 


Posterior  border 


Nutrient  foramen 
Vascular  groove 


Glenoid  cavity 

.     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


subscapular  fossa(  Fossa  subscapularis) ;  this  occupies  nearly  the  whole  of  the  lower 
part  of  the  surface,  but  is  pointed  above  and  separates  two  rough  triangular  areas 
(Facies  serrata),  to  which  the  serratus  magnus  is  attached.  In  the  lower  third 
there  is  a  vascular  furrow  with  several  branches. 

The  anterior  or  cervical  border  (Margo  cranialis)  is  convex  and  rough  above, 
concave  and  smooth  below. 

The  posterior  or  dorsal  border  (Margo  caudalis)  is  slightly  concave.  It  is 
thick  and  rough  in  its  upper  third,  thin  in  its  middle,  and  thickens  again  below. 

The  superior  or  vertebral  border  (Margo  dorsalis  s.  basis)  carries  the  scapular 
cartUage  (Cartilago  scapula;).     In  the  young  subject  the  edge  of  the  bone  is  thick, 


76 


THE    SKELETON    OF   THE    HORSE 


and  is  pitted  by  impressions  into  which  the  cartilage  fits.  The  cartilage  is  the 
unossified  part  of  the  foetal  scapula.  Its  lower  edge  fits  the  depressions  and  eleva- 
tions of  the  bone.  It  thins  out  toward  the  free  edge,  which  is  convex  and  lies 
alongside  of  the  upper  parts  of  the  vertebral  spines.  In  front  it  continues  the  line 
of  the  scapula,  but  iiehind  it  forms  a  rounded  projection.  The  lower  part  of  the 
cartilage  undergoes  more  or  less  ossification,  so  that  the  vertebral  border  of  the 
bone  in  old  sui>je(ts  is  thin,  irregular,  and  jiorous. 

The  anterior  or  cervical  angle  (Angulus  cranialis)  is  at  the  junction  of  the 


DuTsat 


Vascular  ijrooK 


Tuhcrosilij 


Glenoid  cavity  Corncoid  process 

Fio.  42— Left  Scapula  or  HoRsi:.  Costal  SuRFArF..— (.\fter  Schmaltz.  Atlas  d.  .Vnat.  d.  Pferdes.) 

anterior  and  vertebral  borders  and  lies  opposite  to  the  second  thoracic  spine.  It  is 
relatively  thin  and  is  al)out  a  right  angle. 

The  posterior  or  dorsal  angle  (Angulus  caudalis)  is  thick  and  rough:  its 
position  can  be  dctcrtnincd  readily  in  the  living  animal. 

The  inferior  or  articular  angle  (Angulus  glenoidalis)  is  joined  to  the  bodv  of 
the  bone  by  the  neck  of  the  scajnila  (Colluin  scapuhe).  It  is  enlarged,  especially 
in  the  sagittal  direction.  It  iiears  the  glenoid  cavity  (Cavitas  glenoidalis)  for  articu- 
lation wth  the  head  of  the  humerus.  The  cavity  is  oval  in  outline,  and  its  margin 
IS  cut  into  in  front  by  the  glenoid  notch  (Incisura  glenoidalis),  and  is  rounded  off 


THE    HUMERUS 


77 


externally;  just  above  its  postero-external  part  is  a  tubercle  to  which  a  tendon  of 
the  teres  minor  is  attached.  The  bicipital  tuberosity  or  tuber  scapulae  is  the 
large  rough  prominence  in  front,  to  which  ttie  tentlon  of  origin  of  the  biceps  brachii 
is  attached;  projecting  from  its  inner  side  is  the  small  coracoid  process  (Processus 
coracoideus),  from  which  the  coraco-brachialis  muscle  arises. 

Development. — The  scapula  has  four  centers  of  o.ssification, 
for  the  liody  of  the  bone,  the  liicipital  and  cora- 
coid processes,  the  anterior  part  of  the  glenoid 
cavity,  and  the  tuber  spinse.  The  last  ossifies 
after  birth  and  fuses  \^-ith  the  spine  about  the 
third  year.  The  bicipital  tuberosity  and  coracoid 
fuse  with  the  body  of  the  bone  about  the  end  of 
the  first  vear. 


viz.,  one  each 


Tuberosity 


In  old  subjects  the  spongj'  substance  disappears  at  the 
middle  part  of  the  fossae,  so  that  the  bone  consists  here  of 
a  thin  layer  of  compact  substance.  Considerable  ossifica- 
tion of  the  cartilage  is  usual,  tlie  bordei's  become  much 
rougher,  the  muscular  lines  are  more  pronounced,  and  a 
medullary  ca\dty  may  appear  in  the  neck.  Much  varia- 
tion occurs  in  dimensions  and  slope.  The  average  ratio 
between  the  length  and  breadth  (scapular  index)  is  about 
1  :  0.5,  but  in  many  cases  the  base  is  relatively  wider. 
The  inclination  on  a  horizontal  plane  varies  from  50  to  65 
degrees.  Exceptionally  the  coracoid  process  reaches  a 
length  of  an  inch  or  more  (2^^  to  3  cm.),  and  the  chief  nutrient  foramen  may  be  on  the  f)os- 
terior  border  or  in  the  subscapular  fossa. 


Fig.  43.— Distal  Exi 

OF  Horse,  End  ' 
Schmaltz,  Atlas 
Pferdes.) 


THE  HUMERUS 
The  humerus  is  a  long  bone  which  extends  from  the  shoulder  above,  where  it 
articulates  with  the  scapula,  to  the  elbow  below  and  behind,  where  it  articulates 
with  the  radius  and  ulna.     It  is  directed  obliquelj'  downward  and  backward,  form- 


Internal 
tuberosity 


f  Posterior  pa 

\ 


(  Anterior  par 


Posterior  part 
Anterior  port  J 


J.  External 
tuberosity 


Fin.  44. — Proximal  End  of  Lf.ft  Hr: 


Bicipital  groove 
■  OF  Horse,  Exd  \'ie\v.     (.\fter  Schn 


.\tla5  d.  .\nat.  d.  Pferdes.) 


ing  an  angle  of  about  55  degrees  with  a  horizontal  plane.     It  may  be  divided  into  a 
shaft  and  two  extremities. 

The  shaft  or  body  (Corpus  humeri)  is  irregularly  cylindrical  and  has  a  twisted 
appearance.  It  may  be  regarded  as  having  four  surfaces.  The  external  surface 
is  smooth  and  is  spirally  curved,  forming  the  musculo-spiral  groove  (Sulcus  musculi 
brachialis).  which  contains  the  brachialis  muscle:  the  groove  is  continuous  with  the 
posterior  surface  above  and  winds  around  toward  the  front  below.  The  internal 
surface  is  nearly  straight  in  its  length,  rounded  from  side  to  side,  and  blends  with 
the  anterior  and  posterior  surfaces.     Just  above  its  middle  is  the  internal  or  teres 


78  THE  SKELETON  OF  THE  HORSE 

tubercle  (Tuberositas  tores),  to  which  the  tendon  of  the  latissinuis  dorsi  and  teres 
major  nuiscles  is  attaclied.  The  nutrient  foramen  is  in  the  lower  third  of  this  sur- 
face. The  anterior  surface  is  triangular,  wide  and  smooth  above,  narrow  and 
roughened  below.  It  is  separated  from  the  external  surface  by  a  distinct  border, 
wiiicii  ijears  on  its  uijper  part  the  deltoid  tuberosity  (Tuberositas  deltoidea). 
From  the  latter  a  rough  line  curves  upward  and  backward  to  the  outer  surface  of 
the  neck,  and  gives  origin  to  the  external  head  of  the  triceps  muscle.     Below  the 


Cut  red  line 


Deltoid 
tuberosity 


Miisculo-sinrdl 
(jrooi'c 


Olecranon  fossa 


Fill,  45.— LKtT  lU.MKRua  OF  Hon.sK,  Is 
TERNAL  SuRKACK.  (.\fter  Schmallz 
-Atlas  d.  Anat.  d,  Pferdes.) 


Exicrmil 

condyle  ExUrnnl 

epicondylc 

Fio.    46.— Lki-t    HrniF.nus    or    Hor.sk.    Extkrv.u. 
{.\fler  Schmaltz,  .\tla.s  il.  .\nat.  .1.  I'fenles.) 


tuberosity  the  border  inclines  forward,  becomes  less  salient,  and  ends  at  the  coronoid 
fossa,     Tiie  posterior  surface  is  rounded  from  side  to  side  and  smooth. 

Tile  proximal  extremity  consists  of  the  h(>a(l,  neck,  two  tuberosities,  and  the 
l)icipital  groove.  The  head  (Caput  humeri)  presents  an  almost  circular  convex 
articular  surface,  which  is  about  twice  as  extensive  as  the  glenoid  cavitv  of  the 
scapula,  with  which  it  articulates.  In  front  of  the  head  is  a  fossa,  in  which  are 
several  foramina.  The  neck  (("olluni  humeri)  is  well  defined  behind,  but  is  prac- 
tically aiwent  elsewhere.     The  external  tuberosity  (Tuberculum  majus)  is  placed 


THE    HUMERUS 


79 


antero-externally,  and  consists  of  two  parts;  the  anterior  part  forms  the  outer 
houndary  of  tlie  bicipital  groove  antl  gives  attachment  to  the  external  branch  of 
the  supraspinal  us  muscle;  the  posterior  part  gives  attachment  to  the  short  inser- 
tion of  the  infraspinatus,  while  its  outer  surface  is  coated  with  cartilage,  over  which 
the  chief  tendon  of  the  same  muscle  passes  to  be  inserted  into  a  triangular  facet  on 
the  outer  aspect  of  the  anterior  part.  The  internal  tuberosity  (Tuberculum  minus) 
is  less  salient,  and  consists  of  anterior  and  posterior  parts;  the  anterior  part  forms 
the  inner  lioundary  of  the  bicipital  groove,  and  furnishes  insertion  to  the  inner 
branch  of  the  supraspinatus  above,  and  the  posterior  deep  pectoral  muscle  below; 


Inhriud  tuberosity 


Intcrniil  tubercle 


Coronoid  fossa 

Internal  epicondyle 

Internal  condyle 
Fig.  47. — Left  Himehus  of  Horse,  .\nterior  V: 


Exlcnial  I  uberos  ity 


Dilloid  tiiUrusity 


Muscido-spiral  groove 


External  condyloid  crest 

Externid  condyle 
(.\fter  Schmaltz  .Vtliw  d,  .\nat.  d.  Pferdes.) 


the  posterior  part  gives  attachment  to  the  subscapularis  muscle.  The  bicipital 
or  intertubercular  groove  (Sulcus  intertubercularis)  is  situated  in  front;  it  is 
boundetl  l)y  the  anterior  parts  of  the  tuberosities,  and  is  subdivided  by  an  inter- 
mediate ridge.  The  groove  is  covered  in  the  fresh  state  by  cartilage,  and  lodges 
the  tendon  of  origin  of  the  biceps  brachii  muscle.  Just  below  the  intermediate 
ridge  is  a  small  fossa  in  which  several  foramina  open. 

The  distal  extremity  has  an  oblique  surface  for  articulation  with  the  radius 
and  ulna,  which  consists  of  two  condyles  of  very  unequal  size,  separated  by  a  ridge. 
The  internal  condyle  (Condylus  medialis)  is  much  the  larger,  and  is  crossed  by  a 
sagittal  groove,  on  the  anterior  part  of  which  there  is  usually  a  synovial  fossa.    Pos- 


gQ  THE  SKELETON  OF  THE  HOKSE 

tcriorlv  tho  groove  oxteiuls  upward  considerably  above  the  rest  of  the  articular 
surfa.'e  and  reaches  the  olecranon  fossa,  and  this  part  articulates  with  the  semilunar 
notch  of  the  ulna.  The  external  condyle  (Condylus  lateralis)  is  much  smaller  and 
is  placed  somewhat  lower  ami  further  back,  giving  the  extremity  an  oblique  ap- 
pearance ■  it  is  marked  by  a  wide  shallow  groove.  The  coronoid  fossa  ( Fossa  coro- 
noidea)  is  situated  in  front  above  the  groove  on  the  internal  condyle;  it  furnishes 
origin  to  part  of  the  extensor  carpi,  and  external  to  it  is  a  rough  depression  irom 
which  the  anterior  or  common  extensor  of  the  digit  arises.  Behind  and  above  the 
coiKlyles  are  two  thick  ridges,  the  ei)ic()ndyles.  The  internal  or  flexor  epicondyle 
(Epicondylus  medialis  s.  flexorius)  is  the  more  salient;  it  furnislies  origin  to  licxor 
muscles  (if  the  carpus  and  digit,  and  presents  internally  a  tubercle  for  the  attach- 
ment of  the  internal  lateral  ligament  of  the  elbow  joint.  The  external  or  extensor 
epicondyle  (i^picondylus  lateralis  s.  extensorius)  bears  externally  the  external 
supracondyloid  crest  (Cri.sta  condyloidea  lateralis),  which  forms  here  the  outer 
]K)undary  of  the  musculo-spiral  groove,  and  gives  origin  to  the  extensor  carpi. 
Below  tliis  is  a  rough  excavation  in  which  the  external  lateral  ligament  is  attached. 
The  lower  border  of  the  epicondyle  gives  attachment  to  the  flexor  carpi  cxternus. 
Between  the  epicondyles  is  the  deep  olecranon  fossa  (Fossa  olecrani). 

Development.— The  humerus  ossifies  from  six  centers,  viz.,  three  primary 
centers  for  the  shaft  and  epiphy.ses,  ami  three  secondary  centers  for  the  external 
tuberosity,  the  ileltoid  tuberosity,  and  the  internal  condyle.  The  proximal  end 
fuses  witii  the  shaft  at  about  three  and  one-half  years,  the  distal  at  about  one  and 
a  half  years  of  age. 

THE  RADIUS 

The  radius  is  much  the  larger  of  the  two  bones  of  the  forearm  in  the  horse. 
It  extends  in  a  vertical  direction  from  the  elbow,  where  it  articulates  with  the  hum- 
erus, to  the  carpus  below.  It  is  gently  curved,  the  convexity  being  anterior.  It 
consists  of  a  shaft  and  two  extremities. 

The  shaft  (Corpus  radii)  is  curved  in  its  length,  somewhat  flattened  from  before 
backward,  and  exijanded  at  its  ends.  It  presents  for  description  two  surfaces  and 
two  borders.  The  anterior  surface  (Facies  dorsalis)  is  smooth,  slightly  convex  in 
its  length,  and  rounded  from  side  to  side.  The  posterior  surface  (Facies  volaris) 
is  correspondingly  concave  in  its  length  and  is  flattened  in  the  transverse  direction. 
At  its  upper  part  there  is  a  smooth  shallow  groove,  which  concurs  with  the  ulna  in 
the  formation  of  the  interosseous  space  of  the  forearm;  the  nutrient  foramen  is 
in  the  lower  part  of  this  groove.  Below  this  there  is  in  the  young  subject  a  narrow, 
rough,  triangular  area  to  which  tlie  ulna  is  attached  by  an  interosseous  ligament; 
in  the  adult  the  two  bones  are  fused  here.  A  variable  rough  elevation  below  the 
middle  of  tiie  surface  and  cIo.se  to  tlie  internal  border  gives  attachment  to  the 
superior  check  ligament.  The  internal  border  (Margo  medialis)  is  slightly  eon- 
cave  in  its  length  and  is  larg(>ly  subcutaneous;  at  its  proximal  end  there  is  a 
smooth  area  on  which  tiie  tendon  of  insertion  of  tlie  brachialis  muscle  lies,  and  a 
small  rough  area  just  below  gives  attachment  to  that  muscle  and  the  long  internal 
lateral  ligament  of  ttie  elbow-joint.  Th(>  external  border  (JNIargo  lateralis)  is  more 
strongly  curved,  but  presents  no  special  features. 

The  proximal  extremity  or  head  (("aiiituluni  radii)  is  flattened  from  before 
backward  and  wide  transversely.  It  presents  an  articular  surface  (Fovea  capituli) 
wliirh  corresponds  to  that  on  the  distal  end  of  the  humerus;  it  is  crossed  by  a 
central  sagittal  ridge,  wiiich  has  a  synovial  fossa  on  its  posterior  part,  and  ends  in 
front  at  a  prominent  lip,  the  coronoid  process  (Processus  coronoideus).  Just 
i)elow  the  i>osterior  border  there  are  two  concave  facets  for  articulation  with  the 
ulna,  and  between  these  and  the  interosseous  sjiace  is  a  quadrilateral  rough  area 
at  which  the  two  bones  are  united  by  an  interosseous  ligament.     At  the  inner  side 


THE    RADIUS  g] 

of  the  anterior  surface  is  the  bicipital  tuberosity  (Tulierositas  radii),  into  whieh 
the  Ijiceps  tendon  is  inserted.  Tiie  internal  tuberosity  is  continuous  with  the  pre- 
ceding eminence,  and  furnishes  attachment  to  tiie  sliort  part  of  the  internal  lateral 


DIT'S   AND  UlXA    OF  HoRSE,  EXTER' 

NAL  View,     (.\fter  Schmaltz,  Atlas  d.  Anat.  d. 
Pferdes.) 


Distal 

external 
tuberosity 
of  radius 


Facet  for  radial 
carpal 

Fio.  40. — Left  Radius  and  Ulna  of  Horse.  Pos- 
terior View,  (.\fter  Schmaltz.  Atlas  d.  .Anat. 
d.  Pferdes.) 


ligament.  The  external  tuberosity  is  more  salient;  it  gives  attachment  to  the 
external  lateral  ligament  and  to  the  anterior  and  lateral  extensor  muscles  of  the 
digit. 

The  distal  extremity  is  also  compressed  from  before  backward.     It  presents 


S2 


THE    SKELETON    OK   THE    HORSE 


tho  carpal  articular  surface  (Facics  articularis  carpca)  which  consists  of  three  parts. 
The  inner  facet  is  the  largest,  is  quadrihiteral,  concavo-convex  from  before  back- 
ward and  articulates  with  the  radial  carpal  bone  (or  scaphoid);  the  middle  one  is 
somewhat  similar  in  form  but  smaller,  and  articulates  with  the  intermediate  carpal 
bone  (or  semilunar);  the  outer  facet  is  smaller,  is  convex,  and  articulates  below 
witii  tiie  ulnar  carpal  (or  cuneiform)  and  behind  with  the  accessory  carpal  (or  pisi- 
form) The  anterior  surface  presents  three  grooves,  separated  by  ridges.  The 
middle  one  is  vertical  and  gives  passage  to  tiie  tendon  of  the  extensor  carpi  radiahs; 
tlie  outer  one  is  similar  and  contains  the  tendon  of  the  anterior  extensor  oi  the 
digit;  the  inner  one  is  small  and  oblique  and  lodges  the  tendon  of  the  extensor  carpi 
()l4i(iuus.  The  posterior  aspect  is  crossed  by  a  rough  ridge,  below  which  are  three 
depressions.  On  either  side  is  a  tuberosity  (Tul)erculum  ligamenti)  to  which  the 
lateral  ligament  is  attached.  The  outer  one  is  marked  l)y  a  small  vertical  groove 
for  the  passage  of  tlie  lateral  extensor  tendon. 

Development.— The  radius  ossifies  from  four  centers,  viz.,  one  each  for  the 

shaft,  the  two  extremities,  and  the  outer  part 
of  the  distal  end;  the  last  is  morphologically 
the  distal  end  of  the  ulna  which  has  fused 
with  the  radius,  and  the  line  of  fusion  is  often 
indicated  by  a  distinct  groove  on  the  carpal 
articular  surface.  The  proximal  extremity 
unites  with  the  shaft  at  about  one  and  a 
half  years,  the  distal  end  at  about  three 
and  a  half  years. 


Priircssiix 
iiiicottaiis 


nutch 


HoilHI 

Atlna 


■KR  Half  OK  RAnirs  an 
,  Intkrnal  ViKW.  (.\fte 
1.  .\nat.  d.  Pferdes.) 


THE  ULNA 
The  ulna  of  the  horse  is  a  reduced  long 
bone  situated  behind  the  radius,  with  which 
it  is  ]iartially  fused  in  the  adult. 

The  shaft  (Corpus  ulnse)  is  three-sided 
and  tapers  to  a  point  below.  The  anterior 
surface  (Fades  dorsalis)  is  applied  to  the  pos- 
terior surface  of  the  radius,  and  below  the 
interosseous  space  the  two  bones  are  fused  in 
the  adult.  The  surface  which  enters  into  the 
formation  of  the  space  is  smooth  and  usually 
presents  a  small  nutrient  foramen,  directed 
upward.  Above  the  space  it  is  rough  and  is 
attached  to  the  radius  by  an  interosseous  ligament  which  is  usually  permanent .  The 
internal  surface  (Facies  medialis)  is  smooth  and  slightly  concave.  The  external 
surface  (Facies  lateralis)  is  flattened.  The  internal  and  external  borders  are  thin 
and  sharp,  excej)!  at  the  interosseous  s])ace.  Tlie  posterior  border  is  slightly 
concave  in  its  length  and  is  rounded.  The  lower  end  is  pointed  and  is  usually  a 
little  lielow  the  middle  of  the  radius.  It  is  commonly  continued  by  a  fibrous  cord 
to  the  distal  external  tuberosity  of  the  radius,  but  this  band  may  be  replaced  in 
part  or  entirely  by  Ijone. 

The  proximal  extremity  is  the  major  part  of  the  bone.  It  projects  upward 
and  somewhat  backward  behind  the  lower  end  of  the  humerus,  and  forms  a  lever 
arm  for  the  extensor  inuscl(>s  of  the  ell)ow.  The  internal  surface  is  concave  and 
smooth.  Tiie  external  surface  is  convex  and  is  rougheiu'd  above.  The  anterior 
border  bears  on  its  middle  a  pointed  projection,  the  processus  anconaeus  or 
"l)eak,"  which  overhangs  the  semilunar  notch  or  sigmoid  cavity  (Incisura  semihi- 
naris).     The  latter  is  triangular  in  outline,  concave  from  above  downward,  and 


y":!!^-!^' 


THE    CARriS — THE    INTERMEDIATE    CARPAL    BONE  So 

articulates  with  the  humerus;  in  the  middle  of  its  lower  part  is  an  extensive 
synovial  fossa.  Just  below  the  notch  are  two  convex  facets  which  articulate  witii 
those  on  the  posterior  aspect  of  the  proximal  end  of  the  radius.  The  posterior 
border  is  nearlj-  straight,  and  is  thick  and  rounded.  The  free  end  or  summit  is 
a  rough  tuberosity,  the  olecranon,  which  gives  attachment  to  the  triceps  brachii 
and  other  muscles. 

The  primitive  distal  extremity  has,  as  previously  stated,  fused  with  the  radius. 

Development. — The  ulna  ossifies  from  three  centers,  of  which  one  is  f(jr  tiie 
main  part  of  the  bone,  one  for  the  olecranon,  and  one  for  the  tlistal  end.  The 
cartilaginous  embryonic   ulna  extends  the  entire 

length  of  the  forearm.     The  lower  part   of   the  .'lij.'., 

shaft  is  usually  reduced   to  a  small  fibrous  band  .v;;/;'V*!?'^'"'- 

or  may  disappear  entirely' ;  in  some  cases  a  vari- 
able remnant  of  it  ossifies.  The  distal  extremity 
fuses  early  with  the  radius.  The  olecranon  miites 
with  the  rest  of  the  bone  at  three  to  three  and  a 
half  years.  A  medullary  canal  appears  to  occur 
constantly  in  the  adult — contrary  to  the  state- 
ments of  some  authors. 


THE  CARPUS 
The  carpus  of  the  horse  consists  of  seven  or 
eight  bones  (Ossa  carpi)  arranged  in  two  rows, 
proximal  or  antibrachial,  and  distal  or  metacar- 
pal. The  (abbreviated)  names  and  relative  posi- 
tions of  the  bones  of  the  left  carpus  as  seen  from 
in  front  are  indicated  below. 

Proximal  Roic: 
Radial        Intermediate        Ulnar        Accessory 

Distal  Row: 
First  Second  Third  Fourth 

The  Radial  Carpal  Bone 
The   radial  carpal  bone   (Os  carpi  radiale, 
scaphoid)  is  the  largest  bone  of  the  upper  row:  it 

is  somewhat  compressed  laterally,  and  is  clearly  ]i 

six-sided.  The  superior  or  proximal  surface  is 
convex  in  front,  concave  behind,  and  articulates 
with  the  inner  facet  on  the  distal  end  of  the  radius. 
The  inferior  or  distal  surface  is  also  convex  in  front 
and  concave  behind;  it  articulates  with  the  second 

and  third  carpal  bones.  The  external  surface  bears  upper  and  lower  facets  on  its 
anterior  part  for  articulation  with  the  intermediate;  between  and  behind  these  it  is 
excavated  and  rough.  The  anterior  or  dorsal  surface  is  rough  and  slightly  convex. 
The  internal  surface  and  the  posterior  or  volar  surface  are  rough  and  tuherculate. 

The  Intermediate  Carpal  Bone 
The  intermediate  carpal  bone  (Os  carpi  intermedium,  semilunar,  lunar)  is 
somewhat  wedge-shaped,  wider  in  front  than  behind.     The  superior  or  proximal 
sxirface  is  saddle-shaped,  and  articulates  with  the  middle  facet  on  the  distal  ciul  of 


51 

. — Sagittal  Section-   i 

OF    I-PPER 

IT  1 

DF  Radius  and  Ul.va  o 

F  Horse. 

c- 

n,  Mwlullary  cavity  of  i 

ulna. 

84 


THE    SKELETON    OF   THE   HORSE 


the  radius.  The  inferior  or  distal  surface  is  smaller,  convex  in  front,  concave  be- 
hind, and  articulates  with  the  third  and  fourth  carpal  bones.  The  internal  surface 
has  ui)pcr  and  lower  facets  for  articulation  with  the  radial  carpal,  and  between 
these  it  is  excavated  and  rough.  The  external  surface  is  similar  to  the  preceding 
and  articulates  with  the  ulnar  carpal.  The  anterior  or  dorsal  surface  is  rough  and 
slightlj-  convex.     The  posterior  or  volar  surface  bears  a  tuberosity  on  its  lower  part. 

The  Ulnar  Carpal  Bone 
Tlic  ulnar  carpal  bone  (Os  carpi  ulnare,  cuneiform)  is  the  smallest  and  most 
irregular  bone  of  the  ujiiier  ro\v.  The  superior  or  proximal  surface  is  concave,  and 
fits  the  lower  jiart  of  the  outer  facet  on  the  distal  end  of  the  radius.  The  inferior 
or  distal  surface  is  obliciue  anfl  undulating  for  articulation  with  the  fourth  carpal 
lione.  The  internal  surface  has  upper  and  lower  facets  for  articulation  with  the 
intermediate.  The  anterior  or  dorsal  and  external  surfaces  are  continuous,  convex, 
and  rough.  'I'he  posterior  or  volar  surface  is  oblitiue,  and  bears  a  concave  facet 
for  articidation  with  the  accessoiy  carpal  Ijone;    below  this  is  a  tubercle. 


Fig.  S2.— Lkft  Cari-ai.  Bonis  dk  IIobsk,  with  Dis-        Fig.    S3.— Left    Carpal    Bonfs    of    Hor.sf.,    with 
TAI,   End  of  Radius   and   Proximai,  Knd  of  Adjacent  Ends  of  Radius  and  Metacarpus; 

MKTArAiiprs;    Internal  View.  External  View. 

C'a,  Accessiory  carpal  bone;    Cr,  radial  carpal;    Ci,  intermediate  carpal;    Cii,  ulnar  cari)al;    Cl-4,  first  to 

fourth  carpals;  Mc.  II,  III,  IV,  metacarpal  bonef^;  I,  groove  for  tendon  of  extensor  carpi  obliquus;   2,  groove  for 

lateral  extensor  tendon;   3,  groove  for  tendon  of  flexor  carpi  externus;  4.  metacarpal  tuberosity.     (After  Schmaltz, 

.\tlus  d.  .\nat.  d.  Pferdes.) 


The  Accessory  Carpal  Bone 
The  accessory  carpal  bone  (Os  carpi  accessorium,  pisiform)  is  situated  behind 
the  ulnar  carpal  bone  and  the  outer  part  of  the  distal  end  of  the  ulna.  It  is  discoid 
and  presents  for  descrii)tion  two  surfaces  and  a  circumference.  The  internal 
surface  is  concave  and  forms  the  outer  wall  of  the  cari^al  groove.  The  external 
surface  is  convex  and  rough;  a  smooth  groove  for  the  outer  tendon  of  the  flexor 
carpi  externus  crosses  its  anterior  part  obliquely  downward  and  slightly  forward. 
The  anterior  border  bears  two  facets;  the  upper  one  is  concave  and  articulates  with 
the  back  of  the  outer  facet  on  the  distal  end  of  the  radius;  the  lower  one  is  convex 
and  articulates  with  the  ulnar  carpal  bone.  The  remainder  of  the  circumference  is 
rounded  and  rough. 

Tlie  accessory  docs  not  directly  boar  weight,  and  may  bo  regarded  as  a  sesamoid  hone 
interposed  m  the  course  of  the  tendons  of  the  middle  and  external  flexors  of  the  carpus,  which 
it  enables  to  act  at  a  mechanical  advantage.  The  posterior  border  furnishes  attachment  to 
the  tran.sversc  carpal  hganienl,  which  completes  the  carpal  canal  for  the  flexors  of  the  digit. 


THE   FIRST    CARPAL    BONE — THE    SECOND    CARPAL    BONE 


85 


The  First  Carpal  Bone 
The  first  carpal  bone  (Os  carpale  primuni,  trapezium)  is  a  small  inconstant 
bone,  commonly  about  the  size  and  shape  of  a  pea,  which  is  situated  in  the  lower 
part  of  the  internal  lateral  ligament  behind  the  second  carpal  bone. 

This  bone  appears  to  be  absent  on  both  sides  in  about  half  of  tlio  eases;  in  a  good  many 
subjects  it  is  present  on  one  side  only.  In  size  it  varies  from  a  minute  nodule  to  a  discoid  mass 
10  to  12  mm.  in  length.  In  exceptional  cases  it  articulates  with  both  the  second  carpal  and  the 
second  (inner)  metacarpal  bone,  in  other  eases  with  the  former  only,  but  in  the  majority  of 
specimens  no  articular  facet  is  present. 

The  Second  Carpal  Bone 
The  second  carpal  bone  (Os  carpale  secundum,  trapezoid)  is  the  smallest  con- 
stant bone  of  the  lower  row,  and  is  irregularly  hemispherical  in  shape.     The  su- 
perior or  proximal  surface  is  a  convex 

facet  which  is  continued  tipon  the  pos-  2  I 

tenor  or  volar  surface  and  articulates 
■RTth  the  posterior  jxirt  uf  the  radial 
carpal.  The  external  surface  faces  ob- 
liquely outward  and  forward,  and  bears 
three  facets  for  articulation  ■n-ith  the 
third  carpal  bone.  The  anterior  or 
dorsal  and  the  internal  surface  bear  a 
tuberosity  to  which  the  lateral  ligament 
is   attached.      The    inferior    or    distal 


Mc.  IV 


Mczzr 


Fig.  54.— Carpal  Boxes  of  Hohsk,  with  Adjacent       Fig.    55.— Carpal    Articular   Surface    of   Radius 
Ends  of  Radius  axd  Metacarpus;    Anterior  and  Proxi-mal  Articular  Surfaces  of  Car- 

View.     The    Accessort    and    First    Carpal  pal    and    Metacarpal    Bones,    Left    Side. 

Bones  are  Not  Shown.  The  Accessory  and  First  Carpal  Bones  are 

not  Shown. 
Cr.  Radial  carpal;  CI.  interme.liate  carpal;  Cu.  ulnar  carpal;  C3,  CS.  C4.  second,  third,  and  fourth  car- 
pals;  Mc.Il.  second  or  inner  small  metacarpal  bone;  Mc.III.  third  or  large  metacarpal  bone;  Mc.IV,  fourth  or 
outer  small  metacarpal  bone;  1.  2,  grooves  for  tendons  of  anterior  extensor  and  extensor  carpi  radiahs;  3,  meta- 
carpal tuberosity.  Arrows  indicate  relations  of  facets.  Short  arrow  points  to  facet  on  ulnar  carpal  for  articu- 
lation with  accessory  carpal.     (After  Schmaltz,  Atlas,  d.  Anat.  d.  Pferdes.) 


surface  is  articular  and  consists  of  a  large  flattened  facet  for  the  inner  (second) 
metacarpal  bone,  and  a  small  one  for  the  large  (third)  metacarpal  bone.  Some 
specimens  have  a  small  facet  on  the  lower  part  of  the  posterior  surface  which 
articulates  mth  the  first  carpal  bone. 


g6  THE  SKELETON-  OF  THE  HORSE 

The  Thii?d  Carpal  Bone 

Tlic  third  carpal  liono  (Os  carpale  tertium,  os  magnum)  is  much  the  largest 
bone  of  the  lower  row,  forming  more  than  two-thirds  of  the  width  of  the  latter.  It 
is  flattened  from  above  downward,  and  is  twice  as  wide  in  front  as  behind.  The 
superior  or  proximal  surface  consists  of  two  facets  separated  by  an  antero-posterior 
ridge;  the  inner  facet  is  concave  and  articulates  with  the  radial  carpal;  the  outer 
facet— for  the  intermediat(>  carpal— is  concave  in  front  and  convex  behind,  where  it 
encroaches  on  tlie  posterior  surface.  The  inferior  or  distal  surface  is  slightly  un- 
dulating, and  articulates  almost  entirely  with  the  large  (third)  metacarpal  bone, 
but  it  usually  i)ears  a  .small  oiilique  facet  at  its  inner  side  for  the  inner  (second)  meta- 
carpal, and  there  is  connnonly  a  non-articular  depression  externally.  The  internal 
surface  faces  liackward  and  inward,  and  bears  three  facets  for  articulation  with 
the  second  carpal,  between  which  it  is  excavated  and  rough.  The  external  surface 
has  two  facets  for  articulation  witli  the  fourth  carpal,  and  is  depressed  and  rough 
in  its  middle.  The  anterior  or  dorsal  surface  is  convex  and  is  crossed  by  a  rough 
transverse  ridge.  The  posterior  or  volar  surface  is  relatively  small,  and  is  rounded ; 
its  upi)er  jiart  is  encroaclied  upon  by  the  superior  articular  surface,  below  which 
it  is  rough. 

The  Fourth  Carpal  Bone 

The  fourth  carpal  bone  (Os  carpale  ciuartum,  unciform)  is  somewhat  wedge- 
shaped,  and  is  readily  ilistinguished  from  the  second  by  its  greater  size  and  its 
posterior  tui)ercle.  The  superior  or  proximal  surface  articulates  with  the  inter- 
mediate and  ulnar;  it  is  convex  and  curves  outward,  backward,  and  downward, 
encroaching  on  the  external  and  jiosterior  surfaces.  The  inferior  or  distal  surface 
JK-ars  two  inner  facets  for  the  large  (third)  metacarpal  antl  an  outer  one  for  the  ex- 
ternal (fourth)  metacarpal  bone.  The  internal  surface  has  two  or  three  facets  for 
articulation  witli  the  tliird  carpal,  between  which  it  is  excavated  and  rough.  The 
anterior  or  dorsal  surface  is  convex  and  rough.  The  external  surface  is  small, 
ix'iiig  encroached  upon  by  the  superior  articular  surface.  Tlie  posterior  or  volar 
surface  bears  a  tubercle  on  its  lower  part.' 

The  Carpus  as  a  Whole 

The  bones  of  the  carpus,  exclusive  of  the  accessory,  form  an  irregular  quadran- 
gular mass,  the  width  of  which  is  about  twice  the  height  or  the  antero-posterior 
diameter.  Tlie  anterior  or  dorsal  surface  is  convex  from  side  to  side,  depressed 
along  the  line  of  junction  of  the  two  rows,  and  i^rominent  below.  The  posterior 
or  volar  surface  is  in  general  slightly  convex,  but  very  irregular.  It  forms  with  the 
accessory  the  carpal  groove  (Sulcus  carpi),  which  in  the  recent  state  is  rendered 
smooth  l)y  the  posterior  ligament;  it  is  converted  into  the  carpal  canal  (Canalis 
carpi)  for  the  flexor  tendons  by  the  transverse  carpal  ligament,  which  stretches 
a(Toss  from  the  acces.sory  bone  to  the  inner  side.  The  proximal  surface  is  widest  in- 
tiTnally  and  is  elevated  in  front,  concave  behind;  it  is  entirely-  articular  and  adaj^ted 
to  the  carpal  articular  surface  of  the  radius.  The  distal  surface  is  also  articular  and 
is  irregularly  faceted  in  adaptation  to  the  surfaces  of  the  metacarpal  bones;  each 
of  the  lower  Ixjnes  usually  articulates  with  two  metacari)al  bones,  but  sometimes 
the  third  does  not  bear  on  the  inner  metacarpal  bone.  The  lateral  surfaces  are 
both  irregular  and  rough,  the  internal  one  being  the  wider.  With  the  excei)tion  of 
the  acces.sory,  ulnar,  and  .second,  each  bone  articulates  with  two  bcmes  of  the  other 
row. 

Development. — Each  ossifies  from  a  single  center. 

'  'l")ii.s  lione  is  probably  equivalent  to  the  fourth  and  fifth  carpals  of  forms  in  which  five 
carpal  elements  are  present  in  the  lower  row. 


THE  METACARPUS — THE  LARGE  METACARPAL  BONE 


THE  METACARPUS 
Three  metacarpal  bones  (Ossa  metacarpalia)  are  present   in  the  horse.     Of 
these,  only  one,  the  third  or  large  metacarpal  bone,  is  fully  developed  and  carries  a 
digit;  the  other  two,  the  secontl  and  fourth,  are  much  reduced,  and  are  commonly 
called  the  internal  anil  external  small  metacarpal  or  "splint"  hones. 


Tabirosity 


Fin<l  pliahmx 


Scrnnd 
phalanx 


Fiii.  56. — DisT.^L  Row  OF  Carp.ii.  Boxes,  Metac.ir- 
pr.s.     First    .\nd     Second     Ph.^langes,     and 
Proximal  Sesamoid  Bones  of  Horse;    Pos- 
terior View,  Left  Side. 
The  fourth  (external)  metacarpal  bone  is  wrongly 

numbered  as  I.     {.\fter  Schmaltz,  Atlas,  d.  Anat.  d. 

Pferdes.) 


U(  tacarpal 
liihcruhily 


Head  of 
small 
metacar- 
pal bone 


Secniid  pluilanx 


Latend 
cartilage 


Wing     Dur^nl     Wall 

Exteiixin 

gruuix      sur- 
face of 
third 
phalanx 

process 

7.— Left  Metacarpai,  and  Digita 
Horse.     Internai.     View.     (After 
Atlas  d.  Anat.  ,1.  Pferdes. > 

B0NK.-i   o 

Schmailz 

The  Large  Metacarpal  Bo^fE 
This  (Os  metacarpale  tertium)  is  a  very  strong  long  bone,  placed 
between  the  carpus  above  and  the  first  phalanx  below 
two  extremities. 


vertically 
It  consists  of  a  shaft  and 


88  THE  SKELETON  OF  THE  HORSE 

The  shaft  (('(npus)  is  scmicylindrical,  and  presents  two  surfaces  and  two 
Ijorders.  The  anterior  or  dorsal  surface  is  smooth,  convex  from  side  to  side,  and 
nearly  straight  in  its  length.  Tlie  posterior  or  volar  surface  is  somewhat  convex 
from  side  to  side  and,  with  the  small  l)ones,  forms  a  wide  groove  which  lodges  the 
suspensory  ligament.  On  either  side  of  its  upper  two-thirds  it  is  roughened  for  the 
attachment  of  the  small  metacarpal  bones.  The  nutrient  foramen  occurs  at  the 
junction  of  the  upper  and  middle  thirds.  The  lower  third  is  wider  and  flattened. 
The  borders  are  roundetl. 

The  proximal  extremity  (Basis)  bears  an  undulating  articular  surface  adapted 
to  the  lower  row  of  carpal  bones.  The  greater  jnu-t  supports  the  third  carpal  bone; 
the  oblique  outer  ])art,  separated  from  the  precechng  Ijy  a  ridge,  articulates  with 
the  fourth,  and  a  small  facet  for  the  second  is  usually  found  at  the  postero-internal 
angle.  On  either  sitle  is  a  notch  separating  two  small  facets  which  articulate  with 
the  proximal  ends  of  the  small  metacarpal  l)ones.  Toward  the  inner  side  of  the 
anterior  surface  is  the  metacarpal  tuberosity,  into  which  the  extensor  carpi  radialis 
is  inserted.  The  posterior  surface  is  roughened  for  the  attachment  of  the  sus- 
pensory ligament. 

The  distal  extremity  (Trochlea  s.  Capitulum)  presents  an  articular  surface 
for  the  first  phalanx  and  the  proximal  sesamoid  bones,  which  is  composed  of  two 
condyles,  separated  by  a  sagittal  ridge;  the  inner  condyle  is  slightly  the  larger. 
On  either  side  is  a  small  fossa,  surmounted  by  a  tubercle,  for  the  attachment  of  the 
lateral  ligaments  of  the  fetlock  joint. 

The  large  metacarpal  is  one  of  the  strongest  bones  in  the  skeleton.  The  compact  substance 
is  specially  thick  in  front  and  internally.  The  medullary  canal  extends  further  toward  the  ends 
than  in  most  of  the  long  bones  of  the  horse  and  there  is  little  spongy  bone. 

The  Small  Metacarpal  Bones 

These  are  situated  on  either  side  of  the  posterior  surface  of  the  large  metacarpal 
bone,  and  form  the  sides  of  the  metacarpal  groove.  Each  consists  of  a  shaft  and 
two  extremities. 

The  shaft  ((Corpus)  is  three-sided  and  tapers  to  the  distal  end.  It  is  variably 
curved,  convex  toward  the  middle  line  of  the  limb.  The  anterior  surface  is  flattened 
and  is  rough,  except  in  its  lower  part;  it  is  attached  to  the  large  metacarpal  bone 
by  an  interosseous  ligami-nt,  except  near  the  distal  end.  The  abaxial  surface  is 
smooth  and  rounded  from  side  to  side  above,  grooved  below.  The  axial  surface  is 
smooth  and  concave  from  edge  to  edge,  except  below,  where  it  forms  a  rounded 
edge. 

The  proximal  extremity  or  head  (Basis)  is  relatively  large.  In  the  case  of  the 
inner  iioiie  it  usually  bears  two  facets  above  which  support  the  second  and  third 
carpal  bones,  while  the  outer  l)one  has  here  a  single  facet  for  articulation  with  the 
fourth  carpal  bone.  Each  has  also  two  facets  for  articulation  with  the  large  meta- 
carpal, and  is  elsewhere  roughened  for  the  attachment  of  ligaments  and  muscles. 
The  inner  bone  may  present  a  small  facet  behind  for  the  first  carpal  bone. 

The  distal  extremity  (Capitulum)  is  usually  a  small  nodule,  which  projects  to 
a  variable  extent  in  different  subjects,  and  is  easily  felt  in  the  living  animal.  It  is 
situated  two-thirds  to  three-fourths  of  the  way  down  the  region. 

The  small  metacarpal  bones  vary  much  in  length,  thickness,  and  curvature.  In  the  ma- 
jority of  ca-scs  the  inner  bone  is  the  longer;  in  other  subjects  the  outer  one  is  the  longer  or  there 
is  no  material  difference.  Sometimes  the  curvature  is  very  pronounced,  so  that  the  distal'  end 
causes  a  decided  projection.     The  distal  end  is  very  variable  in  size  and  may  be  a  mere  point. 

Development. — The  large  metacarpal  bone  ossifies  from  three  centers.  The 
proximal  extremity  unites  with  the  shaft  before  birth,  the  distal  extremity  toward 
the  middle  of  the  second  ye^ir.  The  small  metacarpal  bones  ossify  from  two  cen- 
ters, one  of  which  is  for  the  proximal  extremity.     Their  distal  ends  are  cartilaginous 


THE    PHALANGES — THE    FIRST    PHALANX — THE    SEfOND    PHALANX  89 

at  birth.     Fusion  of  the  middle  part  of  the  shaft  with  the  large  metacarpal  bone  is 
common. 

THE  PHALANGES 
The  First  Phalanx 

The  first  phalanx  (Phalanx  prima)'  is  a  long  bone,  situated  between  the  large 
metacarpal  bone  above  and  the  second  phalanx  below.  It  is  directed  obliquely 
downwarrl  and  forward,  forming  an  angle  of  50  to  55  degrees  with  the  horizontal 
plane  in  well-formed  limbs.     It  consists  of  a  shaft  and  two  extremities. 

The  shaft  (Corpus)  is  w-ider  and  much  thicker  above  than  below,  and  presents 
two  surfaces  and  two  borders.  The  anterior  or  dorsal  surface  is  convex  from  side 
to  side  and  smooth.  The  posterior  or  volar  surface  is  flattened,  and  bears  a  triangu- 
lar rough  area,  bounded  laterally  by  ridges  which  begin  at  the  tuberosities  above 
and  converge  below;  this  area  furnishes  attachment  to  the  inferior  sesamoidean 
ligaments.  The  borders,  internal  and  external,  are  rounded  and  have  a  rough  area 
or  a  tubercle  on  their  middle  parts. 

The  proximal  extremity  (Basis)  is  relatively  large.  It  bears  an  articular  sur- 
face adapted  to  the  distal  end  of  the  large  metacarpal  bone,  consisting  of  two  glen- 
oid cavities  separated  by  a  sagittal  groove;  the  inner  ca'sitj'  is  a  little  larger  than 
the  outer  one.  The  posterior  angles  are  formed  by  buttress-like  tuberosities  for 
ligamentous  attachment.  The  anterior  surface  has  a  slight  elevation  for  the  at- 
tachment of  the  lateral  extensor  tendon. 

The  distal  extremity  is  smaller,  especially  in  its  antero-posterior  diameter. 
It  presents  a  trochlea  for  articulation  with  the  second  phalan.x,  consisting  of  a 
shallow  central  groove  and  two  lateral  convex  areas  or  condyles;  the  iimer  area  is  a 
little  the  larger.  On  either  side,  just  above  the  margin  of  the  articular  surface,  is  a 
depression  surmounted  by  a  tubercle,  to  both  of  which  the  lateral  ligament  is  at- 
tached. Behind  the  tubercle  is  a  distinct  facet  to  which  the  superficial  flexor  ten- 
don is  attached. 

Development. — The  first  phalanx  ossifies  from  three  centers.  The  distal  end 
unites  with  the  shaft  before  birth,  the  proximal  end  early  in  the  first  year. 

The  first  phalanx  contains  a  small  medullary  canal  in  the  middle  of  the  shaft.  It  may  be 
remarked  that  the  bone  is  tn-isted  slightly;  when  placed  volar  surface  down  on  the  table,  it 
touches  the  latter  by  three  points  only,  the  proximal  tuberosities  and  the  internal  condyle. 

The  Second  Phalanx 

The  second  phalanx  (Phalanx  secunda)-  is  situated  between  the  first  and 
third  phalanges,  its  direction  corresponding  to  that  of  the  first  phalaiLx.  It  is 
flattened  from  before  backward,  and  its  width  is  greater  than  its  height.  It  may 
be  described  as  possessing  four  surfaces. 

The  upper  or  proximal  surface  j^resents  two  glenoid  cavities  separated  by  a 
low  ridge,  and  articulates  with  the  first  phalanx.  The  middle  of  the  anterior  border 
is  elevated  and  roughened  in  front  for  the  attachment  of  the  anterior  or  common 
extensor  tendon.  The  posterior  border  is  thick  and  overhanging;  in  the  fresh 
state  its  middle  part  is  covered  with  cartilage,  over  which  the  deep  flexor  tendon 
passes.  On  either  side  there  is  an  eminence,  to  which  the  lateral  ligament  and  the 
superficial  flexor  tendon  are  attached.  .  •    •      . 

The  inferior  or  distal  surface  is  trochlear,  and  articulates  with  the  third  phal- 
anx and  third  sesamoid  bone.  It  resembles  somewhat  the  trochlea' of  the  first 
phalanx,  but  is  more  extensive  and  encroaches  more  on  the  anterior  and  posterior 
surfaces. 

The  anterior  or  dorsal  surface  is  convex  from  side  to  side  and  smooth  in  its 

1  It  is  also  called  the  large  pastern  bone  or  os  suffraginis. 
^  This  bone  is  also  called  the  small  pastern  bone  or  os  coronae. 


90 


THE    SKELETON    OF   THE    HORSE 


middle;  on  its  U»\ver  part  are  lateral  rough  depressions,  surmounted  Ijy  tuljerosities, 
to  both  of  whicii  ligaments  are  attached. 

The  posterior  or  volar  surface  is  smooth,  flattened,  and  slopes  obliquely  down- 
ward and  forward.  The  borders  which  separate  the  anterior  and  posterior  surfaces 
are  concave  from  above  downward,  rounded  from  before  backwartl. 

Development. — The  second  phalanx  ossifies  like  the  first,  but  the  proximal 
end  unites  with  the  shaft  two  or  three  months  earlier. 

Distnl  border 

Dorsal  or  wall  surface 
^.   Extensor  process 

-  -  Articular  surface 
Coronary  border 
'-T,  '  Dorsal  groove 

Depression  for  Intmil  liyament 


Third  I'lmlnn 


Third  Scs-imM 


Second  I'halam- 


First  Phalanx 


Fig.  .t8.— Pn 


Angle  or  iring 

Articular  surface  of  third  sesatnoiil  or 
nancular  bone 


Distal  articxdar  surface 
Eminence  for  lateral  ligament 
Dorsal  surface 

Proximal  articular  surface 

Distal  articular  surface 
Eminence  for  latind  liyiimetU 

Dorsal  surface 


"  Eminence  for  extensor  tendons 

—  Tuberosity 

—  Proximal  articular  surface 

—  Intermediate  groove 

MOID    OF    IioR8E,    DoRSAL    .ASPECT. 


The  Third  Phalanx 

The  third  or  ungual  phalanx  (Phalanx  tertia)'  is  entirely  inclosed  by  the  hoof, 
to  which  it  conforms  in  a  general  way.  It  presents  for  examination  three  surfaces, 
three  borders,  and  two  angles  or  wings. 

The  articular  surface  (Fades  articularis)  faces  upward  and  backward,  and  is 
chiefly  adai)1ed  to  the  distal  surface  of  the  second  phalanx,  but  a  narrow  flattened 
area  along  the  posterior  liorder  articulates  with  the  third  sesamoid.     The  an- 

'  This  bone  is  also  called  the  os  pedis  or  coffin  bone. 


THE    THIRD    I'HALANX  91 

terior  or  coronary  border  forms  a  central  ciiiinencc,  the  extensor  (or  pyramidal) 
process  (Procei^sus  extensorius),  to  the  front  of  which  the  anterior  extensor  tendon 
is  attacheil.  On  either  side  is  a  depression  for  the  attachment  of  the  lateral  liga- 
m(>nt. 

The  dorsal  or  wall  surface  (Facies  dorsalis)  slopes  downward  and  forward. 
The  angle  of  inclination  on  the  ground  plane  is  about  45  to  50  degrees  in  front. 
Laterally  the  height  diminishes,  and  the  slope  becomes  steeper,  especially  on  the 
inner  side.  From  side  to  side  the  curvature  is  almost  semicircular.  The  surface 
is  rough  and  porous,  resembling  pumice  stone  somewhat.  It  is  perforated  liy  nu- 
merous foramina  of  various  sizes;  a  series  of  larger  ones  is  situated  on  or  near  the 
lower  border.  On  either  side  the  dorsal  (or  preplantar)  groove  (Sulcus  dorsalis) 
passes  forward  from  the  wing  and  ends  at  one  of  the  larger  foramina.  In  the  fresh 
state  this  surface  is  covered  by  the  matrix  of  the  wall  of  the  hoof.  The  inferior  or 
distal  border  is  thin,  sharp,  and  irregularly  notched;  there  is  commonly  a  wider 
notch  in  front. 

The  volar  or  inferior  surface  (Facies  volaris)  is  arched,  and  divided  into  two 
unequal  parts  by  a  curved  rough  line,  the  semilunar  crest  (Crista  semilunaris). 
The  larger  anterior  area  is  crescent-shaped,  concave,  and  comparatively  smooth; 
it  corresponds  to  the  sole  of  the  hoof,  and  may  be  termed  the  sole  surface.  The 
posterior  part  is  much  smaller,  and  is  semilunar;  it  is  related  to  the  deep  flexor 
tendon,  and  is  hence  called  the  flexor  or  tendon  surface  (Facies  flexoria).  It 
presents  a  central  prominent  rough  area,  on  either  side  of  which  is  the  volar  (or 
plantar)  foramen  (Foramen  volare),  to  which  the  volar  (or  plantar)  groove  (Sulcus 
volaris)  conducts  from  the  wing.  The  foramina  lead  into  the  semilunar  canal 
within  the  bone,  from  which  small  canals  lead  to  some  of  the  foramina  of  the  wall 
surface.  The  deep  flexor  tendon  is  inserted  into  the  semilunar  crest  and  the 
central  rough  area  behind  it. 

The  volar  grooves  and  foramina  transmit  the  terminations  of  the  digital  arteries  into  the 
semihmar  canal,  where  they  meet  and  form  a  terminal  arch,  from  wliich  branches  pass  through 
canals  in  tlie  bone  and  emerge  through  the  foramina  on  the  wall  surface. 

The  angles  or  wings  (Anguli)  are  prismatic  masses  which  project  backward  on 
either  side;  the  inner  one  is  usually  the  shorter.  Each  is  divided  into  upper  and 
lower  parts  by  a  notch,  or  is  perforated  by  a  foramen  which  leads  to  the  vascular 
groove  on  the  side  of  the  wall  surface.'  The  upper  border  carries  the  lateral  carti- 
lage. 

The  lateral  cartilages  (C'artilagines  ungulse)  are  rhomboid  curved  plates, 
which  surmount  the  wings  on  either  side.  They  arc  relatively  large  and  extend 
above  the  margin  of  the  hoof  sufficiently  to  be  distinctly  palpable.  The  abaxial 
surface  is  convex,  the  axial  concave.  The  upper  border  is  convex  and  thin;  the 
lower  is  thicker  and  is  in  part  attached  to  the  wing.  The  anterior  end  is  attached 
by  ligament  to  the  side  of  the  second  phalanx.  The  posterior  end  curves  toward 
its  fellow  at  the  heel,  and  is  perforated  by  numerous  foramina  for  the  passage  of 
veins.     The  central  part  is  mainly  hyaline,  the  periphery  mainly  fibrous. 

It  will  be  no*ed  that  the  size  and  form  of  the  wings  vary  mucli  in  different  specimens.  In 
the  new-born  foal  the  wing  is  a  small,  pointed  projection.  Later  the  process  of  o.ssification 
invades  the  lower  part  of  the  cartilage  to  a  var>'ing  extent.  In  some  cases  the  greater  part  of 
the  cartilage  is  ossified — a  condition  commonly  termed  "sidebone." 

Development.— The  ossification  of  the  terminal  phalanx  is  peculiar.  Whih> 
the  proximal  articular  part  is  still  cartilaginous,  a  perichondrial  cap  of  bone  is 
formed  in  relation  to  the  hoof.     Later  the  process  extends  into  the  upper  part. 

Structure.— The  interior  of  this  bone  is  channeled  by  numerous  canals   for 

'  The  upper  and  lower  divisions  of  the  wing  are  sometimes  termed  the  basilar  and  retrossal 
processes  respectively. 


92  THE  SKELETON  OK  THE  HORSE 

vessels,  most  of  which  nuUatc  fruiu  the  st'inihuiar  canal  to  the  wall  surface;  these 
are  not  canals  for  nutrient  vessels  of  the  bone,  but  transmit  arteries  to  the  matrix 
of  the  hoof.  Thick  layers  of  compact  substance  are  found  at  the  articular  ami 
flexor  surfaces  and  the  extensor  process,  ('.  c,  at  the  points  of  greatest  pressure  and 
traction. 

THE  SESAMOID  BONES 
The  two  proximal  or  great  sesamoids  (Ossa  sesamoidea  phalangis  primse)  are 
situated  behind  the  distal  end  of  tlic  large  metacarpal  bone,  and  are  closely  at- 
tached to  the  first  i)halanx  \>y  strong  ligaments.  Each  has  the  form  of  a  three- 
sided  pyramid.  The  anterior  or  articular  surface  conforms  to  the  corresponding 
part  of  the  distal  end  of  the  large  mcta(ari)al  bone.  The  posterior  or  flexor 
surface  is  flattened  and  obliciue;  in  the  fresh  state  it  is  covered  by  a  layer  of  carti- 
lage which  also  fills  the  interval  between  the  opposed  borders  of  the  two  bones,  and 
forms  a  smooth  groove  for  the  deej)  flexor  tendon.  The  abaxial  surface  is  concave, 
and  gives  attachment  to  part  of  the  suspensory  ligament;  it  is  separated  from  the 
posterior  surface  by  a  rough  everted  border.  The  base  faces  downward,  and 
furnishes  attachment  to  the  inferior  sesamoidean  ligaments.  The  apex  is  directed 
u|)ward  and  is  rountled. 

The  third  sesamoid  or  navicular  lione  (Os  sesamoideum  phalangis  tertia^)  is 
shuttle-shai)ed,  and  is  situated  behind  the  junction  of  the  second  and  third  phal- 
anges.    Its  long  axis  is  transverse,  and  it  possesses  two  surfaces,  two  Ijorders,  and 

two  extremities.     The  articular  surface 
(Facies  articularis)  faces  upward  and 
forward;   it  consists  of  a  central  emi- 
.  ,.    ,         ,,,,.,  -  nence,  flanked  by  concave  areas,  and 

phalanx       articulates  with  the  distal  end  of  the 

/'//  bonier       Second  phalanx.     The  flexor  or  tendon 
surface    (Facies   flexoria)    is   directed 
"M,„?!v~Vw',"r«T"'l!"'i,i'    i\"  VV'iJ'"r\"''      downward  and  backward.     It  resem- 

HoKSK.     (.After  Schmait  z,  .\tla3  (1.  .-\uat.  d.  Pfenles.)  i  1  1  •       , 

bles  the  articular  surface  in  form,  but 
is  more  extensive  and  not  so  smooth. 
In  the  fresh  state  it  is  coated  with  cartilage  and  the  dee])  flexor  tendon  plays  over 
it.  The  proximal  border  (Margo  liber)  is  wid(>  and  grooved  in  its  middle,  narrower 
and  rounded  on  either  side.  The  distal  border  (Margo  ligamenti)  bears  in  front  a 
narrow  facet  for  articulation  with  the  third  phalanx.  Behind  this  is  a  groove,  which 
contains  a  number  of  relatively  large  foramina,  and  is  bounded  behind  by  a  promi- 
nent edge.  The  extremities  are  blunt-pointed. 
Development. — It  ossifies  from  a  single  center. 


The  Bones  of  the  Pelvic  Limb 

The  pelvic  girdle  consists  of  the  ossa  coxse,  which  unite  ventrally  at  the  .sym- 
physis pelvis,  and  articulate  with  the  .sacrum  dorsally. 


OS  COXiE 
The  OS  coxae  (or  o.s  innoininatum)  forms  the  skeleton  of  the  hip  or  haunch,  and 
is  the  largest  of  the  flat  liones.  It  consists  primarily  of  three  parts,  the  ilium, 
ischium,  and  pubis,  which  meet  to  form  the  acetabulum,  a  large  cotyloid  cavity  for 
articulation  with  the  head  of  the  femur.  The.se  parts  are  fused  at  about  one  year 
of  age,  but  it  is  convenient  to  describe  them  separately. 


THE    ILIUM 


93 


THE  ILIUM 

The  ilium  (Os  ilium)  is  the  largest  of  the  three  parts.  It  is  irregularly  triangu- 
lar anil  presents  twu  surfaces,  three  borders,  and  three  angles. 

Tlie  gluteal  surface  (Facies  glutica)  faces  upward,  backward,  and  outward.  It 
is  wide  and  concave  in  front,  narrower  and  convex  behind.  The  wide  part  is  crossed 
by  the  curved  gluteal  line  (Linea  glutsea),  which  extends  from  the  middle  of  the 
inner  border  toward  the  external  angle.  This  surface  gives  attachment  to  the 
middle  and  dee]i  gkitcal  muscles. 

The  pelvic  surface  (Facies  pelvina)  faces  in  the  opposite  direction;  it  is  convex, 


Fig.  tiO. — OssA  CoxARUM  of  Mare,  Dorsal  View. 
Oil  Ilium:  O.p.,  pubis;  O./s..  ischium;  .4  .o.>.,  wing  of  ilium;  Co.!.,  shaft  of  ilium;  Cr.o.i  anterior 
border  (crest)  of  iUum;  /,  obturator  foramen;  2,  acetabulum;  S.  internal  angle  of  ilium;  4,  external  angle  of 
ilium-  a  gluteal  line;  S.  psoas  tubercle;  7,  S,  acetabular  and  symphyseal  branches  of  pubis;  S, /O  acetabular 
and  .,'vmphvseal  branches  of  ischium;  13.  lesser  sciatic  notch;  IS.  ischial  arch;  U.  great  sciatic  notch;  ia.  sym- 
physis pelvis;  /r,ilio-pectineal  eminence;  /5.  anterior  borders  of  pubic  bones;  ;9,  posterior  gluteal  hne.  (btruska, 
Anat.  d.  Haustiere.) 


and  consists  of  two  distinct  parts.  The  inner  triangular  part  (Pars  articularis) 
is  roughened  for  ligamentous  attachment,  and  liears  an  irregular  facet,  the  auncu- 
lar  surface  (Facies  auricularis),  for  articulation  wdth  the  sacrum.  The  outer  quad- 
rilateral part  (Pars  iliaca)  is  in  general  smooth.  It  is  crossed  by  the  ibo-pectmeal 
line  (Crista  iliopectinea),  which  begins  below  the  auricular  surface  and  is  contmued 
on  the  shaft  of  the  bone  to  join  the  anterior  border  of  the  pubis.  The  Ime  is  inter- 
rupted bv  furrows  for  the  iliaco-femoral  vessels,  and  below  these  it  bears  the  psoas 
tubercle  (Tuberculum  psoadicum),  which  gives  attachment  to  the  psoas  minor  mus- 
cle.    The  iliacus  muscle  is  attached  to  the  surface  external  to  the  ilio-pectineal  line. 


94 


THK  ski;letox  of  thk  horse 


The  anterior  border  or  crest  (Crista  iliaca)  is  concave,  thick,  and  rough. 

The  internal  border  is  deeply  concave;  its  middle  part  forms  the  lower  bouiid- 
ary  of  the  great  sciatic  foramen,  and  it  is  continuous  behind  with  the  superior 
ischiatic  spine. 

The  external  border  is  concave  and  in  great  part  rough.  Its  fore  part  is 
crossed  i>y  fjruoves  for  the  ilio-lumbar  vessels,  which  are  continued  on  the  pelvic 
surface.  The  nutrient  foramen  is  usually  situated  on  or  near  the  posterior  part  ef 
this  border. 

The  internal  or  sacral  angle  i Tuber  sacrale)  curves  upwaril  and  a  little  back- 


VU:.    til. OSSA    C'OXARVM    OK    Muii:.    \  i:\TBM.    VllW. 

n.  Ilium;  >•.;,..  pubis;  .S,  ischium;  a.  anterior  border  (crest)  of  ilium;  l>.  iTiternal  angle  of  ilium;  <■'. 
external  anRlc  of  ilium;  ft.  great  sciatic  notch;  e.  external  border  of  ilium;  /,  iliac  surface;  a,  linea  arcuata:  li, 
rouKh  ligamentous  area;  /.  auricular  surface;  b,  ilio-pectineal  line;  /,  psoas  tubercle;  m,  transverse  branch,  and 
n.  symphyseal  branch  of  pubis;  o.  o',  symphysis  pelvis;  p,  anterior  border  of  pubis  (peclen);  ./.  tuberculum  pubi- 
cum:  r.  ilio-pectineal  eminence;  «,  tuber  ischii;  (.  ischial  arch;  w,  lesser  sciatic  notch;  r,  acetabular  branch,  and 
w.  symphyseal  branch  of  ischium;  x,  obturator  foramen;  i/,  articular  surface  of  acetabulum;  r  fossa  acetabuli; 
1,  groove  for  ilio-lumbar  artery.  3,  groove  for  iliaco-femoral  artery;  ,•?,  subpubic  groove;  4.  depression  for  inner 
tendon  of  origin  of  rectus  femnris;  .1,  rough  area  for  attachment  of  adductor  muscles.  (Ellenberger-Baum.  Anat. 
d.  Ilauslierc.J 


ward  close  to  tlie  first  sacral  spine,  and  forms  here  the  highest  point  of  the  skeleton. 
It  is  somewhat  thickened  and  rough. 

The  external  or  coxal  angle  (Tulier  coxa»)  forms  the  basis  of  the  point  of  tlie 
hip.  It  is  a  large  quadrangular  mass,  narrow  in  its  middle,  and  enlarged  at  either 
end,  where  it  i)ears  a  pair  of  tuberosities.     It  is  roughened  for  muscular  attachment. 

The  posterior  or  acetabular  angle  meets  the  other  two  bones  at  the  acetabu- 
lum, of  which  it  forms  about  two-fiftlis.  Its  prominent  upper  border  forms  part 
of  the  superior  ischiatic  spine,  which  is  roughened  externally,  smooth  internally. 
Two  depressions  al-ove  and  in  front  of  the  acetabulum  give  attachment  to  the 


THE    I8CHUXI — THE    PVBIS  95 

tendons  of  origin  of  the  rectus  femoris  muscle.  This  angle  is  connected  with  the 
ala  or  wide  part  of  the  bone  by  a  constricted  part,  often  termed  the  shaft.  The 
latter  is  of  three-sided  prismatic  form.  Its  external  surface  is  convex  and  rough. 
and  gives  attachment  to  the  deep  gluteus  muscle.  Its  pelvic  surface  is  smooth  and 
is  grooved  for  the  obturator  vessels  and  nerves.  Its  ventral  surface  is  crossed  by 
vascular  grooves,  below  which  is  a  rough  area,  bounded  internally  by  the  psoas 
tubercle. 

THE  ISCHIUM 

The  ischium  (Os  ischii)  forms  the  posterior  part  of  the  ventral  wall  or  floor  of 
the  bony  pelvis.  It  slopes  a  little  downward  and  inward,  but  is  practically  hori- 
zontal in  the  longitudinal  direction.  It  is  irregularly  quadrilateral,  and  may  be 
described  as  having  two  surfaces,  four  borders,  and  four  angles. 

The  superior  or  pelvic  surface  (Fades  pelvina)  is  smooth  and  slightly  concave 
from  side  to  side. 

The  inferior  surface  (Facies  externa)  is  nearly  flat,  and  is  in  great  part  rough- 
ened for  the  attachment  of  the  adductor  muscles. 

The  anterior  border  forms  the  posterior  margin  of  the  obturator  foramen. 

The  posterior  border  is  thick  and  rough.  It  slopes  obliquely  inward  and  for- 
ward to  meet  the  border  of  the  other  side,  forming  with  it  the  ischial  arch  ( Arcus 
ischiaclicus) . 

The  internal  border  meets  the  opposite  bone  at  the  symphysis. 

The  external  border  is  thick  and  rounded,  but  concave  in  its  length:  it  forms 
the  lesser  sciatic  notch,  the  lower  boundary  of  the  lesser  sciatic  foramen. 

The  antero-intemal  angle  or  symphyseal  branch  (Ramus  symphyseos)  meets 
the  pubis,  with  which  it  forms  the  iiuKT  boundary  of  the  obturator  foramen. 

The  antero-extemal  angle  or  acetabular  branch  joins  the  other  two  bones  at 
the  acetabulum,  of  which  it  forms  more  than  half.  Superiorly  it  bears  part  of  the 
superior  ischiatic  spine  (Spina  ischiadica),  and  internally  it  is  grooved  for  the  ob- 
turator vessels. 

The  postero-extemal  angle  is  a  thick  three-sided  mass,  the  tuber  ischii  (Tuber 
ischiadicum) ;  its  lower  border  is  the  inferior  ischiatic  spine,  to  whicli  the  biceps 
femoris  and  semitendinosus  muscles  are  attached. 


THE  PUBIS 

The  pubis  (Os  pubis)  is  the  smallest  of  the  three  parts  of  the  os  coxje.  It 
forms  the  anterior  part  of  the  pelvic  floor,  and  may  be  described  as  having  two 
surfaces,  three  borders,  and  three  angles. 

The  superior  or  pelvic  surface  (Facies  pelvina)  is  convex  in  the  young  subject 
and  the  stallion,  concave  and  smooth  in  the  mare  and  usually  in  the  gelding  also. 
The  urinary  l)ladder  rests  on  it. 

The  inferior  or  ventral  surface  (Facies  externa)  is  convex,  and  in  great  part 
rough  for  muscular  attachment.  Near  the  anterior  border  it  is  crossed  by  the 
subpubic  groove,  the  inner  part  of  which  is  occupied  by  a  large  vein,  the  outer  part 
by  the  pubo-femoral  ligament. 

The  anterior  border  is  thin  in  its  inner  part  (except  in  the  young  subject  and 
the  stallion),  forming  the  pecten  ossis  pubis.  Externally  it  bears  the  rough  ilio- 
pectineal  eminence  (Eminentia  iliopectinea),  beyond  which  it  is  continuous  with 
the  ilio-pectineal  line. 

The  internal  border  joins  the  opposite  I)one  at  the  symphysis  pubis. 

The  posterior  border  forms  the  anterior  margin  of  the  obturator  foramen,  and 
is  marked  externally  by  the  obturator  groove. 

The  internal  angle  meets  its  fellow  at  the  anterior  end  of  the  symphysis.     This 


96  THE  SKF.LETOX  OK  THE  HORSE 

part  is  very  thick  in  the  young  subject  and  the  stalHon,  but  in  the  mare,  and  usually 
in  the  gelding  also,  it  becomes  thin  with  advancing  age. 

The  external  or  acetabular  angle  joins  the  ilium  and  ischium  at  the  acetabu- 
lum. 

The  posterior  angle  joins  the  ischium,  with  which  it  forms  the  inner  boundary 
of  the  obturator  foramen. 

The  pubis  may  conveniently  be  regarded  as  consisting  of  two  branches  which 
meet  at  a  right  angle;  these  are  termed  the  transverse  or  acetabular  branch 
(Ramus  acetabularis)  and  the  longitudinal  or  symphyseal  branch  (Ranms  sym- 
physeos). 

The  acetabulum  is  a  cotyloid  cavity  which  lodges  the  head  of  the  femur.  It 
faces  downward  and  outward,  and  consists  of  an  articular  and  a  non-articular  part. 
The  articular  part  (Facies  lunata)  is  crescentic,  and  is  cut  into  internally  by  the 
non-articular  part,  which  lies  at  a  lower  level,  and  is  termed  the  acetabular  fossa 
(Fossa  acetalnili).  The  inner  part  of  the  rim  is  correspondingly  cut  into  by  the 
acetabular  notch  (Incisura  acetabuli),  which  is  converted  into  a  foramen  by  the 
transverse  ligament  in  the  fresh  state,  and  transmits  the  pubo-femoral  and  round 
ligaments  to  the  head  of  the  femur. 

The  obturator  foramen  (Foramen  obturatum)  is  situated  between  the  pubis 

and  ischium.  It  is  oval  in  outline,  the 
longer  axis  being  directed  forward  and 
outward.  Its  margin  is  grooved  antero- 
cxternally  for  the  obturator  nerve  and 
vessels. 

Development. — Each  division  of  the  os 
coxffi  o.ssifies  from  one  chief  center.  The 
center  for  the  ilium  appears  first  near  the 
acetabulum,  followed  quickly  by  one  for 
the  ischium,  and  a  httle  later  by  the 
pubic  center.  Secondary  centers  appear 
for  the  crest  and  external  angle  of  the 
ilium,  the  tuber  and  posterior  border  of 
_     -„    „      ^  „  .„  the   ischium,   and   the   acetabular   part   of 

Fio.  62. — OssA  CoxARCM  OF  Stallion,  Dorsal  ,  ,  .  _,,  ,  .  ,     .         .'^ 

ViKw.  (After  Eiienberger-Baum,  Anat.  the  puljis.  1  he  pubis  and  ischmui  are 
fvir  Kiinsticr.)  unltctl    at    birth    or    soon    after,    but   are 

not  fusetl  with  the  ihum  until  the  second 

year.     The  epiphyseal  parts  fuse  with  the  main  mass  at  four  and  a  half  to  five 

years  of  age. 

The  acr(iiliul:ir  p:irt  of  the  pubis  ossifies  from  a  separate  eenter.  It  is  most  distinrt  in  the 
embryo  at  three  iikhiiIis,  and  is  often  ealled  the  os  aeetaljuh.  JMartin  savs  that  the  ilium  has  a 
center  for  the  ai-edibular  part,  one  for  tlie  shaft  and  wing,  and  a  tUrd  for  the  crest.  He  also 
states  that  tln-rc  is  a  special  center  for  the  acetabular  part  of  the  ischium,  and  a  transitory  nucleus 
iu  the  symphyseal  part  of  the  pubis. 

THE  PELVIS 

The  bony  pelvis  is  composed  of  the  ossa  coxarum,  the  sacrum,  and  the  first 
three  coccygeal  vertebra;.  Th(>  dorsal  wall  or  roof  is  formed  by  the  sacrum  and 
first  three  coccygeal  vertebra',  and  tlie  ventral  wall  or  floor  by  the  puliic  and  ischial 
bones.  The  lateral  walls  are  formeil  by  the  ilia  and  the  acetabular  part  of  the 
ischia.  The  defect  in  the  skeleton  here  is  supplied  in  the  fresh  state  by  the  sacro- 
sciatic  ligaments  and  semimembranosus  muscles. 

The  anterior  aperture  or  inlet  (Aj^ertura  pelvis  cranialis)  is  bounded  by  the 
terminal  line  (Linea  terminalis)  or  brim,  composed  of  the  base  of  the  sacrum  dor- 
sally,  the  ilio-pectineal  lines  laterally,  and  the  anterior  border  of  the  pubis  ventrally. 


THE    FEMUR  f)7 

It  is  almost  circular  in  the  marc,  semi-elliptical  in  the  stallion,  and  faces  ob- 
liquely downward  and  forward.  It  has  two  principal  diameters.  Of  these,  tiie 
conjugate  or  sacro-pubic  diameter  (C'onjugata)  is  measured  from  the  sacral  prom- 
ontory to  the  anterior  end  of  the  symphysis.  The  transverse  diameter  (Diameter 
transversa)  is  measured  at  the  greatest  width,  /.  c,  just  ahox-e  the  ])s()as  tubercle. 

The  posterior  aperture  or  outlet  (Apcrtura  pelvis  caudalis)  is  nnich  smaller 
and  is  very  incomplete  in  the  skeleton.  It  is  bounded  above  by  the  third  coccygeal 
vertebra  anil  below  by  the  ischial  arch;  in  the  fresh  state  it  is  comj)leted  laterallv 
by  the  sacro-sciatic  ligament  and  the  semimembranosus  muscle. 

The  axis  of  the  pelvis  is  an  imaginary  line  drawn  through  the  centers  of  the 
inlet,  cavity,  and  outlet. 

Sexual  Differences. — ]\Iarked  differences  exist  in  the  size  and  form  of  the  pel- 
vis in  the  two  sexes.  The  average  conjugate  diameter  is  about  9}  2  inches  (ca.  23  to 
24  cm.)  in  the  mare,  7J-2  inches  (ca.  IS  to  20  cm.)  in  the  stallion.  The  transverse 
diameter  of  the  inlet  averages  about  9  inches  (ca.  22  to  23  cm.)  in  the  mare,  antl  8 
inches  (ca.  20  cm.)  in  the  stallion.  The  obliquity  of  the  inlet  is  greater  in  the  female; 
the  difference  is  indicated  by  the  fact  that  a  vertical  plane  from  the  pecten  cuts 
the  fourth  sacral  segment  in  th(>  female,  the  second  in  the  male.  The  outlet  is 
also  larger  in  the  mare,  the  ischial  arch  being  about  one-third  wider  than  in  the 
stallion.  The  cavity  is  much  more  roomy  in  the  female;  the  transverse  diameter 
between  the  middles  of  the  superior  ischiatic  spines  is  about  8  inches  (20  cm.) 
in  the  mare,  6  inches  (15  cm.)  in  the  stallion.  The  pubic  part  of  the  floor  in  the 
female  is  concave  and  lies  considerably  lower  than  the  ischiatic  part,  which  is  wide 
and  relatively  flat.  In  the  stallion  the  pubis  is  very  thick  centrally,  and  this  part 
of  the  floor  is  convex,  while  the  ischial  part  is  relativelj-  narrow,  and  is  concave  from 
side  to  side.  The  obturator  foramina  are  corresponilingly  larger  in  the  female. 
The  ilium  is  shorter,  and  the  greater  sciatic  notch  deeper  and  narrower  in 
the  male.  The  pelvis  of  the  gelding,  when  castration  has  been  performed  early, 
resembles  that  of  the  mare;  otherwise  the  male  characters  appear  to  be  retained 
to  a  large  degree. 


THE  FEMUR 

The  femur  or  thigh  bone  (Os  femoris)  is  the  largest  and  most  massive  of  the 
long  bones.  It  extends  obliquely  downward  and  forward,  articulating  with  the 
acetabulum  above  and  the  tibia  and  patella  below.  It  presents  for  examination  a 
shaft  and  two  extremities. 

The  shaft  or  body  (Corpus  femoris)  is  in  general  cylindrical,  but  flattened 
behind,  and  larger  al)ove  than  below.  The  anterior  and  lateral  surfaces  are  con- 
tinuous and  .strongly  convex  from  side  to  side;  there  is  often  a  central  vertical 
rough  line  on  the  proximal  part,  l)ut  otherwise  these  surfaces  are  smooth.  They 
are  covered  by  the  quadriceps  femoris  muscle.  The  posterior  surface  is  wide,  flat, 
and  smooth  in  its  proximal  fourth.  Below  this  part  there  is  a  rough  elevation 
externally  for  the  attachment  of  the  femoral  tendon  of  the  biceps  femoris,  and  a 
rough  line  internally  to  which  the  quadratus  femoris  is  attached.  The  middle 
third  is  narrower,  and  is  rough  for  the  attachment  of  the  adductor  muscle.  Just 
below  this  area  an  oblique  groove  crosses  the  surface,  indicating  the  position  of  the 
femoral  vessels.  The  internal  border  bears  on  its  proximal  part  the  internal 
trochanter  or  trochanter  minor,  a  thick  rough  ridge,  to  which  the  ilio-psoas  muscle 
is  attached.  From  this  a  rough  line  curves  up  to  the  front  of  the  neck  and  indicates 
the  limit  of  the  attachment  of  the  vastus  internus  muscle.  A  narrow  rough  area 
about  the  middle  gives  attachment  to  the  pectineus  muscle,  and  the  nutrient 
foramen  is  usually  found  just  in  front  of  this  mark.  The  supracondyloid  crest  is 
situated  below  the  groove  for  the  femoral  vessels,  and  gives  origin  to  the  inner  head 
7 


98 


THE    bKELETOX    OF   THE    HORSE 


-Rit;nT    Femur    of    IIorsk 

EXTKRNAL    ViKW. 


UilT   FKMt'R   OF    HOHS 

TERioR  View. 


Fi<;.  65. — Right  Femur    of  Horse,  In- 
TERXAE  View. 

/,  Anterior  part,  1\  posterior  part  of  trochanter  major;  2,  neck;  S,  fovea  capitis;  4,  crest;  />,  trochanteric  fossa;  6,  ex- 
ternal or  third  trochanter;  7,  trochanter  minor;  8,  eminence  for  attachment  of  biceps  femoris;  9.  internal  border;  10,  nutrient 
foramen;  //,  groo/e  for  femoral  vessels;  /3,  supracondyloid  crest;  IS.  supracondyloid  fossa;  i.^,  trochlea;  /.t,  external  epicon- 
dyle;  16,  external  condyle;  17,  extensor  fo-t-in:  /-V.  internal  condyle;  19,  internal  epicondyle;  SO,  intercondyloid  fossa.  (After 
Schmaltz    Atlas  d.  Anat.  d.  Pferdes.) 


THE    FEMl-R 


99 


of  the  gastrocnemius.  The  external  border  is  prominent  in  its  upper  part,  and 
bears  at  the  junction  of  its  proximal  and  middle  thirds  the  external  or  third  tro- 
chanter (Trochanter  tertius);  this  process  is  curved  forward,  anil  furnishes  in- 
sertion to  the  tendon  of  tlie  superficial  gluteus  muscle.  At  the  lower  part  is  found 
the  supracondyloid  or  plantar  fossa  (Fossa  plantaris),  in  which  the  superficial 
fle.xor  arises;  it  is  bounded  externally  by  a  thick 
rough  margin,  to  which  the  outer  head  of  the  gastroc- 
nemius muscle  is  attached. 

The  proximal  extremity  (Extremitas  proximalis) 
is  large  and  consists  of  the  head,  neck,  and  great  tro- 
chanter. The  head  (Caput  femoris)  is  placed  at  the 
inner  side  and  is  directed  inward,  upward,  and  some- 
what forward.  It  is  approximately  hemispherical 
and  articulates  with  the  acetabulum.  It  is  cut  into 
internally  by  a  deep  notch,  the  fovea  capitis,  in  which 
the  pubo-femoral  and  round  ligaments  are  attached. 
The  articular  surface  is  surrounded  by  a  distinct  mar- 
gin. The  neck  (CoUum  femoris)  is  most  distinct  in 
front  and  internally.  The  great  trochanter  (Tro- 
chanter major)  is  situated  externally;  it  presents 
three  features.  The  anterior  part  or  convexity  is 
situated  opposite  to  the  head  and  rises  little  above 
the  level  of  the  latter;  it  gives  attachment  to  the 
deep  gluteus  muscle,  and  in  the  fresh  state  its  outer 
surface  is  coated  "svith  cartilage,  over  which  a  tendon 
of  the  middle  gluteus  passes,  to  be  inserted  into  the 
crest,  which  is  placed  below  and  behind  the  convex- 
ity. The  posterior  part  or  summit  is  separated  from 
the  convexity  by  a  notch;  it  is  situated  behind  the 
plane  of  the  head  and  rises  to  a  much  greater  height. 
It  furnishes  insertion  to  part  of  the  middle  gluteus 
muscle.  Its  posterior  border  is  continued  downward 
as  the  trochanteric  ridge,  which  forms  the  outer  wall 
of  the  trochanteric  fossa.  A  number  of  foramina  are 
found  in  the  concave  area  internal  to  the  con- 
vexity. 

The  distal  extremity  (Extremitas  distalis)  is 
large  in  both  directions  and  comprises  the  trochlea 
in  front  and  two  condyles  behind.  The  trochlea 
consists  of  two  ridges  separated  by  a  groove,  ami 
forms  an  extensive  surface  (Facies  patellaris)  for 
articulation  with  the  patella.  It  is  very  unsym- 
metrical;  the  inner  ridge  or  lip  is  much  wider, 
more  prominent,  and  extends  up  higher  than  the  ex- 
ternal one,  and  the  two  converge  below.  The  con- 
dyles, internal  and  external  (Condylus  medialis. 
lateralis),  are  separated  Viy  the  deep  intercondyloid 

fossa  (Fossa  intercondyloidea),  and  articulate  with  the  condyles  of  the  tibia  and  the 
semilunar  cartilages  of  the  stifle  joint.  A  ridge  connects  each  condyle  with  the  lower 
part  of  the  corresponding  lip  of  the  trochlea.  The  intercondyloid  fossa  lodges  the 
spine  of  the  tibia  and  the  crucial  ligamentsof  the  stifle  joint,  which  are  attached  here. 

The  condyles  are  obliquely  placed,  with  their  long  axes  directed  downward,  forward,  and 
inward.  The  articular  surface  of  the  external  condyle  is  more  strongly  convex  from  side  to  side 
than  that  of  the  inner  one.  and  the  ridge  which  connects  it  with  the  trochlea  is  much  narrower. 


Fig.  66. — Front 
Femur  o 


.  Section  of  Left 
Horse,  .\ntebior 


The  figure 
dullar>'  cavity  is  tr 
part  by  fi 


:hows  that  the  me- 
y  is  traversetl  for  the  most 
bony  trabecuI.T. 


100  THE  SKELETON  OF  THE  HORSE 

Tlu'  internal  epicondyle  (Epicondylus  medialis)  is  a  roundetl  prominence  on 
the  internal  surface  of  the  internal  condyle,  to  which  the  internal  lat(>ral  ligament 
and  the  adductor  muscle  are  attached.  The  corresponding  external  epicondyle 
(Epicondylus  lateralis)  is  less  distinct;  it  presents  a  mark  where  the  lateral  liga- 
ment is  attached,  below  and  behind  which  there  is  a  depression  (Fossa  musculi 
poplitei)  in  which  the  popliteus  muscle  arises.  Between  the  external  condyle  and 
trochlea  is  the  extensor  fossa  (Fossa  extensoria),  in  which  the  tendon  of  origin  of 
the  anteii(M-  extensor  and  peroneus  tertius  is  attached. 

Development. — The  shaft  and  the  distal  end  each  ossify  from  one  center,  Init 
the  ]iroxiinal  end  has  two  centers,  one  of  which  is  for  the  great  trochanter.  The 
edge  of  the  external  trochanter  al.so  has  a  separate  center.  The  proximal  end  fuses 
with  the  shaft  at  three  to  three  and  a  half  years,  the  distal  at  about  three  and  a 
half  years. 


Trochlea 


Kxlciisiir  fonsa  ^^^^^^         _^^^^ 

Inlrriinl  cpiciiiiihjle 

External  cpii-oiuli/le — | 

Dcjirissioii  for  oriiji))  of 

poplitcwi 

Exlcrnal  condyle -^^^^^^^      \      L^^g^ -Internal  condyle 

Intercondyloid  fossa 
Fig   67. — Distal  Extremity  of  Right  Femur  of  Horse,  End  View. 


THE  TIBIA 

The  tibia  is  a  long  bone  which  extends  obliquely  downward  and  backward 
from  the  stifle  to  the  hock.  It  articulates  above  with  the  femur,  below  with  the 
tarsus,  and  externally  with  the  fibula.     It  possesses  a  shaft  and  two  extremities. 

The  shaft  or  body  (Corpus  tibiie),  large  and  three-sided  above,  becomes  smaller 
and  flattened  in  the  sagittal  direction  below,  but  widens  a  little  at  the  distal  end. 
It  presents  for  notice  three  surfaces  and  three  borders.  The  internal  surface 
(Facies  medialis)  is  broad  above,  where  it  furnishes  insertion  to  the  internal  lateral 
ligament  and  the  sartorius  and  gracilis  muscles;  below  this  it  is  convex  and  sub- 
cutaneous. The  external  surface  (Facies  lateralis)  is  smooth  and  somewhat  spiral. 
It  is  wide  and  concave  in  its  upper  i^art,  below  which  it  becomes  narrower  and 
slightly  convex,  and  winds  gradually  to  the  front  of  the  l)one;  near  the  distal  end 
it  widens  a  little,  becomes  flat,  and  faces  forward.  The  posterior  surface  (Facies 
posterior)  is  flattened,  and  is  divided  into  two  parts  by  the  rough  popliteal  line, 
which  runs  obliquely  from  the  upjier  part  of  the  external  border  to  the  middle  of 
the  internal  border.  The  triangular  area  above  the  line  is  occupied  by  the  popliteus 
muscle,  while  the  area  below  is  marked  by  rough  lines  (Lineae  musculares)  to  which 
the  deep  flexor  muscle  of  the  digit  is  attached;  the  lines  fade  out  below,  where  the 
surface  is  smooth  and  flat.  The  nutrient  foramen  is  situated  on  or  near  the 
popliteal  line.  The  anterior  border  is  very  ijrominent  in  its  uiii)er  third,  forming 
the  tibial  crest  (Crista  tibise) ;   below  it  is  reduced  to  a  rough  line,  which  ends  at  a 


THE    TIBIA 


101 


small  elevation  near  the  distal  end  of  the  hone.  The  internal  border  (Margo  niedi- 
alis)  is  rountled  in  its  upper  half,  to  which  the  popliteus  muscle  is  attached,  and  a 
tubercle  is  found  on  this  part.  The  lower  part  is  a  rough  line  on  well-marked  hones. 
The  external  border  (Crista  interossea)  is  concave  in  its  upper  part  and  concurs 
with  the  fihula  in  the  formation  of  the  interosseous  space  of  the  leg;  a  smooth  im- 
pression indicates  the  course  of  the  anterior  tibial  vessels  through  the  space  to  the 


a  pine 


External  condyh 


Head  of  fibula 


Vascular  impressi 


Shaft  of  Jihula 
External  border  of  tibia  — 


,^Tuberosity 


'  Groove  far  tendon  of  anterior 
extensor  and  peroneus  lertius 


-1 — Cruovefor  lateral  extensor  tendon 


External  malleolus 
Fio.  68. — Right  Tibia  and  Fibula  of  Horse,  Exter.val  View. 


front  of  the  leg.     Lower  clown  the  border  divides  and  incloses  a  narrow  triangular 
surface. 

The  proximal  extremity  (Extreniitas  jiroximalis)  is  large  and  three-.sided.  It 
bears  two  lateral  eminences,  the  internal  and  external  condyles  (Condylus  medialis, 
lateralis).  Each  presents  a  somewhat  .saddle-shaped  surface  for  articulation  with 
the  condyle  of  the  femur  and  the  semilunar  cartilage.  The  spine  or  intercondy- 
loid  eminence  (Eminentia  intercondyloidea)  is  the  central  prominence.  ui)on  which 
the  articular  surfaces  are  continued;   it  consists  of  a  high  inner  jiart  and  a  lower 


102 


THE    SKELETON    OF   THE    HORSE 


outer  part  (Tuherculum  intercoinlyloidcum  mediale,  laterale).  On,  before,  and 
behind  the  spine  are  the  anterior  and  posterior  intercondyloid  fossae,  in  which 
the  anterior  crucial  Hgament  and  the  seniihniar  cartilages  are  attached.  The 
condyles  are  separated  behind  by  the  deep  popliteal  notch  (Incisura  poplitea),  on 
the  inner  side  of  which  is  a  tubercle  for  the  attachment  of  the  posterior  crucial 
ligament.     The  external  condyle  has  an  overhanging  outer  margin,  below  which  is 


Spine 


Intcniiit  condyle 


Tubercle  for  posterior  crucial 
ligament 


Tubercle 

Nutrivnl  foramen  — 


Groom  for  tendon  of  inner  head  _ 
of  flexor  perforans 

Internal  malleolus 


Fig.  r,!).— Ku-.ht  T 


,-  Fossa  for  anterior  crucial  liyament 
Popliteal  notch 

"  External  condyle 

Head  of  fibula 


-'  Impression  of  anterior  tibial  vessels 

-  Interosseous  space 

Shaft  of  fibula 
Muscular  lines 


-  External  malleolus 


Horse.  Postkrior  Vie 


a  facet  for  articulation  with  the  fibula.  The  large  anterior  eminence  is  the  tu- 
berosity of  the  tibia  (Tuberositas  tibiff).  It  is  marked  in  front  by  a  groove,  the 
lower  part  of  which  gives  attachment  to  the  middle  patellar  ligament,  and  the 
groove  is  flanked  by  rough  areas  for  the  attachment  of  the  internal  and  external 
patellar  ligaments.  .\  semicircular  smooth  notch  (Sulcus  muscularis)  separates  the 
tuberosity  from  the  external  condyle,  and  gives  passage  to  the  tendon  of  origin  of 
the  anterior  extensor  and  the  peroneus  tertius. 


THE   TIBIA 


1U3 


The  distal  extremity  (Extrmuitas  distalis)  is  much  smaller  than  the  pruxinial; 
it  is  quaihansular  in  form  and  larger  internally  than  externally.  It  presents  an 
articular  surface  (Cochlea  tibiae),  which  is  adapted  to  the  trochlea  of  the  til)ial 
tarsal  bone  (astragalus),  and  consists  of  two  grooves  separated  by  a  ridge.  The 
ridge  and  grooves  are  directefl  obliquely  forward  and  outward,  and  are  bounded 
laterally  by  the  malleoli,  to  which  the  lateral  ligaments  of  the  hock  joint  are  at- 


Spiiie 


Tubcr<i.<' 
Sulcus  muscularis  -^ 
External  comlyle  — 

Head 

Interosseous  space  -  - 
External  surfn<< 
Shaft  ofjibul.: 


Groove  for  middle  patellar  ligament 
j —  Internal  condyle 


Imprint  for  insertion  of  gracilis 

Crest 

Imprint  for  insertion  of  semitendi- 
nosus 


Internal  surface 


„  ,       „    ,  J  ■  -  ^    -Internal  malleolus 

External  inalleolus  ■ 

Fig    70  — Right  Tibia  and  Fibula  ok  Horse,  Anterior  View. 


tached.  The  internal  malleolus  (Malleolus  tibialis)  is  the  more  prominent  of  the 
two,  and  forms  the  anterior  boundary  of  a  groove  for  the  tendon  of  the  inner 
head  of  the  flexor  perforans.  The  external  maUeolus  (Malleolus  fibularis)  is 
broader,  and  is  marked  by  a  vertical  groove  for  the  jiassage  of  the  lateral  extensor 
tendon. 

Development.— The  tibia  has  the  usual  three  chief  centers  of  ossification  and 
supplementary  ones  for  the  tuberosity  and  the  external  malleolus.     The  latter  is 


104 


THE    SKELETON    OF   THE    HORSE 


really  the  distal  end  of  the  fibula;  it  is  a  separate  piece  at  birth,  and  the  line  of 
union  is  commonly  quite  evident  in  the  adult  in  the  external  articular  groove.  The 
proximal  end  unites  with  the  shaft  at  about  three  and  a  half  years,  and  the  distal 
end  at  about  two  years  of  age. 


THE  FIBULA 

The  fibula  of  tiie  horse  is  a  much  reduced  long  bone,  situated  along  the  outer 
side  of  the  tibia. 

The  shaft  or  body  (Corpus  fil:)ulie)  is  a  slender  rod  which  forms  the  outer  bound- 
ary of  the  interosseous  space;  it  usually  terminates  below  in  a  pointed  end  about 
one-half  to  two-tiiirds  of  the  way  down  the  external  border  of  the  tibia. 

The  proximal  extremity  or  head  (Capitulum  fibulae)  is  relatively  largo,  and  is 
flattened  transversely.  Its  internal  surface  j^resents  a  narrow  area  along  the  upper 
border  for  articulation  with  the  tibia.  The  external  surface  is  rough  and  gives 
attachment  to  the  external  lateral  ligament  of  the  stifle  joint.  It  has  rounded 
anterior  and  posterior  Itorders. 


Grimrr  fur  impUteus  lenilon — 
Extvrniil  cimibjlc  --  " 


'^^m    hitiriml  mttdi/k 


External  and  internal 
-  /  tubercles  of  spine 


(irooi'c  for  taidon  of  crtcn 
lonyiix  and  inroni  us  Icrliii. 

:  for  middle  putdlar  ligament 
Tuberosity 
Tin.  71. — Proximal  Extremity  of  Right  Tibia  of  Horsi:,  End  Vikw. 
l.c.a,^  l.c.p..  Depressions  for  attachment  of  anterior  and  posterior  crucial  ligaments;    /,  m,  m,  depressions  for  at- 
tachment of  semilunar  cartilages. 


The  distal  extremity  is  fused  witli  the  tibia,  constituting  the  external  malleolus. 

Development. — This  resembles  that  of  the  ulna.  The  embryonic  cartilaginous 
fibula  <'xtends  the  entire  length  of  the  leg,  but  does  not  articulate  with  the  femur. 
The  lower  jiart  of  the  shaft  is  usually  reduced  to  a  fibrous  band.  Three  centers  of 
ossification  appear,  one  each  for  the  shaft  and  the  extremities.  The  distal  end 
unites  early  with  the  tibia,  forming  the  external  malleolus. 

It  is  interesting  to  note  tliat  in  some  cases  the  entire  shaft  of  the  fil)uhi  (!o\(lops,  a  reversion 
to  the  condition  in  the  Miocene  ancestors  of  tlie  present  horse. 


THE  PATELLA 

The  patella  is  a  large  sesamoid  bone  which  articulates  with  th(>  troclilea  of 
the  fennir.  It  presents  for  tlescrijjtion  two  surfaces,  two  iHirders,  a  base,  and  an 
apex. 

The  anterior  or  free  surface  (Facies  libera)  is  irregularly  quatlrilateral,  convex, 
and  rough  for  musnilar  and  ligamentous  attachment. 

The  posterior  or  articular  surface  is  smaller  and  is  triangular  in  outline.  It 
presents  a  vertical  rounded  ridge,  which  corresponds  to  the  groove  on  the  trochlea 
of  the  femur,  and  separates  two  concave  areas.     Of  the  latter,  the  inner  cavity  is 


THE    TARSUS 


105 


the 


^■^ 


much  the  hirger,  and  is  not  verj-  well  adapted  to  the  inner  lip  of  the  trochlea 
the  fresh  state,  however,  it  is  coinpletetl  and  rendered  more  congruent  by 
curved  accessory  fibro-cartilage. 

The  lateral  borders  converge  to  the  apex  below,  and 
each  forms  a  jironiinence  or  angle  at  the  base.  The  inner 
angle  and  the  adjacent  part  of  the  border  give  attach- 
ment to  the  fibro-cartilage  of  the  patella,  which  increases 
the  articular  surface.  The  external  border  is  rounded 
and  its  angle  is  less  prominent. 

The  base  (Basis  patelUv)  faces  upward  anil  back- 
ward, and  is  convex  transversely,  concave  from  before 
backward. 

The  apex  forms  a  Ijlunt  point  directed  downward. 

Development. — The  patella  develops  as  a  .sesamoid 
bone  from  a  single  center  in  a  cartilaginous  deposit  in 
the  tendon  of  the  ciuadriceps  femoris  muscle. 


THE  TARSUS 
The  tarsus  or  hock  of  the  horse  usually  comprises 
six  short  bones  (Ossa  tarsi),  but  exceptionally  seven  are 
present. 

The  Tibial  Tarsal  Bone 

The  tibial  tarsal  bone  (Os  tarsi  tibiale,  astragalus, 
or  talus)  is  the  inner  bone  of  the  proximal  row.  It  is 
extremelj'  irregular  in  form,  but  may  be  considered  as 
offering  six  surfaces  for  description. 

The  superior  and  the  anterior  or  dorsal  surface  are 
continuous,  and  form  a  trochlea  for  articulation  «ith  the 
distal  end  of  the  tibia.     The  trochlea  consists  of  two 
oblique  ridges  with  a  deep  groove  between  them,  which 
curve  spirally  forward,  downward,  and  outward.     There. 
is  usually  a  shallow  synovial  fossa  in  the  groove.     The      ^ 
inferior  surface  is  convex  from  before   backward,  and 
most  of  it  articulates  with  the  central  tarsal;  externally 
it  has  an  oblique  facet  for  the  fourth  tarsal,  and  a  non- 
articular  groove  cuts  into  the  surface  to  its  middle.     The  posterior  or  plantar 
surface  is  oblique  and  extremely  irregular;   it  presents  four  facets  for  articulation 
with  the  fibular  tarsal  bone;  the  facets  are  separated  by  rough  excavated  areas,  and 
the  largest  fo.ssa    (Sulcus  tali)    forms  with   a   corresponding  one  on  the  fibular 


[JHT  Tibia 

TEBIOR  Vi 


Accexsory 
cartilage 


Fig.  73.— Right  Patella  of  Horse,  Antehior  View.        Fig.  74.— Right  Patella  or  Horse.  Posterior  View 


tarsal  a  cavity  termed  the  sinus  tarsi.     The  internal  surface  bears  on  its  lower  part 
a  large  tuberosity,  and  on  its  upper  part  a  small  one  for  the  attachment  of  the 


106 


THE    SKELETON    OF   THE    HORSE 


internal  lateral  ligament.     The  external  surface  is  smaller  than  the  internal,  and 
is  marked  by  a  wide  rough  fussa  in  which  the  external  ligament  is  attached. 

The  Fibular  Tarsal  Bone 
Tlie  fibular  tarsal  lione  (Os  tarsi  fibulare,  calcaneum,  os  calcis)  is  the  largest 
bone  of  the  hock,     it  is  elongated,  flattened  from  side  to  side,  and  forms  a  lever 


Tuber  calcis 


Melatars,!! 
luherosihi 
Third  mcln- 
tarsal 


FlQ.  73.— RicHT  TAnsr.s  and  Ui-i-kr  Part  of  Mkta- 
TAnaus  or  House,  Intkrnai.  Vif:w.  (After 
SfhmMltz,  Atla,s  d.  Atiat.  <1.  Pfenlea.) 


Part  of  Mi:ta- 
PosTERioR      (Plantar) 
(After     Schmaltz,    Atla.s    d.  Anat.    d. 


for  the  muscles  which  extend  the  hock  joint.     It  consists  of  a  liody  and  an  inner 
process,  the  sustentaculum  tali. 

The  body  (Corptis  calcanei)  is  enlarged  at  its  proximal  end  to  form  the  tuber 


Groove  of  trochlea 


r  Tibial  Tarsal  Bonk  of  Horse. 
Anterior  View.  (After  Schmaltz,  Atlas  d. 
.\nat.  d.  Pferdes.) 


78. — Right  Tibial  Tarsal  Bone  of  Horse, 
External  View.  (After  Schmaltz,  Atlas  d. 
Anat.  d.  Pferdes.) 


calcis  or  "i)oint  of  the  hock."  The  posterior  part  of  this  eminence  gives  attach- 
ment to  the  tendon  of  the  gastrocnemius,  while  in  front  and  laterally  it  furnishes 
uisertion  to  tendons  of  the  flexor  perforatus,  biceps,  and  semitendinosus  nuiscles. 
The  inferior  extremity  bears  a  concave  facet  for  articulation  with  the  fourth  tarsal 
bone.  The  internal  surface  has  on  its  lower  part  a  strong  process,  the  sustentacu- 
lum tali,  which  projects  inward.     The  process  has  a  large,  oval,  slightly  concave 


THE    TARSUS 


107 


facet  in  front  fur  articulation  with  the  til)ial  tarsal,  and  sonictimcs  a  small  articular 
surface  below  for  the  central  tarsal  bone.  Its  plantar  surface  forms  with  the  smoot  h 
inner  surface  of  the  body  a  groove  for  the  deep  flexor  tendon  (Sulcus  musculi  flexoris 
hallueis  longi).  Its  inner  surface  has  a  prominence  on  the  lower  part  for  the  at- 
tachment of  the  lateral  ligament.  The  external  surface  of  the  body  is  flattened, 
except  below,  where  there  is  a  rough  prominence  for  the  attachment  of  the  lateral 


Facets  fur  tibial 
tarsal  bone 

Fig  79.— Right  Fibular  Taf 
Bone  of  Horse,  .\ntkf 
View.  (After  Schm:i 
Atlas  (l.Anat.d.  Pferde 


80. — Right  Fourth  Tar- 
sal Bone  of  Horse, 
Upper  Surface.  (After 
Schmaltz,  Atlas  d.  Anat. 
d.  I'ferdes.) 


FtiGHT  Central  Tar- 
sal Bone  of  Horse, 
Upper  Surface.  (After 
Schmaltz,  Atlas  d.  Anat. 
d.  I'ferdes.) 


ligament.  The  anterior  or  dorsal  border  is  concave  in  its  length,  smooth  and 
rounded  in  its  upper  ]3art.  About  its  middle  is  a  l)lunt-pointed  pro,iection  (Pro- 
cessus cochlearis)  which  bears  facets  on  its  inner  and  lower  surfaces  for  articulation 
with  the  tibial  tarsal  bone,  and  is  roughened  outwardly  for  ligamentous  attachment. 
Below  this  are  two  facets  for  the  tibial  tarsal,  and  an  extensive  rough  fossa  which 
concurs  in  the  formation  of  the  sinus  tarsi.     The  posterior  or  plantar  border  is 


Fused  first  awl 
second  tarsals 


Facets  for  cen- 
tral tarsal 
Facets  for  central 
larsfd 


Third  tarsal 


Fig.  82.— Right  First,  Second,  and  Third  Tarsa 
Bones  of  Horse,  Uppep  Surface.  (.\fte 
Schmaltz,  .\tlas  d.  .\nat.  d.  Pferdes.) 


Fourth  (external) 
metatarsal 


Facets  for  sec-  "*         Facets  far 

ond  and  third     Facet  far  third      fourtli  tar- 

tarsals  tarsal  sid 

I'll..  .S.!. — Proximal  .Articular  .Surfai 
Metat.irsal  Bonks  of  Hoh: 
Schmaltz,  Atla,-  d.  Anat.  d.  Pferde 


'    I.F.I-T 

(After 


straight  and  thick,  and  widens  a  little  at  either  end:   it 
ment  to  the  long  plantar  ligament. 


rough,  and  gives  attach- 


The  Central  Tarsal  Bone 
The  central  tarsal  bone  (( )s  tarsi  centralc,  scaphoid,  or  navicular)  is  irregularly 
quadrilateral,  and  is  situated  between  the  tibial  tarsal  above  and  the  third  tarsal 
below.     It  is  flattened  from  above  do\TOward,  and  may  be  described  as  luiviim  two 


108 


THE    SKELETON    OF    THE    II0RSE 


surfaces  and  four  liorders.  The  superior  surface  is  concave  from  before  backward, 
and  almost  all  of  it  articulates  with  the  tibial  tarsal;  a  non-articular  depression 
cuts  into  its  outer  part,  and  sometimes  there  is  a  facet  for  the  fibular  tarsal  bone  on 
the  posterior  angle.  The  inferior  surface  is  convex,  and  is  crossed  bj'  a  non-articu- 
lar groove,  which  separates  facets  for  articulation  with  the  third  and  the  first  and 


Tuhtr  calcis 
Fihuliir  liimal 


Fourlh  taiviil  \' 


■  Trochlea  of  tibial  tarsal 

'  Di]>ression  for  external 
lateral  ligament 


.Central  tarsal 
Third  tarsal 


\       J- 
droovc.  for  great  meta-  ,J^-"; 

tarsal  artery  i. 


Fourth  (e.rlernal)  meta-  _^ 
tarsal 


\iiscular  canal 
Third  (large)  metatarsal 


Fig.  84.— Right   T.vrsai,  .\m)    Mi 


Eminence  for  lateral  ligament 

.    Bonks  ok  IIonsK,  Extkrnai.  \'i 
.\n:it.  .1.   I'fenles.) 


;.\ffcr    Schmaltz,  Atlas   d. 


second  (fused)  tarsals.  The  anterior  or  dorsal  border  and  the  internal  border 
are  continuous,  convex,  and  rough .  Tiic  posterior  or  plantar  border  1  lear.s  two  prom- 
inences, separated  bj-  a  notch.  The  external  border  is  oblique,  and  bears  anterior 
and  po.stcrior  facets  for  articulation  with  the  fourth  tarsal,  between  which  it  is  ex- 
cavated and  rough. 


THE   TARSUS  109 

First  and  SEco^fD  Tarsal  Bones 
The  first  and  second  tarsal  bones  (Os  tarsale  primum  et  secundum,  cuneiform 
parvum)  are  usually  fused  in  the  horse,  forming  a  bone  of  very  irregular  shape,  situ- 
ated in  the  inner  and  posterior  part  of  the  lower  row,  below  the  central  and  behind  the 
third  tarsal.  It  is  the  smallest  of  the  tarsal  bones,  and  may  be  described  as  having 
two  surfaces,  two  borders,  and  two  extremities.  The  internal  surface  faces  back- 
ward and  inward,  and  is  convex.  Its  anterior  part  is  ridged,  and  gives  attach- 
ment to  the  internal  lateral  ligament,  and  its  posterior  part  bears  an  imjjriiit  where 
the  inner  tendon  of  the  tibiahs  anterior  is  inserted.  The  external  surface  is  marked 
by  a  deep  notch  which  indicates  the  division  between  the  first  and  second  tarsal 
elements;  it  bears  on  its  anterior  part  a  large  concave  facet  for  the  central 
tarsal.  The  superior  border  is  convex.  The  inferior  border  is  broad  in  front, 
where  it  articulates  with  the  large  and  inner  small  metatarsal  bones.  The 
anterior  extremity  has  a  small  facet  for  articuhitidu  with  the  third  tarsal,  and 
bears  internally  a  ridge  or  tubercle.  The  posterior 
extremity  is  a  blunt  point. 

In  some  cases  the  first  and  .second  tarsal  bones  remain 
separate — a  remarkable  reversion  to  the  condition  in  the  earl_y 
ancestors  of  the  horse.  In  such  specimens  the  first  tarsal  is  a 
discoid  bone,  articulating  above  with  the  central,  below  with 
the  small  metacarpal  bone.  The  second  tarsal  is  quadrangular, 
equivalent  to  the  thick  anterior  part  of  the  bone  as  described 
above,  and  o\-erlapped  by  the  anterior  part  of  the  first  tarsal. 

The  Third  Tarsal  Bone 

The  third  tarsal  bone  (Os  tarsale  tertium,  third  or 
great  cuneiform)  resembles  the  central,  but  is  smaller 
aird  triangular  in  outline.  It  is  situated  between  the 
central  above  and  the  large  metatarsal  bone  below.  It 
possesses  two  surfaces  and  three  borders. 

The  superior  surface  is  concave,  and  is  crossed  by 
a  non-articular  depression  which   divides  it  into  two 

unequal  facets;  it  articulates  with  the  central  tarsal.  The  inferior  surface  is 
slightly  convex,  and  rests  on  the  large  metatarsal  bone;  it  has  an  extensive 
central  rough  excavation.  The  anterior  or  dorsal  border  is  convex  and  bears  a 
rounded  ridge  on  its  inner  part.  The  internal  border  is  deeply  notched  and  has 
a  small  facet  for  the  second  tarsal  on  its  anterior  part.  The  external  border  is 
also  divided  by  a  notch  into  two  parts,  and  bears  two  diagonally  opposite  facets 
for  articulation  with  the  fourth  tarsal.  In  some  cases  there  is  a  facet  for  the  inner 
small  metatarsal  bone. 

The  Fourth  Tarsal  Bone 

The  fourth  tarsal  bone  (Os  tarsale  quartum,  cuboid)  is  the  outer  bone  of 
the  lower  row,  and  is  equal  in  height  to  the  central  and  third  together.  It  is 
cuboid  in  shape  and  presents  six  surfaces. 

The  superior  surface  is  convex  from  side  to  side,  and  articulates  chiefl\-  with 
the  fibular  tarsal,  but  to  a  small  extent  with  the  tibial  tarsal  also.  The  inferior 
surface  rests  on  the  large  and  external  small  metatarsal  bones.  The  internal 
surface  bears  four  facets  for  articulation  with  the  central  and  third  tarsal  bones. 
It  is  crossed  from  before  backward  by  a  smooth  groove,  which  by  apposition  with 
the  adjacent  bones  forms  the  canal  of  the  tarsus  (Canalis  tarsi)  for  the  ])assage  of 
the  perforating  tarsal  vessels.  The  anterior  or  dorsal,  external,  and  posterior  or 
plantar  surfaces  are  continuous  and  rough.  A  tuberosity  behind  gives  attachment 
to  the  plantar  ligament. 


85.— 

CROSS-6ECTION-S 

llETA 

CARP.VL       AND      MkI 

TARS.I 

iL  Bones  of  Hors 

C.\fte: 

r   Schmaltz,  Atlas 

Anat. 

d.  Pferile^.) 

110 


THE    SKELETON    OF   THE    HORSE 


Development. — The  fibular  tarsal  bone  has  two  centers  of  ossification,  one  for 
the  main  mass  and  the  other  for  the  tuber  calcis;  the  latter  fuses  with  the  rest  of  the 
bone  at  about  three  years  of  age.  The  first  and  second  tarsals  have  separate  cen- 
ters, but  fusion  usually  occurs  liefore  birth.  Each  of  the  other  bones  ossifies  from 
a  single  center. 


Tuberosilij 


Flexor 
surface 


Via.  SG. — Digital  Bones  o 
Volar  As 


THE  METATARSUS 

The  metatarsal  bones  (Ossa  metatarsalia),  three  in  number,  have  the  same 
general  arrangement  as  the  metacarpal  bones,  but  present  some  important  differ- 
ences.    Their  direction  is  slightly  ol)lique,  downward  and  a  little  forward 

The  large  or  third  metatarsal  bone  is  about  one-sixth  longer  than  the  corre- 
sponding metacarpal  ;  ill  an  animal  of  medium  size  the  difference  is  about  two  inches. 
The  shaft  is  more  cylindrical,  and  is  almost  circular  on  cross-section,  except  in  its 
lower  part.  At  the  ui)i)er  piirt  of  its  external  surface  there  is  a  groove,  which  is 
directed  ol)li(iuely  downward  and  backward,  and  is  continued  by  the  furrow  formed 
by  the  appt)sition  of  the  external  metatarsal  bone;  it  indicates  the  course  of  the 
great  metatarsal  artery.     A  faint  impression  in  a  similar  place  on  the  inner  side 


THE    PHALANGES   AND   SESAMOIDS  111 

marks  the  position  of  the  corresponding  vein.  The  nutrient  foramen  is  rehitively 
higher  than  on  the  metacarpal  bone.  The  proximal  extremity  is  much  wider  from 
before  Imckward  than  that  of  the  metacarpal  bone.  Its  articular  surface  is  slightly 
concave,  and  is  marked  by  a  large  central  non-articular  depression,  continued  out- 
ward by  a  deep  notch.  The  greater  part  of  the  surface  articulates  with  the  third 
tarsal,  but  there  is  an  outer  facet  for  the  fourth,  and  usually  a  small  facet  postero- 
internally  for  the  second  tarsal  bone.  Posteriorly  there  are  two  pairs  of  facets  for 
articulation  uath  the  small  metatarsal  bones.  The  front  is  crossed  by  a  rough  ridge 
for  insertion,  which  liecomes  larger  and  turns  downward  on  the  outer  side  beliind  the 
vascular  groove.  The  distal  extremitj'  closely  resembles  that  of  the  corresponding 
metacarpal  bone. 

In  some  ca-ses  the  lower  part  of  the  shaft  is  bent  backward  somewliat.  Tlio  artieiihir  sur- 
face extends  a  little  liigher  behind  than  in  the  ca.se  of  the  metacarpal  bone.  The  large  metatarsal 
bone  is  even  more  strongly  constructed  tlian  tlie  metacarpal.  The  shell  of  compact  substance  is 
very  thick  in  the  middle  of  the  shaft,  especially  in  front  and  internally. 

The  small  metatarsal  bones  are  a  little  longer  than  the  corresponding  meta- 
carpals. The  external  (fourth)  metatarsal  is  relatively  massive,  especiallj'  in  its 
upper  part.  The  head  is  large  and  outstanding,  and  bears  two  facets  above  for  the 
fourth  tarsal,  and  two  in  front  and  internally  for  articulation  with  the  large  meta- 
tarsal; elsewhere  it  is  roughened  for  attachment.  The  internal  (second)  meta- 
tarsal is  much  more  slender  than  the  outer  one,  especially  in  its  upper  part.  The 
head  bears  two  facets  above  for  the  first  and  second  tarsals,  and  sometimes  one  for 
the  third  tarsal. 


THE  PHALANGES  AND  SESAMOIDS 

The  axis  of  the  phalanges  of  the  hind  limb  is  about  five  degrees  less  oblique 
than  that  of  the  fore  limb,  and  the  chief  differences  in  the  form  and  size  of  the  bones 
arc  as  follows: 

The  first  phalanx  is  a  little  shorter,  wader  above,  and  narrower  below. 

The  second  phalanx  is  narrower  and  slightly  longer. 

The  third  phalanx  is  narrower,  the  angle  of  inclination  of  the  wall  surface  is  a 
little  (ca.  .5  degrees)  greater,  the  sole  surface  is  more  concave,  and  the  wings  are 
less  prominent  and  closer  together. 

The  proximal  sesamoids  are  a  little  smaller,  except  in  thickness.  The  third 
sesamoid  or  navicular  bone  is  narrower  and  shorter. 


112  SKELETON    OF   THE    OX 


SKELETON  OF  THE  OX 


VERTEBRAL  COLUMN 

The  vertebral  formula  is  C'jT|.,lv,,S5C"y,„_,„. 

The  cervical  vertebrae  are  nuich  shorter  than  those  of  the  horse  and  are  smaller 
in  their  other  dimensions.  The  articular  processes  are  smaller  than  in  the  horse, 
and  a  plate  of  bone  connects  each  two  of  the  same  side.  The  transverse  processes 
of  the  third,  fourth,  and  fifth  are  double;  the  upper  part  projects  backward,  and 
is  short  and  stout;  the  lower  part  is  directed  downward  and  forward,  and  is  longer 
and  more  plate-like.  The  lower  part  of  the  sixth  transverse  process  is  a  large, 
thick,  quadrilateral  and  almost  sagittal  plate,  directed  downward.  The  seventh 
transverse  jorocess  is  single,  short,  and  thick,  and  presents  no  foramen  transvcrsa- 
rium;  it  is  in  series  with  the  upper  part  of  the  preceding  processes.  The  spinous 
processes  are  well  developed,  and  increase  in  height  from  before  backward.  They 
are  directed  upward  and  forward,  with  the  exception  of  the  last,  which  is  nearly 
vertical  and  is  about  four  or  five  inches  (ca.  10  to  12  cm.)  in  height.  The  summit  of 
that  of  the  third  bone  i.s  usually  bifid.  The  ventral  spines  are  ])rominent  and  thick 
in  their  posterior  part;  they  are  absent  on  the  last  two. 

The  atlas  has  a  large  rough  tuberosity  on  its  dorsal  arch.  The  ventral  arch 
is  very  thick.  The  wings  are  less  curved  than  in  the  horse,  and  the  foramen  trans- 
versarium  (posterior  foramen)  is  absent.  The  cavities  for  the  occipital  condyles 
are  divided  into  upper  and  lower  parts  by  a  non-articular  area,  and  are  separated 
by  a  narrow  interval  below.  The  posterior  articular  surfaces  are  flattened  behind 
and  are  continued  into  the  vertebral  canal,  funning  an  extensive  area  for  the  odon- 
toid process  of  the  axis. 

The  axis  is  short.  The  spine  projects  a  little  in  front,  and  increases  in  height 
and  thickness  behind;  its  posterior  border  descends  abruptly.  The  odontoid 
process  (dens)  is  wide,  and  its  upper  surface  is  deeply  concave  from  side  to  side. 
The  intervertebral  foramen  is  circular  and  not  so  close  to  the  anterior  border  of  the 
arch  as  in  the  horse.  The  posterior  notches  are  not  so  deep.  The  transverse 
processes  are  stouter,  but  the  foramen  transversarium  is  small  and  sometimes 
absent. 

The  thoracic  vertebrae,  thirteen  in  number,  are  larger  than  those  of  the  horse. 
The  bodies  are  longer  and  are  distinctly  constricted  in  the  middle.  They  bear  a 
thin-edged  ventral  crest.  The  arches — in  aildition  to  the  usual  notches,  which  are 
shallow — are  perforated  in  the  posterior  part  by  a  foramen.  The  transverse 
processes  are  thick  and  strong,  and  bear  rounded  mammillary  processes  (except 
at  the  pDSterior  end  of  the  series) ;  the  last  two,  although  prominent,  do  not  always 
articulate  with  the  ribs.  The  spinous  processes  are  long.  The  first  is  nuich  higher 
than  in  the  horse,  the  next  two  are  usually  the  most  prominent,  and  behind  this 
there  is  a  very  gradual  diminution  in  height.  The  backward  slope,  slight  at  first, 
increases  to  tlie  tenth;  the  last  is  vertical  and  lumbar  in  character.  The  summit 
is  usually  pointed  on  the  first,  and  the  thickening  on  those  further  back  is  less  than 
in  the  horse.  The  width  diminishes  from  the  fifth  to  the  eleventh  usually.  Both 
borders  of  the  spines  are  in  general  thin  and  sharp,  but  the  last  three  or  four  some- 
times have  thick  {wsterior  margins. 

The  lumbar  vertebrae,  six  in  number,  are  much  longer  than  in  the  horse.  The 
bodies  are  nuich  constricted  in  the  middle,  expanded  at  either  end,  and  bear  rudi- 
mentary ventral  crests.  The  fourth  and  fifth  are  usually  the  longest.  The 
intervertebral  foramina  are  often  double  in  the  anterior  part  of  the  series,  and  are 


VERTEBRAL    COLUMN 


113 


114  SKELETON    OF   THE    OX 

very  large  further  hack.  The  articular  processes  are  large,  and  tiieir  facets  are 
more  .strongly  curved  than  in  the  horse.  The  transverse  processes  all  curve 
forwartl.  Tliey  are  separated  by  consideral>le  intervals,  and  form  no  articulations 
wdth  each  other  or  with  the  sacrum.  Their  borders  are  thin  and  irregular,  and  often 
bear  projections  of  variable  .size  and  form.  The  first  is  the  shortest  and  the  length 
increases  to  the  fifth,  the  last  being  considerably  shorter.  The  spinous  processes 
are  relatively  low  and  ^\-ide,  the  last  being  the  smallest:  their  summits  are  moder- 
ately thickened. 

The  sacrum  is  longer  than  tliat  of  the  horse.  It  consists  originally  of  five 
segments,  but  fusion  is  more  eomjilete  anil  involves  the  spinous  processes,  which 
are  united  to  form  a  median  sacral  crest,  with  a  convex  thick  and  rough  margin. 
A  lateral  crest  is  formed  by  the  fusion  of  the  articular  processes.  The  pelvic 
surface  is  concave  in  both  directions,  and  is  marked  \>y  a  central  groove,  which 
indicates  the  course  of  the  middle  sacral  artery.  The  inferior  sacral  foramina  are 
large.  The  wings  are  quadrangular,  short,  compressed  from  before  backward, 
and  high  dorso-ventrally.  They  have  an  extensive  anterior  surface,  which  is 
concave  from  .side  to  side,  and  non-articular.  The  posterior  surface  is  rough,  and 
bears  a  triangular  area  below  for  articulation  with  the  ihum.  The  body  of  the 
first  segment  is  very  wide,  and  the  entraiut'  to  the  sacral  canal  correspondingly 
wide  and  low.  The  anterior  articular  processes  are  large,  and  are  concave  and 
semi-cylindrical  in  curvature  internally.  The  lateral  borders  are  thin,  sharp,  and 
irregular.  The  apex  is  wider  than  in  the  horse,  antl  tlie  po.sterior  end  of  the  crest 
forms  a  j'Xjinted  projection  over  the  opening  of  the  sacral  canal. 

The  coccygeal  vertebras  are  longer  and  better  developed  than  in  the  horse. 
The  first  five  or  six  have  complete  arches  and  spinous  processes.  The  transverse 
processes  are  relatively  large  in  the  anterior  part  of  the  series,  in  which  there  are 
also  anterior  articular  processes  (which  do  not  articulate),  and  a  pair  of  ventral 
spines  which  form  a  haemal  groove  for  the  middle  coccygeal  artery. 

Vertebral  curves:  The  cervical  curve  is  very  slight  and  is  concave  dorsally.  The  thoracic 
and  lumliar  regions  form  a  gentle  curve,  concave  ventrally.  Tlic  promontory  is  more  pronounced 
than  in  tlie  horse,  especially  in  subjects  in  which  the  sacrum  is  inclined  upward  behind.  Another 
promontory  occurs  at  the  junction  of  the  sacnun  and  first  coccygeal  vertebra^. 

Length:  The  following  table  gives  the  lengths  of  the  regions  of  a  shorthorn  cow  of  medium 
size: 

Cervical 47  cm. 

Thoracic 75  cm. 

Lumbar 40  cm. 

Sacral 24  cm. 

Coccygeal 7.5  cm. 

261  cm. 

Variations:  Sometimes  fourteen  thoracic  vertebra;  and  fourteen  pairs  of  ribs  arc  present; 
reduction  to  twelve  with  the  normal  number  of  lumbar  vertebrje  is  very  rare.  According  to 
Franck,  there  are  sometimes  seven  lumbar  vertebra;  with  the  normal  number  in  the  thoracic 
region.     The  number  of  coccygeal  vertebrae  may  vary  from  sixteen  to  twenty-one. 


THE  RIBS 
Thirteen  pairs  of  ribs  arc  normally  present,  of  which  eight  are  sternal  and  five 
asternal.  They  are  in  general  longer,  wider,  flatter,  less  curved,  and  less  regular 
in  form  than  in  the  horse.  The  eighth,  ninth,  and  tenth  are  the  longest  and  widest. 
The  vridth  of  most  of  the  ribs  increases  considerably  in  the  middle,  and  the  breadth 
of  the  intercostal  spaces  is  correspondingly  diminished.  The  neck  is  long,  and  forms 
(except  in  the  posterior  part  of  the  series)  a  smaller  angle  with  the  shaft  than  in  the 
horse.  The  articular  surface  of  the  tubercle  is  concave  transversely,  except  on  the 
last  two  or  three,  where  the  facet  is  small  and  flat  or  absent.  The  lower  ends  of  the 
second  to  the  tenth  or  eleventh  inclusive  form  diarthrodial  joints  with  the  costal 


THE  THOR.\X BONES  OF  THE  SKULL BONES  OF  THE  CRANIUM      115 

cartilages.     The  first  costal  cartilages  are  very  short;    they  articulate  by  tlieir 
internal  surfaces  wnth  the  sternum,  but  not  with  each  other. 

Tlic  pre:seiice  of  a  fourteenth  rib  is  not  very  rare.  It  is  usually  float ing  ami  may  correspond 
to  an  ail<litional  thoracic  vertebra  or  to  the  first  lumbar.  ReiUiction  of  the  thirteenth  is  more 
common.     The  eighth  cartilage  often  does  not  reach  the  sternum,  but  articulates  with  the  seventh. 

Tiie  sternum  consists  of  seven  sternebrsE,  most  of  which  are  developed  from 
two  lateral  centers.  It  is  wider,  flatter,  and  relatively  longer  than  in  the  horse, 
and  the  ventral  crest  or  "keer"  is  absent.  The  manubrium  is  somewhat  wedge- 
shaped  and  laterally  compressed.  Its  base  forms  a  diarthrodial  joint  with  the 
body  of  the  bone,  and  laterally  it  bears  extensive  facets  for  articulation  with  the 
first  pair  of  costal  cartilages.  The  body  widens  from  before  backward,  but  behind 
the  last  pair  of  costal  facets  it  becomes  much  narrower.  The  ventral  surface  is 
prominent  on  the  second  and  third  segments,  concave  further  back.  The  lateral 
borders  are  notched  for  the  passage  of  vessels.  The  cariniform  cartilage  is  absent. 
The  xiphoid  cartilage  is  like  that  of  the  horse  but  is  smaller. 


THE  THORAX 
The  bony  thorax  is  shorter  than  in  the  horse.     The  inlet  is  higher.     The  roof 
is  short,  and  the  floor  mder  and  relativeh'  longer.     The  transverse  diameter  is 
wider  in  the  posterior  part.     The  summits  of  the  spinous  processes  are  almost  in  a 
straight  line  from  the  second  thoracic  to  the  middle  of  the  lumbar  region. 

Bones  of  the  Skull 

Bones  of  the  Cranium 

The  occipital  bone  is  situated  in  the  lower  part  only  of  the  posterior  surface  of 
the  skull,  and  is  separated  from  the  highest  part  (the  frontal  eminence)  by  the 
parietal  and  interparietal  bones.  The  supraoccipital,  interparietals,  and  parietals 
fuse  before  birth  or  soon  after,  and  the  mass  so  formed  is  separated  from  the  lateral 
parts  of  the  occipital  bone  by  a  transverse  suture  in  the  skull  of  the  calf.  Above 
this  suture  is  a  central  tuberosity,  to  which  the  ligamentum  nucha  is  attached,  and 
the  surface  on  either  side  is  depressed  and  rough  for  muscular  attachment.  Below 
the  suture  the  bone  is  much  wider  than  that  of  the  horse.  The  foramen  magnum 
is  wide,  so  that  the  condyles  are  further  apart  except  below.  The  paramastoid 
processes  are  short  and  wide  and  are  bent  inward.  Two  constant  foramina  are 
found  in  the  condyloid  fo.ssa;  the  anterior  one  is  the  hypoglossal,  the  other  (some- 
times double)  conducts  a  vein  from  the  condyloid  canal.  The  latter  passes  upward 
from  a  foramen  on  the  inner  side  of  the  condyle  and  opens  into  the  parieto-temporal 
canal.  The  cranial  surface  of  the  supraoccipital  presents  a  central  depression,  and 
above  this  is  a  variable  but  never  very  pronounced  eminence,  which  corresponds 
to  the  tentorium  osseum  of  the  horse.  On  either  side  is  a  groove  leading  to  the 
parieto-temporal  canal.  The  basilar  process  is  short  and  wide;  its  cranial  surface 
is  deeply  concave,  and  the  internal  spheno-occipital  crest  is  prominent.  Two  large 
tubercles  below  mark  the  junction  with  the  sphenoid.  The  foramen  laccrum  is 
short  and  very  narrow.  In  the  adult  animal  the  bone  is  excavated  to  contain  an 
air-cavit\-  which  is  regarded  as  a  part  of  the  frontal  sinus. 

The  sphenoid  bone  is  short.  The  cranial  surface  of  the  bod>-  presents  a  deep 
sella  turcica,  in  front  of  which  it  rises  abruptly.  The  high  anterior  part  bears  a 
central  ridge  (Rostrum  sphenoidale),  which  joins  the  crista  galli  of  the  ethmoid. 
Two  foramina  occur  on  either  side.  Of  these,  the  large  anterior  one  is  ef|ui\-alent 
to  the  foramen  rotundum,  lacerum  orbitale,  and  patheticum  of  the  horse.  The 
posterior  one  is  the  foramen  ovale,  which  transmits  the  inferior  maxillary  nerve. 


116 


SKELETON    OF   THE    OX 


The  orbital  wing  is  thick  and  is  overlapped  by  the  frontal  in  such  manner  as  to 
appear  externally  to  divide  into  two  branches;  the  anterior  part  joins  the  ethmoid 
dose  to  the  sphenopalatine  foramen,  and  contains  a  small  sinus  which  communi- 
cates with  an  ethmoidal  meatus.  The  temporal  wing  is  small,  but  forms  a  promi- 
nent thick  pterygoid  crest.  The  pterygoiil  process  is  wide,  and  the  pterygoid  or 
alar  foramen  is  absent.     The  sphenoidal  sinus  is  absent  in  the  calf  and  small  in 


SO' 


Fig.  sn. — Skdll  and  .\tlas  of  0,x.  Lateral  View. 
.9.  Zygomatic  arch:  11,  coronoid  process;  IS,  supraorbital  process;  13",  paramastoid  or  styloid  process: 
IS",  occipital  comlyle;  14,  parietal  bone;  IS,  frontal  bone;  16,  squamous  temporal  bone;  17,  external  audi- 
tory meatus;  IS,  temporal  condyle;  19,  orbital  s\irface  of  lacrimal  bone;  £0,  malar  bone;  SI,  facial  surface  of 
lacrimal  bone;  25,  nasal  bone;  5.j,  nasal  process  of  prema.villa;  24',  incisor  teeth;  26,  maxilla;  ^7,  facial  tuber- 
osity; infraorbital  foramen  in  front  of  gT;  I  SS' .  molar  part  of  ramus  of  mandible;  30,  broad  vertical  part  of  ramus; 
SO",  angle  of  jaw;  SI,  condyle  of  mandible;  .ie,  atlas;  j.  wing  of  atlas,  (.\fter  EUenberger-Baum,  .\nat.  fiir 
Kiinstler.) 


the  adult;  it  communicates  by  one  or  two  small  openings  with  an  ethmoidal  meatus, 
and  so  with  the  nasal  cavity. 

The  ethmoid  bone  has  an  extensive  perpendicular  plate.  The  lateral  mass 
consists  of  five  endoturbinals  and  eighteen  ectoturbinals  (Paulli).  The  largest 
ethmoturbinal  is  so  extensive  as  to  be  termed  a  third  or  middle  turbinal  bone;  it 
proj(>cts  forward  between  the  upper  and  lower  turbinals.  The  lamina  papyracea 
appears  to  a  small  extent  externally  in  the  pterygo-palatine  fossa,  forming  jiart 
of  the  upper  margin  of  the  sphenopalatine  foramen. 

The  interparietals  are  primitively  jiaired,  but  unite  before  birth.     As  already 


BONES    OF   THE    CRANIUM 


117 


mentioned,  fusion  occurs  before  or  shortly  after  birth  mth  the  parietais  and  supra- 
occipital.     Xo  tlistinct  tentorium  osseum  is  present. 

The  parietal  bones  do  not  enter  into  the  formation  of  the  roof  of  the  cranium. 
They  constitute  the  upper  part  of  the  posterior  wall,  and  bend  sharply  forward 


Fig.  90. — Skcli.  of  Ox,  Bas.^l  View,  Without  M.^ndible. 
F,  Pterjgoid  bone;  G.  horizontal  and  C,  perpendicular  part  of  palate  bone;  H,  occipital  bone;  J .  malar 
bone;  A',  sphenoid  bone;  O.  ma.xilla;  P,  vomer;  Sch.,  squamous  temporal;  S(.,  frontal  bone;  Z,  preiua.xiUa; 
1,  for.  magnum;  2,  occipital  condyle;  S,  paramastoid  (styloid)  process  of  occipital;  i,  hypoglossal  and  condy- 
loid foramina;  5,  for.  lacerum;  6,  pharyngeal  tubercles;  7,  bulla  ossea;  S,  muscular  process  (left  one  is  removed 
to  expose  for.  ovale);  9,  hyoid  process;  /O,  ext.  auditon,' meatus;  J ;,  zygomatic  process;  /«.  external  opening  of 
parieto-temporal  canal;  IS,  postglenoid  process;  H,  temporal  condyle;  IB,  for.  ovale;  16.  for.  lac.  orbitale  + 
for.  rotundum;  /T,  optic  foramen;  W,  ethmoidal  foramen;  /9.  orbital  opening  of  supraorbital  canal;  £0,  ptery- 
goid crest;  31,  hamulus  of  pterygoid  bone;  22,  lacrimal  bulla;  2i,  temporal  process  of  malar;  2i.  pterjgoid 
process  of  maxilla;  23,  sphenopalatine  foramen;  26,  maxillary  foramen;  27,  posterior  palatine  foramen;  2S, 
anterior  palatine  foramen;  29,  acces.sory  palatine  foramina;  SO,  palate  process  of  maxilla;  SI,  interalveolar 
border;  32,  palatine  cleft;  33,  palate  process  of  premaxilla;  Si,  fissura  incisiva;  So,  facial  tuberosity;  S6,  pos- 
terior nares.     (EUenberger-Baum,  Anat.  d.  Haustiere.) 


along  the  lateral  wall,  forming  part  of  the  wall  of  the  temporal  fossa.  The  line  of 
inflection  is  marked  by  the  prominent  parietal  crest,  which  is  continuous  with  the 
temporal  crest  below.  The  parietais  are  excavated  to  form  part  of  the  frontal 
sinuses  in  the  adult  animal. 


118 


SKELETON    OF   THE    OX 


Tlie  conilition  in  the  youiiK  subject  is  as  follows:  The  two  parietals  are  united  with  each  other 
and  also  with  the  interparietal  and  supraoccipital.  The  resulting  mass  is  somewhat  horseshoe- 
shaped.  Its  occipital  part  (Planum  occipitale)  forms  the  greater  part  of  the  posterior  wall  of 
the  cranium  and  bears  about  its  center  the  tuberosity  lor  the  attachment  of  the  Ugamentum 
nucha".  From  either  side  of  this  a  line  (■ur\-es  outward,  and  divides  the  stn-face  into  an  upper 
smooth  area  and  a  lower  area  which  is  rough  for  muscular  attachment.  The  upper  border  joins 
the  frontal  bone  and  concurs  in  the  formation  of  the  frontal  eminence.  The  temporal  parts 
(Plana  temporalia)  are  much  smaller  and  are  concave  externally;  they  join  the  frontal  above  and 
the  squamous  temporal  below. 


Fig.  91. — Skull  of  Ox,  Dorb.^l  Vikw  (with  Mandible). 
12,  Supraorbital  process;    14,  parietal  bone;    16,  frontal  bone;    16,  squamous  temporal  bone;    19,  orbit;  SOt 
malar  bone;    St,  lacrimal  bone;  22,  nasal  bone;   2J,  prema.xilla;    26,  maxilla;    27,  facial  tiibcrusily;    24,  incisor 
teeiii.     U-Vfter  EUenberger-Baum,  Anat.  f.  Kiinstler.) 


The  frontal  bones  are  very  extensive,  forming  about  one-half  of  the  entire 
length  of  the  skull,  and  all  of  the  roof  of  the  cranium.  The  posterior  borders 
form  witii  the  i)arietals  a  large  central  frontal  eminence  (Torus  frontalis),  the 
highest  point  of  the  skull.  At  the  junction  of  tht^  posterior  and  the  lateral  borders 
are  the  processus  comu  or  "horn-cores,"  for  the  support  of  the  horns.  These 
processes  arc  of  elongated  conical  form,  and  vary  greatly  in  size,  length,  curvature, 
and  direction.  The  external  surface  is  rough  and  porous,  marked  by  numerous 
grooves  and  foramina ;  in  the  fresh  state  they  are  covered  by  the  matri.x  of  the  horns. 
The  base  has  a  constriction,  the  neck.     The  interior  is  excavated  to  form  a  number 


BONES    OF    THE    CRANIUM 


119 


of  irregular  intercommunicatiiif!;  spaces,  divided  hy  hony  septa,  and  communicat- 
ing with  tiie  frontal  sinus.  In  the  polled  breeds  these  processes  are  absent,  the 
skull  is  narrower  in  this  region,  and  the  frontal  eminence  more  pronounced.  The 
supraorbital  process  is  situated  about  half-way  between  the  anterior  anil  posterior 
margins;  it  is  short  and  joins  the  frontal  process  of  the  malar  bone.  The  supra- 
orbital foramen  (often  double)  is  situated  about  an  inch  inward  from  the  root  of 
the  process;   it  is  the  external  orifice  of  the  supraorbital  canal  (C'analis  supraorbi- 


Winy  of  alia 


Squamous  temporal  Imne 

Zygomatic  arcti 

Angle  of  jaw 

Malar  bone 


Facial  tuberosity- 
Ramus  of  mandible 


Premaiilla 


Exttriial  auditory 
meatus 


Fic.  92.— .Skv: 
IS.  Basi-occipital;    IS".  p.iramastoi.l  or  styloid  process;    l.i".  occipital  comlyb 
body  of  mandible;    .i/.  condyle  of  mandible;    ,J J,  ventral  tubercle  of  all: 
Kunstler.) 


(.\fter  Ellcnl.erger-Bau 


teeth;    28, 
..  Anat.  fiir 


talis),  which  passes  dowTiward  and  forward  into  the  orbit.  The  foramen  is  in  the 
course  of  the  supraorbital  groove  (Sulcus  supraorbitalis),  which  marks  the  course 
of  the  frontal  vein.  The  anterior  ends  of  the  naso-frontal  parts  form  a  notch  which 
receives  the  nasal  Iwnes,  and  sutural  or  Wormian  bones  are  often  found  at  this 
junction  (naso-frontal  suture).  The  orbital  part  is  extensive;  it  is  perforated 
behind  bv  the  orbital  opening  of  the  supraorbital  canal,  and  below  by  the  ethmoidal 
or  internal  orbital  foramen.  It  does  not  articulate  with  the  palatine,  from  which 
it  is  separated  bv  the  orbital  wing  of  the  sphenoid.     The  temporal  part  is  also  more 


120  SKELETON    OF   THE    OX 

extensive  tlum  in  the  horse.     The  frontal  sinus  is  very  extensive,  being  continued 
into  the  parietals  and  oceipital,  and  the  horn  professes  when  present. 

The  squamous  and  petrous  parts  of  the  temporal  bone  fuse  early— in  fact, 
union  is  nearly  complete  at  birth.  The  squamous  part  is  relatively  small.  Its 
external  surface  is  divided  into  two  parts  by  the  prominent  temporal  crest,  which  is 
continuous  with  the  parietal  crest  above  and  turns  forward  below,  ending  at  a 
tubercle  above  the  external  auditory  meatus.  The  part  behind  the  crest  faces 
backward,  and  is  partly  free,  partly  united  with  the  occipital.  The  area  in  front 
of  the  crest  is  concave  and  enters  into  tlie  formation  of  the  temporal  fossa;  it  is 
perforated  by  foramina  which  communicate  with  the  parieto-temporal  canal. 
The  zygomatic  process  is  much  shorter  and  weaker  than  in  the  horse,  and  articu- 
lates with  the  malar  only.  The  condyle  is  convex  in  both  directions.  The  post- 
glenoid  process  is  less  prominent,  and  behind  it  is  the  chief  external  opening  of  the 
parieto-temporal  canal.  The  internal  surface  is  almost  completely  overlapped  by 
the  parietal  and  sphenoid.  The  petrous  part  proper  is  small,  but  the  tympanic 
part  is  extensive.  The  external  auditory  meatus  is  smaller  than  in  the  horse  and  is 
directed  outward.  From  it  a  plate  projects  dowTiward  and  helps  to  inclose  the 
deep  depression  in  which  the  hyoid  process  is  placed.  Behind  this  plate  is  the  stylo- 
mastoid foramen.  The  muscular  process  is  large  and  often  bifid  at  its  free  end. 
The  bulla  ossea  is  large  and  laterally  compressed.  It  is  separated  from  the  occipi- 
tal bone  by  a  narrow  opening  which  is  equivalent  to  part  of  the  foramen  lacerum 
basis  cranii  of  the  horse.  The  parieto-temporal  canal  is  formed  entirely  in  the 
temporal  bone.  The  facial  canal,  on  the  other  hand,  is  bounded  partly  bj*  the  occi- 
pital bone. 

Bones  of  the  Face 

The  maziUa  is  shorter  but  broader  and  relatively  higher  than  in  the  horse. 
Its  external  surface  bears  instead  of  the  facial  crest  a  rough  facial  tuberosity 
(Tuber  malare),  placed  above  the  third  cheek  tooth;  a  rough  curved  line  often 
extends  from  it  to  the  upper  part  of  the  malar  bone.  The  infraorbital  foramen — 
often  double — is  situated  above  the  first  cheek  tooth.  The  tuber  maxillare  is 
small,  laterally  compressed,  and  usually  bears  a  small  pointed  process  (Processus 
pterygoideus).  The  zygomatic  process  is  very  small.  The  interalveolar  border  is 
concave,  and  there  is  no  alveolus  for  a  canine  tooth.  The  palatine  process  is  wider, 
but  somewhat  shorter  than  in  the  horse.  It  incloses  a  large  air-space,  which  is 
continuous  behind  with  a  like  cavity  in  the  horizontal  part  of  the  palate  bone,  form- 
ing the  palatine  sinus.  This  communicates  externally  (over  the  infraorbital  canal) 
with  the  maxillary  sinus;  in  the  macerated  skull  it  communicates  with  the  nasal 
cavity  by  a  large  oval  opening,  which  is  closetl  by  mucous  membrane  in  the  fresh 
state.  A  median  septum  separates  the  two  palatine  sinuses.  The  alveoli  for  the 
cheek  teeth  increase  in  size  from  liefore  backward.  The  maxillary  sinus  proper  is 
small  and  is  undivided.  The  maxillary  foramen  is  a  narrow  fissure,  deeply  placed 
at  the  inner  side  of  the  lacrimal  bulla.  The  maxilla  takes  no  part  in  the  formation 
of  the  palatine  canal.  Sutural  (or  Wormian)  bones  may  be  found  at  its  junction 
with  the  lacrimal  and  malar  liones. 

The  body  of  the  premaxilla  is  thin  antl  flattened,  and  has  no  alveoli,  since 
the  canine  and  upper  incisor  teeth  are  absent.  A  deep  notch  takes  the  place  of 
the  foramen  incisivum.  The  nasal  process  is  short,  convex  externally,  and  is  not 
closely  attached  to  the  nasal  bone;  the  space  between  the  two  processes  is  greater 
than  in  the  horse.  The  palatine  process  is  narrow  and  is  grooved  on  its  nasal  sur- 
face for  the  septal  cartilage  and  the  vomer.     The  palatine  cleft  is  very  wide. 

The  palatine  bone  is  very  extensive.  The  horizontal  part  forms  one-fourth  or 
more  of  the  iiard  palate.  The  anterior  palatine  foranicii  (i|iens  near  the  junction 
with  the  maxilla,  about  half  an  inch  from  the  meilian  jjalatine  suture  and  crest. 


BONES    OF   THE    FACE 


121 


Accessory  palatine  foramina  are  also  prosent.  The  ])alatiiie  groove  is  usually  not 
very  distinrt.  The  palatine  canal  is  formed  entirely  in  this  part,  and  there  is  no 
articulation  with  the  vomer.  A  rounded  ridge  occurs  on  the  nasal  side  of  the 
median  suture.  The  interior  is  hollow,  forming  part  of  the  palatine  sinus.  The 
perpendicular  part  is  an  extensive,  quadrilateral,  thin  plate,  which  forms  the  pos- 
terior part  of  the  lateral  wall  of  the  nasal  cavity  and  in  part  hounils  the  narrow  pos- 
terior nares.  Its  internal  surface  is  nearly  flat,  and  is  smooth  and  free,  except 
behind,  where  it  is  overlapped  liy  the  pterygoid  bone.  The  external  surface  is 
attached  to  a  small  extent  to  the  pterygoid  process  behind,  and  is  free  elsewhere. 
The  spheno-palatine  foramen  is  a  long  elliptical  opening,  formed  l)y  a  deep  notch  in 
the  upper  edge  of  the  palate  bone  and  completed  by  the  ethmoid  and  sphenoid. 
The  edge  behind  this  foramen  articulates  with  the  orbital  wing  of  the  sphenoid, 
not  the  frontal  as  in  the  horse. 

The  pterygoid  bone  is  wider  than  in  the  horse,  and  forms  the  greater  part  of  the 
lateral  boundary  of  the  posterior  nares.     Its  outer  surface  is  almost  entirely  united 


Fig.  93. — Median  Sectiox  of  Skull  of  Ox,  Without  the  M.\ndible. 
The  mucoiLs  membrane  is  retained.  The  septum  nasi  is  removed,  a,  Superior  meatus:  b,  middle  meatus, 
with  b'  and  b",  its  upper  and  lower  divisions:  c,  inferior  meatus:  d,  superior  turbinal:  e.  superior  turbinal  fold: 
/,  inferior  turbinal;  g,  alar  fold:  h,  inferior  turbinal  fold:  i,  lateral  mass  of  ethmoid  (ethmoturbinals):  i',  large 
ethmoturbinal  or  middle  turbinal:  k.  frontal  sinus;  /,  sphenoidal  sinus;  m,  cranial  cavity:  n.  palatine  sinus; 
o,  nasal  bone;  o',  parietal  cartilage;  p,  palate  process  of  maxilla;  q,  palate  bone  (horizontal  part);  1,  sphenoid 
bone:  3,  3,  inner  and  outer  plates  of  frontal  bone;  4,  4',  outer  and  inner  plates  of  parietal  bone;  6,  o* ,  occipital 
bone:  5",  condyloid  and  hypoglossal  foramina;  6,  paramastoid  or  styloid  process;  6' ,  occipital  condyle;  7, 
petrous  temporal  bone;  7' ,  internal  auditory  meatus:  8,  squamous  temporal  bone;  9,  muscular  process;  10, 
pterygoid  bone  (hamulus),     (.\fter  EUenberger,  in  Leisering's  .\tlas.) 


to  the  palate  bone  and  the  pterygoid  process,  but  a  small  part  is  free  in  the  jiterjgo- 
palatine  fossa.     The  hamulus  is  distinctly  hook-like,  thin,  and  sharp. 

The  nasal  bone  is  little  more  than  half  the  length  of  that  of  the  horse.  It  is 
straight  in  its  length,  but  stronglj'  curved  from  side  to  side.  It  does  not  fuse  later- 
ally with  the  adjacent  bones,  even  in  old  age.  The  posterior  extremity  is  pointed 
and  fits  into  the  notch  between  the  frontal  bones.  The  anterior  end  is  broader, 
and  is  divided  into  two  parts  by  a  deep  notch.  In  old  animals  there  is  a  small 
extension  of  tlie  frontal  sinus  into  this  bone. 

The  lacrimal  bone  is  very  large.  The  extensive  facial  part  is  concave  in  its 
length,  and  bears  no  lacrimal  tubercle.  The  orbital  margin  is  marked  by  several 
notches.  The  orbital  part  forms  below  the  remarkable  lacrimal  bulla;  this  is  a 
large  and  very  thin-walled  protuberance,  which  bulges  backward  into  the  lower 
part  of  the  orbit,  and  contains  an  extension  of  the  maxillary  sinus.  The  lacrimal 
fossa  is  small,  and  is  just  behind  the  orbital  margin. 

The  malar  bone  is  relatively  long.  The  facial  surface  is  extensive;  it  bears  a 
curved  crest  (Crista  facialis)  just  below  the  orbital  margin,  and  below  this  it  is 
concave  from  above  downward.     The  zygomatic  process  divides  into  two  branches; 


122 


SKELETON    OF   THE    OX 


of  these,  the  frontal  process  turns  upward  and  backward  and  joins  the  supraorbital 
process  of  the  frontal  bone;  the  temporal  process  continues  backward,  and  is  over- 
lapped by  the  zygomatic  process  of  the  temporal  bone,  completing  the  zygomatic 
arch. 

The  superior  turbinal  bone  is  less  cril)riform  and  fragile  than  in  the  horse,  and 
is  thickest  in  its  middle,  small  at  either  end.  It  is  attached  to  the  turbinal  crest 
of  the  nasal  bone,  and  curves  ilownward,  outward,  and  upward  to  be  applied  out- 
wardly to  th(>  frontal  and  lacrimal  bones.  It  thus  incloses  a  cavity  which  communi- 
cates with  the  mitldle  meatus  nasi.  (In  the  macerated  skull  it  opens  into  the  frontal 
sinus,  l)ut  this  communication  is  closed  by  mucous  membrane  in  the  fresh  state.) 

The  inferior  turbinal  bone  is  shorter  liut  much  broader  than  in  the  horse.  It 
is  attacihed  to  the  ma.xilla  by  a  basal  lamella  about  an  inch  (ca.  2  to  3  em.)  wide, 
which  slopes  downward  and  inward.  At  the  inner  edge  of  this  it  splits  into  two 
plates  which  are  rolled  in  opposite  directions,  and  inclose  two  separate  cavities, 
subdivided  by  several  septa.     The  upper  one  opens  into  the  middle  meatus,  the 

lower   one    into    the   inferior  meatus 
nasi. 

The  vomer  forms  a  wider  and 
deeper  groove  than  in  the  horse.  Its 
anterior  end  rests  in  a  groove  formed 
by  the  ends  of  the  palatine  processes 
of  the  premaxillte.  The  anterior  third 
of  its  thin  lower  edge  fits  into  the 
nasal  crest  of  the  maxilla;  behind 
this  it  is  free  and  separated  bj'  a 
considera!)le  interval  from  the  nasal 
floor. 

The  two  halves  of  the  mandible 
do  not  fuse  completely  even  in  ad- 
vanced age.  The  symphyseal  sur- 
faces are  extremely  rough  and  are 
marked  by  reciprocal  projections  and 
cavities.  The  body  is  shorter,  wider, 
and  flatter  than  in  the  horse,  and  has 
eight  round  and  relatively  shallow 
alveoli  for  the  lower  incisors.  The 
interalveolar  border  is  long,  curved, 
thin  and  sharj).  There  are  no  alveoli  for  the  canine  teeth,  which  are  absent. 
The  anterior  part  of  the  ramus  constitutes  a  long  narrow  neck.  The  mental 
foramen  is  further  forward  than  in  the  horse,  and  is  in  the  posterior  end 
of  a  fossa.  The  rami  diverge  more,  so  that  the  submaxillary  space  is  wider 
than  in  the  horse.  They  are  also  more  strongly  curved,  and  the  angle  is  more 
pronounced.  The  molar  part  is  not  so  high,  especially  in  its  anterior  part.  Its 
lower  border  is  convex  in  its  length.  Its  upper  border  bears  six  alveoli  for  the 
lower  cheek  teeth;  the  first  is  (luite  small,  and  they  increase  in  size  from  before 
backward.  The  vertical  part  is  much  smaller  than  in  the  horse  and  its  posterior 
border  is  relatively  thin  below,  concave  and  wider  above.  The  mandibular  fora- 
men is  about  in  the  middle  of  its  inner  surface,  and  a  groove  for  the  lingual  nerve 
curves  downward  and  forward  from  it.  The  condyle  projects  inward  further  than 
in  the  horse,  and  is  concave  from  side  to  side.  The  coronoid  jirocess  is  extensive 
and  curves  backwartl. 

The  hyoid  bone  has  a  short  tuberous  lingual  process.  The  middle  cornua 
are  almost  as  larfj;e  as  the  small  cornua.  The  great  cornua  are  narrow,  except 
at    the  ends.      The    ujiper    end    divides    into    two    branches,    which    correspond 


a.  Boil 
cartilage,  c';  d,  sin 
j7.   muscular   aiigli 
Haustiere.) 


.  94.— Htoid  Bone  of  Ox. 
'',  lingual  process:    c,  tli,\Toid  cornu  and 
nail  cornu;  e,  middle  cornu;  /,  great  cornu; 
/.       (Ellenberger-Baum,    Anat.   d 


SKULL    OF    THE    OX    AS    A    WHOLK  123 

to  the  two  angles  of  that  of  the  liorse.     The  thyroid  cornua  do  not  fuse  with 
the  l)odv. 


SKULL  OF  THE  OX  AS  A  WHOLE 

The  skull  of  the  ox  is  more  clearly  ])yraniidal  than  that  of  the  horse,  and  is 
shorter  antl  relatively  wider.  The  cranium  is  quadrangular  and  larger  externally 
than  in  the  horse;  its  large  size  is  due  mainly  to  the  great  extent  of  the  frontal  sinus, 
and  does  not  affect  the  cranial  ca^'it^•,  which  is  smaller  than  in  the  horse. 

The  superior  or  frontal  surface  is  formed  by  the  frontals,  nasals,  and  pre- 
maxillae.  The  frontal  part  is  quadrilateral  and  very  ex-tensive,  the  greatest  width 
being  at  the  orbits.  It  presents  a  central  depression  on  its  anterior  part,  and  on 
either  side  are  the  supraorbital  grooves  and  foramina.  Behind  is  the  median  frontal 
eminence,  and  at  the  lateral  angles  the  "horn-cores"  project  in  horned  cattle.  The 
nasal  part  is  very  short.  The  osseous  nasal  aperture  is  wide.  The  premaxillaj 
do  not  bend  downward  as  in  the  horse;  they  are  relatively  thin  and  weak,  and  are 
separated  by  an  interval  which  has  a  mde  anterior  part  in  place  of  the  foramen 
incisivum. 

The  lateral  surface  is  more  triangular  than  in  tb.e  horse.  Tiie  temporal  fossa 
is  confined  to  this  surface.  It  is  deep  and  narrow,  and  its  boundaries  are  more 
complete.  It  is  limited  above  by  a  crest  which  extends  from  the  postero-extemal 
angle  of  the  frontal  to  the  supraorbital  process,  and  is  analogous  to  the  sagittal 
crest  of  the  horse.  Behind  it  is  bounded  by  the  temporal  crest.  It  is  clearly 
marked  off  from  the  orbit  by  the  rounded  posterior  orbital  ridge  and  the  pterygoid 
crest.  The  zygomatic  process  is  short,  weak,  and  flattened,  and  is  formed  by  the 
temporal  and  malar  only.  Its  condyle  is  convex  and  is  ^\•ide  from  before  backward. 
The  glenoid  ca\'ity  and  postglenoid  process  are  small.  The  orbit  is  encroached 
upon  below  by  the  lacrimal  bulla,  and  presents  the  orifice  of  the  supraorbital  canal 
behind.  The  margin  is  completed  behind  by  the  frontal  process  of  the  malar;  its 
lower  part  is  prominent  and  rough,  not  smooth  and  rounded  as  in  the  horse.  The 
pterygo-palatine  fossa  is  much  larger,  deeper,  and  more  clearly  defined.  It  has  a 
long  narrow  forward  extension  (maxillary  hiatus)  between  the  vertical  plate  of 
the  palate  bone  internally  and  the  maxilla  and  lacrimal  bulla  externally;  thus  the 
sphenopalatine  and  maxillary  foramina  are  deeply  placed.  The  preorbital  region 
is  short  but  relatively  high.  A  tuberosity-  and  curved  line  take  the  place  of  the 
facial  crest.  The  infraorbital  foramen  is  situated  above  the  first  cheek  tooth  and  is 
often  double. 

The  basal  siuface  is  short  and  wide,  especially  in  its  cranial  part.  The  occipi- 
tal condyles  are  limited  in  front  by  transverse  ridges.  The  tubercles  at  the  junc- 
tion of  the  occipital  and  sphenoid  are  large.  The  condyloid  fossa;  contain  two 
foramina,  the  hypoglossal  below  and  in  front,  and  the  condyloid  above  and  behind; 
other  inconstant  ones  occur.  The  paramastoid  processes  are  short  and  convergent. 
The  foramen  lacerum  is  slit-like.  The  bulla  ossea  is  a  large,  laterally  compres.sed 
prominence.  The  muscular  processes  are  usually  long  and  narrow  triangular  plates, 
with  one  or  two  sharp  points.  The  ex-ternal  auditory  process  is  directed  almost 
straight  outward.  A  curved  plate  extends  do^\•nward  from  it  and  joins  the  bulla 
ossea  internally,  completing  the  deep  cavity  which  receives  the  articular  angle  of 
the  hyoid  bone.  The  chief  external  opening  of  the  temporal  canal  is  in  front  of 
this  plate,  and  an  accessory  one  lies  behind  it.  The  infratemporal  fossa  is  small, 
and  presents  the  foramen  ovale.  The  posterior  nares  are  very  narrow,  and  the 
vomer  does  not  reach  to  the  level  of  their  margin.  The  hard  palate  is  wide,  and 
forms  about  three-fifths  of  the  entire  length  of  the  skull.  A  small  central  part 
only  of  its  posterior  border  enters  into  the  formation  of  the  posterior  nares;  the 
lateral  parts  are  notched  and  just  above  them  are  the  posterior  palatine  f(,r.nniiia. 


124 


SKELETON'    OF   THE    OX 


Tlie  anterior  i)alatine  I'uruiniiui  arc  an  incli  or  moro  from  tho  posterior  margin, 
and  about  the  same  distance  apart.  The  palatine  grooves  are  tlistinct  for  a  short 
distance  only.  Just  beyond  the  cheek  teeth  the  palate  narrows  and  becomes  con- 
cave;  beyond  this  it  widens  and  flattens. 

The  posterior  or  nuchal  surface  is  extensive  and  somewhat  pentagonal  in 
outline  in  the  adult.  About  its  center  is  the  eminence  for  the  attachment  of  the 
ligamentum  nucha^.  P>om  this  a  median  crest  extends  toward  the  foramen  mag- 
num, and  laterally  two  lines  (Linete  nucha;  superiores)  curve  outward,  marking  the 
upper  limit  of  the  area  which  is  roughened  for  muscular  attachment.  The  surface 
above  the  lines  is  relatively  smooth,  and  is  covered  only  by  the  skin  and  the  thin 
auricular  muscles  in  the  living  animal.  It  is  separated  from  the  cranial  roof  by  a 
thick  border,  which  forms  centrally  the  frontal  eminence,  and  bears  at  its  extremi- 


Fio.  93. — Cnoss-SKCTiON  of  Skoll  of  Ox.     Sfption        Fin.  96. — Cross-section  of  Skull  of  Ox.    Section 
Passes  Through  Fifth  Cheek  Tooth.  Passes  through  Second  Cheek  Tooth. 

a,  b,  c,  Superior,  middle,  inferior  meatus:  h' ,  communication  between  middle  meatus  and  cavity  of  upper 
part  of  inferior  turbinal;  c',  communication  between  inferior  meatus  and  lower  part  of  inferior  turbinal;  d,  cavity 
of  superior  turbinal;  c,  /,  outer  and  inner  walls  of  d:  «,  h,  upper  and  lower  cavities  of  inferior  turbinal  bone;  i, 
basal  lamella  of  inferior  turbinal;  i',  i" ,  upper  and  lower  divisions  of  inferior  turbinal  bone;  k,  floor  of  nasal  cav- 
il, maxillary  sinus;  p,  palatine  sinus;  q,  septum  between  ma.xillary  anil  palatine  sinuses; 
,  septum  between  palatine  sinuses;  (,  common  meatus;  «,  na.so-lacrimal  canal;  v,  floor  of 
of  palatine  sinus;  /,  septum  na.si;  2,  posterior  part  of  second  cheek  tooth;  S,  posterior 
i;  .;,  Iiard  palate,      (.\fter  Ellenberger,  in  Leisering's  .A.tlas.) 


ity;  m,  lacrimal  sin 
r,  infraorbital  canal 
nasal  cavity  and  ro 
part  of  fifth  cheek  to 


ties  the  processus  cornu — except  in  the  polled  breeds.  The  condyles  ar(<  further 
apart,  and  the  articular  surfaces  are  more  clearly  dividetl  into  upper  aiul  U)wer  parts 
than  in  the  horse. 

The  cranial  cavity  is  shorter  and  its  long  axis  is  more  oblique  than  in  the  horse, 
but  it  is  relatively  high  and  wide.  The  anterior  fossa  lies  at  a  much  higher  level 
than  the  rest  of  the  floor.  The  olfactory  fossce  are  smaller,  and  the  sella  turcica  is 
nmch  deeper  than  in  the  horse.  A  deep  groove  leads  from  the  petrous  temporal 
forward  over  the  foramen  ovale  to  the  foramen  rotundum.  Behind  the  sella  there 
is  often  a  distinct  prominence  (Dorsum  sellse).  The  internal  sagittal  crest  is  promi- 
nent anteriorly,  but  absent  further  back.  A  faintly  marked  elevation  takes  the 
place  of  the  tentorium  osseum.  The  small  petrous  temporal  bone  projects  into 
the  cavity  laterally.  The  ridges  and  digital  inijiressions  are  very  pronounced. 
The  parieto-temjK)ral  canal  is  formed  entirely  in  tlie  temjioral  bone,  and  opens  at 


SKULL    OF   THE    OX   AS   A    WHOLE 


125 


the  apex  of  the  petrous,  where  it  is  joined  hy  the  condyloid  canah     The  foramen 
lacerum  is  (Hvided  into  two  parts  (For.  lacerum  anterius  et  posterius). 

Tiie  nasal  cavity  is  inconii)Ietely  divided  by  the  septum,  which  does  not  reacli 
the  floor  posteriorly.  The  floor  is  relatively  long,  and  is  more  concave  from  side  to 
side  than  in  the  horse.  In  the  ilry  skull  it  has  a  large  oval  opening  into  the  palatine 
sinus,  which  is  closed  during  life  hy  mucous  membrane.  The  middle  meatus  is 
divided  behind  into  u]iper  and  lower  branches  by  the  great  ethmoturbinal.  The 
posterior  nares  are  narrow  and  oblique. 


Fig.  97.— Skii  ,  .r.  ~  '  i  ■  ,,  ,i  Vn.w. 
The  outer  plate  of  bone  has  been  removed  to  show  the  sinu.ses.  a.  Frontal  sinus;  a',  cranial  plate  of 
frontal  bone  ;  o",  anterior  part  of  frontal  sinus,  which  is  separated  from  remainder  by  a  septum  (W;  c,  e', 
communications  between  frontal  sinus  and  nasal  cavity;  d,  supraorbital  foramen;  e,  supraorbital  canal;  /,  cavity 
of  superior  turbinal  bone,  and  g,  its  opening  into  the  nasal  cavity;  h,  lacrimal  sinus,  i',  its  communication 
with  the  maxillary  sinus;  k,  maxillary  sinus:  /,  orbit;  /,  frontal  bone;  1' ,  processus  cornu;  ^.  nasal  bone;  S, 
premaxilla  (nasal  process);  .i,  maxiila:  .5.  lacrimal  bone:  ff,  malar  bone;  7,  dotted  line  indicating  course  of  naso- 
lacrimal duct.     (After  EUenberger,  in  Leisering's  .\tlas.) 


The  frontal  sinus  is  very  large.  It  involves  almost  all  of  the  frontal  bone  and 
a  large  part  of  the  posterior  wall  of  the  cranium.  It  also  extends  for  a  variable  dis- 
tance into  the  horn  processes  when  these  are  present.  A  complete  median  septum 
separates  the  right  and  left  sinuses.  The  anterior  limit  is  indicated  by  a  transverse 
plane  through  the  middle  of  the  orbits.  It  extends  externally  to  the  crest  which 
hmits  the  temporal  fossa  aliove,  and  into  the  root  of  the  supraorbital  process.  At 
the  highest  part  of  the  cranial  cavity  and  at  the  tuberosity  on  the  posterior  surface 


126 


SKELETON    OF   THE    OX 


the  two  plates  of  the  bone  come  together.  The  cavity  is  very  irregular  and  is  sub- 
divided into  numerous  spaces  by  ridges  and  partial  septa.  This  multilocular 
character  is  most  marked  in  the  anterior  part,  and  here  several  small  spaces  appear 
to  be  cut  off  from  the  main  cavity  (Baum).  The  supraorbital  canal  passes  through 
the  sinus.  Several  small  openings  lead  from  the  sinus  to  the  ethmoidal  meatuses, 
and  thus  indirectly  to  the  upper  division  of  the  middle  meatus  nasi.  The  communi- 
cations with  the  cavity  of  the  superior  turbinal  and  with  the  lacrimal  part  of  the 
maxillary  sinus  which  are  seen  in  the  macerated  skull  are  closed  in  the  fresh  state 
by  nuicous  memlirane. 

The  maxillary  sinus  is  excavated  chiefly  in  the  maxilla,  lacrimal,  and  malar, 
and  is  not  divitled  by  a  septum  as  in  the  horse.  It  extends  forward  as  far  as  the 
facial  tuberosity,  or  a  little  further  in  old  animals.  Its  upper  limit  is  indicated 
approximately  by  a  line  drawn  from  the  infraorbital  foramen  to  the  u])per  margin  of 
the  orbit.  It  is  continued  directly  backward  into  the  lacrimal  bulla  to  a  point 
nearly  opposite  to  the  bifurcation  of  the  zygomatic  process  of  the  malar.  It  also 
extends  upward  and  backward  through  a  large  opening  into  a  cavity  formed  by  the 


Fig.  9S. — Skull  of  Ox,  Lateral  View  withott  ^lANniBLE. 
The  maxillary,  lacrimal,  and  turbiual  sinuses  have  been  opened,  and  a  ijortion  of  the  orbit  removed,  a. 
Cavity  of  superior  turbinal  bone;  6,  lacrimal  sinus;  c,  maxillary  sinus;  d,  communication  between  ma,\illary  and 
palatine  sinuses;  e,  opening  between  maxillary  and  lacrimal  sinuses;  /,  thin  osseous  bulla;  f/,  lacrimal  bulla; 
It,  orbit;  1-6,  cheek  teeth;  7,  nasal  bone;  S,  premaxilla  (nasal  process):  9,  maxilla;  9',  infraorbital  foramen; 
10,  frontal  bone;  11,  lacrimal  bone;  IS,  malar  bone;  13,  fissure  between  nasal  bone  and  maxilla;  14,  temporal 
bone  (squamous);  15,  external  auditory  meatus;  16,  styloid  or  paramastoid  process;  17,  occipital  condyle; 
18,  palate  bone  (perjjendicular  i)art);  19,  pterygoid  bone  (hamulus);  BO,  tympanic  part  of  temporal;  £0' ,  mus- 
cular i)roce99  of  i>etri>us  teinjioral.     (After  EUenberger,  in  Leisering's  Atlas.) 


lacrimal,  frontal,  ethmoid,  and  turbinal  bones,  at  the  inner  side  of  the  orbit.' 
The  floor  of  the  cavity  is  irregular  and  the  roots  of  the  last  three  or  four  cheek 
teeth  pro,ject  up  into  it,  covered  by  a  plate  of  bone.  The  sinus  communicates  with 
the  jialatine  sinus  freely  over  the  infraorbital  canal  through  an  oval  oj^ening  about 
two  to  three  inches  (ca.  5  to  7.5  cm.)  long.  Above  this  it  communicates  by  a 
.shorter  and  much  narrower  opening  with  the  middle  meatus  nasi. 

The  palatine  sinus  is  excavated  in  the  hard  palate,  and  is  separated  from  that 
of  the  opjiosite  side  by  a  median  septum.  It  extends  from  the  posterior  border  of 
the  palate  to  a  plane  an  inch  or  more  (2. .5  to  3  cm.)  in  front  of  the  first  cheek  tooth. 
As  mentioned  above,  there  is  a  large  communication  with  the  maxillary  sinus  over 
the  infraorbital  canal, so  that  thecavity  is  sometimes  regarded  as  a  partof  that  sinus. 
The  large  defect  in  the  bony  roof  of  the  sinus  is  closed  by  two  layers  of  nmcous 
membrane  in  the  fresh  state.  The  palatine  canal  passes  oblicnidy  through  the 
posterior  part  of  the  sinus. 

'  This  is  termed  the  lacrimal  sinus  by  some  authors.  It  is  similar  in  location  and  in  the  posi- 
tion of  i(s  orifice  to  the  turliinal  part  of  the  frontal  sinus  of  the  horse,  with  the  important  difference 
that  it  iloos  not  cominimicate  with  the  frontal  shui.ses  in  the  o.\. 


BONES    OF   THE    THORACIC    LIMB  127 

The  sphenoidal  sinus  is  almost  entirely  in  the  sjjhenuid  bone  and  does  not 
communicate  with  the  palatine  and  maxillary  sinus.  It  has  one  or  two  openings 
into  the  ventral  ethmoidal  meatuses.  There  is  no  cavity  in  the  perpendicular  part 
of  the  palate  bone. 

There  are  several  small  air-cavities  between  the  lateral  mass  of  the  ethmoid 
and  the  anterior  part  of  the  frontal  sinus,  which  communicate  separately  with 
ethmoidal  meatuses. 


BONES  OF  THE  THORACIC  LIMB 

The  scapula  is  more  regularly  triangular  than  in  the  horse,  relatively  wider  at 
the  verteliral  end  and  narrower  at  the  lower  end.  The  scapular  index  is  about 
1  :  0.6.  The  spine  is  more  prominent  and  is  placed  further  forward,  so  that  the 
supraspinous  fossa  is  narrow  and  does  not  extend  to  the  lower  part  of  the  bone. 
The  spine  is  sinuous,  bent  backward  in  its  middle,  forward  Ijelow.  Its  free  border 
is  somewhat  tliickened  in  its  middle,  but  bears  no  distinct  tubercle.  Instead  of 
subsiding  below  as  in  the  horse  the  spine  becomes  a  little  more  prominent,  and  is 
prolonged  by  a  pointed  projection,  the  acromion,  from  which  part  of  the  deltoid 
muscle  arises.  The  subscapular  fossa  is  shallow.  The  areas  for  the  attachment 
of  the  serratus  muscle  are  not  very  distinct.  The  nutrient  foramen  is  usually  in 
the  lower  third  of  the  posterior  border.  The  glenoid  cavity  is  almost  circular  and 
without  any  distinct  notch.  The  tuberosity  is  small  and  close  to  the  glenoid 
cavity.  The  coracoid  process  is  short  and  rounded.  The  cartilage  resembles 
that  of  the  horse. 

The  humerus  has  a  shallow  musculo-spiral  groove.  The  deltoid  tuberosity 
is  less  prominent  than  in  the  horse,  and  the  curved  line  running  from  it  to  the  neck 
bears  a  well-marked  tubercle  on  its  upper  part.  The  nutrient  foramen  is  usually 
in  the  lower  third  of  the  posterior  surface.  The  external  tuberosity  is  very  large, 
and  rises  an  inch  or  more  (ca.  3  cm.)  above  the  level  of  the  head.  Its  anterior  part 
curves  inward  over  the  bicipital  groove,  and  below  it  externally  there  is  a  promi- 
nent circular  rough  area  for  the  insertion  of  the  tendon  of  the  supraspinatus.  The 
anterior  part  of  the  internal  tuberosity  has  a  small  projection  which  curves  over 
the  groove.  The  groove  is  undivided.  The  distal  articular  surface  is  decidedly 
oblique,  and  the  grooves  and  ridge  are  very  well  marked.  The  coronoid  and 
olecranon  fossae  are  deep  and  wnde.  The  external  condyloid  crest  is  represented  b_y 
a  rough  raised  area.  The  proximal  end  unites  with  the  shaft  at  three  and  one-half 
to  four  years,  and  the  distal  at  about  one  and  one-half  years. 

The  radius  is  short  and  relatively  broad.  It  is  somewhat  oblique,  the  lower 
end  being  nearer  the  median  plane  than  the  upper.  The  curvature  is  more  pro- 
nounced below  than  above.  The  shaft  is  prismatic  in  its  middle  part  and  has 
anterior,  external,  and  posterior  faces.  There  is  a  marked  increase  in  width  and 
thickness  below.  The  proximal  articular  surface  presents  a  synovial  fossa  which 
extends  inward  from  the  deep  groove  between  the  two  glenoid  cavities.  The 
bicipital  tuberosity  is  represented  by  a  slightly  elevated  rough  area.  The  posterior 
facets  for  the  ulna  are  larger  than  in  the  horse.  The  two  bones  commonly  fuse 
above  the  proximal  interosseous  space  and  always  fuse  below  it,  except  near  the 
distal  end,  where  there  is  a  small  distal  interosseous  space.  A  groove  connects 
the  two  spaces  externally.  The  distal  extremity  is  large,  and  is  thickest  internally. 
Its  articular  surface  is  oblique  in  two  directions,  i.  e.,  from  within  upward  and 
backward.  The  grooves  for  the  extensor  tendons  are  shallow.  The  proximal  end 
unites  with  the  shaft  at  one  to  one  and  one-half  years,  and  the  distal  at  three  and 
one-half  to  four  years. 

The  approximation  of  the  lower  ends  of  the  forearms  and  the  carpi  gives  the  "knock-kneed" 
appearance  in  cattle.     The  obliquity  of  the  joint  surfaces  produces  lateral  deviation  of  the  lower 


128 


SKELETON    OF   THE    OX 


part  of  the  limb  in  flexion.  The  facets  for  the  radial  and  intermediate  carpals  are  narrower  than 
in  tlie  horse  and  run  obliquely  forward  and  outward.  The  surface  for  the  ulnar  carpal  is  extensive 
and  saddle-shaped;   its  outer  part  is  furnished  by  the  ulna. 

The  ulna  is  more  fully  developed  than  in  the  horse.     The  shaft  is  complete, 


Bicipilal  groove 


External  tnberosily  of  humerus 


Deltoid  tuberosity 

Musculo-si)iral  groove 
ExteriKit  eoiidijloiil  crest 


_  •_    y-  HxleriKU  eoiu 


Exlcnial  tuberosity  of  radius 


Shaft  of  radium 


Radial  carpal  bone . 
Fused  second  and  third  carpal  bones . 


Ulnar  carpal  bone 
.  Intermediate  carpal  bone 
Fourth  carpal  bone 
Metacarixd  tuberosity 

Anterior  groove  of  large  metacarpal  bone 


First  phalanx 


-  Second  phalanx 

■  Third  pludjinx 

Fig.  99. — Skelkton  of  Lkft  Fore  Limb  of  Ox,  from  SnorLDKn  Downward,  Anterior  \'iew.     (After  Ellen- 
herger-Baum,  .\nat.  fiir  Kvinstler.) 

throe-sided,  and  strongly  curved.  It  is  fused  with  the  radius  in  the  adult,  excejit 
at  the  two  interosseous  spaces  mentioned  above.  Its  upper  part  contains  a  medul- 
lary canal  which  extends  somewhat  into  the  proximal  end.  The  olecranon  is 
large  and  bears  a  rounded  tuberositv  above.     The  distal  end  is  fused  with  the 


BONES    OF   THE   THORACIC    LIMB 


129 


radius;  it  projects  belowthe  level  of  the  latter, formingthe  styloid  process  (Processus 
styloideus  ulnse),  which  furnishes  part  of  the  facet  for  the  ulnar  carpal.  The  proxi- 
mal and  distal  ends  unite  with  the  shaft  at  three  and  one-half  to  four  years. 

The  carpus  consists  of  six  bones,  four  in  the  upper  row,  and  two  in  the  lower. 
The  upper  row  is  oblique  in  conformity  with  the  carpal  articular  surface  of  the 
radius.     The  ratlial  and  intermediate  resemble  in  general  those  of  the  horse,  but 


External  condyle  of  humerus 
External  tuberosity  of  radius 


Proximal  interosseous  space 
Shaft  of  ulna 


Distal  end  of  radius  - 

Intermediate  carpal  bone 

Radial  carpal  bone 

Fused  second  and  third  carpal  bones 

Metacarpal  tuberosity 


> 


-  Distal  interrosseous  space 
Sliihiid  jtrocess  of  ulna 
Accessory  carpal  bans 

.  Ulnar  carpal  hone 
.  Fourth  carp(d  bone 
.  Small  metacarpal  bone 


Large  metacarpal  bone 


Proximal  sesamoid 


■  First  phalanx 


Pig.  100.— Skel 


-  Second  phalanx 

■  Distal  scsa7nmd 

Third  phalanx 

Fore  Limb  of  Ox.  from  Elbow  Downward,  External  Vi 
lierger-Baum,  .\nat.  fur  Kunstler.) 


are  less  regular  in  shape,  and  their  long  axes  are  directed  obliquely  backward  and 
inward.  The  radial  is  narrower  tlian  in  the  horse  and  curves  upward  hehinrt.  i  no 
intermediate  is  constricted  in  its  middle,  and  wider  behind  than  in  front,  ine 
ulnar  is  large  and  verv  irregular.  Its  proximal  surface  is  extensive  and  sinuous  ana 
articulates  with  both  radius  and  ulna.  Behind  is  a  large  oval  facet  for  ;"-t>;"la  'OT 
with  the  accessory  carpal.  The  accessory  is  short,  thick,  and  rounded;  it  articu- 
9 


130  SKELETON    OF   THE    OX 

latos  with  the  uhiar  carpal  only.  The  first  carpal  is  absent.  The  second  and  third 
carpals  arc  fused  to  form  a  large  quadrilateral  bone.  The  fourth  carpal  is  a  smaller 
quadrilateral  bone. 

The  metacarpus  consists  of  a  large  metacarpal  and  an  external  small  meta- 
carpal bone.  The  large  metacarpal  bone  (JNIc.  3  +  4)  results  from  the  fusion  of  the 
third  and  fourth  bones  of  the  foetus,  and  bears  evidences  of  its  double  origin  even 
in  the  adult  state.  The  shaft  is  shorter  than  in  the  horse,  and  is  relatively  wider  and 
flatter.  The  anterior  surface  is  rounded,  and  is  marked  by  a  vertical  vascular 
groove  connecting  two  canals  which  traverse  the  ends  of  the  shaft  from  before 
backward.  The  iwsterior  surface  is  flat  and  presents  a  similar  but  much  fainter 
groove.  The  borders  are  rough  in  the  ujiper  third.  The  proximal  end  bears  two 
slightly  concave  facets  for  articulation  with  the  bones  of  the  lower  row  of  the  car- 
pus; the  inner  area  is  the  Lirger,  and  they  are  separated  by  a  ridge  in  front  and  a 
notch  behind.  The  outer  angle  has  a  facet  behind  for  the  small  metacarpal  bone. 
The  inner  ]iart  of  the  extremity  has  anterior  and  posterior  tuberosities.  The  distal 
end  is  divided  into  two  parts  by  a  sagittal  notch.  Each  division  bears  an  articular 
surface  similar  to  that  in  the  hors(>,  but  nuich  smaller.  The  medullary  canal  is 
divided  into  two  parts  by  a  vertical  septum  which  is  usually  incomplete  in  the  adult. 

The  small  metacarpal  bone  (^Ic.  5)  is  a  rounded  rod  about  an  inch  and  a 
half  (ca.  3.5  to  4  cm.)  in  length,  which  lies  against  the  upper  part  of  the  outer  border 
of  the  large  bone.  Its  upper  end  articulates  with  the  latter,  but  not  with  the  carpus. 
The  lower  end  is  pointed. 

Four  cartilaginous  metacarpals  are  present  in  the  early  foetal  state,  viz.,  the  second,  third, 
fourth,  and  tiftli.  The  second  commonly  either  disappears  or  unites  with  the  third;  sometimes 
it  develops  as  a  small  rod  of  bone.  The  third  and  fourth  gradually  unite,  but  can  be  cut  apart 
at  birth.  Each  has  three  centers  of  ossification;  the  proximal  epiphysis  fuses  with  the  shaft 
before  birth,  the  distal  at  two  to  two  and  one-half  years 

Four  digits  are  present  in  the  ox.  Of  these,  two — the  third  and  fourth — are 
fully  develojied  and  liave  three  phalanges  and  three  sesamoids  each.  The  second 
and  fifth  are  vestiges  and  are  placed  behind  the  fetlock;  each  contains  one  or  two 
small  bones  which  do  not  articulate  with  the  rest  of  the  skeleton. 

The  first  phalanges  are  shorter  and  narrower  than  in  the  horse  and  are  three- 
sided.  The  intcrdigital  surface  is  flattened  and  its  posterior  part  bears  a  promi- 
nence for  the  attachment  of  the  intcrdigital  ligaments.  The  proximal  extremity  is 
relatively  large,  and  is  somewhat  compressed  from  side  to  side.  The  articular 
surface  is  concave  from  before  backward  and  is  divided  by  a  sagittal  groove  into 
two  areas,  of  which  the  abaxial  one  is  the  larger  and  higher.  Behind  these  are 
two  facets  for  articulation  with  the  sesamoid  bones.  The  posterior  surface  bears 
two  tuberosities  separated  by  a  deep  depression.  The  distal  extremity  is  smaller 
than  the  proximal,  especially  in  the  antero-posterior  direction.  Its  articular 
surface  is  divided  by  s.  sagittal  groove  into  two  convex  facets,  of  which  the  abaxial 
one  is  decidedly  the  larger.  There  are  depressions  on  either  side  for  ligamentous 
attachment.  The  bone  consists  at  birth  of  two  pieces — the  distal  end  and  the  fused 
shaft  and  upper  extremity.     Union  occurs  at  one  and  one-half  to  two  years. 

The  second  phalanges  are  about  two-thirds  of  the  length  of  the  first  and  are 
distinctly  tlircr-sidcd.  The  proximal  articular  surface  is  divided  by  a  sagittal 
ridge  into  two  glenoid  cavities,  of  which  the  abaxial  one  is  much  the  larger.  There 
is  a  central  prominence  in  front  and  two  lateral  tuliercles  behind.  The  distal  ex- 
tremity is  smaller  than  the  proximal.  Its  articular  surface  encroaches  consider- 
ably on  the  anterior  and  posterior  surfaces,  and  is  divided  into  two  lateral  parts  by 
a  groove.  There  is  a  deep  depression  for  ligamentous  attachment  on  the  inter- 
digital  side.  The  bone  contains  a  small  medullary  canal.  The  distal  end  unites 
with  the  rest  of  the  bone  about  the  middle  of  the  second  year. 

The  third  phalanges  resemble  in  a  general  way  one-half  of  the  bone  of  the  horse. 


BONES    OF   THE    PELVIC   LIMB  131 

Each  has  four  surfaces.  The  dorsal  or  wall  surface  is  marked  in  its  lower  part  V)y  a 
shallow  groove,  along  which  there  are  several  foramina  of  considerable  size;  tlie 
posterior  one  of  the  series  is  the  largest,  and  conducts  to  a  canal  in  the  interior  of 
the  bone.  Below  the  groove  the  surface  is  prominent,  rough,  and  porous.  Near 
and  on  the  extensor  process  are  several  relatively  large  foramina.  The  slope  of  the 
surface  is  very  steep  posteriorly,  but  in  front  it  forms  an  angle  of  25  to  30  degrees 
with  the  ground  plane.  The  articular  surface  is  narrow  from  side  to  side,  and 
slopes  downward  and  backward.  It  is  also  oblicjue  transversely,  the  interdigital 
side  being  the  lower.  It  is  adapted  to  the  distal  surface  of  the  second  phalanx,  with 
the  exception  of  a  facet  behind  for  the  distal  sesamoid.  The  extensor  process  is 
very  rough.  The  volar  or  sole  surface  is  narrow  and  slightly  concave,  and  presents 
two  or  three  foramina  of  considerable  size.  It  is  separated  from  the  wall  surface 
by  a  border  which  is  sharp  in  front,  rounded  behind.  There  is  no  semilunar  crest, 
since  the  deep  flexor  tendon  is  attached  to  the  thick  posterior  border  of  the  sole 
surface.  The  interdigital  surface  is  smooth  and  grooved  below,  rough  and  porous 
above.  At  the  upper  angle  it  is  perforated  by  a  large  foramen,  which  is  equivalent 
to  the  volar  foramen  of  the  horse  and  leads  to  a  cavity  in  the  middle  of  the  bone. 
The  surface  is  separated  by  a  rounded  border  from  the  wall  surface,  and  by  a  sharp 
edge  from  the  sole  surface.  The  wing  or  angle  is  very  short  and  l)lunt,  and  there 
is  no  lateral  cartilage. 

Four  proximal  sesamoids  are  present,  two  for  each  digit.  They  are  much 
smaller  than  in  the  horse.  The  bones  of  each  pair  articulate  with  the  correspond- 
ing part  of  the  distal  end  of  the  large  metacarpal  bone  by  their  anterior  surfaces, 
Vvith  each  other  and  with  the  first  phalanx  by  small  facets. 

The  two  distal  sesamoids  are  short  and  their  ends  are  but  little  narrower  than 
the  middle. 

BONES  OF  THE  PELVIC  LIMB 

The  ilia  are  almost  parallel  to  each  other  and  are  also  less  olslique  with  regard 
to  the  horizontal  plane  than  in  the  horse.  They  are  relatively  small.  The  gluteal 
line  is  prominent  and  is  nearly  parallel  to  the  external  border;  it  joins  the  superior 
ischiatic  spine.  A  rounded  ridge  separates  the  two  parts  of  the  ventral  surface. 
The  surface  for  articulation  with  the  sacrum  is  triangular.  The  internal  angle  is 
truncated,  does  not  extend  as  high  as  the  vertebral  spines,  and  is  separated  from 
the  opposite  angle  by  a  wider  interval  than  in  the  horse.  The  external  angle  is 
relatively  large  and  prominent ;  it  is  not  so  oblique  as  in  the  horse,  and  is  wide  in 
the  middle,  smaller  at  either  end.  The  shaft  is  short  and  compressed  from  side 
to  side. 

The  ischium  is  large.  Its  long  axis  is  directed  obliquely  upward  and  back- 
ward, forming  an  angle  of  about  45  to  50  degrees  with  the  horizontal  plane.  The 
transverse  axis  is  oblique  downward  and  inward  at  a  similar  angle,  so  that  this 
part  of  the  pelvic  floor  is  deeply  concave  from  side  to  side.  The  middle  of  the 
ventral  surface  bears  a  rough  ridge  or  imprint  for  muscular  attachment.  Tlie 
superior  ischiatic  spine  is  high  and  thin,  and  bears  a  series  of  almost  vertical  rough 
lines  externally.  The  tuber  ischii  is  large  and  three-sided,  bearing  upper,  lower, 
and  external  tuberosities.  The  ischial  arch  is  narrow  and  deep.  The  symphysis 
bears  a  ventral  ridge,  which  fades  out  near  the  ischial  arch. 

The  acetabular  branch  of  the  pubis  is  narrow,  and  is  directed  outward  and  a 
little  forward.  The  anterior  border  is  marked  by  a  transverse  groove  which  ends 
below  the  rough  ilio-pectineal  eminence.  The  longitudinal  branch  is  wide  and 
thin.  .      . 

The  acetabulum  is  smaller  than  in  the  horse.  The  nm  is  rounded  and  !s 
usually  marked  bv  two  notches.  One  of  these  is  postero-internal  and  is  narrow 
and  deep;  it  leads  to  the  deep  acetabular  fossa  and  is  commonly  almost  converted 


132 


SKELETON'    OF   THE    OX 


into  a  foramen  by  a  bar  of  bone.     The  other  notch  is  antoro-internal,  small,  and 
sometimes  replaced  by  a  foramen  or  absent. 

The  obturator  foramen  is  large  and  elliptical.     Its  inner  border  is  thin  and 
sharp. 


External  condyle  of  femur  ■ 
External  tuberosity  of  tibia  ■ 


Exlcrnnl  iiiiilUohis 
Filiiilftr  larsiil  bune 


Inieriitil  ninllrohis 
Tibial  tarsal  bone 

■  Central  +  fourth  lorsnl  bone 

'  Scconil  Inrsal  hone 
Fir^l  l,ii:<„l  hnnr 
Si/iiill  iiiitiiUirsal  bone 


Proximal  sisinnnid  ' 
First  jihtilaiix 

Second  phiilinii- 

Distal  .■^csiniiunl 
Third  jihatanx 

Fig.  101. — Skeleton  of  Left  Hind  Limb  of  Ox,  from  Middle  of  Thigh  Dow.nward.  Posterior  View. 
SI,  Tibia;   S4,  tiihcr  oalcis;   ^5,  large  metatarsal  bone,     (.\fter  Ellcnbergcr-Baiim,  .Viial.  fiir  KOnstler.) 


The  pelvic  inlet  is  elliptical  and  is  more  oblique  than  in  the  honse.  In  a  cow 
of  medium  size  the  conjugate  diameter  is  about  nine  and  a  half  inches  (ca.  23  to  24 
cm.),  and  the  transverse  al)0ut  seven  inches  (ca.  18  cm.).  The  anterior  end  of  the 
symphysis  lies  in  a  transverse  plane  throush  the  junction  of  the  third  and  fourth 


BONES    OF   THE    PELVIC    LIMB 


133 


sacral  segments.  The  roof  is  concave  in  l)otli  directions.  The  floor  is  deeply  con- 
cave, particularly  in  the  transverse  direction.  The  cavity  is  narrower  and  its  axis 
is indineil  strongly  upward  in  the  posterior  part.  The  distance  between  theacetah- 
ulum  and  the  external  angle  of  the  ilium  is  only  a  little  (ca.  3  to  4  cm.)  more  than 
the  distance  between  the  former  and  the  tuber  ischii. 

The  femur  has  a  relatively  small  shaft,  which  is  cylindrical  in  its  middle,  pris- 
matic below.  The  trochanter  minor  has  the  form  of  a  rough  tuberosity,  and  is 
situated  higher  up  than  in  the  horse  and  encroaches  on  the  posterior  surface.  The 
trochanteric  ridge  (Crista  intcrtrochanterica  posterior)  connects  it  with  the  tro- 


Front.ii-  Slctio-v  of  Left  Tibia  or  Ox, 
Anterior  View. 


Fig.  102.— Froktal  Section  of  LEt-r  FEiwrR  of  Ox,       Fio.  103.- 

Fron't  View. 

These  figures  show  the  internal  architecture  of  these  bones,  and  e,si,eeiaU.v  the  great  extent  of  the  me<iullar.v  cav- 
ity as  compared  with  those  of  the  horse  (Figs.  67  and  72). 

chanter  major.  The  third  trochanter  is  absent.  The  supracondyloid  (plantar)  fossa 
is  shallow.  The  proximal  extremity  is  very  wide.  The  head  is  smaller  than  ni  the 
horse  and  the  articular  surface  extends  considerably  on  the  upper  surface  of  the 
neck.  Instead  of  the  notch  there  is  a  small  depression  on  the  middle  ot  the  head 
for  the  attachment  of  the  round  ligament.  The  neck  is  well  defined  except  above. 
The  trochanter  major  is  verv  massive  and  is  undivided;  its  external  surlace  is 
very  rough.  The  trochanteric  fossa  is  deep,  but  does  not  extend  so  far  downward  as 
in  t"lie  horse.  The  distal  end  presents  no  very  st riking  differential  features.  1  .ut  the 
lips  of  the  trochlea  are  less  oblique  than  in  the  horse,  and  converge  very  slightly 


134  SKELETON    OF   THE    OX 

below.  Tlio  ])ru.\iiiial  extremity  unites  with  the  shaft  at  aliout  throe  and  one-half 
years,  the  distal  at  three  and  one-half  to  four  years. 

The  tibia  resembles  that  of  the  horse  rather  closely,  but  is  somewhat  shorter. 
The  shaft  is  distinctly  curved,  so  that  the  inner  side  is  convex.  The  jxjsterior 
surface  is  not  divitled  into  two  areas,  and  the  linese  musculares  are  fewer  and  extend 
up  higher  than  in  the  horse.  The  articular  grooves  and  ridge  of  the  distal  end  arc 
almost  sagittal  in  direction,  and  present  an  extensive  but  shallow  synovial  fossa. 
The  external  groo\-e  is  separated  l)y  a  sh^rp  ridge  from  an  outer  area  which  is  for 
articulation  with  the  external  malleolus.  The  anterior  part  of  the  internal  malle- 
olus is  prolonged  downward  and  has  a  pointed  end.  The  groove  behind  it  is  broad 
and  well  defined.  Externally  there  is  a  deep  narrow  groove  which  separates  two 
prominences.  The  proximal  extremity  fuses  w'ith  the  shaft  at  three  and  one-half 
to  four  years,  the  distal  at  two  to  two  and  one-half  years. 

The  fibula  usually  consists  of  the  two  extremities  only.  The  head  is  fused  with 
the  external  condyle  of  the  tibia  and  bears  a  small  blunt-pointed  prolongation 
below.  The  distal  end  remains  separate  and  forms  the  external  malleolus  (some- 
times called  the  os  malleolare).  It  is  quadrilateral  in  outline  and  compressed  from 
side  to  side.  The  proximal  surface  articulates  with  the  distal  end  of  the  tibia,  and 
bears  a  small  spine  which  fits  into  the  groove  on  that  bone.  The  distal  surface 
rests  on  the  fibular  tarsal,  and  the  inner  articulates  with  the  external  ridge  of  the 
tibial  tarsal  bone.     The  outer  surface  is  rough  and  irregular. 

The  early  cartilaginous  fibula  is  complete,  but  later  the  shaft  is  reduced  and  is 
usually  represented  by  a  fibrous  cord  which  connects  the  two  ends.  In  some  cases, 
however,  the  upper  part  undergoes  partial  ossification,  forming  a  slender  rod  which 
is  usually  united  with  the  outer  border  of  the  tibia  and  is  joined  to  the  head  by 
fibrous  tissue. 

The  patella  is  long,  narrow,  and  very  thick.  The  anterior  surface  is  strongly 
convex  and  very  rough  and  irregular.  The  articular  surface  is  convex  from  side 
to  side  and  nearly  straight  in  the  vertical  direction.  The  large  prominence  on  the 
inner  side  for  the  attachment  of  the  accessor}^  cartilage  allows  prompt  determina- 
tion of  the  side  to  which  the  bone  belongs.  The  apex  is  more  pointed  than  in  the 
horse. 

The  tarsus  consists  of  five  pieces;  the  central  and  fourth,  and  the  second  and 
third  tarsal  bones  are  fused. 

The  tibial  tarsal  bone  is  relatively  long  and  narrow,  and  is  somewhat  flattened 
from  l)efore  backward.  It  bears  a  trochlea  at  either  end.  The  groove  and  ridges 
of  the  proximal  trochlea  are  not  spiral,  but  almost  sagittal;  the  outer  ridge  is  the 
wider,  and  articulates  with  both  tibia  and  fibula.  The  distal  trochlea  consists 
of  two  condyles  divided  by  a  groove,  and  articulates  with  the  combined  central 
and  fourth  tarsals.  The  posterior  surface  bears  a  large  oval  facet  for  articulation 
with  the  fibular  tarsal;  this  occupies  most  of  the  surface,  and  is  convex  and  grooved 
from  above  downward.  The  outer  surface  presents  two  facets  for  articulation  with 
the  fibular  tarsal,  and  is  excavated  and  rough  elsewhere.  The  inner  surface  bears 
a  tuberosity  at  its  upper  part,  and  is  flattened  below. 

The  fibular  tarsal  Ijone  is  longer  and  more  slender  than  in  the  horse.  The 
distal  i)art  of  the  body  is  compressed  laterally,  and  bears  a  projection  in  front  which 
articulates  with  the  external  malleolus.  The  tuber  calcis  is  marked  ])osteriorly  by 
a  wide  shallow  groove,  which  is  coated  with  cartilage  in  the  fresh  state. 

The  central  and  fourth  tarsals  an>  fused  to  form  a  large  bone  (Os  centrotarsale 
quartum,  scapho-cuboid),  which  extends  across  the  entire  width  of  the  tarsus  and 
articulates  with  all  of  the  other  bones.  The  greater  part  of  the  upper  surface  is 
molded  on  the  distal  trochlea  of  the  tibial  tarsal,  and  its  inner  part  rises  high  above 
the  rest  posteriorly.  Externally  there  is  a  narrow  undulating  surface  for  articula- 
tion with  the  distal  end  of  the  fibular  tarsal  bone.     The  posterior  surface  bears  two 


BOXES    OF    THE    PELVIC    LIMB 


135 


tuberosities,  of  which  the  outer  one  is  rounded,  the  inner  more  prominent  and  nar- 
rower. 

The  first  tarsal  bone  is  quadrihiteral  anil  small.  It  articulates  with  the  central 
above,  the  metatarsus  below,  and  the  second  tarsal  in  front. 

The  second  and  third  tarsals  are  fused  to  form  a  rhomboid  piece.  The  proxi- 
mal surface  is  concavo-convex,  and  articulates  with  the  central  component.  The 
distal  surface  is  undulating  and  rests  on  the  metatarsus.  The  external  surface 
bears  a  small  facet  in  front  for  the  fourth  tar-sal  component,  and  the  posterior  sur- 
face a  very  small  one  for  the  first  tarsal  bone. 

The  large  metatarsal  bone  is  about  one-seventh  (ca.  3  cm.)  longer  than  the 
corresponding  metacarpal.     Its  shaft   is   compressed  laterally   and   is  distinctlj' 


Central  +  fourth  tarsal  bone 
First  tarsal  bone 


Proximal  sesamoid 


Distal  sesamoid 


Tibial  tarsal  bone 
Second  +  third  tarsal  bone 


Fig.  104. — ^Skeleton"  of  Distal  Part  of  Left  Hind  Limb  of  Ox.  Internal  View. 

S4,  Tuber  ealcis;   i?-5.  large  metatarsal  bone;   30,  first  phalanx;   3/,  second  phalanx;   35,  third  phalan.x.     (.\fter 

EUenberger-Baum,  Anat.  fur  Kunstler.) 


four-sided.  The  groove  on  the  anterior  surface  is  deep  and  wide.  The  posterior 
surface  is  marked  by  variable  grooves.  The  upper  foramen  on  this  surface  does 
not  perforate  the  shaft,  but  passes  obhquely  through  the  extremity,  opening  on  the 
posterior  part  of  its  proximal  surface.  The  postero-internal  angle  of  the  pro.ximal 
end  bears  a  facet  for  articulation  with  the  small  metatarsal  bone. 

The  small  metatarsal  bone  is  a  quadrilateral  disc  a  little  less  than  an  inch  in 
width  and  height.  Its  anterior  face  bears  a  facet  for  articulation  with  the  large 
metatarsal  bone. 

The  large  metatarsal  bone  is  usually  regarded  as  consisting  of  the  fused  third  and  fourth 
metatarsal  bones.  The  medullary  ca\'ity  is  subdi\-ided  like  that  of  the  large  metacarpal  bone. 
Some  anatomists,  however,  consider  that  the  ridges  at  the  upper  end  of  each  border  represent  the 
second  and  fifth  metatarsals  (Rosenberg  and  Retterer).  On  this  basis  the  small  bone  would  be 
the  first  metatarsal. 


136 


SKELETON    OF   THE    PIG 


The  phalanges  and  sesamoids  resemble  those  of  the  thoracic  hmb  so  closely 
as  to  render  separate  description  unnecessary. 


SKELETON  OF  THE  PIG 
VERTEBRAL  COLUMN 

The  vertebral  formula  is  CjT,,_,5L„-7^4*^"y2o-23- 

The  cervical  vertebrae  are  short  and  wide.  The  bodies  are  elliptical  in  cross- 
section,  the  long  diameter  being  transverse.  The  anterior  articular  surfaces  are 
slightly  convex  from  side  to  side  and  concave  dorso-ventrally ;  the  posterior  ones 
are  slightly  concave.  A  ventral  crest  is  not  present.  The  arches  are  wide  from 
side  to  side,  but  the  laminae  are  narrow,  so  that  a  considerable  interval  (Spatium 
interarcuale)  separates  adjacent  arches  dorsally.  The  pedicles  are  perforated  by  a 
foramen  on  either  side  in  addition  to  the  usual  intervertebral  foramina.     The 


Fig.  105. — Skeleton  of  Pig,  L.\terai.  View. 
a,  Cranium;  h,  upper  jaw;  c,  lower  jaw;  III. -711 .,  cervical  vertebra-;  IR.w.,  first  thoracic  vertebra;  IS 
R.W.,  thirteenth  thoracic  vertebra  (ne.xt  to  last);  IL..  first  lumbar  vertebra;  61..,  sixth  lumbar  vertebra  (next 
to  last  usually);  A'.,  sacrum;  .S.,  coccygeal  vertebra;  IR.,  first  rib;  HR.,  last  rib;  R.kn.,  costal  cartilages;  St., 
sternum;  d,  supraspinous  fossa  of  scapula;  d\  infraspinous  fossa;  /,  spine  of  scapula;  2,  neck  of  scapula;  c, 
humerus;  S,  head  of  humenis;  4,  tuberosities  of  humerus;  S,  deltoid  tuberosity;  6,  external  epicondyle  of 
humerus;  /,  radius;  o,  ulna;  7,  olecranon;  /j,  carpus;  1S~25,  carpal  bones;  i-i"" ,  metacarpus;  k-k"" ,  proximal 
phalanges;  l-l"" ,  middle  phalanges;  m-m"" ,  distal  phalanges;  n,o,  sesamoids;  p.  ilium;  8,  external  angle  of 
ilium  (tuber  coxae);  9.  internal  angle  of  ilium  (tuber  sacrale);  /O,  superior  ischiatic  spine;  ((.ischium;  //.tuber 
ischii;  r,  pubis;  12,  acetabulum;  s.  femur;  13,  trochanter  major;  /4,  trochanter  minor;  15,  external  epicondyle; 
(,  patella;  w.  tibia;  W,  crest  of  tibia;  17,  external  condyle  of  tibia;  r,  fibula;  w,  tarsus;  26-31,  tarsal  bones; 
SB',  tuber  calcis.     (.\fter  Ellcnberger,  in  Leisering's  Atlas.) 


transverse  processes  divide  into  two  branches,  both  of  which  increase  in  size  from 
the  third  to  the  sixth.  The  upper  branch  projects  outward  and  backward;  it 
is  short  and  i.^  thickened  at  its  free  end.  The  lower  branch  is  a  quadrilateral  plate 
directed  ventrally;  each  overlaps  the  succeeding  one  to  a  small  extent,  and  the 
series  forms  the  lateral  boundary  of  a  deep  and  wide  groove  beneath  the  bodies. 
The  spines  increase  in  height  from  the  third  to  the  last;  the  anterior  ones  are  in- 
clined backward,  the  posterior  ones  forward.  The  last  cervical  is  recognized  by 
the  groat  length  of  its  spine  (ca.  10  cm.  in  the  adult),  the  absence  of  the  ventral 
plate  of  the  transverse  process,  and  the  flatness  of  the  liody,  which  liears  a  pair  of 


VERTEBRAL    COLUMN  137 

small  facets  on  its  posterior  margin  for  the  heads  of  the  first  ribs.  It  has  foramina 
transversaria,  and  usually  two  foramina  in  cither  side  of  the  arch. 

The  dorsal  arch  of  the  atlas  hears  a  large  tuberosity.  The  ventral  tubercle  is 
long,  compressed  laterally,  and  projects  back  under  the  axis.  The  wing  is  flattened 
and  bears  a  posterior  tuberosity.  The  foramen  transversarium  jias.ses  through  tiie 
po.sterior  border  of  the  wing  to  the  fossa  under  the  latter,  and  is  not  visible  dorsally ; 
it  is  sometimes  very  small  or  absent.  The  sides  of  the  vertebral  foramen  bear 
two  lateral  projections  which  partially  divide  it  into  a  ventral  narrow  ])art,  which 
receives  the  odontoid  process,  and  a  dorsal  larger  part  for  the  spinal  cord.  In  the 
fresh  state  the  division  is  completed  by  the  transverse  ligament,  which  is  attached 
to  the  projections. 

The  axis  has  a  large  spinous  process,  which  is  directed  upward  and  backward. 
The  odontoid  process  is  a  thick  cylindrical  rod.  The  transverse  process  is  very 
small  and  the  foramen  transversarium  is  often  incomplete. 

The  thoracic  vertebrse  are  often  fifteen  in  number.  Their  bodies  are  relatively 
long,  constricted  in  the  middle,  and  without  ventral  crests.     Their  extremities  are 


Fig.  106. — Atlas  of  Pig,  Dorsal  View.  Fig.   107. — Axis  of  Pig.  Lkft  Lateral  View. 

a,  Wing;  b,  ventral  tubercle;  c,  foramen  transver-  a,  Odontoitl  process  (dens);  b,  spinous  process; 

;  d,  alar  foramen;  e,  intervertebral  foramen;  /,  ilor-  c.  anterior  articular  process;  d,  posterior  articular  pro- 
sal  tuberosity;  ff,  articular  surface  corresponding  to  that  of  cesses;  e,  transverse  process;  /.foramen  transversar- 
posterior  articular  process  of  typical  vertebra;  h.  facet  on  ium;  n,  bar  of  bone  which  bounds  h.  intervertebral 
ventral  arch  for  odontoid  process.  (Ellenberger-Baum,  foramen;  i,  vertebral  foramen.  (Ellenberger-Baum, 
Anat,  d.  Haustiere.)  Anat.  d.  Haustiere.) 

elliptical,  depressed  in  the  middle  and  prominent  at  the  periphery.  The  arch  is 
perforated  by  a  foramen  on  either  side,  and  in  most  of  the  series  there  is  also  a 
foramen  in  the  posterior  part  of  the  root  of  the  transverse  process  which  communi- 
cates with  the  former  or  with  the  posterior  intervertebral  foramen.  Sometimes 
there  is  a  foramen  in  the  anterior  part  of  the  process  also.  There  are  manmiillary 
processes  except  on  the  first  two;  in  the  posterior  five  or  six  vertebra?  they  project 
from  the  anterior  articular  processes.  The  facet  for  the  tubercle  of  the  rib  is 
absent  or  fused  with  that  for  the  head  in  the  last  five  or  six.  The  last  transverse 
process  is  lumbar  in  character,  plate-like,  and  about  an  inch  (2  cm.)  long.  Small 
accessory  processes  occur  in  the  posterior  part  of  the  region.  The  first  spinous 
process  is  broad,  very  high,  and  inclined  a  little  forward.  The  others  diminish 
very  gradually  in  length  to  the  tenth,  beyond  which  they  are  al)out  equal.  The 
second  to  the  ninth  are  inclined  backward,  the  tenth  is  vertical  (anticlinal),  and  the 
rest  incline  forward.  The  width  decreases  decidedly  from  the  fourth  to  the  tenth, 
lieyond  which  there  is  a  gradual  increase.  The  summits  are  slightly  enlarged  and 
lie  almost  in  a  straight  line. 


138 


SKELETON    OF   THE    PIG 


The  occurrence  of  fifteen  tlioracic  vertebrae  appears  to  be  quite  common,  and  some  observers 
have  recorded  the  existence  of  sixteen  and  even  seventeen;  a  reduction  to  thirteen  is  rare. 

The  lumbar  vertebrae  are  six  or  seven  in  number.  The  bodies  are  longer  than 
in  the  thoracic  region  and  bear  a  ventral  crest.  They  become  wider  and  flatter 
in  the  i)()storior  part  of  the  series.  The  arches  are  deeply  notched,  and  are  separated 
l)y  an  increasing  sjiace  dorsally.  The  mammillary  processes  project  outward  and 
jjackward.  The  transverse  processes  are  bent  downward  and  incline  a  little  for- 
ward. Their  length  increases  to  the  fifth  and  is  much  diminished  in  the  last.  They 
form  no  articulation  with  each  other  or  with  the  sacrum.  The  ])osterior  edge  of  the 
root  of  the  process  is  marked  by  a  notch  in  the  anterior  part  of  the  series,  a  fora- 
men in  the  posterior  part.  The  spines 
are  broad  and  incline  forward,  with  the 
exception  of  the  last,  which  is  narrow 
and  vertical. 

Lesbre  states  that  six  and  seven  lumbar 
vertebrae  occur  with  ahiiost  equal  frequency. 
The  number  may  be  reduced  to  five,  and  the 
number  of  presacral  vertebra;  varies  from 
twenty-six  to  twenty-nine. 

The  sacrum  consists  usually  of  four 
vertebrae,  which  fuse  later  and  less  com- 
pletely than  in  the  other  domesticated 
animals.  It  is  less  curved  than  in  the 
ox.  The  spines  are  absent,  excepting 
small  rudiments  on  the  last  two  seg- 
ments. The  middle  of  the  dorsal  surface 
is  flattened  and  smooth,  and  presents 
openings  into  the  sacral  canal  between 
adjacent  arches  (Spatia  interarcualia) .  On 
either  side  are  the  superior  sacral  fora- 
mina, and  tubercles  which  indicate  the 
fused  articular  processes.  The  wings  re- 
semble those  of  the  ox.  The  anterior 
articular  processes  are  very  large.  The 
pelvic  surface  resembles  that  of  the  ox, 
but  is  not  so  strongly  curved,  and  the 
transverse  lines  are  very  distinct. 
The  coccygeal  vertebrae  are  specially  characterized  by  the  presence  of  func- 
tional articular  processes  on  the  first  four  or  five,  beyond  which  these  processes 
become  non-articular  and  smaller.  The  arches  of  the  first  five  or  six  are  complete. 
The  transverse  processes  are  broad  and  ]ilate-like  in  the  anterior  part  of  the  series 
and  diminish  very  gradually. 

The  numerical  variation  here  is  twenty  to  twenty-six  according  to  the  observation  of  several 
anatomists.     Lesbre  states  that  he  has  found  twenty-three  most  frequently. 

Curves. — The  cervical  region  is  practically  straight.  The  thoracic  and  lumbar 
regions  form  a  gentle  curve,  concave  ventrally,  the  highest  point  of  %vhich  is  at  the 
jtmction  of  the  two  regions.  The  sacral  promontory  is  not  so  pronounced  as  in  the 
ox,  and  the  sacral  curve  is  flatter. 


Fiti.  lOS. — Sacrum  of  Pig,  Dorsal  \'i 
a.  Wing;  b,  dorsal  sacral  foramina;  c,  :i 
process;    I-4,  segments  or  sacral  vertebrse. 
berger-Baum.  Anat.  (1.  Haustiere.) 


The  Ribs 
The  ribs  number  fourteen  or  fifteen  pairs,  of  which  seven  are  sternal  and  seven 
or  eight  asternal  usually.     They  are  in  general  strongly  curved  in  the  improved 


THE    STERNUM — BOXES    OF    THE    SKULL — CRANIUM 


139 


breeds,  so  tliat  there  is  a  fairly  distinct  angle,  except  toward  the  end  of  the  series. 
The  liackward  slope  of  the  posterior  ribs  is  slight.  The  first  rib  is  prismatic,  has  a 
large  sternal  end,  and  a  very  short  cartilage.  The  width  is  greatest  in  the  third 
to  the  sixth,  and  the  length  in  the  sixth  and  seventh  usually.  The  tuberosity  fuses 
with  the  head  on  the  last  five  or  six.  The  second  to  the  fifth  form  diarthrodial 
joints  with  their  cartilages,  which  are  wide  and  plate-like. 


THE  STERNUM 

The  sternum  consists  of  six  segments  and  resembles  that  of  the  ox  in  general 
form.  The  first  segment  (Manubrium)  is  long,  flattened  laterally,  and  bears  a 
blunt-pointed  cartilage  on  its  anterior  end;  its  posterior  end  forms  a  diarthrodial 
joint  with  the  body.  The  latter  is  flattened,  wide  in  its  middle,  narrow  at  either 
end.  The  widest  segments  are  formed  of  two  lateral  parts,  which  are  not  com- 
pletely fused  in  the  adult.  The  last  segment  has  a  long  narrow  part  which  liears 
the  xi])hoid  cartilage. 

The  thorax  is  long  and  is  more  barrel-shaped  than  in  the  horse  or  ox,  since  the 
ribs  are  more  strongly  curved  and  differ  less  in  relative  length. 


Parietal 
bone        Fronlal 

bone        Supraorbital 


I'remaxilla 


■^       12     // 


Fig.  109. — Skull  of  Pig,  Lateral  View  without  Mandible. 
1,  Occipital  condyle;    2,  paramastoid  or  styloid  process;    3,  bulla  ossea;    i,  e.TiternaI  auditory  meatus, 
5,  zygomatic  process  of  temporal  bone;    6,  sphenoid  bone;    7,  orbital  opening  of  supraorbital  canal;    ^,  malar 
bone:    B,  pterygoid  bone;    10,  pterygoid  process  of  sphenoid;    11,  pterygoid  process  of  palate  bone;   11-S, 
teeth;    C,  canine  tooth;   Pl-A,  premolars;   Ml-3,  molars. 


BONES  OF  THE  SKULL 
Cranium 
The  occipital  bone  has  an  extensive  squamous  part  or  supraoccipital,  which 
forms  a  very  broad  and  prominent  crest.  The  latter  is  concave,  and  is  thick  and 
rough  above,  where  it  forms  the  highest  part  of  the  skull;  laterally  it  becomes 
thinner,  turns  downward,  and  is  continuous  with  the  temporal  crest.  Two  diver- 
gent ridges  pass  upward  from  the  foramen  magnum,  and  the  surface  between  them 
is  concave  and  smooth.  The  greater  part  of  the  inner  (or  anterior)  surface  of  the 
supraoccipital  is  united  with  the  parietal  bones,  but  a  lower  concave  area  faces 


140 


SKELETON    OK    THE    PIG 


into  the  cranial  cavity.  The  foramen  magnum  is  ahnost  triangular,  and  is 
narrow  above,  where  it  is  flanked  by  two  small  tuberosities.  The  paramastoid 
processes  are  extremely  long  and  project  almost  straight  downward.  The  hypo- 
glossal foramen  is  at  the  inner  side  of  the  root  of  the  process.  The  basilar 
part  is  short  and  wide;  its  lower  surface  bears  a  thin  median  ridge  and  two 
lateral  imprints  or  tubercles  which  converge  at  the  junction  with  the  sphenoid 
bone. 


Parietal  bone 
Temporal  fo! 


Squamous  leiiiijora 
bone 
External  auiL 
meatus 


Zygomatic  process 
of  temporal  bone 
Supraorbital  tyro- 
cess 
Frontal  hone 

Supraorbital  fora- 
men 
Zygomatic  process 
of  malar  bone 
Lacrimal  bone 


I nfraorbilal  foramen 

Nasal  process  of  premaxilla 

Nasal  bone 

Canine  tootli 

Palatine  cleft 
Body  of  premaxilla 


Occipital  crest 
Temporal  crest 
Parietal  crest 


Lacrimal  foramen 
Preorbital  fossa 


Fin.  110.— Skfi.i.  of  Pin.  Oorsai.  V 


The  interparietal  fuses  bcfon;  l)irth  with  the  occipital.  The  tentorium  osseum 
is  absent. 

The  parietal  is  o^'crlappod  by  the  occipital  bone  behind  and  concurs  in  the 
formation  of  the  occipital  crest.  Its  external  surface  is  divided  liy  the  parietal 
crest  into  two  parts.  The  inner  part  (Planum  parictale)  faces  upward  and  forward, 
and  is  flattened  and  smooth.  Its  inner  border  is  short  and  straight  and  unites  early 
with  the  opposite  bone.  Its  anterior  border  is  concave  and  joins  the  frontal  bone. 
The  outer  part  (Planum  temporale)  faces  outward  and  is  more  extensive;  it  is 
conca^•e,  forms  a  large  part  of  the  temporal  fossa,  and  is  overlapped  below  by  the 
squamous  temporal.     The  parietal  crest  extends  in  a  curve  from  the  occipital  crest 


141 


forward  and  outward  to  the  supraorbital  process.  The  internal  surface  is  concave 
and  is  niarketl  by  digital  impressions.  The  lower  border  projects  into  the  cranial 
cavity  and  forms  a  crest  which  separates  the  cerebral  and  cerebellar  compartments 
laterally.  The  interior  forms  part  of  the  frontal  sinus  in  the  adult.  There  is  no 
paricto-tcm]ioral  canal. 

The  frontal  bone  is  long.  The  frontal  surface  slopes  downward  and  forward, 
the  inclination  varying  in  different  subjects.  The  anterior  part  is  concave  and  is 
marked  by  the  sujDraorbital  foramen  and  the  groove  leading  forward  from  the 
foramen  to  the  nasal  bone.  The  supraorbital 
canal  opens  into  the  orbit  at  the  upper  part  of 
the  inner  w-all  of  the  latter.  The  supraorbital 
process  is  short  and  blunt-pointed,  and  is  not 
connected  with  the  zygomatic  arch.  The  gap 
in  the  orbital  margin  is  closed  by  the  orbital 
ligament  in  the  fresh  state.  The  orbital  part 
is  extensive  and  forms  the  greater  part  of  the 
inner  wall  of  the  orbit.  Its  upper  part  is  per- 
forated by  the  orbital  orifice  of  the  supraorbital 
canal,  in  front  of  which  is  the  distinct  fovea 
trochlearis.  The  ethmoidal  or  internal  orbital 
foramen  is  situated  in  the  lower  part  near  the 
junction  with  the  orbital  wnng  of  the  sphenoid. 
The  temporal  part  is  very  narrow  antl  is  separ- 
ated from  the  orbital  plate  by  a  ridge  which 
joins  the  pterygoid  crest  below.  The  interior 
of  the  bone  is  excavated  by  the  frontal  sinus  in 
practically  its  entire  extent  in  the  adult.  In 
the  young  subject  the  cavity  is  confined  to  the 
anterior  part  and  the  rest  of  the  bone  is  thick. 

The  temporal  bone  has  a  general  resem- 
blance to  that  of  the  ox.  The  zygomatic  pro- 
cess is  short  and  stout  and  is  bent  at  a  right 
angle.  The  upper  border  of  the  process  is  thin ; 
traced  from  before  backward  it  curves  sharply 
upward  and  forms  a  high  prominence  in  front 
of  the  external  auditory  meatus;  beyond  this 
it  drops  rather  abruptly  and  is  then  continued 
upward  to  the  occipital  crest.  The  anterior 
part  of  the  lower  border  joins  the  zygomatic 
process  of  the  malar,  which  is  deeply  notched. 
The  condyle  is  concave  in  the  transverse  direc- 
tion. The  postglenoid  process  is  absent,  but 
the  articular  surface  is  bounded  behind  and  in- 
ternally by  a  crest.  There  is  no  parieto-tem- 
poral  canal.  The  external  auditorj'  canal  is  very 

long  and  is  directed  upward  and  outward.  The  bulla  ossea  is  large,  compressed 
laterally,  and  bears  a  pointed  muscular  process  in  front.  A  narrow  space  intervenes 
between  the  bulla  and  the  basilar  part  of  the  occipital  bone,  so  that  the  foramen 
lacerum  resembles  that  of  the  horse.  The  small  hyoid  process  is  situated  in  a  deep 
depression  in  front  of  the  root  of  the  paramastoid  process,  and  the  stylo-mastoid 
foramen  is  immediately  external  to  it.  The  petrous  part  presents  no  important 
differential  features.  The  squamous  part  (including  the  root  of  the  zyg;omatic 
process)  contains  an  air-cavity,  which  is  continuous  with  the  sphenoidal  sinus. 

The  sphenoid  bone  is  short  and  resembles  that  of  the  ox  in  general.     The-  body 


Fig.  111. — Basal  Scrface  of  .Skull  of 
Young  Pig,  without  the  Mandible. 
Sq.o.,  Supraoccipitai;  £".0.,  exoccipital; 
B.O.,  basioccipital;  B.s..  body  of  sphenoid; 
Sfj.,  squamous  temporal  bone;  V,  vomer;  J/x., 
maxilla;  Pa.,  horizontal  part  of  palate  bone; 
P.p.,  palate  process  of  maxilla;  Z ..  malar  bone; 
J.  premaxilla;  D.c,  canine  tooth;  Jl-S,  in- 
cisor teeth;  O,  temporal  fossa;  /.occipital  crest; 
2.  for.  magnum;  J,  occipital  condyle;  4.  para- 
mastoid (styloid)  process;  o,  bulla  ossea;  fi, 
for.  lacerum  basis  cranii;  7,  pterjgoid  process 
of  sphenoid;  S,  posterior  nares;  9,  anterior 
palatine  foramen;  /(?,  palatine  cleft.  (Struska, 
.\nat.  d.  Haustiere.) 


142  SKELETON    OF   THE    PIG 

is  narrow.  The  pituitary  fossa  is  very  deej),  and  is  limited  behind  hy  a  prominent 
dorsum  sellae;  the  dorsum  bears  lateral  projections,  the  posterior  clinoid  processes. 
The  foramen  ovale  is  absent,  being  included  in  the  foramen  laccrum  anterius. 
The  other  foramina  are  like  those  of  the  ox.  The  pterygoid  process  is  broad  and 
twisted.  Its  base  is  not  perforated  and  its  free  edge  is  thin  and  sharp.  It  concurs 
\v\th  the  pterygoid  and  palate  bones  in  the  formation  of  the  pterygoid  fossa,  which 
opens  Inickward  and  is  not  present  in  the  horse  or  ox.  The  sphenoidal  sinus  is 
very  large  and  occupies  the  body,  the  temporal  wings,  and  a  great  part  of  the  ptery- 
goid processes  in  the  adult;  it  is  continued  into  the  temporal  bone  as  mentioned 
above. 

The  ethmoid  bone  has  a  relatively  long  perpendicular  plate,  which  is  marked 
by  ridges  corresj^onding  to  the  ethmoidal  meatuses.  The  cribriform  plate  is  ex- 
tensive and  very  oblique,  so  that  it  and  the  crista  galli  are  almost  in  line  with  the 
basi-cranial  axis.  A  linear  series  of  relatively  large  foramina  is  found  on  either 
side  of  the  crista.  The  lateral  mass  consists  of  five  endoturljinals  and  eighteen 
ectoturbinals  (Paulli).  The  lamina  papyracea  concurs  in  the  formation  of  the 
pterygo-palatine  fossa. 

Face 

The  maxilla  is  extensive.  Its  external  surface  forms  a  longitudinal  groove, 
which  is  continued  upon  the  premaxilla  in  front  and  the  facial  parts  of  the  lacrimal 
and  malar  behind.  The  infraorbital  foramen — sometimes  double — is  large  and 
is  situated  above  the  third  or  fourth  cheek  tooth.  The  alveolus  for  the  canine 
tooth  produces  a  ridge  at  the  anterior  end  which  is  very  pronounced  in  the  boar. 
The  facial  crest  extends  forward  from  the  root  of  the  zygomatic  process  and  fades 
out  behind  the  infraorbital  foramen;  in  some  specimens  it  is  prominent  and  thin- 
edged,  in  others  it  is  rounded  and  projects  little.  The  zygomatic  process  is  short 
but  stout  and  buttress-like;  it  is  overlapped  externally  by  the  malar.  The  maxil- 
lary tuberosity  forms  in  the  young  subject  a  long  bulla,  which  occupies  most  of  the 
pterygo-palatine  fossa  and  contains  the  developing  permanent  molars;  after  the 
eruption  of  the  teeth  the  tuberosity  flattens  and  joins  the  vertical  part  of  the  palate 
bone.  The  palatine  process  is  very  long  and  is  marked  in  its  anterior  part  by  trans- 
verse ridges  corresponding  with  those  of  the  mucous  membrane  of  the  palate. 
The  anterior  palatine  foramen  is  near  the  junction  with  the  palate  bone;  from  it  the 
palatine  groove  can  be  traced  distinctly  along  the  entire  length  of  the  process. 
The  alveolar  border  presents  a  large  alveolus  for  the  canine  tooth  at  its  anterior 
end;  behind  this  are  seven  alveoli  for  the  cheek  teeth,  which  increase  in  size  from 
first  to  last.  The  maxillary  foramen  and  infraorbital  canal  are  very  large.  The 
maxillary  sinus  is  small. 

The  Ijody  of  the  premaxilla  is  narrow  and  prismatic.  It  presents  three  alveoli 
for  the  incisor  teeth,  which  are  separated  b^'  short  intervals  and  diminish  in  size 
from  before  backward.  As  in  the  ox,  a  narrow  space  separates  the  right  and  left 
bones  and  takes  the  place  of  the  foramen  incisivum.  The  palatine  process  is  long 
and  narrow.  The  nasal  process  is  very  extensive  and  is  somewhat  rhomljoid  in 
outline.  Its  upper  border  forms  a  very  long  suture  with  the  nasal  bone,  and  the 
lower  articulates  to  about  the  same  extent  with  the  maxilla.  The  palatine  fissure 
is  relatively  wide. 

The  horizontal  part  of  the  palate  bone  forms  a  fourth  to  a  fifth  of  the  length  of 
the  palate;  its  i^alatine  surface  is  triangular,  the  apex  being  anterior;  its  nasal 
surface  is  deeply  grooved  and  smooth.  A  pterygoid  process  (processus  pyramidalis 
of  man)  projects  backward  and  downward,  and  its  thick  rounded  end  is  received 
between  the  pterygoid  process  of  the  sphenoid  and  the  pterygoid  bone.  The 
perpendicular  part  is  largely  overlapped  externallj^  by  the  maxilla  and  concurs  in 
forming  part  of  the  palatine  canal.     Superiorly  the  two  plates  separate  and  inclose 


FACE  143 

an  air-cavity  which  opens  into  an  etlinioidal  meatus.  The  inner  jilatc  curves 
inward  and  unites  with  the  vomer  and  ethmoid  to  form  a  horizontal  plate  (Lamina 
transversalis),  which  ilivides  the  posterior  part  of  the  nasal  cavity  into  an  upper 
olfactory  part  and  a  lower  respiratory  part. 

The  pterygoid  bone  is  nearly  vertical  in  direction,  and  is  narrow  in  its  middle, 
wide  at  each  end.  The  external  surface  is  free  below  and  forms  the  inner  wall  of 
the  pterj'goitl  fossa.     The  lower  end  is  notched  and  forms  a  distinct  hamulus. 

The  nasal  bone  is  very  long  and  its  width  is  almost  uniform,  except  at  the 
anterior  end,  which  is  pointed  and  reaches  almost  as  far  forward  as  the  premaxilla. 
The  facial  surface  is  flattened  from  side  to  side.  In  profile  it  is  nearly  straight  in 
some  subjects,  variably  concave  in  others.  The  external  border  is  free  to  a  small 
extent  in  front  only;  otherwise  it  is  firmly  connected  with  the  premaxilla  and 
maxilla.     In  the  adult  the  frontal  sinus  extends  into  the  posterior  part  of  the  bone. 

The  lacrimal  bone  is  very  sharply  bent.  Its  facial  surface  presents  a  deep 
depression,  surmounted  l)y  a  ridge  or  tubercle.  On  or  close  to  the  orbital  margin 
are  two  lacrimal  foramina  which  lead  to  the  lacrimal  canals.  The  orbital  surface 
presents  a  fossa  in  which  the  inferior  oljlique  muscle  of  the  eyel)all  arises,  and  its 
lower  part  bears  a  crest,  which  is  crossed  obliquely  by  a  vascular  furrow.  The 
upper  border  articulates  with  the  frontal  only.  The  bone  concurs  in  the  formation 
of  the  maxillary  sinus. 

The  malar  bone  is  strongly  compressed  from  side  to  side.  Its  facial  surface 
is  small  and  presents  a  fossa  which  is  continuous  with  the  depressions  of  the  maxilla 
and  lacrimal.  The  orbital  surface  is  still  smaller  and  is  smooth  and  deeply  grooved. 
The  zygomatic  process  is  very  extensive,  especially  in  the  vertical  direction.  Its 
external  surface  is  convex  and  free,  and  bears  a  rough  eminence  in  its  middle.  Its 
internal  surface  is  concave;  it  is  overlapped  in  front  by  the  maxilla,  and  in  the 
remainder  of  its  extent  is  free  and  smooth.  The  upjier  border  is  thick  and  rounded 
in  front,  where  it  forms  the  lower  part  of  the  orbital  margin;  behind  this  it  forms 
an  extensive  notch  which  receives  the  zygomatic  process  of  the  temporal.  (It 
might  be  regardefl  as  dividing  into  frontal  and  temporal  branches.)  The  lower 
border  is  convex  and  becomes  thinner  behind. 

Theturbinal  bones  resemble  those  of  the  ox.  Thesuperiorturbinalis, however, 
relatively  longer,  less  fragile,  and  more  firmly  attached  to  the  nasal  bone.  There 
is  no  middle  turbinal. 

The  vomer  is  very  long.  The  anterior  extremity  reaches  to  the  body  of  the  pre- 
maxilla or  very  close  to  it.  The  lower  border  is  received  into  a  groove  formed  by 
the  nasal  crest  of  the  maxillse  and  palate  bones  and  in  front  by  the  palatine  processes 
of  the  premaxillte.     The  posterior  border  is  concave,  thin,  and  sharp. 

The  OS  rostri  (or  prenasal  bone)  is  situated  in  the  snout  between  the  nostrils. 
It  has  the  form  of  a  short  three-sided  prism.  The  upper  surface  is  convex  and  is 
notched  at  each  end.  The  lateral  surfaces  are  concave,  smooth,  and  converge 
below,  forming  a  grooved  lower  border.  The  posterior  surface  is  triangular, 
notched  centrally,  and  rough  laterally.  The  anterior  surface  is  deeply  pitted  and 
is  surrounded  liy  an  irregular  sharp  border. 

The  mandible  is  very  strong,  and  differs  very  much  from  that  of  the  horse  or 
ox.  The  body  narrows  decidedly  in  front;  the  lingual  surface  is  deeply  concave; 
the  mental  surface  is  strongly  convex,  slopes  downward  and  backward,  and  forms 
a  distinct  prominence  at  the  point  of  divergence  of  the  rami.  Above  this  promi- 
nence is  a  pair  of  foramina.  The  alveolar  border  presents  six  alveoli  for  thi^  in- 
cisor teeth,  and  a  little  further  back  two  large  cavities  for  the  canine  teeth.  There 
are  two  pairs  of  mental  foramina  of  considerable  size  and  a  variable  numlier  of 
smaller  ones.  The  rami  diverge  more  than  in  the  horse  or  ox,  and  the  upper  part 
is  somewhat  incurved.  The  horizontal  part  is  very  thick  and  strong.  Its  outer 
surface  is  strongly  convex  from  above  downward.     The  inner  surface  is  prominent 


144 


SKELETON    OF    THE    PIG 


over  the  roots  of  the  molar  teeth  and  overhangs  the  concave  lower  part.  The 
alveolar  border  is  thin  in  front  and  widens  behind;  it  does  not  follow  the  axis  of 
the  ramus,  l)ut  runs  nearly  straight  and  produces  the  marked  overhang  noted  above. 
There  are  seven  alveoli  for  the  lower  cheek  teeth,  which  increase  in  size  from  before 
backward.  The  first  is  small,  not  always  present  in  the  adult,  and  is  separated  by 
short  spaces  from  the  second  and  the  canine  alveolus.  The  vertical  part  is  rela- 
tively wide  above.  The  condyle  is  convex  in  both  directions,  wide  in  front,  narrow 
and  declivitous  behind.  The  very  small  and  thin-edged  coronoid  process  is  not 
quite  so  high  as  the  condyle,  from  which  it  is  separated  by  a  very  wide  notch.  The 
mandibular  foramen  is  large.  The  two  halves  of  the  bone  unite  soon  after  birth 
in  the  improved  breeds. 

The  body  of  the  hyoid  bone  is  broad  from  before  backward,  short  transverselj-, 
and  bears  on  its  ventral  aspect  a  very  short  pointed  lingual  process.  The  thyroid 
cornua  are  wide  and  curved,  concave  and  grooved  dorsally;  their  ends  are  attached 
to  the  thyroid  cartilage  of  the  larynx  by  rather  long  bars  of  cartilage.  The  small 
cornua  are  short,  wide,  and  flattened  dorso-ventrally ;  they  are  attached  to  short 
bars  which  project  from  the  junction  of  the  body  and  thyroid  cornua.     The  middle 

cornu  is  a  little  longer  than  the 
small  cornu,  but  is  relatively 
slender;  it  is  largely  cartila- 
ginous in  the  young  subject 
and  does  not  ossify  at  either 
end.  The  great  cornu  is  a 
very  slender  rod,  slightly  en- 
larged at  either  end ;  the  upper 
extremity  is  attached  to  the 
hyoid  process  of  the  temporal 
by  a  rather  long  and  wide  bar 
of  cartilage. 


t'TXl^'^^ 


,/ 


Fig.   lis 


-Mandible  of  Pig. 
a,  Body  of  mandible;  b,  horizontal  part  of  ramus;  /,  vertical 
part  of  ramus;  c,  interalveolar  border;  c',  interval  between  canine 
and  corner  incisor;  c"  ,  interval  between  first  and  second  premolars; 
d,  mental  foramina;  c,  vascular  impression;  g,  coronoid  proces.s; 
h.  condyle;  i,  sigmoid  notch;  k\  mandibular  foramen;  I~7,  cheek 
teeth,  8,  canine  tooth;  9,  10,  11,  incisors.  (Ellenberger-Baum, 
Anat    d.  Haustiere.) 


THE  SKULL  AS  A  WHOLE 
The  length  and  the  profile 
contour  vary  greatly  in  dif- 
ferent subjects.  Primitively 
the  skull  is  long — especially  in 
its  facial  ]5art — and  the  frontal 
profile  is  almost  st  raight .  The  condition  is  very  ])ronounced  in  wild  or  semi-feral  pigs, 
and  exists  also  in  the  improved  breeds  during  extreme  youth.  Most  of  the  latter  are 
decidedly  brachyccphalic  when  full.y  tlcveloped;  the  face  is  "dished"  in  a  pro- 
nounced fashion.  The  frontal  region  slopes  sharply  upward,  and  the  nasal  region 
is  shortened,  and  in  some  specimens  even  distinctly  concave  in  profile.  The  supra- 
orbital foramina  are  about  midway  between  the  orbital  margin  and  the  frontal 
suture.  The  supraorbital  grooves  extend  forward  from  the  foramina  to  the  nasal 
region  and  turn  outward  and  downward  toward  the  infraorbital  foramina  over  the 
ridges  which  seijanito  the  nasal  and  lateral  regions. 

The  lateral  surface  is  triangular  when  the  mandilile  is  included.  The  tem- 
poral fossa  is  entirely  lateral  and  its  long  axis  is  almost  vertical.  It  is  bounded 
above  by  the  occipital  crest,  behind  by  the  temporal  crest,  in  front  by  the  parietal 
crest,  and  is  marked  off  from  the  orbital  cavitj'  by  the  supraorbital  process  and  a 
curved  crest  which  extends  from  it  to  the  root  of  the  pterygoid  process.  The 
zygomatic  arch  is  strong,  high,  and  flattened  from  side  to  side.  Its  root  is  notched 
above  and  bears  a  projection  below.  It  curves  sharply  upward  behind  antl  forms 
a  pointed  recurved  projection  al)Ove  and  in  front  of  the  external  auditory  meatus. 


THE    SKULL   AS   A   WHOLE  145 

The  orbit  is  small.  Its  margin  is  deficient  behind  in  the  dry  skull,  thick  and  rounded 
in  front  and  Ijclow.  The  ca'V'ity  is  limited  below  by  a  ridge  on  the  frontal  and 
lacrimal  bones,  and  is  separated  by  a  crest  from  the  temporal  fossa.  The  inner 
wall  is  perforated  above  by  the  orbital  opening  of  the  supraorbital  canal,  and  below 
by  the  optic  and  ethmoidal  foramina;  on  its  antero-inferior  part  is  the  fossa  in 
which  the  inferior  oblique  muscle  of  the  eye  takes  origin.  Two  lacrimal  foramina 
are  found  on  or  close  to  the  anterior  margin.  The  ptery go-palatine  fossa  is  well 
defined;  its  upper  part  forms  a  deep  groove  which  leads  from  the  large  foramen 
in  the  sphenoid  (like  that  of  the  ox)  to  the  very  large  maxillary  foramen.  The  pre- 
orbital  region  is  deeply  grooved  in  its  length  and  is  clearlj'  marked  off  by  a  ridge 
from  the  nasal  and  frontal  regions.  The  facial  crest  is  short,  usually  thin-edged, 
and  lies  above  the  fifth  and  sixth  check  teeth.  A  little  (ca.  2  cm.)  in  front  of  it  is 
the  infraorbital  foramen.  There  is  a  ridged  prominence  over  the  canine  alveolus. 
In  some  skulls  the  anterior  part  of  the  upper  jaw  is  inclined  upward. 

The  most  striking  features  of  the  basal  surface  are  as  follows:  The  paramas- 
toid  processes  are  extremely  long,  less  flattened  than  in  the  horse  and  ox,  and  nearly 
vertical.  At  the  inner  side  of  the  root  of  each  is  the  hypoglo-ssal  foramen,  and  in 
front  of  it  are  the  stjdo-mastoid  foramen  and  a  deep  cavity  in  which  the  hyoid 
process  is  concealed.  The  bulla  ossea  is  long,  compressed  lateralh',  and  bears  a 
sharp,  short,  muscular  process.  The  basioccipital  is  wide  and  flattened;  it  bears 
a  median  crest  and  two  lateral  tubercles.  The  posterior  nares  are  small  and  are 
wider  below  than  above.  On  either  side  of  them  is  the  tuberosity  of  the  palate 
bone,  and  above  this  is  the  pterygoid  fossa.  The  palate  is  remarkably  long  and  is 
relatively  narrow.  It  constitutes  about  two-thirds  of  the  entire  length  of  the  skull. 
It  is  widest  between  the  canines  and  premolars  and  narrow  at  each  end.  It  is 
marked  by  a  crest  medially  and  by  the  palatine  foramen  and  groove  laterally. 
The  anterior  part  bears  transverse  ridges.  It  is  moderately  arched  from  side  to 
side.  In  some  specimens  it  is  nearly  straight  or  slightly  concave  in  its  length; 
in  others  it  curves  upward  to  a  variable  degree  in  front.  The  posterior  end  always 
slopes  upward  more  or  less. 

The  posterior  or  nuchal  surface  is  remarkable  for  its  height  and  the  breadth 
of  the  occipital  crest.  The  central  part  above  the  foramen  magnum  is  smooth  and 
concave  from  side  to  side,  and  is  bounded  laterally  by  ridges,  which  converge  below 
and  end  on  two  tubercles  at  the  upper  margin  of  the  foramen  magnum.  The  sur- 
face is  separated  from  the  temporal  fosste  by  the  temporal  crests,  which  curve 
downward  and  outward  and  blend  with  the  external  auditory  canals.  The  mastoid 
process  has  the  form  of  a  plate  which  overlaps  the  root  of  the  paramastoid  process 
and  bears  a  crest  on  its  anterior  part. 

The  cranial  cavity  is  small,  in  spite  of  the  great  size  of  the  cranium;  the 
discrepancy  is  due  to  the  enormous  development  of  the  frontal  sinuses  in  the  adult. 
It  is  relatively  longer,  but  much  lower  than  that  of  the  ox.  Its  width  is  greatly 
diminished  between  the  orbits.  The  olfactory  fossae  are  extensive  and  very  oblique. 
The  floor  resembles  that  of  the  ox,  but  the  foramen  ovale  is  absent,  the  dorsum 
sellae  is  more  developed,  and  the  foramen  lacerum  basis  cranii  is  like  that  of  the 
horse.  Two  oblique  lateral  crests  clearly  mark  the  limit  between  the  cerebral  and 
cerebellar  compartments.  The  tentorium  osseum  and  the  parieto-temporal  canals 
are  absent. 

The  nasal  cavity  is  very  long.  Its  posterior  part  is  divided  by  a  horizontal 
plate  into  olfactory  and  respiratory  parts.  The  olfactory  part  or  fundus  is  above, 
and  contains  the  ethmoturbinals  and  ethmoidal  meatuses.  The  lower  part  is 
continuous  with  the  inferior  meatus  and  leads  to  the  pharyngeal  orifice;  hence  it  is 
sometimes  called  the  naso-pharyngeal  meatus.  The  bony  roof  is  almost  complete 
in  front  on  account  of  the  great  length  of  the  nasal  bones. 

The  frontal  sinus  is  a  vast  excavation  in  the  adult  animal.  It  involves  all  of 
10 


146  SKELETON    OF    THE    PIG 

the  roof  and  almost  all  of  the  sides  of  the  cranium,  and  extends  forward  into  the 
roof  of  the  nasal  cavity  a  variable  distance — sometimes  as  far  as  a  transverse  plane 
through  the  infraorbital  foramina.  The  septum  between  the  right  and  left  sinuses 
is  usually  deflected  in  an  irregular  manner  in  its  middle  part,  but  is  practically 
median  at  either  end.  Each  sinus  is  subdivided  by  numerous  septa,  some  of  which 
are  complete.  Thus  the  sinus  is  divided  into  compartments,  each  of  which  com- 
municates with  an  ethmoidal  meatus. 

In  the  young  pig  the  sinus  is  small  and  is  confined  to  the  anterior  part  of  the  frontal  bone. 
Later  it  extends  backward,  outward,  and  to  a  less  extent  forward.  In  the  old  subject  it  penetrates 
laterally  into  the  supraorbital  process  and  the  root  of  the  zygomatic  process  of  the  temporal  bone, 
and  behind  almost  down  to  the  foramen  mafinum  and  the  occipital  condyles.  It  then  consists 
of  six  to  eight  compartments  usually. 

The  maxillary  sinus  is  relatively  small.  Its  anterior  end  is  a  little  less  than 
an  inch  (ca.  2  cm.)  behind  the  infraorbital  foramen,  and  it  extends  upward  into 
the  lacrimal  and  backward  into  the  malar  bone.  The  infraorbital  canal  passes 
along  its  fioor,  and  the  roots  of  the  molar  teeth  do  not  project  up  into  it.  It  does 
not  communicate  with  the  frontal  and  sphenoidal  sinuses,  but  with  the  posterior 
part  of  the  middle  meatus  by  means  of  a  considerable  orifice. 

The  sphenoidal  sinus  is  very  large.  It  involves  the  bod.y,  pterygoid  processes, 
and  temporal  wings  of  the  sphenoid  bone,  and  extends  into  the  squamous  temporal. 
It  communicates  with  the  ventral  ethmoidal  meatus. 

There  is  a  small  sinus  in  the  perpendicular  part  of  the  jDalate  bone  which  com- 
municates with  an  ethmoidal  meatus. 


BONES  OF  THE  THORACIC  LIMB 

The  scapula  is  very  wide,  the  index  being  about  1 : 0.7.  The  spine  is  tri- 
angular and  is  very  wide  in  its  middle,  which  curves  backward  over  the  infra- 
spinous  fossa  and  bears  a  large  tuberosity.  Its  lower  part  bears  a  small  projection 
(rudimentary  acromion).  The  anterior  border  is  strongly  convex  in  profile,  sinuous 
when  viewed  from  the  front,  and  thick  and  rough  in  its  middle.  The  posterior 
border  is  wide,  slightly  concave,  and  bears  an  outer  rough  lip.  The  vertebral 
border  is  convex,  and  the  cartilage  is  not  so  extensive  as  in  the  horse  and  ox.  The 
cervical  angle  is  thin  and  bent  inward  a  little.  The  dorsal  angle  is  thick  and  is 
about  a  right  angle.  The  neck  is  well  defined.  The  rim  of  the  glenoid  cavity  is 
rounded  and  not  notched.  The  tuberosity  is  just  above  the  antero-internal  part 
of  the  glenoid  cavity  and  bears  no  distinct  coracoid  process. 

The  humerus  has  an  appearance  in  profile  somewhat  like  an  italic  /  minus  the 
cross-bar;  this  is  due  to  the  marked  backward  and  forward  inclination  of  the  prox- 
imal and  distal  ends  respectively.  The  shaft  is  decidedly  compressed  from  side  to 
side.  The  internal  surface  is  extensive  and  flattened;  it  is  separated  from  the 
anterior  surface  by  a  distinct  border,  and  bears  no  teres  tubercle.  The  musculo- 
spiral  groove  is  shallow.  The  deltoid  tuberosity  is  small,  and  there  is  a  larger 
roundetl  eminence  midway  between  it  and  the  external  tuberosity.  The  nutrient 
foramen  is  on  the  posterior  surface  below  its  middle.  The  head  is  more  strongly 
curved  and  the  neck  better  marked  than  in  the  horse  or  ox.  The  external  tuber- 
osity is  very  large  and  extends  upon  the  front  of  the  extremity.  It  is  divided  into 
two  high  prominences  by  a  wide  deep  groove.  There  is  a  third  eminence  below 
and  externally  for  the  attachment  of  the  supraspinatus  muscle.  The  bicipital 
groove  is  at  the  front  of  the  inner  side;  it  is  undivided  and  is  almost  converted  into 
a  canal.  The  outer  groove  on  the  distal  articular  surface  is  so  shallow  as  to  give 
the  appearance  of  two  condyles  of  similar  size.  The  olecranon  fossa  is  very  deep, 
and  the  phite  of  bone  which  separates  it  from  the  coronoid  fossa  is  thin  and  some- 


BONES    OF   THE    THORACIC    LIMB 


147 


times  perforated.     The  proximal  end  unites  with  the  shaft  at  three  and 
years,  the  distal  at  one  year. 

The  radius  is  short  antl  narrow,  hut  thick.  The  shaft 
increases  in  size  from  above  downward.  The  greater  part 
of  the  posterior  surface  is  in  apposition  with  the  ulna;  this 
part  is  marked  by  a  vascular  furrow  which  runs  downward 
from  the  upper  interosseous  space,  and  has  the  nutrient 
foramen  at  its  proximal  end.  The  bicipital  tuberosity  is 
represented  by  a  rough  area.  The  distal  end  is  relatively 
large.  Its  carpal  surface  consists  of  concavo-convex  facets 
for  the  radial  and  intermediate  carpal  bones.  There  is  a 
wide  shallow  groove  on  the  middle  of  the  front.  The 
proximal  end  fuses  with  the  shaft  at  one  year,  the  distal 
at  three  and  a  half  years. 

The  ulna  is  massive.  It  is  much  longer  and  con- 
siderably heavier  than  the  radius.  The  shaft  is  curved. 
The  anterior  surface  is  convex  and  most  of  it  is  rough 
and  attached  to  the  radius  by  the  interosseous  liga- 
ment. There  is  a  smooth  area  on  the  upper  third, 
which  concurs  with  the  radius  in  forming  the  upper 
interosseous  space,  and  is  marked  in  its  upper  part 
by  the  nutrient  foramen.  From  this  space  a  vascular 
furrow  passes  downward  to  the  lower  part  of  the  shaft, 
where  there  is  often  a  distal  interosseous  space  for 
the  passage  of  vessels.  The  internal  surface  is  exten- 
sive, concave,  and  smooth.  The  external  surface  is 
slightly  convex,  and  its  upper  part  is  marked  by  an 
oblique  rough  line  or  ridge.  The  proximal  extremity  is 
large  and  is  bent  inward  somewhat;  its  length  is  more 
than  one-third  of  that  of  the  entire  bone.  The  distal  ex- 
tremity is  relatively  small;  it  articulates  with  the  ulnar 
and  accessory  carpal  bones,  and  is  notched  in  front  to 
accommodate  the  ridge  on  the  radius.  The  bone  contains 
a  considerable  medullary  canal.  The  bone  is  consolidated 
at  three  to  three  and  a  half  years. 

The  carpus  comprises  eight  bones,  four  in  each  row. 
The  bones  of  the  proximal  row  resemble  those  of  the  ox, 
with  the  exception  of  the  accessory,  which  is  more  like 
that  of  the  horse,  but  has  no  external  groove.  The  first 
carpal  is  small,  elongated  from  before  backward,  rounded, 
and  articulates  in  front  with  the  second  carpal.  The  latter 
is  high  and  narrow,  and  articulates  with  the  second  and 
third  metacarpal  bones  below.  The  third  carpal  articu- 
lates with  the  radial  and  intermediate  above,  the  third 
metacarpal  bone  below.  The  fourth  is  the  largest  bone 
of  the  row;  it  articulates  with  the  intermediate  and  ulnar 
above,  the  fourth  and  fifth  metacarpals  below,  and  bears 
a  tuberosity  on  its  volar  aspect. 

Four  metacarpal  bones  are  present.  The  first  is 
absent,  the  third  and  fourth  arc  large  and  carry  the  chief 
digits,  while  the  second  and  fifth  are  much  smaller  and 
bear  the  accessory  digits.  Their  proximal  ends  articulate 
with  each. other  and  with  the  carpus  as  indicated  above, 
solidated  at  about  two  years  of  age. 


half 


Fig. 


Ma 


Forearm 

OF     Pig,     Axtero-ex- 

TKRNAL  View. 

a,  Radius;  b,  ulna;  c, 
radial  carpal;  d,  intermediate 
carpal;  c,  ulnar  carpal;  /,  ac- 
cessory carpal;  g,  first  carpal; 
/(,  second  carpal;  /,  third  car- 
pal; k,  fourth  carpal;  l-o, 
second  to  fifth  metacarpal 
bones;  ;>-«,  second  to  fifth  dig- 
its; /,  olecranon;  2.  beak  of 
ulna  (proc.  anconeus);  S.  semi- 
lunar notch;  4,  styloid  process 
of  ulna;  6,  styloid  process  of 
radius;  6.  distal  epii>hyseal 
lines;  7,  first  phalanx;  S.  second 
phalanx;  9,  third  phalanx. 
(Ellenberger-Baum,  Anat.  d. 
Haustiere.) 


The  bones  are  con- 


148  SKELETON    OF   THE    PIG 

The  third  aiui  fourth  metacarpals  are  flattened  from  l)efore  backward,  three-sided,  and 
phiced  close  together.  The  distal  end  of  each  bears  a  trochlea  for  articulation  with  the  first 
phalanx  and  the  sesamoids.  The  third  is  the  wider  of  the  two,  and  articulates  with  all  of  the 
lower  row  of  the  carpus  except  the  first.  The  fourth  articulates  with  the  fourth  carpal  chiefly, 
but  has  a  small  facet  for  the  third.  The  second  and  fifth  metacarpals  are  placed  further  back 
than  the  chief  bones.  The  fifth  is  considerably  the  thicker  of  the  two.  The  proximal  ends  are 
small  and  articulate  with  the  corresponding  carpal  and  metacarpal  bones.  The  distal  end  is 
relatively  large;   its  articular  surface  is  condyloid  in  front,  trochlear  behind. 

Each  chief  digit  comprises  three  phalanges  and  three  sesamoids.  The  bones 
of  the  chief  digits  resemble  those  of  the  ox  in  form,  but  there  is  no  foramen  on  the 
interdigital  side  of  the  extensor  process  and  the  proximal  sesamoids  are  narrow  and 
ridged  laehind.  The  phalanges  of  the  accessory  digits  (which  do  not  reach  the' 
ground  ordinarily)  are  similar  in  form  but  much  smaller. 


BONES  OF  THE  PELVIC  LIMB 

The  OS  coxae  is  long  and  narrow.  The  ilium  and  ischium  are  almost  in  line 
with  each  other  and  sagittal  in  direction.  The  wing  of  the  iliiun  bends  outward 
much  less  than  in  the  horse  or  ox.  The  gluteal  surface  is  divided  into  two  fossae 
by  a  ridge,  which  is  continuous  with  the  superior  ischiatic  spine  behind.  The 
inner  surface  presents  an  extensive  rough  area  behind,  which  is  in  apposition  with 
the  wing  of  the  sacrum.  The  smooth  iliac  area  is  narrow,  and  is  bounded  above 
by  a  ridge.  The  crest  or  anterior  border  is  convex,  and  is  thick,  rough,  and  prom- 
inent in'its  middle,  which  forms  the  highest  point  of  the  bone.  The  internal  angle 
is  lower  than  the  crest,  is  directed  backward,  and  articulates  internally  with  the 
sacrum.  The  external  angle  is  lower  still  and  is  very  little  thickened.  The 
ischia  in  the  female  are  somewhat  divergent  and  flattened  behind.  The  tubera 
are  everted  and  bear  three  prominences.  There  is  a  crest  or  tuberosity  on  the 
ventral  surface.  The  superior  ischiatic  spine  is  like  that  of  the  cow,  but  is  slightly 
incurved  and  the  muscular  ridges  on  its  outer  face  are  more  pronounced.  The 
symphyseal  part  of  the  pubis  is  thick  and  the  two  bones  are  almost  in  a  horizontal 
plane.  The  ilio-pectincal  eminence  is  prominent  and  the  psoas  tubercle  is  well 
marked. 

The  acetabulum  is  placed  a  little  further  back  than  in  the  ox.  The  rim  is 
thick  and  is  cut  into  posteriorly  by  a  narrow  fissure,  which  leads  into  the  deep  fossa 
acetabuli.  The  three  pieces  of  the  os  coxoe  are  fused  by  the  end  of  the  first  year, 
but  the  crest  and  the  ischial  tubera  are  partially  separate  till  the  sixth  or  seventh 
year.  The  symphysis  does  not  usually  undergo  complete  anchjdosis.  Interischial 
bones  are  present. 

The  inlet  of  the  pelvis  is  elliptical  and  very  oblique.  In  a  sow  of  full  size  the 
conjugate  diameter  is  about  five  to  six  inches  (10  to  12  cm.)  and  the  transverse 
about  three  and  a  half  to  four  inches  (ca.  8.75  to  10  cm.).  In  the  female  the  floor 
is  relatively  wide  and  flattened,  especially  at  the  outlet,  where  the  tubera  are 
everted;  it  also  has  a  decided  downward  inclination  behind.  The  pelvic  axis 
is  therefore  correspondingly  oblique.  The  ischial  arch  is  wide.  In  the  boar  the 
pubis  is  much  thicker  and  the  ischia  are  not  everted  posteriorly.  The  inlet  is 
smaller.  The  floor  is  concave  from  side  to  side  and  slopes  decidedly  less  than  in 
the  sow.  The  su])erior  ischiatic  spines  are  more  incurved,  and  the  ischial  arch  is 
nmch  narrower  and  tlceper. 

The  femur  has  a  relatively  wide  and  massive  shaft,  on  which  four  surfaces  might 
be  recognized.  The  principal  nutrient  foramen  is  situated  in  the  proximal  third 
of  the  anterior  surface.  The  posterior  surface  is  wide,  and  is  limited  outwardly 
by  a  ridge  which  extends  from  the  trochanter  major  to  the  large  external  supra- 
condyloid  crest.  There  is  no  supracondyloid  (plantar)  fossa.  The  head  is  strongly 
curved,  and  is  marked  toward  the  iimer  side  by  a  rather  large  depression  for  the 


BONES    OF   THE    PELVIC    LIMB 


149 


attachment  of  the  round  Hgament.  The  neck  is  distinct.  The  trochanter  major, 
ahhough  massive,  does  not  extend  up  as  high  as  the  head.  The  trochanteric 
ridge  and  fossa  resemble  those  of  the  o.\.  The  external  (third)  trochanter  is  absent. 
The  ridges  of  the  trochlea  are  similar  and  almost  sagittal. 

The  shaft  of  the  tibia  is  slightly  curved,  convex  internally.  The  tuberosity 
is  grooved  in  front,  and  a  narrow  sulcus  separates  it  from  the  external  condyle. 
The  facet  for  the  fibula  is  on  the  posterior  border  of  the  latter,  and  is  bounded 
internally  by  an  eminence.  The  upper  part  of  the  crest  is  very  prominent  and 
curves  outward.  The  distal  end  resembles  in  general  that  of  the  ox,  but  is  rela- 
tively narrower  transversely  and  thicker  from  before  liackward. 

The  fibula  extends  the  entire  length  of  the  region,  and  is  separated  from  the 
tibia  by  a  wide  interosseous  space.  The  shaft  is  flattened  from  side  to  side; 
the  proximal  part  is  wide  and  deeply  grooved  externally;  the  lower  part  is  narrower 
and  thicker.  The  proximal  end  is  flattened,  grooved  externally,  and  articulates 
internally  with  the  external  condyle  of  the  tibia.  The  di.stal  end  forms  the  external 
malleolus.  It  is  grooved 
externally,  and  articulates 
wnth  the  tibia  and  tibial 
tarsal  internally,  with  the 
fibular  tarsal  bone  dis- 
tally. 

The  patella  is  very 
much  compressed  lateralh' 
and  presents  three  sur- 
faces. 

The  tarsus  comprises 
seven  bones.  The  tibial 
and  the  fibular  tarsal  re- 
semble in  general  those  of 
the  ox.  The  axis  of  the 
tibial  is,  however,  slightly 
oblique  downward  and  in- 
ward, and  its  distal  end 
bears  a  double  trochlea  for 
articulation  with  the  cen- 
tral and  fourth  tarsals. 
The  tuber  calcis  is  deeply 
grooved   posteriorly.      The 

central  tarsal  is  narrow  transversely  and  thick.  Its  proximal  surface  is  deeply 
concave,  and  the  posterior  bears  a  large  tubercle.  The  first  tarsal  is  high  and 
narrow;  it  articulates  with  the  central  and  second  tarsals  and  the  second  metatarsal 
bone.  The  second  tarsal  is  small  and  somewhat  prismatic;  it  articulates  with 
the  central  above,  the  third  in  front,  the  first  behind,  and  the  second  and  third 
metatarsals  lielow.  The  third  tarsal  is  much  larger,  and  is  compressed  from  above 
downward,  wide  in  front,  narrow  behind.  It  articulates  with  the  central  tarsal 
above,  the  third  metatarsal  below,  the  second  tarsal  internally,  and  the  fourth  tarsal 
externally.  The  fourth  tarsal  is  large.  Its  external  face  is  crossed  l)y  an  oblique 
groove  for  the  tendon  of  the  peroneus  longus.  The  internal  surface  articulates 
with  the  central  and  third  tarsals.  The  proximal  surface  supports  the  tibial  and 
fibular  tarsal  bones,  and  the  distal  surface  rests  on  the  fourth  and  fifth  metatarsals. 
It  ossifies  from  two  centers. 

The  four  metatarsal  bones  resemble  the  corresponding  bones  of  the  fore  limb, 
but  are  somewhat  longer.  The  proximal  ends  of  the  third  and  fourth  each  have  a 
considerable  projection  behind;  the  process  on  the  third  has  a  facet  for  articulation 


Fig.  114. — Cox.\l  Boxes  of  Pig,  Left  Po-sterior  View. 
a.  Wing,  b.  shaft,  c,  external  angle,  d.  anterior  border,  <■,  internal 
angle,  /,  gluteal  line  of  ilium;  g,  great  sciatic  notch;  h,  smooth,  i,  rough 
part  of  ventral  surface  of  ilium;  k,  psoas  tubercle;  (,  ilio-pectineal  emi- 
nence; m,  acetabular  branch,  n.  symphyseal  branch  of  pubis;  o,  obtur- 
ator foramen;  p,  p',  ischium;  q,  9',  tuber  ischii;  r,  symphysis;  s,  ischial 
arch;  t.  (',  superior  ischiatic  spine;  n,  acetabulum;  r,  epiphyseal  line. 
(EUenberger-Baum,  Anat.  d.  Haustiere.) 


150  SKELETON    OF   THE    DOG 

with  a  discoid  sesamoid  bone.     The  second  and  fifth  are  placed  more  on  the  pos- 
terior aspect  of  the  large  Ijones  tlian  is  the  case  in  the  fore  limb. 

The  first  and  second  phalanges  are  a  little  longer  and  narrower  than  those  of 
the  fore  linil). 


SKELETON  OF  THE  DOG 

VERTEBRAL  COLUMN 

The  vertebral  formula  is   CjT^Ljfj^SjCyjj.^s- 

The  cervical  vertebrae  are  relatively  longer  than  in  the  ox  and  the  pig.  The 
bodies  of  the  typical  vertebrae  diminish  in  length  from  first  to  last  and  are  com- 
pressed dorso-ventrally.  The  anterior  extremity  is  moderately  convex  and  the 
posterior  slightly  concave;  both  are  oblique.  The  median  ridge  and  lateral  grooves 
on  the  upper  surface  of  the  body  are  very  well  marked.  The  second,  third,  and 
fourth  have  distinct  ventral  spines.  The  spinous  process  of  the  third  has  the 
form  of  a  long  low  crest;  in  the  remainder  it  is  higher,  blunt-pointed,  and  inclined 
forwaril.  The  transverse  processes  of  the  thirtl,  fourth,  and  fifth  project  downward 
and  backward,  and  divide  into  two  branches;  of  these,  the  anterior  one  is  thin, 
and  the  posterior  is  thick  and  tuberculate  at  its  free  end.  The  process  of  the 
sixth  has  two  parts;  one  of  these  is  an  extensive  quadrilateral  plate  directed  down- 
ward and  outward  and  ridged  on  its  inner  surface;  the  other  part  is  short  and  blunt, 
and  is  directed  outward  and  a  little  backward  and  upward.  The  seventh  is  readily 
distinguished  by  its  shortness,  the  length  of  its  spine,  and  the  single  transverse 
process.  The  posterior  articular  processes  bear  tubercles  which  are  large  on  the 
third,  fourth,  and  fifth. 

The  ventral  arch  of  the  atlas  is  narrow  from  before  backward,  and  bears  a 
small  tubercle  posteriorly.  The  upper  surface  of  the  dorsal  arch  is  strongly 
convex  and  rough  centrally.  The  wings  are  wide,  flattened,  and  almost  horizontal. 
The  ujipcr  svu'face  is  rough.  There  is  an  alar  notch  (Incisura  alaris)  on  the  anterior 
border  instead  of  the  anterior  foramen.     The  foramen  transversarium  is  present. 

The  body  of  the  axis  is  flattened  dorso-ventrally,  especially  in  front.  The 
odontoid  process  is  rounded  and  relatively  long,  reaching  almost  to  the  occipital 
bone;  it  is  inclined  upward  a  little.  The  articular  surfaces  which  flank  it  are 
condyloid  in  form  and  very  oblique.  The  inferior  surface  is  wide,  and  is  divided 
by  a  median  crest  into  two  fossae.  The  transverse  processes  are  single,  pointed, 
directed  backward  and  outward,  and  perforated  by  relatively  large  foramina 
transversaria.  The  spinous  process  is  thin  and  of  moderate  height,  but  very  long; 
it  is  prolonged  forward  so  as  to  overhang  the  dorsal  arch  of  the  atlas,  and  is  ter- 
minated behind  by  a  tuberosity  which  is  connected  by  two  crests  with  the  posterior 
articular  processes.  The  anterior  notches  are  large  and  are  never  converted  into 
foramina. 

The  bodies  of  the  thoracic  vertebrae  are  wide  and  com]3ressed  dorso-ventrally, 
especially  at  each  end  of  the  region.  Their  convex  anterior  surfaces  are  depressed 
in  the  middle.  The  posterior  facets  for  the  heads  of  the  ribs  are  absent  on  the 
last  three  or  four.  The  transverse  processes  resemble  those  of  the  horse.  They 
bear  manmiillary  processes  except  at  the  anterior  end  of  the  region.  The  facets 
for  the  tubercles  of  the  ribs  are  large  and  concave  in  the  anterior  part  of  the  series, 
and  become  smaller  and  slightly  convex  further  back.  The  last  three  have  acces- 
sory processes  also.  The  first  three  or  four  spinous  processes  are  about  equal 
in  length.  Behind  this  they  become  gradually  shorter  to  the  tenth,  and  then  remain 
equal.  The  backward  slope  is  most  marked  in  the  ninth  and  tenth.  The  eleventh 
is  practically  vertical  (anticlinal  vertebra)  and  the  last  two  incline  slightly  forward. 


VERTEBRAL    COLUMN 


151 


The  bodies  of  the  lumbar  vertebrae  are  decidedly  flattened  dorso-ventrallj', 
and  increase  in  width  from  first  to  last.  The  length  increases  to  the  sixth.  The 
transverse  processes  are  plate-like  and  are  directed  forward  and  downward.  Their 
length  increases  to  the  fifth  and  sixth.  They  form  no  joints  with  each  other  or 
with  the  sacrum.  Their  extremities  are  enlarged,  with  the  exception  of  the  last. 
The  accessory  processes  project  Ijackward  over  the  posterior  notches  of  the  first 
five.     The  anterior  articular  processes  are  large,  compressed  laterally,  and  bear 


Fig.  lis. — Skeleton  of  Dog,  Lateral  View. 
a,  Cranium;  b,  face;  c,  mandible;  1H-7H,  cervical  vertebrae;  ISB,  last  thoracic  vertebra;  1L~7L.  lumbar 
vertebra";  iv,  sacrum;  6',  coccygeal  vertebrae;  lR-lSl{,T\hs\  iif.A-M.,  costal  cartilages;  ^7.,  sternum;  c^,  scapula;  </', 
supraspinous  fossa;  rf",  infraspinous  fossa;  i,  spine  of  scapula;  5,  acromion;  5,  tuberosity  of  scapula;  3',  articular 
end  of  scapula;  e,  humerus;  4.  bead  of  humerus;  5,  external  tuberosity  of  humerus;  5',  deltoid  ridge;  6,6',epicon- 
dyles  of  humerus;  7,  external  condyloid  crest;  7',  coronoid  fossa;  /.radius;  p.  ulna;  S,  olecranon;  5,  "beak"  of 
ulna;  A,  carpus;  /.metacarpus;  A:,  proximal  phalanges;  Z,  middle  phalanges;  77i,  distal  phalanges;  n,  sesamoid;  p, 
ilium;  70,  wing  of  ilium;  ii,  shaft  of  ilium;  /2,  crest  of  ilium;  /S,  external  angle  of  ilium  (tuber  coxa-);  i.<,  inter- 
nal angle  of  ilium  (tuber  sacrale);  75,  superior  ischiatic  spine;  (/.pubis;  r,  ischium;  iff,  tuber  ischii;  /r.  acetabulum; 
S,  femur;  IS,  head  of  femur;  19,  trochanter  major;  20.  trochanter  minor;  St,  trochanter  tertius;  S2,  23,  con- 
dyles; Si,  25,  epicondyles;  28,  trochlea;  t.  patella;  v,  tibia;  27,  tuberosity  of  tibia;  2S,  29,  condyles  of  tibia; 
30,  internal  malleolus;  r,  fibula;  St.  external  malleolus;  32,  head  of  fibula;  w,  tarsus;  x,  metatarsus;  i/,  phal- 
anges; 33,  occipital  bone;  34,  paramastoid  (styloid)  process;  .3c,  parietal  bone;  36,  frontal  bone;  37,  lacrimal 
bone;  SS,  malar  bone;  39,  squamous  temporal;  iO.  maxilla;  W ,  infraorbital  foramen;  it,  premaxilla;  42, 
nasal  bone;  43.  external  auditory  meatus;  44.  canine  tooth;  45.  masseteric  fossa;  4S,  angular  process  of  man- 
dible.     (.\fter  EUenberger,  in  Leisering's  Atlas.) 


mammillary  processes.  The  spinous  processes  are  broad  below,  narrower  above, 
and  with  the  exception  of  the  last,  incline  a  little  forward.  Their  height  diminishes 
behind  the  fourth. 

The  sacrum  results  from  the  early  fusion  of  three  vertebra.  It  is  short, 
wide,  and  quadrangular.  The  spines  are  fused  to  form  a  median  crest,  which  is 
notched,  however,  between  the  summits  of  the  spines.  On  either  side  are  two 
tubercles,  vestiges  of  the  fused  articular  processes.     The  pelvic  surface  is  deeply 


152 


SKELETON    OF   THE    DOG 


concave  and  presents  two  pairs  of  foramina.  The  wings  are  prismatic  and  very 
high.  Their  lateral  surfaces  are  extensive,  face  almost  directly  outward,  and  bear 
an  auricular  surface  on  the  lower  part.  The  anterior  surface  of  the  body  of  the 
first  vertebra  is  extensive,  depressed  in  its  middle,  and  bears  a  prominent  lip  below. 
The  anterior  articular  processes  are  large  and  have  extensive,  slightly  concave 


Fig.  116. — .\TLAS  or  Dog,  Viewed  from  Above  and 

Behind. 

a.  Wing;  b,  dorsal  .irch  and  tubercle;  r,  ventral 

tubercle;  d,  intervertebral  foramen;  e,  foramen  trans- 

a;  /,  articular  surface  for  axis.     (Ellenberger- 

.-Vnat.  d.  Hundes.) 


\-J> 


Fig.  117. — Axis  of  Dog,  Left  Lateral  View. 
a.  Odontoid  process;  b,  articular  surface  for  atlas; 
c,  transverse  process;  d;  foramen  transversarium;  d',  pos- 
terior opening  of  d;  e,  spine;  /,  posterior  articular  pro- 
cess.    (EUenberger-Baum,  Anat.  d.  Hundes.) 


facets  which  face  upward  and  inward.  The  posterior  articular  processes  are  small. 
The  transverse  processes  of  the  last  vertebra  project  backward  and  may  articulate 
or  fuse  with  those  of  the  first  coccygeal.  The  sacral  canal  is  strongly  compressed 
dorso-ventrally. 

The  coccygeal  vertebrae  are  fully  developed  in  the  anterior  part  of  the  region. 
The    arch    is    complete  in  the  first  six 
usually.     The  first  three  or  four   have 
well   developed    articular   processes   at 
each   end.     Behind    this   the    posterior 

pair   quickly  disappears,    and   the   an-  ,,,,1 

terior  ones  become   non-articular  and  flj 

gradually  reduced  in  size.     The  trans- 
verse processes  of  the  first  five  or  six 


Fig.  lis. — Sixth  Cervical  Vertki 
View. 
a,  Ventral  plate,  6,  lateral  part  of  transverse 
process;  c,  foramen  transversarium;  rf,  anterior  artic- 
ular process;  /,  accessory  process;  ff,  spinous  process: 
h,  articular  head  of  body.  (EIlenberger-Baum,  Anat. 
d.  Hundes.) 


Dog,  Left       Fig.  119. — Fourth  Thoracic  Vertebra  of  Dog,  Left- 


View. 
n.  Head;  b,  glenoid  cavity;  c,  facet  for  head  of 
rib;  d,  transverse  process;  e,  facet  for  tubercle  of  rib; 
/,  mammillary  process;  f?,  posterior  articular  process; 
h,  spinous  process.  (EUenberger-Baum,  .\nat.  d. 
Hundes.) 


are  relatively  large;  behind  this  they  (luickly  disappear.  Haemal  arches  (or 
chevron  bones)  in  the  form  of  a  V  or  Y  occur  ventrally  at  the  intercentral 
junctions  of  the  third,  fourth,  and  fifth  usually.  They  transmit  the  middle 
coccygeal  artery,  which  pas.ses  between  pairs  of  ventral  tubercles  further  back. 


THE    RIBS — THE    STERNUM — BONES    OF   THE    SKULL 


153 


Curves. — A  gentle  curve,  convex  ventrally,  is  formed  by  the  cervical  and  the 
anterior  part  of  the  thoracic  region.  The  posterior  thoracic  and  the  lumbar 
vertebrae  form  a  second  curve,  concave  ventrally.  The  sacral  promontory  is  well 
marked.  The  sacrum  and  the  anterior  part  of  the  coccygeal  region  constitute 
a  third  and  more  pronounced  curve,  concave  \'entrally.  In  long-tailed  dogs  the 
sacro-coccygoal  region  is  somewhat  S-shaped. 

Variations. — Numerical  variations  are  not  common  except  in  the  coccygeal 
region.  The  number  of  thoracic  vertebra;  may  be  twelve  or  fourteen,  with  or 
without  compensatory  change  in  the  lumbar  region.  Girard  recorded  a  case  with 
eight  lumbar  and  the  usual  number  of  thoracic  vertebrae.  Six  lumbar  with  fourteen 
thoracic  vertebric  have  been  met  with.  The  first  coccygeal  sometimes  unites 
•with  the  sacrum. 

THE  RIBS 
Thirteen  pairs  of  ribs  are  present,  of  which  nine  are  sternal  and  four  a.sternal. 

They  are  strongly  curved,  narrow,  and 
thick.  Those  in  the  middle  of  the 
series  are  the  longest.  The  first  eight 
or  nine  increase  in  width  in  their  lower 
part.     The  last  rib  is  usually  floating. 


Fig.  120. — Fourth  Lumbar  Vertebra  of  Dog.  Left 
View. 
a,  b.  Articular  surfaces  of  body;  c,  transverse 
process;  d,  accessory  process;  e,  anterior  articular  pro- 
cess; e',  mammillarj' process;  /,  jjosterior  articular  pro- 
cess: g,  spinous  process.  (Ellenberger-Baum,  Anat.  d. 
Hundes.) 


Fir,.  121. — Sacrum  or  Dog,  Dorsal  View. 

a.  Dorsal  sacral  foramina;  b,  articular  surface 
of  body  of  first  segment;  c,  d,  anterior  articular  pro- 
cesses; f,  wing;  /,  rudiments  of  articular  processes; 
g,  lateral  part;  h,  spinous  processes.  (Ellenberger- 
Baum,  .\nat.  d.  Hundes.) 


The  costal  cartilages  are  long  and  curve  forward;  the  length  and  curvature  of 
the  first  pair  is  a  striking  special  feature. 

THE  STERNUM 

This  is  long,  laterally  compressed,  and  consists  of  eight  sternebrae,  which  fuse 
only  in  exceptional  cases  and  in  extreme  old  age.  The  first  segment  is  the  longest; 
its  anterior  end  is  blunt-pointed  and  bears  a  short  conical  cartilage.  It  widens 
at  the  point  of  articulation  of  the  first  pair  of  cartilages.  The  last  segment  is 
also  long,  thinner  than  its  predecessors,  wide  in  front,  and  narrow  behind,  where  it 
bears  a  narrow  xiphoid  cartilage. 

The  thorax  is  distinctly  barrel-like  and  is  not  decidedly  compressed  anteriorly 
like  that  of  the  horse  and  ox.  The  inlet  is  oval  and  is  relatively  wide  on  account 
of  the  marked  curvature  of  the  first  pair  of  ribs  and  cartilages. 


BONES  OF  THE  SKULL 
In  the  follo\\-ing  descriptions  of  the  separate  bones  an  intermediate  type — e.  g.,  a  fox  terrier- 
is  selected,  and  the  most  striking  differences  in  the  brachycephalic  and  dohchocephahc  breeds 
will  be  considered  in  the  section  on  the  skull  as  a  whole. 


154 


SKELETON    OF   THE    DOG 


Cranium 
The  occipital  bone  is  similar  in  position  to  that  of  the  horse.     The  crest  is 
prominent,  angular,  and  directed  Ijackward.     Just  below  the  crest  are  two  rough 


Fig.  122. — Base  of  Skull  of  Dog.  without  Mandible. 
/,  Occipital;  //,  tympanic  part  of  temporal;  lla,  squamous  part  of  temporal:  lib,  mastoid  part  of  tem- 
poral; ///,  sphenoid;  'IV ,  pterygoid:  V,  palate  bone;  1'/,  vomer;  VII,  malar;  VIII ,  zygomatic  arch;  IX,  inner 
wall  of  orbit;  A',  palatine  process  of  maxilla;  .X/,  premaxilla;  A'//,  orbital  cavity;  /,  i,  tubercles  above  foramen 
magnum;  S,  foramen  magnum;  S,  occipital  condyle;  i,  notch  between  occipital  condyles;  B,  condyloid  fossa; 
6,  hypoglossal  foramen;  7,  paramastoid  (styloid,  jugular)  process;  S,  for.  lacerum  and  posterior  opening  of  carotid 
canal;  9,  pctro-occipital  synchondrosis;  10,  petro-tympanic  fissure;  11,  tubercle;  12,  bulla  ossea;  IS,  muscular 
process  of  petrous;  H,  carotid  foramen;  lo,  osseous  Eustachian  tube;  16,  postglenoid  process;  /~,  glenoid 
cavity;  IS,  for.  ovale;  19,  posterior  opening  of  alar  canal;  SO,  external  opening  of  parieto-temporal  canal;  21, 
stylomastoid  foramen:  23,  e.xternal  auditory  meatus;  2S,  temporal  crest;  24,  zygomatic  process  of  temporal 
bone;  25,  body  of  postsphenoid;  26,  body  of  presphenoid;  27,  anterior  opening  of  alar  canal;  2S,  for.  lacerum 
orbitalc;  29,  optic  foramen;  30,  hamulus  of  pterygoid;  SI,  horizontal  part  of  palate  bone;  32,  perpendicular 
part  of  palate  bone;  S3,  median  palatine  suture;  Si,  palato-maxillary  suture:  SB,  jjosterior  nasal  spine;  Se, 
anterior  palatine  foramen:  S7,  palatine  groove;  3.9,  alveolar  border  of  maxilla;  39,  palatine  process  of  maxilla; 
40,  pterygoid  process  of  maxilla:  41,  palatine  fissure:  42,  body  of  premaxilla:  43,  palatine  process  of  premaxilla; 
4.4,  alveolar  border  of  premaxilla;  .{fl.  supraorbital  process  of  frontal  bone.      (Ellenherger-Baum,  Anat.  d.  llundes.) 

imprints  or  tubercles  for  muscular  attachment.     The  surface  below  these  is  convex 
from  side  to  side  and  concave  from  above  downwaril.    On  either  side,  at  the  junction 


CRANIUM  155 

with  the  squamous,  there  is  a  foramen  wliich  coiumunicates  with  the  parieto- 
temporal canal.  The  condyles  an;  somewhat  Hattened  and  are  widely  separated 
above;  at  the  inner  side  of  each 
is  a  short  condyloid  canal,  which 
opens  into  the  parieto-temporal 
canal.  The  paramastoid  processes 
are  very  short.  The  basilar  part 
is  wide  and  joins  the  liulla  ossea  on 
either  side;  its  lower  surface  is 
flattened  and  the  tubercles  are  at 
the  junction  with  the  bulla.  The 
hj-poglossal  foramen  is  small  and 
is  close  to  the  foramen  lacerum 
posterius;  the  latter  is  bounded  in 
front  by  the  l^ulla  ossea,  behind  and 
internally  by  the  occipital  bone. 

The  interparietal  bone  fuses 
with  the  occipital  before  birth. 
It  forms  the  high  posterior  part  of 
the  sagittal  crest,  and  is  wedged  in 
between  the  two  parietal  bones. 
The  tentorium  osseum  is  thin  and 
curved,  concave  ventrally.  Its  base 
concurs  with  the  occipital  and  parie- 
tal bones  in  the  formation  of  a  trans- 
verse canal  which  is  continuous  with 
the  parieto-temporal  canals. 

The  parietal  bone  is  rhomboid 
in  outline  and  is  strongly  curved.  It 
is  extensive  and  forms  the  greater 
part  of  the  roof  of  the  cranial  cavity. 
At  the  junction  of  the  right  and  left 
bones  there  is  a  prominent  sagittal 
crest  which  is  continued  upon  the 
frontal  bones.  The  lower  border 
articulates  with  the  temporal  wing 
of  the  sphenoid  by  its  anterior  part 
and  mth  the  squamous  temporal  in 
the  remainder  of  its  extent.  The 
external  surface  enters  into  the  for- 
mation of  the  temporal  fossa.  The 
internal  surface  is  marked  by  digital 
impressions,  and  by  grooves  for  the 
middle  meningeal  artery  and  its 
branches. 

The  external  surface  of  the 
frontal  bone  is  crossed  by  a 
frontal  crest,  which  extends  in  a 
curve  from  the  sagittal  crest  to  the 
supraorbital  process,  and  separates 
the   frontal     and    temporal    parts. 

The  frontal  parts  of  the  two  bones  form  a  central  depression  and  slope  downward 
and  forward.  The  supraorbital  process  is  very  short,  so  that  the  orbital  m^^rgm 
is  incomplete  as  in  the  pig.     The  supraorbital  foramen  is  absent. 


mala 


Fig.  123. — Skull  of  Dog,  Dorsal  View. 
/.  Occipital;  //,  parietal;  ///,  frontal;  IV,  lacrimal; 
VI,  squamous  temporal;  VII,  nasal;  VIII,  max- 
illa; IX,  premaxilla;  i,  supraoccipital;  S,  interparietal;  3, 
parieto-occipital  suture;  4,  occipital  crest;  6,  sagittal  crest; 
6,  parieto-frontal  suture;  7,  squamous  suture;  S,  parietal  emi- 
nence: 9,  antero-external  angle  of  parietal  bone;  10,  frontal 
crest;  11,  14,  orbital  margin;  1£,  supraorbital  process;  IS, 
frontal  fossa;  13,  temporal  part  of  frontal  bone;  16,  nasal 
process  of  frontal  bone;  IT,  frontal  suture;  IS,  lacrimal  fora- 
men; 19,  maxillary  process  of  frontal  bone;  20,  lacrimo-ma.xil- 
lary  suture;  31,  frontal  process  of  malar  bone;  23,  lacrimal 
process  of  malar;  23,  zygomatic  process  of  malar;  24,  zygo- 
matic process  of  squamous  temporal;  24',  posterior  end  of 
nasal  bone;  Bo,  nasal  suture;  2e,  anterior  end  of  nasal  bone; 
27,  infraorbital  foramen;  2S,  canine  tooth;  29,  cheek  tooth; 
30.  frontal  process  of  maxilla;  31,  body,  32,  nasal  process, 
33.  palatine  process  of  premaxilla;  34.  palalii 
incisor  teeth.     (Ellenberger-Ba 


,  Anat. 


i.les.) 


In  front  there 


15G 


SKELETON    OF   THE    DOG 


is  a  narrow  pointed  nasal  part  which  fits  in  between  the  nasal  bone  and  the  maxilla. 
Theorliital  and  temporal  parts  are  reiativelj' extensive.  Two  ethmoidal  foramina 
are  commonly  present.     The  frontal  sinus  is  confined  to  the  frontal  bone. 

The  parts  of  the  temporal  bone  fuse  early.  The  zygomatic  process  curves 
widely  outward  and  forwanl.  Its  anterior  part  is  beveled  below  and  articulates 
extensively  with  the  corresponding  process  of  the  malar.  The  articular  surface 
for  the  condyle  of  the  mandible  consists  of  a  transverse  groove  which  is  continued 
upon  the  front  of  the  large  postglenoid  process.  Behind  the  latter  is  the  lower 
opening  of  the  parieto-temporal  canal.  There  is  no  condyle.  The  mastoid  part 
is  small,  but  bears  a  distinct  mastoid  process.  The  external  auditory  meatus  is 
large  and  the  canal  very  short,  so  that  one  can  see  into  the  tympanum  in  the  dry 
skull.  The  bulla  ossea  is  very  large  and  is  rounded  and  smooth;  the  inner  side 
is  united  to  the  basioccipital.     Above  this  junction  and  roofed  in  by  the  union 

of  the  petrous  part  and  the  basi- 
/  occipital    is    the    petro-basilar 

canal  (Canalis  petrobasilaris) ; 
this  transmits  a  vein  from  the 
floor  of  the  cranium  to  the 
foramen  lacerum  posterius. 
The  latter  is  in  reality  a  de- 
pression and  is  situated  behind 
the  bulla  ossea.  In  its  pos- 
_  ^  terior  part  is  a  foramen  which 

I  /   {J^ILII    '**'    ^-»'  ^nr^^^^a-^tj^       transmits  the  ninth,  tenth,  and 

^'^— !_  ^     -   ^  ^^^Haai^B^^i^HaM^^M^:.      eleventii   cranial   nerves.      The 

carotid  canal  branches  off  from 
the  i^etrobasilar,  passes  forward 
external  to  it  through  the  inner 
part  of  the  bulla  ossea,  and 
opens  in  front  at  the  carotid 
foramen;  it  transmits  the  in- 
ternal carotid  artery.  The  Eu- 
stachian opening  is  immedi- 
ately external  to  the  carotid 
foramen.  The  muscular  and 
hyoid  processes  are  extremely 
rudimentary.  The  petrous  part 
projects  into  the  cranial  cavity 
and  forms  a  sharp  prominent 
petrosal  crest.  The  inner  sur- 
face presents  a  deep  floccular 
fossa  above  the  internal  auditory  meatus.  The  anterior  surface  is  also  fre(>. 
The  anterior  angle  is  perforated  by  a  canal  for  the  fifth  ci'anial  nerve  (Canalis 
nervi  trig(>mini). 

The  body  of  the  sphenoid  bone  is  flattened  dorso-ventrally.  The  sella  turcica 
is  shallow,  but  the  dorsum  sellic  is  well  developed  and  bears  posterior  clinoid 
processes.  A  jxiir  of  anterior  clinoid  processes  project  back  from  the  roots  of  the 
orbital  wings.  The  latter  are  relatively  small  and  are  crossed  externally  by  a 
crest,  which  is  continued  forward  upon  the  palate  bone.  The  temporal  wings  are 
extensive  and  articulate  above  with  the  parietals.  Perforating  the  roots  of  the 
wings  are  the  following  foramina,  named  from  before  backward:  The  optic  passes 
through  the  orbital  wing.  The  foramen  lacerum  orbitale  is  a  little  lower  and  is 
at  the  junction  of  the  wings.  The  foramen  rotundum  opens  into  the  alar  canal, 
which  passes  through  the  root  of  the  short  but  wide  pterygoid  process.     The 


Fig.  124. — Cranial  Cavity  of  Dog,  as  Seen  on  Sagittal  Sec- 
tion OF  Skull. 
/,  Roof  of  cranium;  //,  base  of  cranium;  ///,  posterior  wall 
of  cranium:  IV,  anterior  wall  of  cranium;  .1,  anterior  cranial  fossa; 
B,  middle  cranial  fossa;  C,  posterior  cranial  fossa;  a,  body  of  pre- 
sphenoid;  a',  body  of  postsphenoid;  c,  palate  bone;  rf,  vomer;  e, 
occipital;  /,  occipital  condyle;  g,  sagittal  crest;  h,  frontal  sinus; 
h',  cranial  plate  of  frontal  bone;  i,  cribriform  plate  of  ethmoid  bone; 
i',  ethmoidal  foramen;  A-,  ethmoturbinals;  I,  parietal  bone;  V ,  I", 
SQuamotis  temporal  hone;  /'",  temporal  wing  of  .sphenoid  bone; 
m,  sella  turcica;  ?«'.  dorsum  selljc;  w,  optic  foramen:  o,  foramen 
lacerum  orbitale:  p,  foramen  rotundum:  g,  foramen  ovale:  >',  r', 
carotid  foramina:  s,  tentorium  osseum;  /,  foramen  lacerum;  v,  u' , 
orifices  of  parieto-temporal  canal;  r,  condyloid  canal;  w,  canal  for 
trigeminal  nerve;  x,  internal  auditory  meatus;  ?/, )/.  orifices  of  canal 
for  inferior  occipital  sinu.s;  2,  floccular  fossa,  (.\fter  Ellenberger, 
in  Leisering's  Atlas.) 


FACE  157 

foramen  ovale  is  near  the  posterior  border  of  the  temporal  wing.     There  is  no 
sphenoidal  sinus. 

The  ethmoid  bone  i.s  highly  developed.  The  cribriform  plate  is  extensive, 
and  the  olfactory  fossae  are  very  deep.  The  crista  galli  is  little  developed,  and  often 
incomplete.  The  perpendicular  plate  is  long.  The  lateral  masses  are  greatly 
developed  and  bulge  upward  into  the  frontal  sinus.  There  are  four  large  endo- 
turbinals  and  six  ectoturbinals.  The  lamina  papyracea  is  extensive  and  forms 
the  inner  wall  of  the  maxillary  sinus.  Its  lower  border  joins  the  palatine  process 
of  the  maxilla  and  the  horizontal  part  of  the  palate  bone.  A  shelf-like  plate  extends 
inward  from  its  lower  part  and  concurs  with  the  similarly  incurved  ])art  of  the 
palate  hone  in  forming  the  transverse  lamina  (Lamina  transversalis),  which  divides 
the  olfactory  fundus  of  the  nasal  cavity  from  the  naso-pharyngcal  meatus. 

Face 

The  maxilla  is  short,  but  very  high  posteriorly.  The  facial  crest  is  absent. 
The  infraorliital  foramen  is  over  the  alveolus  for  the  third  premolar.  The  frontal 
process  fits  into  a  deep  notch  between  the  nasal  and  orbital  parts  of  the  frontal 
bone,  and  the  middle  part  of  the  posterior  border  lies  along  the  orbital  margin. 
There  are  more  or  less  pronounced  ridges,  juga  alveolaria,  over  the  canine  and 
molar  teeth.  The  zygomatic  process  is  short  and  thin;  it  is  completely  overlapped 
outwardly  by  the  malar,  and  is  perforated  by  a  number  of  foramina  (Foramina 
alveolaria).  A  maxillary  tuberosity  is  not  present  in  the  adult,  but  there  is  a 
pointed  projection,  the  pterygoid  process,  behind  the  last  alveolus.  The  internal 
surface  bears  a  short  turbinal  crest  on  its  anterior  part,  behind  which  it  is  deeply 
concave  and  forms  the  outer  wall  of  the  maxillary  sinus.  The  palatine  process  is 
short,  wide  behind,  and  moderately  arched  from  side  to  side.  The  anterior  palatine 
foramen  is  situated  at  or  close  to  the  transverse  palatine  suture  about  midway 
between  the  median  suture  and  the  alveolar  border.  The  palatine  groove  is 
distinct.  The  large  alveolus  for  the  canine  tooth  is  completed  by  the  premaxilla. 
The  small  alveolus  for  the  first  premolar  is  separated  from  the  preceding  one  by  a 
small  interval.  The  next  two  consist  of  anterior  and  posterior  parts  for  the  roots 
of  the  teeth.  The  fourth  and  fifth  are  much  larger  and  are  divided  into  three 
parts.  The  last  is  small  and  consists  of  three  divisions.  The  infraorbital  canal  is 
short. 

The  body  of  the  premaxilla  is  compressed  dorso-ventrally,  and  contains  three 
alveoli  for  the  incisor  teeth,  which  increase  in  size  from  first  to  third;  it  also  com- 
pletes the  inner  wall  of  the  large  alveolus  for  the  canine  tooth.  The  foramen 
incisivum  is  verj-  small  except  in  large  skulls.  The  interalveolar  border  is  wide 
and  very  short.  The  nasal  process  is  wide  at  its  origin  and  tapers  to  a  sharp  point 
behind;  the  anterior  part  curves  upward,  backward,  and  a  little  inward,  and  forms 
the  lateral  margin  of  the  osseous  nasal  aperture;  the  posterior  part  extends  back- 
ward a  long  distance  between  the  nasal  lione  and  the  maxilla.  The  palatine  process 
turns  upward  and  outward,  forming  with  its  fellow  a  wide  groove  for  the  septal 
cartilage;  the  posterior  end  is  pointed  and  fits  into  a  notch  between  the  palatine 
processes  of  the  maxillae,  and  supports  the  end  of  the  vomer.  The  palatine  fissure 
is  short  but  wide. 

The  horizontal  part  of  the  palate  bones  is  extensive,  forming  about  one-third 
of  the  hard  palate.  It  presents  a  variable  number  of  lesser  palatine  foramina. 
There  is  usually  a  pointed  posterior  nasal  spine  at  the  end  of  the  median  suture. 
The  palatine  canal  is  sometimes  formed  entirely  in  this  bone.  The  perpendicular 
part  is  even  more  extensive.  Its  external  surface  is  chiefly  free  and  forms  most  of 
the  inner  wall  of  the  large  pterygo-palatine  fossa.  The  maxillary  foramen  is 
situated  in  a  deep  recess  between  this  bone  and  the  zygomatic  process  of  the  maxilla. 
Just  above  it  there  is  commonlv  another  foramen  which  opens  into  the  nasal 


158 


SKELETON    OF    THE    DOG 


cavity.  The  ])osterior  palatine  and  si)lieno-palatine  foramina  are  situated  furtiier 
back  and  a  little  lower;  the  former  is  immediately  below  the  latter.  A  horizontal 
plate  extends  from  tlie  inner  surface,  meets  that  of  the  opposite  bone  and  com- 
pletes the  lamina  transversalis  spoken  of  in  the  description  of  the  ethmoid  bone. 
There  is  no  palatine  sinus. 

The  pterygoid  bones  are  very  wide  and  short.  They  form  a  considerable  part 
of  the  lateral  boundaries  of  the  posterior  nares.  The  lower  and  posterior  borders 
are  free  and  at  their  angle  of  junction  there  is  a  variable  hamulus. 

The  nasal  bones  are  (in  most  breeds)  long  and  wider  in  front  than  behind. 
The  external  surface  is  variably  concave  in  its  leng-th  and  is  inclined  toward  the 
median  suture  so  as  to  fonn  a  central  groove.  The  inner  liorders  turn  do\raward 
and  form  an  internal  nasal  crest  which  becomes  very  prominent  behind.  The  pos- 
terior parts  fit  into  a  notch  formed  by  the  frontal  bones.  The  anterior  ends  form 
an  almost  semicircular  nasal  notch. 

The  lacrimal  bone  is  very  small.  The  facial  part  extends  very  little  or  not 
at  all  beyond  the  orbital  margin.     The  orbital  surface  is  small  and  triangular, 

and  presents  the  entrance  to  the  lacri- 
mal canal. 

The  large  zygomatic  process  con- 
stitutes the  bulk  of  the  malar  bone. 
It  is  very  long  and  is  strongly  curved. 
The  upper  border  is  convex,  free  in 
front,  where  it  forms  jiart  of  the  orliital 
margin,  lieveled  behind  for  articulation 
with  the  similar  process  of  the  temporal 
bone.  Between  these  it  bears  an  emi- 
nence, the  processus  frontalis,  to  which 
the  orbital  ligament  is  attached.  The 
body  of  the  bone  may  be  considered  to 
consist  of  a  lacrimal  process  directed 
upward  and  fitting  in  between  the  lacri- 
mal and  maxilla,  and  a  maxillary  pro- 
cess directed  downward.  The  facial 
surface  is  convex. 

The  superior  turbinalbone  is  in  its 

.  anterior  part  a  simple  plate,  attached 

by  one  edge  to  the  nasal  bone;  it  curves  downward  and  inward,  and  its  free  border 

is  thickened  and  everted.     The  posterior  part  is  witler  and  resembles  the  ethmo- 

turbinals,  with  wliich  it  is  connected. 

The  inferior  turbinal  bone  is  short  and  very  complex.  It  is  attacheil  to  th(> 
nasal  surface  of  the  maxilla  by  a  basal  lamina,  which  divides  into  two  secondary 
lamellse.  The  latter  detach  numerous  tertiary  lamella,  which  are  coiled  and  have 
thick  free  edges  (Fig.  373). 

The  vomer  is  not  in  contact  with  the  posterior  jiart  of  the  floor  of  the  nasal 
cavity,  and  does  not  divide  the  posterior  nares.  The  posterior  end  is  narrow  and 
deeply  notdied.  Near  the  posterior  nares  the  two  plates  curve  outwartl  and  join 
the  palate  bones  and  assist  in  forming  the  lamina  transversalis. 

The  two  halves  of  the  mandible  do  not  fuse  completely  even  in  old  age.  The 
body  presents  six  alveoli  for  the  incisor  teeth  and  two  for  the  canines.  The  incisor 
alveoli  increase  in  size  from  first  to  third.  The  canine  alveoli  extend  deeply  down- 
ward and  backward.  There  are  usually  two  or  more  foramina  on  the  mental 
surface.  The  rami  diverge  less  than  in  the  pig.  The  inferior  border  of  the  hori- 
zontal part  is  convex  in  its  length  and  is  thick  and  rounded.  The  alveolar  border 
is  slightly  concave  in  its  length  and  is  a  little  everted,  esjiecially  in  its  middle; 


Fig.  125. — Mandible  of  Dog,  Right  Anterior  View. 
a,  Right  ramus;  b,  left  ramus;  c,  body:  rf,  alveolar 
border;  e,  processus  angularis;  /,  condyle:  ff,  coronoid 
process;  A,  masseteric  fo.ssa;  i,  k,  crests  which  form  the 
upper  and  lower  boundaries  of  fossa;  /,  mandibular  fora- 
men; m,  mental  foramina;  «,  masseteric  line;  o,  sigmoid 
notch.     (Ellenberger-Baum,  .\nat.  d.  Hundes.) 


THE    SKULL   AS    A    WHOLE  159 

it  presents  seven  alveoli  for  the  lower  cheek  teeth,  which  resemble  those  of  the 
upper  jaw  except  that  the  fourth  and  sixth  arc  much  smaller  and  the  fifth  is  like 
the  fourth  of  the  upper  series.  The  interalveolar  space  is  very  short  or  even  absent. 
There  are  two  or  three  mental  foramina  on  either  side.  The  vertical  part  is 
relatively  small.  Its  external  surface  presents  a  deep  masseteric  fossa  which 
encroaches  on  the  coronoid  process  and  is  limited  by  ridges  in  front  and  below. 
The  internal  surface  is  convex  and  is  marked  by  the  usual  foramen.  At  about  the 
same  level  as  the  latter  is  the  rough  angular  process  (Processus  angularis),  which 
projects  backward  from  the  posterior  border,  and  is  eciuivalent  to  the  angle  of  the 
other  animals.  The  condyle  is  placed  very  low — not  much  higher  than  the  apex 
of  the  canine  tooth  when  the  bone  is  resting  on  a  flat  surface.  It  is  long  trans- 
versely and  the  inner  part  of  the  articular  surface  is  much  the  wider  and  extends 
over  the  posterior  surface.  Its  long  axis  is  a  little  oblique,  the  inner  end  being 
inclined  somewhat  do\^^lward  and  forward.  The  coronoid  process  is  very  exten- 
sive and  is  bent  slightly  outward  and  backward. 

The  body  of  the  hyoid  bone  is  a  slightly  curved  transverse  rod ;  it  is  compressed 
from  before  backward,  and  bears  no  lingual  process.  The  thyroid  cornua  are 
permanently  attached  to  the  body  by  cartilage;  they  diverge  widely,  curve  inward, 
and  are  compressed  laterally.  The  small  cornua  are  short,  prismatic,  and  strong. 
The  middle  cornua  are  commonly  a  little  longer  than  the  great  cornua;  they  are 
compressed  laterally,  and  are  slightly  enlarged  at  the  ends,  which  are  joined  by 
cartilage  to  the  adjacent  cornua.  The  great  cornua  are  bent  outward  and  are 
somewhat  twisted. 


THE  SKULL  AS  A  WHOLE 
The  different  breeds  of  dog  display  great  variations  in  the  form  and  size  of 
the  skull.  Those  which  liave  a  long  narrow  skull  (e.  <?.,  greyhound,  collie)  are 
designated  dolichocephalic.  Other  dogs  (e.  g.,  bulldog,  small  spaniels,  pugs)  have 
very  broad,  short  skulls  and  are  termed  brachycephalic.  Intermediate  forms 
(e.  g.,  fox  terrier,  dachshund)  are  mesaticephalic. 

The  length  is  usually  measured  from  the  occipital  crest  to  the  anterior  end  of  the  premaxil- 
lary  suture,  and  the  breadth  between  the  summits  of  the  zygomatic  arches.  The  cephaUc  index 
is  the  relation  of  the  breadth  to   the   length,  assuming   the   latter   equal  100;   the   formula   is: 

=  cephalic  index.     The  index  of  extreme  doUchocephaUc  breeds  is  about  50  or 

length 
even  less,  as  in  the  greyhound,  and  that  of  brachycephalic  specimens  may  be  as  high  as  90,  as  in 
the  bulldog  and  pugs,  .\mong  the  mcsaticeplialic  types  are  the  fox  terrier,  with  an  index  of  about 
70,  and  the  white  Pomeranian,  mth  one  about  72  to  75.  The  cranio-facial  index  is  the  relation 
of  the  distance  from  the  occipital  crest  to  the  fronto-nasal  suture  to  that  between  the  latter  and 
the  nasal  notch.  It  varies  from  10  :  3  in  extreme  brachycephalic  breeds  to  10  :  7  in  extreme 
dolichocephalic  subjects. 

The  superior  surface  shows  the  \\-\de  outward  curve  of  the  zygomatic  arches, 
and  the  great  extent  of  the  temporal  fossffi.  The  latter  are  separated  by  the  sagittal 
crest,  which  in  the  larger  breeds  is  very  strong  and  prominent,  and  is  continued  by 
the  diverging  frontal  ridges  to  the  supraorbital  processes.  The  frontal  and  nasal 
regions  are  centrally  depressed,  and  are  more  or  less  concave  in  profile.  The  nasal 
region  is  narrow  and  is  terminated  in  front  by  a  nasal  notch.  In  the  extreme 
brachycephalic  breeds  the  differences  are  very  striking.  The  cranium  is  .strongly 
convex  in  both  directions  and  is  considerably  longer  than  the  face.  The  sagittal 
crest  is  more  or  less  effaced  and  is  formed  by  the  interparietal  only.  The  parieto- 
frontal crests  are  separated  by  an  interval  behind  and  diverge  to  the  supraorbital 
processes,  so  that  the  temporal  fosss  are  widely  separated.  The  frontal  region  is 
wide,  strongly  convex,  and  has  a  shallow  central  depression.  The  nasal  region  is 
very  short,  relatively  wide,  and  centrally  depressed.     In  profile  there  is  a  marked 


160 


SKELETON    OF   THE    DOG 


depression  at  the  fruiito-nasal  junction,  producing  what  is  termed  b.y  fanciers  the 
"stop"  of  the  face. 

On  the  lateral  siuface  the  great  extent  of  the  temporal  fossa  is  seen.  The 
orbit  communicates  freely  with  the  fossa,  the  posterior  part  of  the  orbital  margin 
being  absent  in  the  dry  skull.  The  axis  of  the  orbital  cavity  forms  a  much  smaller 
angle  with  the  median  plane  than  in  the  horse  and  ox.  A  distinct  crest  marks  the  limit 
between  the  orbital  cavity  proper  and  the  extensive  pterygo-palatine  fossa.  The 
preorbital  region  is  somewhat  triangular,  concave  in  its  length,  and  convex  from 
above  downward.  The  infraorbital  foramen  is  on  its  lower  part  above  the  third 
cheek  tootk     In  extreme  brachycephalic  breeds  the  orbit  is  relatively  very  large 

and  the  preorbital  region 
extremely  short  but  high. 
In  the  bulldog  the  lower 
jaw  protrudes  beyond  the 
upper — a  condition  known 
as  prognathism.  The  op- 
posite condition,  brachy- 
gnathism,  is  seen  in  the 
dachslnmd. 

Striking  features  on 
tlie  basal  surface  of  the 
cranium  are  the  width  and 
flatness  of  the  basioccipi- 
tal,  the  small  size  of  the 
]iaramastoid  processes,  the 
large  size  and  rounded 
shape  of  the  bulla  ossea, 
and  the  grooved  form  of 
the  articular  surfaces  for 
the  mandible.  The  pos- 
terior nares  are  long  and 
narrow  and  are  not  divided 
by  the  vomer.  The  hard 
palate  is  usually  about  half 
the  length  of  tlie  skull.  It 
is  connnonly  marked  by  a 
median  crest  or  rough  line, 
and  on  each  side  are  the 
anterior  and  accessory 
palatine  foramina  and  the 
palatine  grooves.  The 
wiilth  is  greatest  between 
the  fourth  pair  of  cheek 
teeth,  and  here  there  is  in 
The   length,    width,    and 


View  without 


most  skulls   a  pronounccnl   depression    on   either   side 
contour  vary  greatly  in  different  breeds. 

The  angle  of  divergence  of  the  rami  of  the  mandible  \aries  from  2.5  to  30 
degrees;  it  is  smallest  in  the  greyhound,  largest  in  extreme  brachycephalic  types, 
e.  g.,  bulldog,  pug. 

The  posterior  or  nuchal  surface  is  somewhat  triangular,  with  the  base  below. 
The  sununit  is  formed  1)\-  the  ()ccii)ital  crest,  which  projects  very  strongly  backward 
in  the  large  breeds.  Below  it  there  are  two  very  distinct  rough  imprints  for 
muscular  attachment.  In  some  skulls  there  is  a  thin  median  crest,  in  others  a 
rounded  elevation.     Laterallj-  are  the  temiwral  crests  anil  the  mastoid  processes. 


THE    SKULL   AS   A    WHOLE  161 

There  is  usually  a  foramen  in  the  teniporo-occipital  suture  above  the  root  of  the 
paramastoid  process.  The  foramen  magnum  varies  greatly  in  form;  most  often 
the  transverse  diameter  is  the  greater,  but  in  some  skulls  it  is  ecjualed  or  exceeded 
by  the  vertical  diameter. 

The  cranial  cavity  (Fig.  124)  corresponds  in  form  and  size  with  the  cranium, 
specially  in  those  breeds  in  which  the  various  crests  are  more  or  less  effaced  and  the 
frontal  sinuses  are  small.  The  basi-cranial  axis  is  almost  parallel  with  the  palate, 
and  the  floor  is  flattened.  The  anterior  fossa  is  narrow  and  is  only  slightly  higher 
than  the  middle  one.  The  olfactory  fossiE  are  very  deep  and  the  crista  galli  is  little 
developed.  The  sella  turcica  is  variable  in  depth,  and  the  dorsum  sellse  is  relatively 
high  and  bears  clinoid  processes  laterally.  The  cerebral  and  cerebellar  compart- 
ments are  well  marked  off  laterally  by  the  petrosal  crests  and  al)ove  l)y  the  ten- 
torium osseum.  The  base  of  the  latter  is  traversed  by  a  canal  which  connects 
the  two  parieto-temporal  canals.  The  anterior  angle  of  the  petrous  temporal  is 
perforated  by  a  canal  for  the  fifth  cranial  nerve. 

The  nasal  cavity  (I'lg.  373)  conforms  to  the  shape  of  the  face.     Its  anterior 


aperture  is  large  and  nearly  circular  in  most  dogs.  The  complex  inferior  turbinals 
occupy  the  anterior  part  of  the  cavity  to  a  large  extent,  except  near  the  aperture. 
Behind  the  inferior  turbinals  is  the  large  opening  of  the  maxillary  sinus.  Behind 
this  the  cavity  is  divided  by  a  horizontal  plate  (Lamina  transversalis)  into  a  large 
upper  olfactory  region  or  fundus  nasi  and  a  lower  naso-pharyngeal  canal.  The 
fundus  is  occupied  largely  by  the  ethmoturbinals.  The  posterior  nares  are  undi- 
vided and  are  in  general  long  and  narrow,  but  vary  with  the  shape  of  the  skull. 

The  frontal  sinus  is  of  considerable  size  in  the  large  breeds,  but  is  confined  to 
the  frontal  bone.  It  is  usually  divided  into  a  small  anterior  and  a  much  larger 
posterior  compartment,  each  of  which  opens  into  the  superior  ethmoidal  meatus. 
The  sinus  is  very  small  in  extreme  brachycephalic  types. 

The  maxillary  sinus  is  small,  and  is  in  such  free  communication  with  the 
nasal  ca\'ity  as  to  make  it  rather  a  recess  than  a  true  sinus.  It  is  bounded 
internally  by  the  lamina  papyracea  of  the  ethmoid,  and  its  outer  wall  is 
crossed  obliquely  by  the  lacrimal  canal.  The  roots  of  the  molar  teeth  do 
not  project  up  into  it. 
11 


162  SKELETON    OF   THE    DOG 

BONES  OF  THORACIC  LIMB 

The  clavicle  is  a  small,  thin,  irregularly-triangular  bony  or  cartilaginous  plate. 
It  is  embedded  in  the  mastoido-humeralis  muscle  in  front  of  the  shoulder-joint 
and  forms  no  articulation  with  the  rest  of  the  skeleton.  (It  is  nearly  an  inch  long 
in  a  large  cat  and  is  a  slender  curved  rod.) 

The  scapula  is  relatively  long  and  narrow.  The  sjiine  increases  gradually 
in  height  from  above  downward  and  divides  the  external  surface  into  two  nearly 
equal  fossae.  Its  free  edge  is  thick  and  rough  above,  and  at  the  lower  part  is  thin 
and  bent  backward.  The  acromion  is  short  and  blunt  and  is  opposite  the  rim  of 
the  glenoid  cavity.  The  subscapular  fossa  is  very  shallow  and  is  marked  by  rough 
lines.  The  rough  area  above  it  for  the  attachment  of  the  serratus  magnus  is  large 
and  quadrilateral  in  front,  narrow  and  marginal  behind.  The  anterior  border  is 
thin,  strongly  convex,  and  sinuous.  The  posterior  border  is  straight  and  thick. 
The  vertebral  border  is  convex  and  thick  and  bears  a  band  of  cartilage.  The 
cervical  angle  is  rounded.  The  dorsal  angle  is  thick  and  square.  The  neck  is  well 
defined  and  bears  a  rough  eminence  posteriorly.     The  glenoid  cavity  is  continued 


Fig.  128. — Right  Scapula  of  Dog,  External  View.  Fig.  129. — Left  Scapula  of  Dog.  Costal  SuHFAcr.. 
a.    Supraspinous    fossa;     b,    infraspinous    fossa;  a,  Subscapular  fossa;    b,  b,  b,  muscular  lines; 

c,  spine;    d,  upper  broad  end  of  spine;    e,  acromion;  r,  c,  limiting  line  between  subscapular  fossa  and  serra- 

/,  Elenoid  cavity;    g,  tuberosity;    h,  vertebral  bonier;  tus  area;    d,  glenoid  cavity;    e,  f,  tuberosity;    g,  nutri- 

;,  ijosterior  angle;     k,  scapular  notch.     (Ellenberger-  ent  foramen.     (Ellenberger-Baum,  .\nat.  d.  Hundes.) 
Baum,  .Vnat.  d.  Hundes.) 

forward  upon  the  lower  face  of  the  scapular  tuberosity,  which  is  blunt  and  bears 
no  distinct  coracoid  process.  There  is  a  rough  eminence  on  the  posterior  surface 
of  the  neck,  from  which  the  long  head  of  tiie  triceps  arises.  The  cervical  angle  is 
opposite  the  first  thoracic  spine,  the  dorsal  angle  lies  above  the  vertebral  end  of 
the  fourth  rib,  and  the  articular  angle  at  a  point  just  in  front  of  the  sternal  end 
of  the  first  rib  in  the  ordinary  standing  position.  The  shoulder  has  a  great  range 
of  movement  on  the  chest  wall. 

The  humerus  is  relatively  very  long,  rather  slender,  and  has  a  slight  sjiiral 
twist.  The  shaft  is  somewhat  compressed  laterally,  especially  in  its  upper  iwo- 
thirds;  this  part  is  curved  in  varying  degree,  convex  in  front.  The  deltoid  tuber- 
osity has  the  form  of  a  low  ridge,  and  it  is  continued  by  a  crest  which  runs  upward 
and  backward  and  bears  a  tubercle  on  its  upper  part.  Another  line  runs  from  it 
down  the  anterior  aspect  and  forms  the  inner  boundary  of  the  very  shallow  musculo- 
spiral  groove.  The  nutrient  foramen  is  about  in  the  middle  of  the  posterior 
surface.  A  slight  elevation  on  the  proximal  third  of  the  inner  surface  represents 
the  teres  tubercle.    The  head  is  long  and  strongly  curved  from  before  backward. 


BONES    OF    THE    THORACIC    LIMB 


163 


The  neck  is  better  marked  than  in  the  horse.  The  undivided  external  tuberosity 
is  placed  well  forward  and  extends  little  above  the  level  of  the  head.  The  internal 
tuberosity  is  small.  The  bicipital  groove  is  undivided  and  is  displaced  to  the  inner 
side  by  the  extension  forward  of  the  external  tuberosity.  The  distal  end  bears 
an  oblique  trochlear  articular  surface  for  articulation  with  the  radius  and  ulna, 
the  outer  part  of  which  is  the  more  extensive  and  is  faintly  grooved.  The  epi- 
condyles  are  prominent.  The  coronoid  and  olecranon  foss;i^  often  communicate 
through  a  large  supratrochlear  foramen. 

The  two  bones  of  the  forearm  are  relativelj'  long  and  articulate  with  each 
other  at  either  end  in  such  a  manner  as  to  allow  of  slight  movement.  A  narrow 
interosseous  space  separates  their  shafts.  The  rddius  is  flattened  from  before 
backward  and  increases  in  size  from  above  downward.  The  shaft  forms  two 
curves;   one  of  these,  an  anterior  convexity,  involves  the  whole  shaft;   the  other, 


^?o 


Fig.  130. — Left  Hvmerus  of  Dog,  External  Vikw. 
a.  Head;  b,  neck;  c,  crest;  d,  external  tuber- 
osity; €,  mark  for  insertion  of  infraspinatus  tendon; 
/,  external  condyle;  g,  external  condyloid  crest;  h, 
coronoid  fossa;  i,  olecranon  fossa.  (Ellenberger- 
Baum,  Anat.  d.  Hundes.) 


exte 


,31. — Left  Radius  and  Ui.na  of  Dog,  Axtero- 

EXTERNAL    ViEW. 

A,  Radius;    B,  ulna;    a,  groove  for  tendon  of 
5or  carpi  radialis;    b,  groove  for  common  exten- 


sor tendon;  c,  proximal  articular  surface  of  radius; 
d,  olecranon;  c,  beak  (proc.  anconeus)  of  ulna;  /, 
semilunar  notch;  g.  coronoid  process;  h,  facet  for 
radius;  i,  groove  for  lateral  extensor  tendon;  fr, 
groove  for  tendon  of  extensor  carpi  obtiquus.  (EUen- 
berger-Baum,  Anat.  d.  Hundes.) 


an  inner  convexity,  affects  the  upper  part.  The  anterior  surface  is  convex  in  both 
directions  and  is  marked  by  a  groove  for  the  obhque  extensor  of  the  carpus.  The 
posterior  surface  presents  the  nutrient  foramen  in  its  upper  third,  and  bears  a 
rough  hne  (Crista  interossea)  externally  for  the  attachment  of  the  interosseous 
ligament.  The  proximal  end  (Capitulum  radii)  is  relatively  small  and  is  supported 
by  a  distinct  neck  (Collum  radii).  It  bears  a  concave  surface  (Fovea  capituli) 
above  for  articulation  ^\-ith  the  humerus,  and  a  convex  marginal  area  (C'ircumfcr- 
entia  articularis)  behind  for  the  ulna.  The  bicipital  tuberosity  is  small.  There 
is  a  large  external  tuberosity  and  below  this  a  rough  eminence.  The  distal  ex- 
tremity is  much  -u-ider.  It  has  an  extensive  concave  carpal  articular  surface. 
Its  inner  border  projects  downward,  forming  the  styloid  process  of  the  radius. 
Externally  there  is  a  concave  facet  (Incisura  ulnaris  radii)  for  the  ulna.  In  front 
are  three  distinct  grooves  for  the  extensor  tendons.     The  ulna  is  well  develo]:»ed, 


164 


SKELETON    OF   THE    DOG 


but  diminishes  in  size  from  above  downward.  It  crosses  the  posterior  surface  of 
the  radius  from  within  outward.  The  shaft  is  large  and  three-sided  in  its  upper 
two-thirds,  .smaller  and  more  rounded  below.  Its  anterior  surface  is  in  general 
rough.  The  nutrient  foramen  is  near  the  proximal  end.  A  vascular  groove 
descends  from  it  and  indicates  the  course  of  the  interosseous  artery.  The  proximal 
end  is  relatively  short.  It  is  concave  and  smooth  internally,  convex  and  rough  ex- 
ternally. The  olecranon  is  grooved  and  bears  three  prominences,  of  which  the  pos- 
terior one  is  large  and  rounded.  The  semilunar  notch  is  wide  below  and  completes 
the  surface  for  articulation  with  the  trochlea  of  the  humerus.  Below  it  is  a  concave 
surface  (Ineisura  radialis)  which  articulates  with  the  back  of  the  head  of  the  radius, 
and  below  this  is  a  fossa,  which  receives  a  tuberosity  of  the  radius.  The  distal 
end  (C"a]iitulum  ulna)  is  small  and  is  produced  to  a  blunt  point  (Processus  sty- 
loideus  ulnffi).  It  articulates  with  the  ulnar  carpal 
below,  and  has  a  convex  facet  on  its  antero-internal 
aspect  for  the  radius. 

The  carpus  comprises  seven  bones,  three  in 
the  proximal  row  and  four  in  the  distal.  The 
numerical  reduction  in  the  upper  row  is  appar- 
ently due  to  the  fusion  of  the  radial  and  inter- 
mediate, constituting  a  large  bone  which  articu- 
lates with  almost  all  of  the  distal  surface  of  the 
radius  and  with  the  bones  of  the  lower  row.  It 
projects  prominently  on  the  posterior  surface  of 
the  carpus.  The  ulnar  carpal  is  long;  it  articu- 
lates with  the  radius  and  ulna  above  and  the  acces- 
sory behind;  below  it  rests  on  the  fourth  carpal  and 
is  prolonged  downward  to  articulate  with  the  fifth 
metacarpal  also.  The  accessory  is  cylindrical,  con- 
stricted in  its  middle  and  enlarged  at  each  end;  the 
anterior  extremity  articulates  with  the  ulna  and 
ulnar  carpal  bone.  The  first  carpal  is  the  smallest 
bone  of  the  lower  row;  it  articulates  with  the  second 
carpal  externally  and  the  first  metacarpal  distally. 
The  second  carpal  is  wedge-shaped,  the  liase  being 
posterior;  its  upper  surface  is  convex,  and  its  lower 
is  concave  and  rests  on  the  second  metacarpal.  The 
third  carpal  is  somewhat  like  the  second;  its  lower 
surface  is  concave  and  articulates  chiefly  with  the 
third  metacarpal.  The  fourth  carpal  is  the  largest 
of  the  row;  it  articulates  with  the  fourth  and  fifth 
metacarpals  below.  Two  small  bones  or  cartilages 
maj'  lie  found  at  the  junction  of  the  two  rows 
behind,  and  a  third  small  bone  articulates  with  the  inner  side  of  the  radio- 
intermediate.' 

Five  metacarpal  bones  are  present.  The  first  is  much  the  shortest;  the  third 
and  fourth  arc  the  longest,  and  are  about  one-fifth  longer  than  the  second  and  fifth. 
The  fifth  is  the  widest  at  the  proximal  end  and  is  slightly  shorter  than  the  second. 
They  are  close  together  above,  but  diverge  somewhat  below;  the  first  is  separated 
from  the  second  by  a  considerable  interosseous  space.  They  are  so  arranged  as  to 
form  a  convex  dorsal  surface,  and  a  concave  volar  surface,  which  corresponds  to 
the  hollow  of  the  palm  of  the  hand  in  man.  Each  consists  of  a  shaft  and  two  extremi- 
ties.    The  shaft  is  compressed  from  before  backward.     In  the  third  and  fourth  it 

'  This  third  hone  was  termed  the  phaeoid  in  the  eat  by  Strauss-Durckeim,  and  i.s  regarded  by 
some  authors  as  the  vestige  of  an  additional  digit,  the  prepollex. 


Fig 


DiSTA 


132. — Skeleton 

OF    Thoracic    Limh    of    Don, 

External  View. 

4,  Radial  +  intermediate  car- 
pal bone;  5,  ulnar  carpal;  6,  accessory 
carpal;  7,  second  carpal;  8,  third  car- 
pal; 9,  fourth  carpal;  10-14,  first  to 
fifth  metacarpals;  15,  first  phalanx; 
le.  second  phalanx;  17,  third  phalanx. 
(After  Leisering's  Athts.) 


BONES    OF   THE    PELVIC    LIMB  165 

is  almost  four-sided,  in  the  second  and  fifth  three-sided,  in  the  first  rounded. 
The  proximal  ends  (Bases)  articulate  with  each  other  and  with  the  corresponding 
carpal  bones.  The  carpal  articular  surface  formed  by  them  is  concave  from  side 
to  side,  convex  from  before  backward.  The  distal  ends  (Capitula)  have  articular 
surfaces  of  the  nature  of  a  head,  but  bear  a  sagittal  ridge  behind,  except  the  first, 
which  is  grooved. 

The  five  digits  have  three  phalanges  each,  except  the  first,  which  has  two. 
The  third  and  fourth  digits  are  the  longest ;  the  first  is  very  short  and  does  not  come 
in  contact  with  the  ground  in  walking.  The  first  phalanges  of  the  chief  digits 
have  four-sided  shafts,  which  are  slightly  curved  forward.  The  proximal  enfl 
of  each  has  a  concave  surface  for  articulation  with  the  metacarpal  bone  and  is 
deeply  notched  behind.  The  distal  end  has  a  trochlea  for  articulation  with  the 
second  phalanx,  and  lateral  depressions  for  ligamentous  attachment.  The 
second  phalanges  are  about  two-thirds  of  the  length  of  the  first  phalanges. 
The  proximal  articular  surface  consists  of  two  cavities  separ- 
ated by  a  sagittal  ridge.  The  distal  extremity  is  wider  and 
flatter  than  that  of  the  first.  The  third  phalanges  correspond 
in  general  to  the  form  of  the  claws.  The  base  has  an  articu- 
lar surface  adapted  to  the  second  phalanx  and  is  encircled 
by  a  collar  of  bone.  The  volar  surface  bears  a  wing  or  tuber- 
osity, and  on  either  side  of  this  is  a  foramen.  The  ungual 
part  is  a  curved  rod  with  a  blunt-pointed  free  end.  It  is 
rough  and  porous.  Its  base  forms  with  the  collar  pre\aously 
mentioned  a  deep  groove,  into  which  the  proximal  border  of 
the  claw  is  received.  The  two  phalanges  of  the  first  digit 
resemble  in  arrangement  the  first  and  third  phalanges  of  the 

other  digits.  Fig.     1.33.— Second     and 

Nine  volar  sesamoids  are   usually  present.     Two   are  third  phala.nges 

found  at  each  metacarpo-phalangeal  joint  of  the  chief  digits.  "^  ^°°'    ^^  ^^^.^^ 

They  are  high  and  narrow,  articulate  with  the  distal  end  of  phalanx!  6,  coronary  ndge; 

the  metacarpal  bone  in  front,  and  have  a  small  facet  on  the  c  foramen  for  digital  ar- 

base  for  the  first  phalanx.     On  this  joint  of  the  first  digit  ;-•  ^;^  -t^Ll 

there  is  usually  a  single  flattened  sesamoid,  but  exceptionally  phalanx;  /,  first  phalanx; 

two  are  present.     The  distal  volar  sesamoids  remain  cartila-  "•  <-ia-stic  dorsal  ligamente. 

'^  ^  ,    ,  ,  ,  ..  -iU  i-  (From  Leisenngs  .\tlas.) 

gmous.     A  nodular  dorsal  sesamoid  occurs  m  the  anterior 

part   of   the    capsule    of   the    metacarpo-phalangeal   joints, 

and    cartilaginous   nodules    are    found  in  a  similar  position  in  connection  ^\-ith 

the  joints  between  the  first  and  second  phalanges. 

BONES  OF  THE  PELVIC  LIMB 

The  ilium  is  nearly  parallel  witli  the  median  plane  and  its  axis  is  only  slightly 
oblique  with  regard  to  the  horizontal  plane.  The  gluteal  surface  is  concave.  The 
iliac  surface  is  almost  flat.  The  auricular  surface  faces  almost  directly  inward, 
and  in  front  of  it  there  is  an  extensive  rough  area.  The  iho-pectineal  line  is  very 
distinct  and  is  uninterrupted.  The  anterior  border  or  crest  is  strongly  convex, 
thick,  and  rough.  The  internal  angle  is  represented  by  a  thickened  part  which 
bears  two  eminences,  homologous  with  the  posterior  superior  and  posterior  hifenor 
iliac  spines  of  man.  The  external  angle  also  has  two  prominences,  which  are 
equivalent  to  the  two  anterior  spines  present  in  man.  The  shaft  is  almost  sagittal 
and  is  compressed  laterally.  Above  it  is  smooth  and  rounded,  and  below  it  bears  a 
crest  externally  which  terminates  at  a  tuberosity  in  front  of  the  acetabulum. 

The  ischium  has  a  twisted  appearance  owing  to  the  fact  that  its  acetabular 
part  is  nearly  sagittal  while  the  posterior  part  is  almost  horizontal.     The  two  bones 


166 


SKELETON    OF   THE    DOG 


also    diverge   behind   and   the   tubera   are   flattened  and  everted.     The  superior 
ischiatic  spine  is  low  and  thick;  its  posterior  part  is  marked  by  transverse  grooves 


Fig.  134. — Ossa  Coxarvm  of  Dog.  Left  Posterior  View. 
a,  Crest;  6.  c,  internal  angle;  rf,  great  sciatic  notch;  e./,  external  angle;  j7,  posterior  gluteal  line;  A,  gluteal 
fossa  of  wing;  i,  shaft  of  ilium;  k,  anterior  gluteal  line;  I,  auricular  surface;  m,  ilio-pectineal  line;  n,  depression 
for  origin  of  rectus  femoris;  o,  acetabulum;  p,  acetabular,  and  q,  symphyseal  branch  of  pubis;  r,  psoas  tubercle; 
s,  obturator  foramen;  s',  obturator  notch;  t,  line  for  origin  of  coccygeus;  w,  superior  ischiatic  spine;  i\  external 
border  of  ischium;  w,  tuber  ischii;  x,  ischial  arch.     (.EUenberger-Baum,  Anat.  d.  Hundes.) 


M 


Fig.  135. — Left  Femur  op  Dog,  Anterior  View. 
a.  Head;  b,  neck;  c,  trochanter  major;  d,  trr>- 
chanter  minor;  e,  rudimentary  trochanter  tertius; 
/,  rough  line;  (;,  trochlea;  h,  i,  condyles;  k,  supra- 
patellar fossa.     (EUenberger-Baum,  Anat.  d.  Hundes.) 


Fig.  136, — Left  Tibia  and  Fibula  of  Dog,  Antero- 

EXTKRNAL    ViEW. 

A,  Tibia;  B,  fibula;  a,  external  condyle  of 
tibia;  b.  spine;  c,  crest  of  tibia;  d,  muscular  notch; 
e,  internal  malleolus;  /.  head  of  fibula;  fjt  intero.sseoua 
space:  h,  external  malleolus  (distal  end  of  fibula);  i, 
groove  for  tendon.  (Ellenberger-Baura,  Anat.  d. 
Hundes.) 


and  has  a  prominent  outer  lip.     There  is  no  lesser  sciatic  notch. 
is  relatively  small  and  is  semi-elliptical. 


The  ischial  arch 


BOXES    OF   THE    PELVIC    LIMB 


167 


It  is  almost  circular  in  the  female, 


The  symphyseal  part  of  the  pubis  is  thick  and  fuses  late  with  the  opposite  bone. 
There  is  no  subpubic  groove. 

The  acetabulum  is  about  twice  as  far  from  the  external  angle  of  the  ilium  as 
from  the  tul>er  isrhii.  The  fossa  acetabuli  is  deep,  and  is  bounded  internally  by  a 
fiat  plate  of  bone;  its  floor  is  so  thin  as  to  be  translucent.  There  is  a  small  notch 
behind. 

The  obturator  foramen  resembles  in  outline  an  eciuilatcral  triangle  with  the 
angles  rounded  off. 

The  inlet  of  the  pelvis  is  very  obliciue. 
but  in  the  male  it  is  elliptical  and  the  con 
jugate  diameter  is  the  longer.  The  cavity  is 
narrowest  between  the  acetabula,  and  very 
wide  behind.  The  floor  is  concave  antl  rela- 
tively narrow  in  front,  wide  and  flat  behind. 

The  femur  is  relatively  much  longer  than 
in  the  horse  or  ox.  The  shaft  is  regularly 
cylindrical,  except  near  the  extremities,  where 
it  is  wider  and  compressed  from  before  back- 
ward. It  is  strongly  curved  in  its  lower  two- 
thirds,  convex  in  front.  The  posterior  surface 
is  flattened  transversely,  narrow  in  the  middle, 
and  widens  toward  each  end.  It  is  bounded 
by  two  rough  lines  (Labium  laterale,  mediale) 
which  diverge  toward  the  extremities.  The 
third  trochanter  and  the  plantar  (supracondy- 
loid)  fossa  are  absent.  There  are  two  supra- 
condyloid  crests,  the  inner  one  being  small. 
The  nutrient  foramen  is  in  the  upper  third  of 
the  posterior  surface.  The  head  is  a  little  more 
than  a  hemisphere  and  has  a  shallow  depression 
behind  and  external  to  its  center.  The  neck  is 
well  defined.  The  trochanter  major  does  not 
extend  as  high  as  the  head;  a  thick  ridge  runs 
from  its  anterior  surface  to  the  neck.  The  in- 
ternal trochanter  has  the  form  of  a  blunt  tuber- 
osity. The  trochanteric  fossa  is  round  and 
deep.  The  ridges  of  the  trochlea  are  practi- 
cally sagittal  in  direction  and  are  almost  similar. 
The  intercondyloid  fossa  is  wide.  Just  above 
each  condyle  posteriorly  there  is  a  facet  for 

articulation  with  the  sesamoid  (of  \'esal),  which  is  developed  in  the  origin  of  the 
gastrocnemius  muscle. 

The  tibia  is  about  the  same  length  as  the  femur.  The  shaft  forms  a  double 
curve ;  the  upper  part  is  convex  internally,  the  lower  part  externally.  The  proximal 
third  is  prismatic,  but  is  compressed  laterally  and  is  long  from  Ijefore  backward. 
The  remainder  is  almost  regularly  cylindrical.  The  crest  is  short  but  very  prominent. 
The  nutrient  foramen  is  usually  in  the  upper  third  of  the  external  border.  The 
tuberosity  is  not  grooved,  Init  bears  a  distinct  mark  where  the  ligamentum  patella; 
is  attached.  There  is  a  small  facet  for  the  fibula  on  the  postero-external  part  of 
the  external  condyle,  and  a  small  sesamoid  bone  in  the  tendon  of  origin  of  the 
popliteus  is  in  contact  with  the  posterior  angle  of  the  latter.  The  distal  end  is 
quadrangular  and  relatively  small.  The  articular  grooves  and  ridge  are  almost 
sagittal.  There  is  a  facet  externally  for  articulation  with  the  fibula.  There  is  a 
vertical  groove  internally  and  a  shallower  one  behind — both  for  tendons. 


Fig.  137.— Skeleton  of  Disx.ti.  P.vrt  of 
Pelvic  Limb  of  Dog,  External  View. 
6,  Tibial  tarsal  bone:  7,  fibular  tarsal; 
S,  central  tarsal;  9,  second  tarsal;  10,  third 
tarsal;  11,  fourth  tarsal;  13,  metatarsal 
bone-s;  13.  first  phalanx.  The  first  tarsal 
bone  is  not  vLsible  in  the  figure,  (.\fter 
Leisering's  .\tlas,) 


168  SKELETON    OF   THE    DOG 

Tlic  fibula  extends  the  entire  length  of  the  region.  It  is  slender,  somewhat 
twisted,  and  enhirged  at  either  end.  The  upper  part  of  the  shaft  is  separated  from 
the  tibia  by  a  considerable  interosseous  space,  but  the  lower  part  is  flattened  and 
closely  applied  to  the  tibia.  The  proximal  end  is  flattened  and  articulates  with 
the  external  condyle  of  the  tibia.  The  distal  end  is  somewhat  thicker  and  forms 
the  external  malleolus.  It  articulates  internally  with  the  tibia  and  the  tibial  tarsal 
bone.     Externally  it  bears  two  tubercles. 

The  patella  is  long  and  narrow.  The  anterior  surface  is  convex  in  both  direc- 
tions. The  articular  surface  is  convex  from  side  to  side  and  slightly  concave  from 
above  downward. 

The  tarsus  comprises  seven  bones.  The  tibial  tarsal  consists  of  a  body,  neck, 
and  head,  like  the  bone  in  man.  The  body  presents  a  trochlea  above  for  articula- 
tion with  the  tibia  and  fibula.  The  posterior  surface  has  three  facets  for  articulation 
with  the  fibular  tarsal  bone.  The  head  is  directed  a  little  inward  and  articulates 
with  the  central.  The  fibular  tarsal  has  a  long  anterior  process  or  "beak,"  but 
the  inner  process  (sustentaculum)  is  short.  The  tuber  calcis  is  grooved  from 
before  backward.  The  central  has  a  concave  proximal  surface  adapted  to  the  head 
of  the  tibial  tarsal.  Its  distal  surface  articulates  with  the  first,  second,  and  third 
tarsals.  It  bears  two  tubercles  posteriorly.  The  first  tarsal  is  flattened  and  ir- 
regularly quadrangular;  it  articulates  above  with  the  central  and  below  with  the 
first  metatarsal.  The  second  tarsal  is  the  smallest  and  is  wedge-shaped;  it  articu- 
lates below  with  the  second  metatarsal  bone.  The  third  tarsal  is  also  wedge- 
shaped,  the  base  being  in  front;  it  articulates  with  the  third  metatarsal  below. 
The  fourth  tarsal  is  remarkably  high,  and  resembles  a  quadrangular  prism;  it 
articulates  with  the  fibular  tarsal  above,  the  fourth  and  fifth  metatarsal  below,  and 
the  central  and  third  tarsal  bones  internally.  A  groove  for  the  tendon  of  the  pero- 
neus  longus  crosses  its  outer  and  posterior  surface,  and  above  it  are  one  or  two 
tubercles. 

Five  metatarsal  bones  are  present.  The  first  is  conuiionly  very  small  and  has 
the  form  of  a  blunt  cone,  somewhat  compressed  laterally.  It  articulates  with  the 
first  tarsal  and  furnishes  insertion  to  the  tibialis  anterior  muscle.  In  some  cases 
it  fuses  with  the  first  tarsal;  when  the  first  digit  is  well  developed,  its  metatarsal 
may  resemble  the  others  (except  in  size)  or  be  reduced  in  its  proximal  part  to  a 
fibrous  band.  The  other  metatarsals  are  a  little  longer  than  the  corresponding 
metacarpals.  Their  proximal  ends  are  elongated  from  before  backward  and  have 
posterior  projections,  which  in  the  case  of  the  third  and  fourth  usually  bear  facets 
for  articulation  with  two  small  rounded  sesamoid  bones.  In  other  respects  they 
resemble  the  metacarpals. 

The  first  digit  is  often  absent.  When  present,  its  development  varies  and  it 
contains  one  or  two  phalanges.  In  other  cases  the  digit  is  double.  The  phalanges 
of  the  other  digits  resemble  those  of  the  fore  limb. 


ARTHROLOGY 

THE  ARTICULATIONS  OR  JOINTS 

An  articulation  or  joint  is  formed  by  the  union  of  two  or  more  bones  or  carti- 
lages bj'  other  tissue.  Bone  is  the  fundamental  part  of  most  joints;  in  some  cases 
a  bone  and  a  cartilage,  or  two  cartilages,  form  a  joint.  The  uniting  medium  is 
chiefly  fibrous  tissue  or  cartilage,  or  a  mixture  of  these.  Union  of  parts  of  the 
skeleton  b^'  muscles  (Synsarcosis),  as  in  the  attachment  of  the  thoracic  limb  in 
the  horse,  will  not  be  considered  in  this  section. 

Joints  may  be  classified — (a)  anatomically,  according  to  their  mode  of  develop- 
ment, the  nature  of  the  uniting  media,  and  the  form  of  the  joint  surfaces;  (6) 
physiologically,  with  regard  to  the  amount  and  kind  of  movement  or  the  absence 
of  mobility  in  them;   (c)  by  a  combination  of  the  foregoing  considerations. 

The  classification  of  joints  is  still  in  a  very  unsatisfactory  state,  and,  unfortunately,  the  same 
term  is  used  in  various  senses  by  different  authors.  The  two  main  subdivisions  proposed  by  Hep- 
burn are:  (1)  Tliose  in  which  the  uniting  medium  is  coextensive  with  the  opposed  joint  surfaces, 
and  in  which  a  direct  union  of  these  surfaces  is  thereby  effected.  (2)  Those  in  which  the  uniting 
medium  has  undergone  interruption  in  its  structural  continuity,  and  in  which  a  cavity  of  greater 
or  less  extent  is  thus  formed  in  the  interior  of  the  joint.  This  distinction  is  of  considerable  im- 
portance clinically. 

Three  chief  subdivisions  of  joints  are  usually  recognized — viz.,  synarthroses, 
diarthroses,  ami  amphiarthroses. 


SYNARTHROSES 
In  this  group  the  segments  are  united  by  fibrous  tissue  or  cartilage,  or  a  mix- 
ture of  the  two  in  such  a  manner  as  practically  to  preclude  movement;  hence  they 
are  often  termed  fixed  or  immovable  joints.  There  is  no  joint  cavity.  Many  of 
these  joints  are  temporary,  the  uniting  medium  being  invaded  by  the  process  of 
ossification,  with  a  resulting  ankylosis  or  synostosis.  The  chief  classes  in  this 
group  of  joints  are  as  follows: 

(1)  Suture. — This  term  (Sutura)  is  applied  to  those  joints  in  the  skull  in  which 
the  adjacent  bones  are  closely  united  by  fibrous  tissue — the  sutural  ligament.  In 
many  cases  the  edges  of  the  bones  have  irregular  interlocking  margins,  forming  the 
sutura  serrata,  e.  g.,  the  frontal  suture.  In  others  the  edges  are  lieveled  and 
overlap,  forming  the  sutura  squamosa,  e.  g.,  the  parieto-temporal  sutia-e.  If  the 
edges  are  plane  or  slightly  roughened,  the  term  sutura  harmonia  is  ap])lied  to  the 
joint,  e.  g.,  the  nasal  suture. 

(2)  Synchondrosis. — In  these  the  two  bones  are  united  by  cartilage,  e.  g., 
the  joint  between  the  basioccipital  and  the  sphenoid  bone.  Very  few  of  these 
joints  are  permanent. 

(3)  Symphysis. — This  term  is  usually  limited  to  a  few  median  joints  which 
connect  symmetrical  parts  of  the  skeleton,  e.  g.,  symphysis  pelvis,  symphysis 
mandibulte.  The  uniting  media  are  cartilage  and  fibrous  tissue.  In  some  cases 
a  cleft -like  rudimentary  joint  cavity  occurs. 

(4)  Gomphosis. — This  term  is  applied  to  the  implantation  of  the  teeth  in  the 
alveoli. 

169 


170 


THE    ARTICULATIONS    OK   JOINTS 


DIARTHROSES 
These  joints  are  characterized  by  the  i)resence  of  a  joint  cavity  and  by  their 
mobility.     They  are  often  called  movable  or  true  joints.     The  structures  which 
enter  into  their  formation  are: 

1.  The  joint  surfaces  (Facies  articulares),  which  are  usually  more  or  less  ex- 
panded. They  are  in  most  cases  smooth,  and  vary  much  in  form.  They  are 
formed  of  specially  dense  bone,  which  differs  histologically  from  ordinary  compact 
substance.  In  certain  cases  (ridr  Osteology)  the  surface  is  interrupted  by  non- 
articular  cavities  known  as  synovial  fossae. 

2.  The  articular  cartilages  (C'artilagines  articulares),  usually  hyaline  in  type, 
form  a  covering  over  the  articular  surfaces  of  the  })ones.  They  vary  in  thickness 
in  different  joints;  they  are  thickest  on  the  areas  of  the  greatest  pressure,  and 
usually  tend  to  accentuate  the  curvature  of  the  bone,  i.  e.,  on  a  concave  surface 
the  peripheral  part  is  the  thickest,  while  on  a  convex  surface  the  central  part  is  the 
thickest.     The  articular  cartilages  are  non-vascular,   very  smooth,   and  have  a 

bluish  tinge  in  the  fresh  state.     They  diminish  the 
effects  of  concussion  and  greatly  reduce  friction. 

3.  The  joint  capsule  (Capsula  articularis)  is,  in 
its  simplest  form,  a  sac,  the  margins  of  which  are 
attached  around  the  articulating  surfaces.  It  con- 
sists of  two  layers — an  external  one,  composed  of 
fibrous  tissue  (Stratum  fibrosum),  and  an  internal 
one,  the  synovial  layer  or  membrane  (Stratum  syno- 
viale).  Th(>  fibrous  layer,  sometimes  termed  the 
capsular  ligament,  is  attached  either  close  to  the 
margins  of  the  articular  surfaces  or  at  a  variable 
distance  from  them.  Its  thickness  varies  greatly  in 
different  situations:  in  certain  places  it  is  extremely 
thick,  and  sometimes  cartilage  or  bone  develops  in 
it;  in  other  places  it  is  practically  absent,  the  cap- 
sule then  consisting  only  of  the  synovial  membrane. 
Parts  of  the  capsule  may  undergo  thickening  and  so 
form  ligaments,  which  are  not  separable,  except 
artificially,  from  the  rest  of  the  capsule.  The  syno- 
vial layer  lines  the  joint  cavity  except  where  this 
is  bounded  by  the  articular  cartilages;  it  stops  normally  at  the  margin  of  the  latter. 
It  is  a  thin  membrane,  and  is  richly  .supplied  by  close  networks  of  vessels  and 
nerves.  It  frequently  forms  folds  (Plicae  synoviales)  and  villi  (Villi  synoviales), 
which  project  into  the  cavity  of  the  joint.  The  folds  commonly  contain  pads  of 
fat  which  fill  up  interstices  and  vary  in  form  and  position  in  various  phases  of 
movement.  The  synovial  membrane  secretes  a  fluid,  the  synovia,  which  resembles 
white-of-egg  and  lubricates  the  joint.'  In  many  places  the  membrane  forms  extra- 
articular ]i()uches,  which  facilitate  the  play  of  nmsdes  and  tendons. 

The  joint  cavity  (C'avum  articulare)  is  inclosed  by  the  synovial  membrane  and 
the  articular  cartilages.  Normally,  it  is,  strictly  .speaking,  only  a  potential  cavity, 
which  contains  nothing  but  a  small  amount  of  .synovia. 

The  student  rnu.st  guard  against  a  false  conception  of  the  joint  cavity  which  may  result  from 
dissections  and  diagrams,  in  which  an  actual  cavity  of  considerable  extent  appears  to  exist. 
A  correct  idea  of  the  intimate  apposition  of  the  parts  is  best  obtained  from  the  study  of 
frozen  .sections.  It  is  also  instructive  to  examine  joints  which  have  been  injected  so  as  to  distend 
the  capsule  fully.     It  is  then  seen  that  the  cavity  is  often  of  much  greater  potential  extent  than 

'  It  is  doubtful  whether  the  synovia  is  a  true  secretion  or  a  transudate  containing  products  of 
friction.     The  view  given  above  is  that  which  is  more  commonly  accepted. 


Fig    13b — Di\gr\m  of   Section  of 

DiARTHROSIS. 

/./.,  Fibrous  layer,  s.l.,  synovial 
layer  of  joint  capsule.  Tiie  articular 
cartilages  are  white,  bones  dotted,  ami 
the  joint  cavity  black  in  the  figure. 


DIAKTHROSE3  171 

one  might  suppose,  and  that  the  capsule  is  often  very  irreguhir  in  form,  i.  e.,  forms  a  variety  of 
sacculations. 

The  foregoing  are  constant  and  necessary  features  in  all  diarthroses.  Other 
structures  which  enter  into  the  formation  of  these  joints  are  ligaments,  articular 
tliscs  or  menisci,  and  marginal  cartilages. 

4.  Ligaments. — These  are  strong  bands  or  membranes,  usually  composed 
of  white,  hbrous  tissue,  which  bind  the  bones  together.  They  are  pliable,  l)ut 
practically  inelastic.  In  a  few  cases,  however,  e.  g.,  ligamenta  flava,  ligamentum 
nuchae,  they  are  composed  of  elastic  tissue.  They  may  be  subdivided,  according 
to  position,  into  periarticular  anil  intraarticular.  Periarticular  ligaments  are  fre- 
quently blended  with  or  form  part  of  the  hbrous  capsule;  in  other  cases  they  are 
quite  distinct.  Strictly  speaking,  intraarticular  ligaments,  though  within  the 
fibrous  capsule,  are  not  in  the  joint  cavity;  the  synovial  membrane  is  reflected 
over  them.  The  term  seems  justifiable,  however,  on  practical  grounds.  Liga- 
ments which  coimect  directh'  opposed  surfaces  of  bones  are  termed  interosseous. 
The  special  names  are  ba.sed  usually  on  their  position,  form,  and  attachments,  e.  g.. 
lateral  or  collateral,  cruciate,  sacro-iliac,  etc.  In  many  places  muscles,  tendons, 
and  thickenings  of  the  fasciae  function  as  ligaments  and  increase  the  security  of  the 
joint.  Atmospheric  pressure  and  cohesion  play  a  considerable  part  in  keeping  the 
joint  surfaces  in  apposition. 

0.  Articular  discs  or  menisci  are  plates  of  fibro-cartilage  or  dense  fibrous  ti.ssue 
placed  between  the  articular  cartilages,  and  divide  the  joint  cavity  partially  or 
completely  into  two  compartments.  They  render  certain  surfaces  congruent, 
e.  g.,  femoro-tibial  joint,  allow  greater  range  or  variet}'  of  movement,  and  diminish 
concussion. 

6.  A  marginal  cartilage  (Labruni  glenoidale)  is  a  ring  of  fibro-cartilage  which 
encircles  the  rim  of  an  articular  cavity.  It  enlarges  the  cavity  and  tends  to  pre- 
vent fracture  of  the  margin. 

Vessels  and  Nerves. — The  arteries  form  anastomoses  around  the  larger  joints, 
ami  give  off  l:)ranehes  to  the  extremities  of  the  bones  and  to  the  joint  capsule.  The 
synovial  memljrane  has  a  close-meshed  network  of  capillaries;  the  latter  form  loops 
around  the  margins  of  the  articular  cartilages,  but  do  not  usually  enter  them. 
The  veins  form  plexuses.  The  synovial  membrane  is  also  well  supplied  with  lymph- 
atics. Nerve-fibers  are  especially  numerous  in  and  around  the  synovial  membrane 
and  there  are  special  nerve-endings,  e.  g.,  Pacinian  bodies  and  the  articular  end- 
bulbs  described  by  Krause. 

Movements. — The  movements  of  a  joint  are  determined  chiefly  by  the  form 
and  extent  of  the  joint  surfaces  and  the  arrangement  of  the  ligaments.  They  are 
usually  classified  as  follows: 

1.  Gliding. — This  refers  to  the  sliding  of  one  practically  plane  surface  on 
another,  as  in  the  joints  between  the  articular  processes  of  the  cervical  vertebrae. 

2.  Angular  Movements. — In  these  cases  there  is  movement  around  one  or 
more  axes.  Motion  which  diminishes  the  angle  included  liy  the  segments  forming 
the  joint  is  termed  flexion,  while  that  which  tends  to  bring  the  segments  into  line 
with  each  other  is  called  extension. 

With  reference  to  the  joints  of  the  lower  parts  of  the  limbs,  it  seems  advisable 
to  employ  the  terms  dorsal  and  volar  or  plantar  flexion,  since  these  joints  can  be 
"overextended."  Similarly,  the  terms  dorsal  and  ventral  flexion  should  be  applied 
to  the  corresponding  movements  of  the  spinal  column.  The  meaning  of  the  term 
lateral  flexion  is  evident.  These  movements  are  all  rotations  around  axes  which 
are  approximately  either  transverse  or  vertical.  Depression,  elevation,  and  lateral 
movement  of  the  lower  jaw  fall  in  this  category. 

3.  Circumduction. — This  designates  movements  in  which  the  distal  part  of 
the  limb  describes  a  circle  or  a  segment  of  one.     In  man  such  movement  is  easily 


172  THE    ARTICULATIONS    OR   JOINTS 

performed,  but  in  quadrupeds  it  is  possi])le  to  a  limited  degree  only,  and  is  to  be 
regarded  usually  as  an  indication  of  disease. 

4.  Rotation. — As  a  matter  of  convenience,  this  term  is  reserved  to  indicate 
rotation  of  one  segment  around  the  longitudinal  axis  of  the  other  segment  forming 
the  joint.     It  is  seen  typically  in  the  atlanto-axial  joint. 

5.  Adduction  and  abduction  designate  respectively  movement  of  a  limb  to- 
ward and  away  from  the  median  plane,  or  of  a  digit  toward  and  away  from  the 
axis  of  the  limb. 

Classification. — This  is  based  on  the  form  of  the  joint  surfaces  and  the  move- 
ments which  occur.     The  following  chief  classes  may  be  recognized: 

1.  Arthrodia,  or  gliding  joint.  In  these  the  surfaces  are  practically  flat,  ad- 
mitting of  gliding  movement.  Examples:  carpo-metacarpal  joints;  joints  be- 
tween the  articular  processes  of  the  cervical  and  thoracic  vertebrae. 

2.  Gingl}rmus,  or  hinge-joint.  In  this  class  the  joint  surfaces  consist  usually 
of  two  condyles,  or  of  a  segment  of  a  cylinder  or  cone,  which  are  received  by  cor- 
responding cavities.  In  typical  cases  the  movements  are  flexion  and  extension, 
i.  e.,  around  a  single  transverse  axis.  Examples:  occipito-atlantal  and  elbow- 
joints. 

3.  Trochoid,  or  pivot  joint.  In  these  the  movement  is  limited  to  rotation  of 
one  segment  around  the  longitudinal  axis  of  the  other.  Example:  atlanto-axial 
joint. 

4.  Enarthrosis,  or  ball-and-socket  joint.  These  are  formed  by  a  surface  of 
approximately  spherical  curvature,  received  into  a  corresponding  cavity.  They 
are  multiaxial,  and  allow  of  the  greatest  variety  of  movement,  e.  g.,  flexion,  ex- 
tension, rotation,  abduction,  adduction,  circumduction.  Examples:  hip  and 
shoulder  joints.' 

AMPHIARTHROSES 
These  joints,  as  the  name  indicates,  share  some  characters  with  both  of  the 
preceding  groups.  In  them  the  segments  are  directly  united  by  a  plate  of  fibro- 
cartilage,  and  usually  by  ligaments  also.  The  amount  and  kind  of  movement  are 
determined  by  the  shape  of  the  joint  surfaces  and  the  amount  and  pliability  of  the 
uniting  medium.-  These  joints  are  all  medial  in  position,  and  are  best  illustrated 
by  the  joints  between  the  bodies  of  the  vertebrae.  There  is  usually  no  joint  cavity, 
but  in  certain  situations  a  rudimentary  one  exists. 


THE  ARTICULATIONS  OF  THE  HORSE 
Joints  and  Ligaments  of  the  Vertebrae 

The  m()vai)le  vertebra'  form  two  sets  of  articulati(ins,  viz.,  those  formed  by  the 
bodies,  and  those  formed  by  the  articular  processes  of  adjacent  vertebra'; 
the  fot-mer  are  termed  intercentral,  and  the  latter,  intemeural.  Associated  with 
these  are  ligaments  uniting  the  arches  and  processes;  some  of  these  are  special, 
i.  e.,  confined  to  a  single  joint,  while  others  are  common,  i.  e.,  extend  along  the  entire 

'This  classification  makes  no  claims  to  scientific  acruraey,  but  is  simply  a  statement  of  tlie 
terms  in  general  use.  A  grouping  based  on  mechanical  principles  seems  desirable,  but  appears  to 
be  almost  impossible  on  account  of  the  great  variety  and  irregularity  of  form  of  the  articular 
surfaces. 

'^The  movements  in  .some  of  these  joints  are  more  extensive  anil  varied  tlian  in  some  diar- 
throses.  To  illustrate  this  we  may  compare  the  movements  of  the  cer\-ical  or  coccygeal  vertebra; 
with  those  possible  in  the  carpo-metacarpal  or  the  sacro-iliac  joints. 


IN'TERCENTRAL   ARTICULATIONS — INTERNEURAL   ARTICULATIONS 


173 


vertebral  column  or  a  consitlerable  part  of  it.     The  joints  between  the  atlas  and 
axis  and  between  the  former  and  the  skull  require  separate  consideration. 


INTERCENTRAL  ARTICULATIONS 
These  are  amphiarthroses,  formed  l)y  the  junction  of  the  extremities  of  the 
bodies  of  adjacent  vcrtclirie.  The  articular  surfaces  in  the  cervical  region  consist 
of  a  cavity  on  the  posterior  end  of  the  body  of  the  anterior  vertebra,  and  a  cor- 
responding convexity  or  head  of  the  succeeding  vertebra.  In  the  other  regions  the 
surfaces  are  much  fiattencil.     The  uniting  media  are: 

1.  The  intervertebral  fibro-cartilages  (Fibrocartilagines  intervertebrales). 
Each  of  these  is  a  disc  which  fits  into  the  space  between  the  bodies  of  two  adjacent 
vertebrae,  to  which  it  is  intimatelj'  attached.  The  discs  are  thinnest  in  the  middle 
of  the  thoracic  region,  thicker  in  the  cervical  and  lumbar  regions,  and  thickest  in 
the  coccygeal  region.  Each  consists  of  a  dense  fibrous  peripheral  part  (Annulus 
fibrosus),  and  a  soft  pulpy 
central  part  (Nucleus  pul-  Supraspi- 
posus).  nousliga- 
'^  merit 

The  fibrous  ring  consists 
of  lamina?  of  fibrous  tissue  and 
fibro-cartilage,  whieli  pass  ob- 
liquely between  the  two  verte- 
bra^ and  alternate  in  direction, 
forming  an  X-shaped  arrange- 
ment. The  central  part  of  the 
ring  is  largely  cartilaginous,  and 
gradually  assumes  the  character 
of  the  pulpy  center.  The  latter 
is  very  elastic  and  is  compressed, 
so  that  it  bulges  considerably 
from  the  surface  of  sections;  it 
consists  of  white  and  elastic 
fibers,  connective-tissue  cells, 
and  pecuUar  clear,  transparent  Fm.  139. — g, 
cells  of  various  sizes.     It   is  a  Lvmba 

remnant      of     the      notochord.  (Mkdui 

There  are  joint  cavities   in  the 
cervical  intercentral  joints,  and 

in  those  between  the  last  cer\-ical  and  the  first  thoracic,  and  between  the  last  lumbar  and  the 
sacrum.  In  the  latter  the  cavity  is  coextensive  with  the  extremities  of  the  bodies;  in  the  former, 
it  is  usually  not  so  extensive. 

2.  The  inferior  common  ligament  (Ligamentum  longitudinale  ventrale)  lies 
on  the  ventral  surface  of  the  bodies  of  the  vertebrae  and  the  intervertebral  fibro- 
cartilages,  to  which  it  is  firmly  attached.  It  begins  about  the  fourteenth  or  fifteenth 
thoracic  vertebra,  and  is  at  first  a  narrow,  thin  band.  Further  back  it  becomes 
gradually  thicker  and  wider,  and  terminates  on  the  pelvic  surface  of  the  sacrum 
by  spreading  out  and  blending  with  the  periosteum.  It  is  strongest  in  the  lumbar 
region,  where  the  tendons  of  the  crura  of  the  diaphragm  fuse  with  it. 

3.  The  superior  common  ligament  (Ligamentum  longitudinale  dorsale)  lies  on 
the  floor  of  the  vertebral  canal  from  the  dens  or  odontoid  process  to  the  sacrum. 
It  is  narrow  over  the  middles  of  the  vertebral  bodies,  and  widens  over  the  inter- 
vertebral fibro-cartilages,  to  which  it  is  very  firmly  attached. 

This  ligament  is  in  relation  \%nth  the  spinal  veins  on  either  .side,  and  in  the  middle  of  each 
vertebra  a  transverse  anastomotic  branch  passes  under  the  ligament. 


GITTAL     Sf.OTIOX     OF     LaST    TwO    ThORACIC    AND     FiRET 
;     VeRTEBR.E.     SHOWIXG     L1GAMENT.S     AND     SPINAL    CORD 

la).     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


INTERNEURAL  ARTICULATIONS 

Each  tvpical  vertebra  presents  two  pairs  of  articular  processes,  which  form 
diarthroses  with  the  two  adjacent  vertebra;.     The  articular  surfaces  are  extensive, 


174 


THE    ARTICULATIONS    OF    THE    HORSE 


flat,  and  oval  in  the  cervical  region,  small  and  flat  in  the  thoracic  region,  while  in 
the  lumbar  region  the  anterior  ones  are  concave  and  the  posterior  convex.  The 
joint  capsule  is  strong  and  ample  in  the  cervical  region,  in  conformity  with  the  large 
size  and  greater  mobility  of  tliese  joints  in  the  neck.  In  the  thoracic  and  lumbar 
regions  the  capsule  is  small  and  close.     These  joints  are  arthrodia. 

Associated  with  these  joints  are  the  ligamenta  flava,  which  connect  the  arches 
of  adjacent  vcrtebrte.     They  arc  membranous  and  consist  largely  of  elastic  tissue. 

The  supraspinous  ligament  extends  medially  from  the  occipital  bone  to  the 
sacrum.  From  the  withers  backward  it  consists  of  a  strong  cord  of  fibrous  tissue, 
attached  to  the  summits  of  the  vertebral  spines.     In  the  neck  and  withers  it  is 


Expansion  at  ivilhcrs 


Last  cervical 
ivrlcbra 


First  thoracic 
vertebra 


^^*% 


1,  .Scajjula;    /',  cartilage  of  srapviia; 


.   140. — Li{;.\MKXTrM  Nuch. 

,  lamellar  part  of  Hgamentur 

Baum,  Anat.  fiir  Kiinsi 


ng  of  atla.>i.      (After  Ellenberger- 


remarkably  modified  to  form  the  ligamentum  nucha',  which  requires  more  extended 
notice. 

The  ligamentum  nuchae  is  a  powerful  elastic  apjiaratus,  the  princiixil  function 
of  which  is  to  assist  the  extensor  muscles  of  the  head  and  neck.  It  extends  from 
the  occipital  bone  to  the  withers,  where  it  is  directly  continuous  with  the  supra- 
si)in(>us  ligament.  It  consists  of  two  parts— funicular  and  lamellar.  The  funic- 
ular part  (Pars  occipitalis)  arises  from  the  external  occipital  protul)erance  and  the 
fossa  below  it,  and  is  in.serted  into  the  summits  of  the  vertel)ral  sjiines  at  the 
withers.  Two  bursse  are  usually  found  under  it  in  the  adult.  The  supra-atloid 
bursa  lies  between  th(>  ligament  and  the  dorsal  arch  of  tlie  atlas.     The  supra- 


MOVEMENTS    OF   THE    VEKTEBRAL   COLUMN  175 

spinous  bursa  oicurs  usually  over  the  fourth  thoracic  spine,  but  may  be  over  the 
third  and  may  extend  to  the  fifth.'  In  the  neck  the  funicular  part  consists  for  the 
greater  i)art  of  two  bands  closely  applied  and  attached  to  each  other.  Near  and  at 
the  withers  it  broadens  greatly,  forming  an  expansion  three  to  five  inches  (ca.  8  to 
12.5  cm.)  in  width,  the  lateral  margins  of  which  are  thin  and  overlie  the  trapezius 
antl  rhomboideus  muscles.  Behind  the  higher  spines  it  becomes  narrower  and 
thinner,  and  is  continued  by  the  white  fibrous  lumbo-dorsal  ligament.^  A  mass 
of  fat  and  elastic  tissue  lies  upon  the  ligament  as  far  back  as  the  withers.  It 
varies  greatly  in  amount  in  different  subjects,  and  is  most  developed  in  stallions  of 
draft  breeds,  in  which  it  forms  the  basis  of  the  "  crest."  The  lamellar  portion  (Pars 
cervicalis)  consists  of  two  lamiuie  separated  medially  by  a  layer  of  loose  connective 
tissue.  Each  lamina  is  formed  of  digitations  which  arise  from  the  second  and  third 
thoracic  spines  antl  from  the  funicular  portion,  are  directed  downward  and  forward, 
and  end  on  the  spines  of  the  cervical  vertebra^,  except  the  first  and  last.  The  digita- 
tion  which  is  attached  to  the  spine  of  the  axis  is  very  thick  and  strong.  Behind 
this  they  diminish  in  size  and  strength;  that  to  the  sixth  cervical  is  ciuite  thin  and 
feeble,  or  may  be  absent. 

The  interspinous  ligaments  (Ligamenta  interspinalia)extend between  the  spines 
of  contiguous  vertebrae.  In  the  cervical  region  they  are  narrow  elastic  bands,  and 
in  the  thoracic  and  lumbar  regions  the.y  consist  of  white  fibers  directed  obliquely 
ilownward  and  forward. 

The  intertransverse  ligaments  (Ligamenta  intertransversaria)  are  membranes 
which  connect  adjacent  transverse  processes  in  the  lumbar  region. 


INTERTRANSVERSE  ARTICULATIONS 
These  joints  (peculiar  to  eriuicke)  are  diarthroses  formed  l\v  the  transverse 
processes  of  the  last  two  lumbar  vertebrae  and  the  alae  of  the  sacrum.  A  similar 
joint  between  the  fourth  and  fifth  lumbar  processes  is  frequently  present.  The 
articular  surfaces  have  an  elongated  oval  form,  the  anterior  one  being  concave  and 
the  posterior  one  convex.     The  capsule  is  tight,  and  is  reinforced  ventrally. 

SACRAL  AND  COCCYGEAL  ARTICULATIONS 
In  the  foal  the  bodies  of  the  five  sacral  vertebrae  form  joints  which  resemble 
somewhat  those  in  the  posterior  part  of  the  lumbar  region.     These  joints  are  in- 
vaded l)y  the  process  of  ossification  early,  so  that  the  consolidation  of  the  sacrum 
is  usually  complete,  or  nearly  so,  at  three  years. 

The  coccygeal  vertebrae  are  united  by  relatively  thick  intervertebral  fibro- 
cartilages,  which  have  the  form  of  biconcave  discs.  Special  ligaments  are  not 
present,  but  there  is  a  continuous  sheath  of  fibrous  tissue.  The  movement  in  this 
region  is  extensive  and  varied.  In  old  horses  the  first  coccygeal  vertebra  is  often 
fused  with  the  sacrum. 

MOVEMENTS   OF  THE  VERTEBRAL   COLUMN 
The  movements  of  the  spine,  exclusive  of  those  at  the  atlanto-axial  joint,  are 
dorsal,  ventral,  and  lateral  flexion,  and  rotation.     The  range  of  movement  at  a 
single  joint  is  verj'  small,  but  the  sum  of  the  movements  is  considerable.     The 

'  In  (li.ssecting-room  subjects  these  bursae  and  the  adjacent  structures  are  commonly  the  seat 
of  pathological  changes.  They  appear  to  be  the  starting-point  of  "poll  evil"  and  "fistulous 
withers." 

-  Xo  natural  line  of  demarcation  exists  between  the  ligamentum  nucha  and  the  lumbo-dorsal 
continuation  of  the  supraspinous  ligament,  since  the  change  from  the  purely  elastic  to  the  white 
fibrous  structure  is  gradual. 


176 


THE    ARTICULATIONS    OF   THE    HORSE 


movements  are  freest  in  the  cervical  and  coccygeal  regions, 
limited  in  the  thoracic  and  lumbar  regions. 


Rotation  is  extremely 


ATLANTO-AXIAL  ARTICULATION 
This  is  a  trochoid  or  pivot  joint,  of  a  rather  peculiar  character.  The  articular 
surfaces  are:  (1)  On  the  lateral  masses  of  the  atlas, 
two  somewhat  saddle-shaped  facets,  which  are  usually 
confluent  ventrally;  (2)  on  the  axis,  reciprocal  saddle- 
shaped  surfaces  which  extend  upon  the  odontoid  pro- 
cess and  are  confluent  on  its  ventral  aspect.  It  will  be 
observed  that  the  joint  surfaces  are  not  at  all  accur- 
ately adapted  to  each  other,  so  that  only  limited  areas 
are  in  contact  at  any  time. 

The  joint  capsule  is  attached  around  the  margins 
of  the  articular  surfaces.  It  is  loose  and  ample  enough 
laterally  to  allow  extensive  movement. 

The  superior  atlanto-axial  ligament  (Ligament uin 
interarcuale)  is  memljranous  and  reinforces  the  capsule 
dorsally. 

The  interspinous  ligament  (Ligamentum  inter- 
spinale)  consists  of  two  elastic  bands  which  extend 
from  the  dorsal  arch  of  the  atlas  to  the  spine  of  the 
axis. 

The  inferior  atlanto-axial  ligament  (Ligamentum 
dentis  externum)  arises  from  the  ventral  tubercle  of  the 
atlas  and  is  attached  by  two  branches  on  the  ventral 
spine  of  the  axis. 

The  odontoid  ligament  (Ligamentum  dentis  in- 
ternum) is  short,  very  strong,  and  somewhat  fan- 
shaped.  It  extends  from  the  rough  concave  dorsal 
surface  of  the  dens  or  odontoid  process,  widens  in 
front,  and  is  attached  to  the  transverse  rough  area  on 
the  inner  surface  of  the  ventral  arch  of  the  atlas. 

Movements. — The  atlas  and  the  head  rotate  upon 
the  axis ;  the  axis  of  rotation  passes  through  the  center 
of  the  odontoid  process  and  body  of  the  axis. 


Fig.    141.  —  Atlanto -OCCIPITAL 
AND  Ati.anto-axial  Joints 
OP  Horse,    Dorsal  View 
after  Removal  of   Dor- 
sal Arch  of  Atlas. 
a,  Joint  capsule  of  left  part 
of  atlanto-occipital  joint;    6,  lat- 
eral ligament  of  same;   c,  c',  odon- 
toid ligament;  d,  atlanto-occipital 
joint  capsule;    e,  joint  capsule  of 
articulation     between     axis     anti 
third  cer\'ical  vertebra:    /,  inter- 
spinous    ligament;      /,     occipital 
bone;    «,  atlas;    .*.  axis;    4,  third 
cervical     vetrebra.     (Ellenberger- 
Baum,  Anat.  d.  Haustiere.) 


THE  ATLANTO-OCCIPITAL  ARTICULATION 
Tliis  joint  maybe  classed  as  a  ginglymus.     The 
articular  surfaces  of  this  joint  are:   (1)  On  the  atlas, 
two  deep  oval  cavities;   (2)  the  corresponding  condyles 
of  the  occipital  bone. 

The  joint  surfaces  are  oblique,  coming  very  close  to   the 
median  line  ventrally,  but  separated  by  a  considerable  interval 
dorsally.     Posteriorly,  a  triangular  rough  area  cuts  into  tlio  middle  of  each  articular  surface 
on  the  atlas. 

There  are  two  roomy  joint  capsules,  which  sometimes  communicate  ventrally, 
especially  in  old  subjects. 

The  superior  atlanto-occipital  membrane  extends  from  the  dorsal  arch  of  the 
atlas  to  the  upper  margin  of  the  foramen  magnum.  It  is  blended  with  the  ca])sules 
and  contains  many  elastic  fibers. 

The  inferior  atlanto-occipital  membrane  extends  from  the  ventral  arch  of  the 


ARTICULATIONS    OF    THE    THOUAX — COSTO-VERTEBRAL   ARTICULATIONS 


177 


atlas  to  the  lower  margin  of  the  foramen  magnum.  It  is  narrower  and  thinner  than 
the  superior  memlirane,  and  also  fuses  with  the  joint  capsules. 

The  lateral  ligaments  are  two  short  hands  which  are  partiall.y  blended  with 
the  capsules.  Each  is  attached  to  the  border  of  the  wing  of  the  atlas  near  the 
intervertebral  foramen,  and  to  the  outer  surface  of  the  paramastoid  or  styloid 
process  of  the  occipital  bone. 

Movements. — These  are  chiefly  flexion  and  extension.  A  small  amount  of 
lateral  oblique  movement  is  also  possible. 


Articular  processes 
//    r^-  Transverse  process 


Articulations  of  the  Thorax 
costo-vertebral  articulations 

Each  typical  rib  forms  two  joints  with  the  vertebral  column,  one  by  its  head, 
and  one  by  its  tubercle.  They  are  termed  respectively  costo-central  and  costo- 
transverse joints. 

I.  The  costo-central  articulations  (Articulationes  capitulorum)  are  trochoid 
or  rotatory  joints,  formed  b.y  the 

junction  of  the  head  of  the  rib 
with  the  bodies  of  two  adjacent 
vertebra  and  the  intervertebral 
fibro-cartilage.  The  two  facets 
on  the  head  of  the  rib  are  separ- 
ated by  a  non-articular  groove, 
and  correspond  to  the  tv/o  con- 
cave facets  (Fovese  costales)  on 
the  vertebral  bodies.  The  cap- 
sules are  rather  tight,  and  are 
covered  by  the  accessory  liga- 
ments, which  are  as  follows:  1. 
The  radiate  ligament  (Ligamen- 
tum  capituli  costs  radiatum)  ex- 
tends ventrally  from  the  neck  of 
the  rib  to  spread  out  on  the 
vertebral  bodies  and  the  inter- 
vertebral fibro-cartilage.  2.  The 
conjugal  ligament  (Ligamentum 
conjugale) — absent  from  the  first 
joint — is  attached  to  the  groove 

on  the  head  of  the  rib,  j^asses  transversely  into  the  vertebral  canal,  and  divides 
under  the  superior  common  ligament  into  two  branches;  one  of  these  is 
attached  to  the  body  of  the  anterior  vertebra;  the  other  is  continued  across 
to  the  head  of  the  opposite  rib,  and  is  attached  to  the  intervertebral  fibro- 
cartilage.  The  joint  cavity  is  divided  into  two  compartments  by  the  conjugal 
ligament.  3.  The  ligament  of  the  neck  of  the  rib  (Ligamentum  colli  costs)  is 
a  strong  band  which  crosses  the  joint  dorsally.  It  is  attached  on  the  vertebra 
above  the  costal  facet  and  on  tlie  neck  of  the  rib. 

II.  The  costo-transverse  articulations.  These  occur  between  the  facets  on 
the  tubercles  of  the  ribs  and  those  on  the  transverse  processes  of  the  vertebra-. 
They  are  gliding  joints.  The  capsule  is  reinforced  by  the  superior  costo-trans- 
verse ligament  (Ligamentum  costo-transversarium  dorsale),  a  distinct  strong  band 
which  arises  on  the  transverse  process  and  ends  on  the  non-articular  part  of  the 
tubercle.  It  is  covered  by  the  levator  costse  muscle,  and  begins  to  be  quite  distinct 
at  the  fifth  joint. 

12 


erse  ligament 
lament  of  neck 
Capsule 

Radiate  ligament 
Conjugal  ligament 


Fig.  142. — CosTo- 

(After  Schmalt 


178  THE    ARTICULATIONS    OF    THE    HORSE 

The  cavity  for  thp  head  of  the  first  rilj  is  formed  by  concave  facets  on  the  bodies  of  the  last 
cervical  and  first  thoracic  vertebra?.  The  conjugal  ligament  is  absent,  but  the  ligament  of  the 
neck  is  short  and  strong.  The  radiate  ligament  is  very  strong,  and  consists  of  two  bands.  In 
the  case  of  the  last  two  or  three  ribs  the  costo-central  and  costo-transverse  joints  arc  conflueiit, 
and  the  various  structures  are  correspondingly  modified. 

Movements. — The  chief  movement  is  rotation  around  an  axis  which  connects 
till'  centers  of  the  head  and  tubercle  of  the  rib.  The  movement  is  very  limited  in 
the  anterior  part  of  the  series  of  joints,  but  very  considerable  in  the  posterior  part. 

In  the  case  of  the  first  rib,  the  movement  is  evidently  extremely  limited.  The  facet  for  the 
tubercle  of  the  rib  is  deeplj'  concave,  and  the  axis  of  rotation  is  almost  transverse.  Further  back 
the  facets  on  the  transverse  processes  become  flat,  and  the  axis  of  rotation  gradually  approaches  a 
longitudinal  direction.  This,  in  connection  with  the  mobility  of  the  ventral  ends  of  the  asternal 
ribs  and  their  elasticity,  allows  a  great  increase  here  in  the  range  of  movement,  the  cfTcct  nf  which 
is  to  enlarge  (chiefly)  the  transverse  diameter  of  tlic  thorax. 


COSTO-CHONDRAL   ARTICULATIONS 
The  costo-chondral  junctions  are  synarthroses.     The  rib  has  a  concave  surface 
which  receives  the  convex  end  of  the  cartilage.     They  are  united  by  the  continuity 
of  the  strong  periosteum  and  perichondrium. 


CHONDRO-STERNAL  ARTICULATIONS 
These  joints  (Articulationes  sternocostales)  are  diarthroses  formed  by  the 
junction  of  the  cartilages  of  the  sternal  ribs  with  the  sternum.  The  articular  ends 
of  the  cartilages  (except  the  first)  are  somewhat  enlarged,  and  present  surfaces  of 
cylindrical  curvature.  The  articular  surfaces  on  the  sternum  for  the  first  pair  of 
cartilages  are  placed  close  together  on  the  dorsal  border  of  the  cariniform  cartilage 
(Manubrium  sterni) ;  the  other  seven  are  placed  laterally  at  the  junction  of  the 
segments.  The  capsules  are  strong  and  tight;  the  first  pair  of  joints  has  a  common 
capsule,  and  the  cartilages  articulate  with  each  other  medially.  The  lower  ends 
of  the  first  pair  of  ribs  are  firmly  attached  to  each  other  by  dense  fibrous  tissue, 
which  is  prolonged  forward  along  the  upper  margin  of  the  cariniform  cartilage  and 
is  continuous  behind  with  tlic  sternal  ligament.  Each  of  the  other  capsules  is 
reinforced  dorsally  by  the  superior  costo-sternal  ligament  (Ligamentum  sterno- 
costale  radiatum),  composed  of  radiating  fibers  whicli  blend  with  the  sternal  liga- 
ment. The  movement  is  rotation  around  a  nearly  vertical  axis,  except  in  the  case 
of  the  first  pair  of  joints. 


INTERCHONDRAL  LIGAMENTS 

The  eighth  and  ninth  costal  cartilages  are  firmly  united  by  fibrous  tissue.  The 
chondro-xiphoid  ligament  attaches  the  ninth  costal  cartilage  to  the  xijihoid  carti- 
lage. The  remaining  cartilages  are  rather  loosely  attached  to  each  other  by  elastic 
tissue. 

STERNAL  ARTICULATIONS 
In  the  new-born  foal  the  sternum  has  seven  bony  segments  (Sternebrse) , 
united  by  persisting  cartilage.  The  last  two  segments  coalesce  within  a  few  weeks 
after  birth.  In  old  subjects  there  is  more  or  less  ossification  of  the  intersegmental 
cartilage,  which  may  lead  to  partial  fusion  of  adjacent  segments,  especially  pos- 
teriorly. The  sternal  ligament  (Ligamentum  .sterni  iiroprium  internum)  lies  on  the 
thoracic  surface  of  the  sternum.  It  arises  on  the  first  segment,  and  divides  oppo- 
site the  second  chondro-sternal  joint  into  three  bands.  The  median  band  passes 
backward  and  spreads  out  on  the  last  segment  and  the  xiphoid  cartilage.     The 


THE  SYNARTHROSES  OF  THE  SKULL  179 

lateral  liranrhes — thicker  and  wider — lie  along  the  lateral  borders  above  the  chon- 
dro-sternal  joints,  and  end  at  the  cartilage  of  the  eighth  rib;,  they  are  covered  by 

the  trans  versus  thoracis  muscle. 


The  Articulations  of  the  Skull 
temporo-mandibular  articulation 

This  joint  (Articulatio  niantlibularis)  is  the  only  diarthrosis  formed  lictween 
bones  of  the  skull. 

The  articular  surfaces  are  dissimilar  in  form  and  size.  That  on  the  squamous 
temporal  bone  is  concavo-convex,  and  the  long  axis  is  directed  outward  and  some- 
what forward;  it  consists  of  a  glenoid  cavit^y,  which  is  continued  upon  the  post- 
glenoid  process  behind,  and  a  condj'le  in  front.  The  mandible  presents  a  trans- 
versely elongated  condyle. 

The  articular  disc  is  placed  between  the  joint  surfaces,  which  it  renders  con- 
gruent. Its  upper  and  lower  surfaces  are  molded  upon  the  temporal  and  mandibular 
surfaces  respectively,  and  its  circumference  is  attached  to  the  joint  capsule:  thus 
it  divides  the  joint  cavity  into  upper  and  lower  compartments,  the  former  being 
the  more  roomy. 

The  joint  capsule  is  strong  and  tight.  It  is  reinforced  by  two  ligaments.  The 
external  ligament  (Ligamentum  laterale)  extends  obliquely  across  the  anterior 
part  of  the  outer  surface  of  the  capsule,  from  which  it  is  not  distinctly  separable. 
The  posterior  ligament  (Ligamentum  posterius)  is  an  elastic  band  which  is  attached 
above  to  the  ]}ostglenoid  process,  and  below  to  a  line  on  the  posterior  face  of  the 
neck  of  the  mandible. 

Movements. — The  chief  movements  take  place  around  a  transverse  axis  pass- 
ing through  both  joints.  Associated  with  this  hinge-like  action  is  .slight  gliding 
movement,  as  in  opening  and  shutting  the  mouth.  When  the  mouth  is  shut, 
the  condyle  lies  under  the  glenoid  cavity.  When  the  mandible  is  depressed, 
the  condyle  moves  forward  under  the  articular  eminence  of  the  temporal  bone, 
carrying  the  disc  with  it.  In  protrusion  and  retraction  of  the  lower  jaw  the  gliding 
movement  just  described  occurs  without  the  hinge-like  rotation  of  the  condyle. 
These  movements  are  similar  in  both  joints.  In  the  lateral  movements  (as  usually 
performed  in  mastication)  the  action  consists  of  rotation  of  the  condyles  around  a 
vertical  axis,  while  the  disc  glides  forward  on  one  side  and  backward  on  the  other. 


THE  SYNARTHROSES  OF  THE  SKULL 
Most  of  the  bones  of  the  skull  are  united  with  the  adjacent  bones  by  sutures; 
a  few  are  united  by  cartilage.  The  difference  in  the  uniting  medium  depends  on 
the  fact  that  most  of  these  bones  are  developed  in  membrane,  but  some  are  pre- 
formed in  cartilage.  Most  of  these  joints  are  temporary,  and  are  obliterated  at 
various  periods  during  development  and  gro^\'th.  Their  importance  rests  on  the 
fact  that  so  long  as  they  persist,  continuous  growth  is  possible.  They  are  usually 
designated  according  to  the  bones  which  enter  into  their  formation,  e.  q.,  spheno- 
squamous, naso-frontal,  internasal,  etc.  Special  names  (borrowed  froni  human 
anatomy)  are  sometimes  used;  thus  the  interparietal,  the  parieto-occipital,  and 
the  parieto-frontal  sutures  are  often  called  the  sagittal,  lambdoid,  and  coronal  re- 
spectively. 

Detailed  description  of  the  sutures  has  not  sufficient  chnical  value  to  justif.v  much  addition 
to  the  statementsTmade  in  the  osteology  in  this  connection.  The  obliteration  or  closure  of  the 
sutures  is,  however,  worthy  of  brief  mention.  The  cranial  sutures  are  usuall.v  all  closed  at  se\-en 
years,  but  the  apex  only  of  "the  petrous  temporal  is  fused  with  the  occipital  and  squamous  temporal. 
Most  of  the  facial  sutures  are  practically  closed  at  ten  years,  although  complete  synostosis  may  in 


180  THE    ARTICULATIONS    OF    THE    HORSE 

some  be  delayed  for  years  or  may  not  occur  at  all;   the  nasal  suture,  for  example,  often  persists 
even  in  advanced  age,  so  far  as  its  anterior  part  is  concerned. 

The  principal  synchondroses  are:  (1)  That  between  the  basioccipital  and  the 
body  of  the  sphcnt)i(l  (Synchonch-osis  sphenooccipitaUs) ;  (2)  that  between  the 
presphenoid  and  postsphenoid  (Synchondrosis  intersphenoidalis) ;  (3)  those 
Ijetween  the  parts  of  the  occipital  bone  (Synchondroses  intraoccipitales).  The  first 
is  usually  ossified  at  four  years,  the  second  at  three  years,  and  the  occipital  bone  is 
consolidated  at  two  years. 

The  symphysis  of  the  lower  jaw  (Symphysis  mandibulae)  ossifies  at  one  to  six 
months. 

THE  HYOIDEAN  ARTICULATIONS 

The  temporo-hyoid  articulation  is  an  amphiarthrosis,  in  which  the  dorsal  angle 
of  the  proximal  end  of  the  great  cornu  (Stylo-hyal)  is  attached  by  a  short  liar  of 
cartilage  to  the  hyoid  process  of  the  petrous  temporal  bone.  The  cartilage  (Arthro- 
hyal)  is  about  half  an  inch  (ca.  1  to  1.5  cm.)  in  length.  The  chief  movement  is  hinge- 
like, the  axis  of  motion  passing  transversely  through  both  joints. 

The  intercomual  articulation  is  an  amphiarthrosis  formed  by  the  junction  of 
the  distal  extremity  of  the  great  cornu  with  the  proximal  end  of  the  small  cornu 
(kcrato-hyal).  They  are  united  by  a  very  short  piece  of  cartilage,  in  which  there 
is  usually  a  small  nodule  of  bone  in  the  young  subject.  This  nodule,  the  epihyal 
or  middle  cornu,  is  usually  fused  with  the  great  cornu  in  the  adult.  The  chief 
movement  here  is  also  hinge-like,  the  angle  between  the  cornua  being  increased  or 
diminished. 

The  basi-comual  articulation  is  a  diarthrosis  formed  ])y  the  junction  of  each 
small  cornu  (kerato-hyal)  with  the  body  (basi-hyal).  The  small  cornu  has  a  con- 
cave facet  which  articulates  with  the  convex  facet  on  either  end  of  the  dorsal  sur- 
face of  the  body.  The  capsule  is  ample  enough  to  allow  considerable  movement, 
which  is  chiefly  hinge-like.  The  movements  of  the  hyoid  bone  are  concerned 
chiefly  in  the  acts  of  mastication  and  swallowing.  In  the  latter  the  distal  parts  of 
the  hyoid  bone  are  moved  forward  and  upward,  carrying  the  root  of  the  tongue  and 
the  larynx  with  them,  and  then  return  to  their  former  position. 


The  Articulations  of  the  Thoracic  Limb 

In  the  absence  of  the  clavicle  the  thoracic  limb  forms  no  articulation  with  the 
trunk,  unless  we  regard  as  such  the  imion  by  muscles.  The  movement  of  the 
shoulder  on  the  chest-wall  is  chiefly  rotation  around  a  transverse  axis  passing 
through  the  scapula  behind  the  upper  part  of  the  spine. 


THE  SHOULDER   JOINT 

The  shoulder  or  scapulo-humcral  joint  (Articulatio  scapulo-humeralis)  is 
formed  by  the  junction  of  the  distal  end  of  the  scapula  with  the  proximal  end  of 
the  humerus.  The  articular  surfaces  arc:  (1)  On  the  scapula,  the  glenoid  cavity; 
(2)  on  the  humerus,  the  head.  Both  surfaces  are  approximately  spherical  and 
similar  in  curvature,  but  the  humeral  surface  is  much  more  extensive  than  that  of 
the  scapula. 

The  joint  capsule  is  ample  enough  to  allow  the  bones  to  be  drawn  apart  about 
an  inch  (ca.  2  to  3  cm.) ;  but  this  requires  a  very  considerable  amount  of  force  unless 
air  is  admitted  into  the  joint  cavity.  The  fibrous  layer  (or  capsular  ligament)  is 
not  attached  to  the  margin  of  the  joint  surfaces,  but  at  a  distance  of  one  to  two 
centimeters  from  it.     It  is  strengthened  in  front  by  two  diverging  elastic  bands, 


THE    ELBOW   JOINT 


181 


which  arise  on  the  scapular  tuberosity  and  end  on  the  Hps  of  the  bicipital  groove. 
A  pad  of  fat  is  interposed  between  the  capsule  and  the  tendon  of  the  biceps. 

Ligaments  are  absent  from  this  joint,  but  the  muscles  and  tendons  around  it 
afford  remarkable  security,  so  that  dislocation  seldom  or  never  occurs.  The  large 
extent  of  the  head  of  the  humerus  is  also  of  importance  in  this  regard. 

The  principal  muscles  which  are  attached  around  the  joint  and  act  as  ligaments  are:  ex- 
ternally, the  supraspinatus,  infraspinatus,  and  teres  minor;  internally,  the  subscapularis;  in 
front,  the  biceps  and  supraspinatus;   behind,  the  triceps. 

Movements. — While  it  is  a  typical  enarthrosis  in  structure,  and  capable  of  the 
various  movements  of  the  ball-and-socket  joint,  the  chief  normal  movements  are 
fiexion  and  extension.  In  the  position  of  rest  the  angle  formed  between  the  scapula 
and  humerus  posteriorly  is  about  110°  to  120°;  in  flexion  it  is  reduced  to  about  80°, 
and  in  extension  it  is  increased  to  about  145°.  Adduction  and  abduction  are  very 
restricted,  the  former  being  limited  chiefly  by  the  infraspinatus,  the  latter  by  the 
subscapularis  and  the  low  insertion  of  the  superficial  pectoral  muscles.  Rotation 
is  somewhat  freer,  but  does  not  exceed 
33°,  when  all  the  muscles  are  removed 
(Franck). 

Olecrniiou 
fossa 
THE  ELBOW  JOINT  " 

This,  the  cubital  articulation  (Articu- 
latio  cubiti),  is  a  ginglymus  formed  be- 
tween the  distal  extremity  of  the  humerus 
and  the  proximal  ends  of  the  bones  of  the 
forearm. 

The  articular  surfaces  are:  (1)  A 
trochlear  surface  formed  by  the  condyles 
of  the  humerus  and  the  groove  between 
them;  (2)  the  corresponding  glenoid  cavi- 
ties and  ridge  on  the  proximal  extremity 
of  the  radius,  together  with  the  semilunar 
notch  of  the  ulna. 

The  articular  surface  of  the  condyles  does 
not  extend  upon  the  back  of  the  extremity,  but 
the  groove  which  receives  the  semilunar  notch 
of  the  ulna  extends  up  into  the  olecranon  fossa. 
In  the  fore  part  of  the  groove  there  is  a  synovial 
fossa.  The  surface  on  the  outer  condyle  is  smaller 
than  that  of  the  inner  one,  and  is  subdivided  into  two  unequal  parts  by  a  shallow  furrow.  On 
the  lower  part  of  the  semilimar  notch  and  the  adjacent  part  of  the  ridge  on  the  radius  are  synovial 
foss£e. 

The  joint  capsule  is  extremely  thin  behind,  where  it  forms  a  pouch  in  the  ole- 
cranon fossa  under  the  anconeus  muscle  and  a  pad  of  fat.  In  front  it  is  strength- 
ened by  oblique  fibers  (Ligamentum  obliquum  or  anterior  ligament),  and  laterally 
it  fuses  with  the  lateral  ligaments.  Small  pouches  of  the  synovial  membrane 
lubricate  the  origins  of  the  flexors  of  the  carpus  and  digit  and  the  small  radio-ulnar 
joints.     There  are  two  lateral  ligaments. 

The  internal  lateral  ligament  (Ligamentum  collaterale  radiale)  is  attached 
above  to  an  eminence  on  the  internal  epicondyle  of  the  humerus,  and  divides  into 
two  parts:  the  long,  superficial  part  ends  on  the  inner  border  of  the  radius,  just 
below  the  level  of  the  interosseous  space;  the  deep,  short  part  is  inserted  into  the 
internal  tuberosity  of  the  radius.  (The  superficial  part  represents  the  pronator  teres 
muscle,  which  is  only  exceptionally  present  in  the  horse.) 


External  lateral 
ligament 


43. — Left  Elbow  Joint  of  Horse,  Poste- 
rior View.  The  CAPsrLE  is  Removed. 
C.\fter  Schmaltz,  .\tlas  d.  .\nat.  d.  Pferdes.) 


182 


THE    ARTICULATIONS    OF   THE    HORSE 


The  external  lateral  ligament  (Ligament  um  collaterale  ulnare)  is  short  and 
strong.  It  is  attaclicil  above  to  a  depression  on  the  external  epicondyle  of  the 
humerus,  and  below  to  the  external  tuberosity  of  the  radius,  just  below  the  margin 
of  the  articular  surface. 

Movements. — This  joint  is  a  typical  ginglymus,  the  only  movements  being 
flexion  and  extension  around  an  axis  which  passes  through  the  upper  attachments 
of  the  lateral  ligaments.  In  the  standing  position  the  articular  angle  (in  front)  is 
about  140°  to  150°.  The  range  of  movement  is  about  55°  to  60°.  Complete  ex- 
tension is  prevented  chiefly  by  the  tension  of  the  lateral  ligaments  and  the  biceps 
muscle.  (The  axis  of  movement  is  slightly  oblique,  so  that  in  flexion  the  forearm 
is  carried  somewhat  outward.) 


External  dis- 
tal tuberosity 
of  radius 


External 

metacarpal 

bone 


Internal  dis- 
tal tuberosity 
of  radius 


Internal 

lateral 

ligajncnt 

Metacarpal^ 
tuberosity' 


.External  dis- 
tal tuberosity 
of  radius 

External 
lateral 
ligament 


.External 
metacarpal 
bone 


Fig.   144. — Left  Carpal  Joints  of  Horse,  Exter-        Fk;.  145. — Left  Carpal  Joints  of  Horse,  .\\terior 
NAL  \'iEW  View. 

i  been  removeil.     The  smaller  liga- 
(After   Ellenberger-Baum,   Anat. 


The  capsule  has  been  removed,  g,  Radius;  1£, 
large  metacarpal  bone.  (After  Ellenberger-Baum, 
Anat.  f.  Kunstler.) 


The  capsule  h£ 
ments  are  shown. 
f,  Kunstler.) 


THE   RADIO-ULNAR    ARTICULATION 

In  the  foal  the  shaft  of  the  ulna  is  attached  to  the  radius  above  and  below  the 
interosseous  space  by  the  interosseous  ligament.  Below  the  space  the  two  bones 
become  fused  before  adult  age  is  reached.  Above  the  space  the  ligament  usually 
persists,  but  may  undergo  more  or  less  ossification  in  extreme  old  age.  The 
transverse  or  arciform  ligaments  (Ligamentum  transversum  ulnare  et  radiale 
ulna^  ct  radii)  consist  of  fibers  which  pass  aliove  the  interosseous  space  from  either 
ijorder  of  the  shaft  of  the  ulna  to  the  posterior  surface  of  the  radius.  The  proximal 
radio-ulnar  articulation,  formed  by  two  small  convex  facets  on  the  ulna  and  the 
corresponding  facets  on  the  posterior  surface  of  the  proximal  extremity  of  the  radius, 
is  inclosed  in  the  capsule  of  the  elbow-joint  and  does  not  require  separate  consider- 
ation. The  distal  extremity  of  the  ulna  fuses  early  with  the  radius,  and  is,  there- 
fore, regarded  usually  as  a  part  of  the  latter. 

Movement. — This  is  inappreciable,  the  forearm  being  fixed  in  the  position  of 
pronation. 


THE   CARPAL   JOINTS 


183 


THE  CARPAL   JOINTS 

These  joints  taken  together  eonstitvite  the  composite  articulatio  carpi,  or  what 
is  popularly  termed  the  "knee-joint"  in  animals.'  This  consists  of  three  chief 
joints,  viz.,  (1)  The  radio-carpal  joint,  formed  by  the  distal  end  of  the  radius  and 
the  proximal  row  of  the  carpus;  (2)  tlic  intercarpal  joint,  formed  between  the  two 
rows  of  the  carpus;  (3)  the  carpo-metacarpal  joint,  formed  between  the  distal  row 
of  the  carpus  and  the  proximal  ends  of  the  metacarpal  bones.  The  proximal  and 
middle  joints  may  be  regarded  as  ginglymi,  although  they  are  not  typical  or  pure 
examples  of  hinge-joints.  The  distal  joint  is  arthrodial.  In  addition  there  are 
arthrodial  joints  formed  between  adjacent  bones  of  the  same  row  (Articulationes 
interosseae).  All  these  constitute  a  very  composite  joint,  with  numerous  ligaments. 
The  articular  surfaces  have  been  described 
in  the  Osteology. 

The  joint  capsule  may  be  regarded, 
so  far  as  the  fibrous  part  is  concerned,  as 
being  common  to  all  three  joints.  It  is 
attached  close  to  the  margin  of  the  articu- 
lar surface  of  the  radius  above  and  the 
metacarpus  below;  its  deep  face  is  also 
attached  to  a  considerable  extent  to  the 
carpal  bones  and  to  the  small  ligaments. 
Its  anterior  part,  the  dorsal  or  anterior 
common  ligament,  is  rather  loose,  and 
assists  in  forming  tlie  fil:)rous  canals  for 
the  extensor  tendons.  Its  jiosterior  part, 
the  volar  or  posterior  common  ligament, 
is  very  thick  and  dense,  and  is  closely 
attached  to  the  carpal  bones.  It  levels 
up  the  irregularities  of  the  skeleton  here, 
and  forms  the  smooth  anterior  wall  of  the 
carpal  canal.  It  is  continued  downward 
to  form  the  subcarpal  or  inferior  check 
ligament,  which  blends  with  the  tendon  of 
the  flexor  perforans  about  the  middle  of 
the  metacarpus. 

The  synovial  membrane  forms  three 
sacs  corresponding  to  the  three  joints. 
The  radio-carpal  sac  is  the  most  volum- 
inous; it  includes  the  joints  formed  by  the 
accessory  carpal  bone,  and  also  those  be- 
tween the  proximal  carpal  bones  as  far  as  the  interosseous  ligaments.  The 
intercarpal  sac  sends  extensions  upward  and  downward  between  the  bones  of 
the  two  rows  as  far  as  the  interosseous  ligaments;  it  communicates  between 
the  third  and  fourth  carpal  bones  with  the  carpo-metacarpal  sac.  The  latter  is 
very  limited  in  extent,  and  is  closely  applied  to  the  bones;  it  incloses  the  carpo- 
metacarpal joint,  and  lubricates  also  the  lower  parts  of  the  joints  between  the 
distal  carpal  bones  and  the  intermetacarpal  joints. 

The  external  lateral  ligament  (Ligamentum  carpi  collaterale  ulnare)  is  attached 
above  to  the  e.xternal  tuberosity  of  the  distal  end  of  the  radius.  Its  long  superficial 
part  is  attached  below  to  the  proximal  end  of  the  external  small  metacarpal  chiefly, 

'  The  term  is  a  very  unfortunate  one,  since  it  is  a  distinct  misapplication  of  the  name  as  it  is 
used  in  regard  to  man.  "  It  is,  however,  very  firmly  established,  and  appears  hkely  to  persist  m- 
definitely  in  the  absence  of  a  convenient  popular  equivalent. 


Fig.  146. — Froxt.vi.  Section  of  Carpal  Joints  of 
Horse  (Right  Side). 
/.».,  External,  I.r.,  internal,  lateral  ligament; 
Cr,  radial  carpal;  Ci",  intermediate  carpal;  Cu.  ulnar 
carpal;  CB,  second  carpal;  CS,  third  carpal;  C'i, 
fourth  carpal;  McB,  second  (internal)  metacarpal; 
Mc3,  third  (large)  metacarpal;  Mc4,  fourth  (exter- 
nal) metacarpal. 


184 


THE   ARTICULATIONS    OF   THE    HORSE 


-  Internal  lat- 
eral ligament 


but  some  fibers  end  on  the  large  metacarpal  bone.  A  canal  for  the  lateral  extensor 
tendon  separates  a  short  deep  band  which  ends  on  the  ulnar  carpal  bone.  Other 
deep  fibers  connect  the  latter  with  the  fourth  carpal  bone,  and  the  fourth  carpal 
with  the  metacarpus. 

The  internal  lateral  ligament  (Ligamentum  carjii  collateralc  radiale)  resembles 
the  preceding  in  general,  but  is  stronger  and  wider  distally.  It  is  attached  above 
to  the  internal  tuberosity  of  the  distal  end  of  the  radius  and  ends  below  on  the 
proximal  ends  of  the  large  antl  inner  small  metacarpal  bones.  Deep  fasciculi  are 
detached  to  the  radial  and  second  carpal  bones.  The  first  carpal  bone,  when  pres- 
ent, is  usually  embedded  in  the  posterior  part  of  the  distal  end  of  the  ligament. 
The  posterior  part  of  the  ligament  is  fusetl  with  the  posterior  annular  ligament 
(Ligamentum  carpi  transversum),  and  concurs  in  the  formation   of  a  canal   for 

the  tendon    of  the  flexor  carpi  in- 

ternus. 

A  number  of  special  .short  ligaments 
connect  two  or  more  adjacent  bones;  only 
the  most  distinct  of  these  will  be  described 
here. 

The  accessory  carpal  bone  is  con- 
nected with  adjacent  bones  by  three  liga- 
ments (Fig.  444).  The  pro.ximal  one  is  a 
short  band  which  extends  from  the  acces- 
sory carpal  in  front  of  the  groove  on  its 
outer  face  and  is  inserted  into  the  distal 
end  of  the  radius  behind  the  groove  for 
the  lateral  extensor  tendon.  A  middle 
band  connects  the  accessory  with  the 
ulnar  carpal.  The  distal  ligament  consists 
of  two  strong  bands  which  pass  from  the 
lower  margin  of  the  accessory  to  the  fourth 
carpal  and  the  proximal  end  of  the  outer 
metacarpal  bone;  these  bands  transmit 
the  action  of  the  muscles,  which  are  in- 
serted into  the  accessory  carpal  bone. 
The  other  bones  of  the  proximal  row  are 
connected  by  two  anterior  or  dorsal  liga- 
ments, which  are  trans\erse  in  direction, 
and  two  interosseous  ligaments.  An  ob- 
lique ligament  passes  from  an  eminence 
on  the  posterior  surface  of  the  radial  car- 
pal bone  to  a  small  depression  on  the 
radius  internal  to  the  facet  for  the  acces- 
sory carpal  bone. 

Two  ligaments  connect  the  proximal 
and  distal  rows  posteriorly.  Tlie  inner 
one  joins  the  radial  to  the  second  and 
third  carpal,  and  the  outer  one  attaches 
the  ulnar  to  the  third  and  fourth  carpals. 
The  bones  of  the  distal  row  are  connected  by  two  strong  trans\erse  anterior  or  dorsal  liga- 
ments and  two  interosseous  ligaments. 

There  are  four  carpo-metacarpal  ligaments.  Two  oblique  anterior  bands  connect  the  third 
carpal  with  the  large  metacarpal.  Two  interosseous  ligaments  pass  downward  from  the  inter- 
osseous ligaments  of  the  distal  row  to  end  in  depressions  in  the  interstices  between  the  proximal 
ends  of  the  metacarpal  bones. 

Movements. — Taking  the  joint  as  a  whole,  the  chief  movements  are  flexion 
and  extension.  In  the  standing  position  the  joint  is  extended.  When  the  joint  is 
flexed,  slight  lateral  movement  and  rotation  can  be  produced  by  manipulation. 
The  anterior  ]iart  of  the  capsule  is,  of  course,  tense  during  flexion,  the  posterior 
part  in  extension. 

The  movement  practically  .all  occurs  at  the  radio-carpal  and  intercarp.al  joints,  the  articular 
surfaces  of  which  are  widely  separatcil  in  front  during  flexion,  but  remain  in  contact  behind.  The 
distal  row  remains  in  contact  with  the  metacarpus.  The  intermediate  and  ulnar  carpals  move 
together  as  one  piece,  but  the  radial  does  not  move  .so  far  as  the  intermediate,  so  that  the  anterior 
and  intero-sseous  ligaments  connecting  these  bones  become  tense  .and  oblique  in  direction. 


Internal  distal 

tuberosity  of 

radius 

Accessory  car- 
pal bone 


Inferior  liga- 
ments of  acces- 
sory carpal 


Internal 
(second)  meta- 
carpal bone 


Fig.  147. — Left  Carpal  Joints  of  Horse 

(7,  Radius;    12,  large  (third)  metacarpal  bone. 

berger-Iiaum,  .\nat.  fur  Kunstler.) 


Mrlnciirpal 
tuberosity 


(After  Ellen- 


THE    FETLOCK    JOINT 


185 


THE   FETLOCK    JOINT 
This,  the  metacarpo-phalangeal  articulation  (Articulatio  metucarpo-phalangea), 
is  a  ginglymus  formed  by  the  junction  of  the  distal  end  of  the  large  (third)  meta- 
carpal hone,    tlie  proximal  end  of   the  first  phalanx,  and  the  proximal  sesamoid 
bones. 

Articular  Surfaces. — The  surface  on  the  large  metacarpal  lione  is  approxi- 
mately cylindrical  in  curvature,  l)ut  is  divided  into  two  slightly  uneciual  parts  by  a 
sagittal  ridge.     This  is  received  into  a  sort  of  socket  formed  by  the  first  phalanx 

below  and  the  two  sesamoids  together 
with  the  intersesamoid  ligament  be- 
hind. The  latter  is  a  mass  of  fibro- 
cartilage  in  which  the  sesamoid  bones 
are  largely  embedded.  It  extends 
above  the  level  of  the  sesamoids, 
and  is  grooved  to  receive  the  ridge 
on  the  metacarpal  bone;  its  posterior 
surface  forms  a  smooth  groove  for  the 
deep  flexor  tendon. 

The  joint  capsule  is  attached  around 
the  margin  of  the  articular  surfaces.     It 

Branches  of 
suspensory  ligament 


Fig.  148 


.  Sectiox  of  Dist.\ 
OF  Horse. 
/,  Large  metacarpal  bone;  3,  fetlock  joint;  4, 
proximal  sesamoid  bone;  5,  first  phalanx;  6,  pastern 
joint;  7,  second  phalanx;  S,  coffin  joint;  9,  third  phal- 
anx; 10.  distal  .sesamoid  (navicular  bone);  12,  sus[)en- 
sory  ligament;  14,  deep  flexor  tendon;  Id,  superficial 
flexor  tendon:  16,  posterior  annular  ligament  of  fetlock; 
SO,  inferior  sesamoidean  ligaments:  21,  extensor  tendon; 
S4,  plantar  cushion;  £5,  periople;  2S,  wall  of  hoof;  29, 
sole  of  hoof:  -1 ,  navicular  bursa,  proximal  part.  (After 
Ellenberger-Baum,  Anat.  fiir  Kiinstler.) 


OF  Limb  Fig.  149. — .\hticui,ar  Surfaces  of  First  Phalanx 
AND  Sesamoids  at  Fetlock,  with  Intersesa- 
moid .\ND  Suspensory  Ligaments.  (After 
Schmaltz,  .\tlas  d.  Anat.  d.  Pferdes.) 


is  thick  and  ample  in  front;  here  a 
bursa  is  interposed  Ijetween  it  and 
the  extensor  tendons,  but  the  tendons 
are  also  attached  to  the  capsule.  Pos- 
teriorly it  forms  a  thin-walled  pouch 
which  extends  upward  bet^\een  the 
metacarpal  bone  and  the  suspensory  ligament  about  as  high  as  the  point  of 
bifurcation  of  the  latter.     The  capsule  is  reinforced  by  two  lateral  ligaments. 

The  lateral  ligaments,  external  and  internal  (Ligamentum  collateralo  ulnare, 
radiale)  are  partially  divided  into  two  layers:  the  superficial  layer  arises  from  the 
eminence  on  the  side  of  the  distal  end  of  the  large  metacarpal  lione.  and  passes 
straight  to  the  rough  lateral  area  below  the  margin  of  the  articular  surface  of  the 
first  phalanx;  the  deep  layer,  shorter  and  much  stronger,  arises  in  the  lateral 
depression  on  the  distal  end  of  the  metacarpal  bone,  and  passes  obliquely  downward 
and  backward  to  he  inserted  into  the  outer  surface  of  the  sesamoid  and  the  proxi- 
mal end  of  the  first  phalanx. 


186 


THE    ARTICULATIONS    OF   THE    HORSE 


The  capsule  is  further  strengthened  by  a  layer  of  obUque  fibers  which  pass  o\er  the  lateral 
ligament  on  either  side  and  end  on  the  extensor  tendon  and  the  proximal  extremit\-  of  the  first 
phalanx.     It  may  properly  be  regarded  as  fascia  rather  than  ligament. 

Movements. — These  are  of  the  nature  of  flexion  and  extension,  the  axis  of 
motion  ]:assins  through  the  upper  attachments  of  tlie  lateral  ligaments.  In  the 
ordinary  standing  position  the  joint  is  in  a  state  of  partial  dorsal  flexion,  the  articu- 
lar angle  (in  front)  being  about  140°  to  150°.  (In  the  hind  liinl)  it  is  about  5° 
greater.)     Diminution  of  this  angle  (sometimes  ternietl  "overextension")  is  nor- 


ExtensoT  temhm 


Upper  end  of  capsuU-  of  fdUick 
joint 

Bursa 
Lalcrnl  ligament  of  fetlock  joint 


Fascia  — !*— 


Superficial  flexor  tendon 
Deep  flexor  tendon 
Suspensory  ligament 
Lateral  interrosseous  tendon 

Upper  end  of  digital  sheath 

Ring  of  superficial  flexor  tendon 
iilersrsatnoidean  ligament 
Posterior  annidar  ligament  (cut) 


Lateral  sesamoidean  ligament 
Snp<rficial  inferior  sesamoidean 
1 1  ligament 

jr~  Middle  inferior  sesamoidean 
ligament 
;  xlttach?nents  of  proximal  digitul 
annular  ligament 


Pouch  of  digital  sheath 

Distal  digital  annular  ligament 
Lateral  cartilage 


Branch  of  suspensory  ligament   — i?^ 


Lateral  rolar  ligament  of  pastern 
joint 


Suspensory  ligament  of  namcular 
bone 
Band  from  lateral  cartilage  to 
extensor  tendon 
Lateral  ligament  of  coffin  joint 


Tic.   150. — Ligaments  and  Tendons  of  Distal  Part  of  Limb  of  Horse. 

Mc. Ill,  L-irEe  metacarpal  bone;   Ph. I,  first  phalanx;   Ph.II,  second  phalanx;    I'h. Ill,  third  phalanx;    1 ,  deep  flexor 

tendon;  2,  band  from  first  phalanx  to  plantar  cushion.      C.\fter  Hchinaltz,  .\lla.s  d.  .\nat.  d.  Pferdes.) 

mally  very  limited  on  account  of  the  resistance  offered  by  the  sesamoidean  a])i)ara- 
tus,  but  it  varies  considerably  in  amount  in  different  subjects.  Volar  flexion  is 
limited  only  by  contact  of  the  heels  with  the  metacarpus.  Durin,e;  volar  flexion 
a  small  amount  of  lateral  flexion  is  jwssible. 


THE  SESAMOIDEAN   LIGAMENTS 
Under  this  heatl  will  be  described  a  number  of  important  ligaments  which  are 
connected  with  the  sesamoid  bones  and  form  a  sort  of  stay  apixiratus  or  lirace. 


THE    SESAMOIDEAN    LIGAMENTS 


187 


The  intersesamoidean  ligament  (Ligamentum  intersesamoideuni)  not  only  fills 
the  space  between  an<.l  unites  the  sesamoid  hones,  but  also  extends  above  them, 
entering  into  the  formation  of  the  articular  surface  of  the  fetlock  joint.  Other 
facts  in  regard  to  it  have  iieen  given  above. 

The  lateral  sesamoidean  ligaments,  outer  and  inner  (Ligamenta  sesamoidea 
ulnare  et  radiale),  arise  on  the  abaxial  surface  of  each  sesamoid  bone,  pass  forward, 
and  divide  into  two  branches,  one  of  which  ends  in  the  depression  on  the  distal  end 
of  the  large  metacarpal  bone,  the  other  on  the  eminence  on  the  i)roximal  end  of  the 


B  if  urea  I  ion  of  common  digital  arlenj 
Internal  digital  artery 


Oblique  or  middle  inferior  sesamoid 
ligament 
Straight  or  superfieial  inferior 
sesamoid  ligament 


Distal  annular  ligament  of  digit  (. 
aivl  reflected) 


Large  nietaeariial  hone 

External  small  metacarpal  bone 

Bifurcation  of  suspensory 
ligament 


Capsule  of  fetlock  joint  {upper 

pouch) 
Si'samoid  groove 

Posterior  annular  ligament  of 
fetlock  (cut  and  reflected) 

Ldtirid  sesamoid  ligament 

Slump  of  digital  annular 

ligament 
Extensor  branch  of  suspensory 

ligament 
^  'olar  ligaments  of  pastern  joint 

Insertion  of  superficial  flexor 

tendon 
Fibrous  plate 

Deep  flexor  tendon 

Lateral  ligament  of  pastern  joint 
Distal  end  of  digital  sheath 
Suspensory  ligament  of 

naricular  bone 
Dorsal  branch  of  digital  artery 
Volar  branch  of  digital  artery 


■CD  Lick 


TS, 


Fig.  151. — Dekp  Dissectio.v  of  Distal  Part  of  Right  Fore  Limb  of  Horse.  Seowi.Nti  Ji 

Posterior  View. 
1,  Lateral  cartilage:    2,  tendon  surface  of  navicular  bone;    3.  inferior  navicular  or  interos.seous  ligament; 
4,  insertion  of  deep  flexor  tendon.     Small  arrows  point  to  openings  made  in  capsules  of  pastern  and  coffin  joints. 
(After  Schmaltz,  .\tlas  d.  Anat.  d.  Pferdes.) 


first   phalanx.     They  are  partly  covered    liy  the   brandies  of  the  suspensory  or 
superior  sesamoidean  ligament. 

The  suspensory  or  superior  sesamoidean  ligament  (IMusculus  interosseus 
medius)  lies  for  the  greater  part  in  the  metacarpal  groove,  where  it  has  the  form  of 
a  wide,  thick  band.  It  is  attached  above  to  the  upper  part  of  the  posterior  surface 
of  the  large  metacarpal  bone  and  to  the  distal  row  of  carpal  bones.  At  the  lower 
fourth  of  the  metacarpus  it  divides  into  two  diverging  branches.  Each  branch 
passes  to  the  abaxial  face  of  the  corresponding  sesamoid,  on  which  a  considerable 


188  THE   ARTICULATIONS    OF   THE    HORSE 

part  is  attached.  The  remainder  passes  obliquely  downward  and  forward  to  the 
anterior  surface  of  the  first  phalanx,  where  it  joins  the  extensor  tendon.  This 
ligament  possesses  considerable  elasticity,  and  is  the  highly  modified  interosseous 
medius  muscle.  It  consists  mainly  of  tendinous  tissue,  but  contains  a  variable 
amount  of  striped  muscular  tissue,  especially  in  its  deep  part  and  in  young  subjects. 
Its  principal  function  is  to  support  the  fetlock,  i.  e.,  to  prevent  excessive  dorsal 
flexion  of  the  joint  when  the  weight  is  put  on  the  limb.  The  branches  which  join 
the  common  extensor  tendon  limit  volar  flexion  of  the  interphalangoal  joints  in 
certain  phases  of  movement. 

The  inferior  sesamoidean  ligaments  arc  three  in  number — superficial,  middle, 
and  deep.  The  superficial  or  straight  ligament  (Liganientum  sesamoidcum  rec- 
tum) is  a  flat  bantl  and  is  somewhat  wider  aliove  than  lielow.'  It  is  attached  above 
to  the  bases  of  the  sesamoid  bones  and  the  intersesamoid  ligament,  lielow  to  the 
complementary  fibro-cartilage  of  the  proximal  end  of  the  second  phalanx.  The 
middle  ligament  is  triangular,  with  thick,  rounded  margins  (Ligainenta  obliqua)  and 
a  thin  central  portion."  Its  base  is  attached  to  the  sesamoid  bones  and  intersesa- 
moid ligament,  and  its  deep  face  to  the  triangular  rough  area  on  the  posterior 
surface  of  the  first  phalanx.  The  deep  or  cruciate  ligament  (Ligamenta  scsamoidea 
cruciata)  consists  of  two  thin  layers  of  fibers  which  arise  on  the  base  of  the  sesa- 
moid bones,  cross  each  other,  and  end  on  the  opposite  eminence  on  the  proximal 
end  of  the  first  ])halanx. 

The  short  sesamoidean  ligaments  (Ligamenta  sesamoidea  brevia)  are  best 
seen  by  opening  the  joint  in  front  and  pushing  the  sesamoid  bones  backward;  they 
are  covered  by  the  synovial  membrane.  Each  is  a  short  band  which  extends  from 
the  anterior  part  of  the  base  of  the  sesamoid  bone  outward  to  the  posterior  margin 
of  the  articular  surface  of  the  first  phalanx. 

The  inferior  sesamoidean  ligaments  may  be  regarded  as  digital  continuations 
of  the  suspensory  ligament,  the  sesamoid  bones  being  intercalated  in  this  remark- 
able stay  apparatus  by  which  the  fetlock  is  supported  and  concussion  diminished. 


THE   PASTERN   JOINT 

This,  the  proximal  interphalangeal  articulation  (Articulatio  phalangis  se- 
cundie),  is  a  ginglymus  formed  by  the  junction  of  the  distal  end  of  the  first  phalanx 
and  the  proximal  end  of  the  second  i)halanx. 

The  articular  surfaces  are:  (1)  On  the  first  phalanx,  two  slightly  unequal  con- 
vex areas  with  an  intermediate  shallow  groove;  (2)  on  the  second  phalanx,  a  cor- 
responding surface,  completed  behind  by  a  plate  of  fibro-cartilage. 

The  joint  capsule  is  close-fitting  in  front  and  laterally,  where  it  blends  with  the 
extensor  tendon  and  tiie  lateral  ligaments  respectively.  Behind  it  pouches  upward 
a  little  and  is  reinforced  by  the  straight  sesamoidean  ligament  and  the  branches  of 
the  superficial  flexor  tendon. 

There  are  two  lateral  and  four  volar  ligaments. 

The  lateral  ligaments,  internal  and  external  (Ligamentum  coUaterale  radiale, 
ulnare)  are  very  short  and  strong  bands  which  are  attached  above  on  the  emi- 
nence and  depression  on  each  side  of  the  distal  end  of  the  first  phalanx,  and  below 
on  the  eminence  on  either  side  of  the  jiroximal  end  of  the  second  phalanx.  The 
direction  of  the  ligaments  is  about  \-ertical  and,  therefore,  does  not  correspond  to 
the  digital  axis. 

The  volar  or  posterior  ligaments  consist  of  central  and  lateral  pairs  of  bands 
which  are  attached  below  to  the  jiosterior  margin  of  the  proximal  end  of  the  second 

'This  is  often  called  the  Y-'^lmpeil  lif^ament — a  rather  unde.sirahlc  name,  since  it  is  not 
bifurcate. 

^It  is  also  calleil  the  V-^'i^'Pf'J  lipament. 


THE    COFFIN    JOINT 


189 


phalaiix  and  its  complementary  fibro-cartilage.  The  lateral  pair  is  attached  aliove 
to  the  middle  of  the  borders  of  the  first  phalanx,  the  central  pair  lower  down  and 
on  the  margin  of  the  triangular  rough  area. 

Tliese  ligaments  are  very  commonly  tliickened  as  a  result  of  chronic  inflammation,  and  then 
are  not  well  defined.  Tlie  central  ones  blend  below  with  the  branches  of  tlie  superficial  flexor 
tendon  and  with  the  straight  sesamoidean  ligament. 

Movements. — These  are  very  limited,  and  consist  of  flexion  and  extension. 
The  axis  of  motion  passes  transversely  through  the  distal  end  of  the  first  i^halanx. 
In  the  standing  position  the  joint  is  extended.  A  small  amount  of  volar  flexion  is 
possible,  and  in  this  jiosition  slight  lateral  flexion  and  rotation  can  be  produced  by 
manipulation.  Dorsal  flexion  is  prevented  by  the  lateral,  volar,  and  straight  sesa- 
moidean ligaments. 


Lateral  cartilage 


f  lA     Lntn-nll, .laments  of 


inc/ils  of  navicu- 
lar bone 


Tendon  snrface 
of  navicular 
bone 


Fig.   152. — Lateral  Ligament.^i  of  P. 
SORY   Ligaments   of   Nav 
.\tlas  (1.  Anat.  d.  Pferdes.) 


THE  COFFIN  JOINT 

This  joint,  technically  termed  the  distal  interphalangeal  articulation  (Articu- 
latio  phalangis  tertiae),  is  a  ginglymus  formed  by  the  junction  of  the  second  and 
third  phalanges  and  the  third  sesamoid  bone. 

Articular  Surfaces. — The  surface  on  the  distal  end  of  the  second  phalanx  is 
convex  from  before  l)ackward, 

concave    transversely.       The  jp        /^^|    Latimi  i,,i,iiii<nts  of 

articular  surface  of  the  third 
phalanx  slopes  sharply  up- 
ward and  forw^ard;  its  cen- 
tral part  is  prominent,  and  is 
flanked  by  two  glenoid  cavi- 
ties. It  is  completed  behind 
by  the  articular  surface  of 
the  third  sesmoid  or  navicular 
bone. 

Joint  Capsule. — This  is 
attached  around  the  margins 
of  the  articular  surfaces.  In 
front  and  laterally  it  is  tight, 
and  is  blended  with  the  exten- 
sor tendon  and  the  lateral  liga- 
ments respectively.  Posteriorly,  it  forms  a  considerable  pouch  which  extends 
upward  to  about  the  middle  of  the  second  phalanx,  where  it  is  separated  by  a 
fibrous  membrane  from  the  digital  synovial  sheath.  Laterally  small  pouches  pro- 
ject outward  (especially  during  volar  flexion)  against  the  lateral  cartilages,  just 
behind  the  lateral  ligaments.' 

Ligaments. — The  lateral  ligaments,  external  and  internal  (Ligamentum  colla- 
teral ulnare,  radiale),  are  short  strong  bands  which  are  attached  above  in  the 
depressions  on  either  side  of  the  lower  part  of  the  second  phalanx,  under  cover  of 
the  lateral  cartilage.  They  widen  below  and  end  in  the  depressions  on  either  side 
of  the  extensor  process  and  on  the  anterior  end  of  the  lateral  cartilages. 

The  suspensory  navicular  ligaments,  external  and  internal  (Ligamentum  sesa- 
moideum  coUaterale  ulnare,  radiale),'  are  strong,  somewhat  elastic  bands,  which 
form  a  sort  of  suspensory  apparatus  for  the  third  sesamoid.  They  are  attached 
superiorly  in  and  above  the  depressions  on  either  side  of  the  distal  end  of  the  first 

'  This  should  be  noted  in  regard  to  resection  of  the  lateral  cartilage  or  other  operations  in 
this  vicinity. 

-  These  are  termed  the  postero-lateral  ligaments  by  M'Fadyean.  They  may  well  be  called, 
as  by  German  authors,  the  suspensory  ligaments  of  the  navicular  bone. 


Joint  and 

;.     (.\fter   Schmaltz 


190  THE    ARTICULATIONS   OF   THE    HORSE 

phalanx  and  are  here  partly  blended  with  the  lateral  ligaments  of  the  pastern  joint. 
They  are  directed  obliquely  downward  and  backward,  and  end  chieflj'  on  the 
ends  and  proximal  border  of  the  thiril  sesamoid,  l)ut  detach  a  branch  to  the  inner 
surface  of  each  lateral  cartilage  and  wing  of  the  third  phalanx. 

The  inferior  navicular  ligament  (Ligamentum  phalangeo-sesamoideum)  rein- 
forces the  capsule  inferiorly.  It  is  a  strong  layer  of  fibers  which  extend  from  the 
distal  border  of  the  third  sesamoid  to  the  tendon  surface  of  the  third  phalanx, 
near  the  posterior  margin  of  the  articular  surface. 

Movements. — The  chief  movements  arc  flexion  and  extension.  In  the  stand- 
ing ])ositiou  the  joint  is  extended.  During  volar  flexion  a  very  small  amount  of 
lateral  movement  and  rotation  can  be  produced  by  mani])tilation.  Dorsal  flexion 
is  very  limited. 

Dorsal  flexion  appears  to  be  checked  mainly  by  the  deep  flexor  tendon,  since  in  cases  of  rup- 
ture of  the  latter  the  toe  turns  up.  The  sUght  mobility  of  the  posterior  part  of  the  socket  for  the 
second  phalanx  (formed  by  the  third  sesamoid)  diminishes  concussion  when  the  weight  comes 
on  the  foot. 

LIGAMENTS  OF  THE  LATERAL  CARTILAGES 

In  addition  to  the  liands  mentioned  above,  which  attach  the  lateral  cartilages 
to  the  extremities  of  the  navicular  bone,  there  are  three  ligaments  on  either  side 
which  attach  the  cartilages  to  the  phalanges. 

An  ill-defined  elastic  band  passes  from  the  middle  part  of  the  border  of  the 
first  ])halanx  to  the  ujjper  part  of  the  cartilage,  detaching  a  branch  to  the  plantar 
cusliion. 

A  short  strong  band  connects  the  anterior  extremity  of  the  cartilage  with  the 
rough  eminence  on  the  second  phalanx  in  front  of  the  attachment  of  the  lateral  liga- 
ment of  the  coffin  joint. 

The  lower  border  of  the  cartilage  is  covered  externally  l)y  fillers  which  attach 
it  to  the  wing  of  the  third  phalanx. 


The  Articulations  of  the  Pelvic  Limb 
the  sacro-iliac  articulation 

This  joint  (Articulatio  sacro-iliaca)  is  a  diarthrosis  formed  between  the  auricu- 
lar surfaces  of  the  sacrum  and  ilium.  These  surfaces  are  not  smooth  in  the  adult, 
but  are  marked  by  eminences  and  depressions,  and  are  covered  by  a  thin  layer  of 
cartilage.     The  joint  cavity  is  a  mere  cleft,  and  is  often  crossed  by  fibrous  bands. 

The  capsule  is  very  close  fitting,  and  is  attached  around  the  margins  of  the 
articular  surfaces.  It  is  reinforced  by  the  ventral  sacro-iliac  ligament  (Ligamentum 
sacro-iliacum  ventrale),  which  surrounds  the  joint,  and  is  (exceedingly  strong  above. 

The  movements  are  inappreciable  in  the  adult — stability,  not  moliility, 
being  the  chief  desideratum. 

The  following  ligaments  may  be  regarded  as  accessory  to  the  joint,  although 
not  directly  connected  with  it. 

The  dorsal  sacro-iliac  ligament  (Ligamentum  sacro-iliacum  dorsale  breve)  is  a 
strong  l)and  which  is  attached  to  the  internal  angle  (Tul)er  sacrale)  of  the  ilium  and 
the  smnmits  of  the  sacral  sjiines. 

The  lateral  sacro-iliac  ligament  (Ligamentum  sacro-iliacum  dorsale  longum) 
is  a  triangular,  thick  sheet  which  is  attached  in  front  to  the  internal  angle  and  border 
of  the  ilium  alwve  the  great  sciatic  notch,  and  below  to  the  lateral  border  of  the 
sacrum.  It  blends  aljove  with  the  dorsal  sacro-iliac  ligament,  below  with  the 
sacro-sciatic  ligament,  and  l)ehind  with  the  coccygeal  fascia. 

The  sacro-sciatic  ligament   (Ligamentum  sacrospinosimi  et  tuberosum)  is  a 


SYMPHYSIS    PELVIS OBTURATOR   MEMBRANE 


191 


quadrilateral  slu'it  which  completes  the  lateral  pelvic  wall.  Its  upper  border  is 
attachetl  to  the  border  of  the  sacrum  and  the  transverse  processes  of  the  first  and 
second  coccygeal  vertebrae.  Its  lower  border  is  attached  to  the  superior  ischiatic 
spine  and  tuber  isehii.  Between  these  it  bridges  over  the  external  border  of  the 
ischium  and  completes  the  lesser  sciatic  foramen.  The  anterior  border  is  concave, 
and  completes  the  greater  sciatic  foramen.  The  posterior  border  is  fusetl  with  the 
vertebral  head  of  the  semimembranosus  muscle. 

The  ilio-lxmibar  ligament  (Ligamentum  ilio-lumbale)  is  a  triangular  sheet  which 
attaches  the  ends  of  the  lumbar  transverse  processes  to  the  ventral  surface  of  the 
ilium  below  the  attachment  of  the  longissimus  muscle  (Fig.  184). 


Veiilrat  sacro-iliuc  Uyamenl 


Fig.  153.— Left  Os  Cox.i 


Psoas  tubercle 

Depression  for  origin  of  inner  tendon  of 
biceps  femoris 

osterior  part  of  trochanter  major 
Anterior  part  of  trochanter 
major 


Trochanter  minor 

Mi-R  OF  Horse,     (.\fter  .Schmaltz,  .\tla 


d.  .Aiiat.  d.  Pferdes.) 


SYMPHYSIS  PELVIS 
The  symphysis  pelvis  is  formed  by  the  junction  of  the  two  ossa  coxarum  at 
the  ventral  meilian  line.  In  the  young  subject  the  bones  are  united  by  a  layer  of 
cartilage;  in  the  adult  the  latter  is  gradually  replaced  bj'  bone,  the  process  beginning 
in  the  pubic  portion  and  extending  backward.  The  union  is  strengthened  by  white 
fibrous  tissue  above  and  below,  and  a  transverse  band  also  covers  the  anterior  border 
of  the  pubis  (pecten).  No  appreciable  movement  occurs  even  before  sjTiostosis 
takes  place. 

OBTURATOR  MEMBRANE 
This  (Membrana  obturatoria)  is  a  thin  layer  of  fibrous  ti-ssue  which  covers  the 
obturator  foramen,  leaving,  however,  a  passage    (Canalis  obturatorius)   for   the 
obturator  vessels  and  nerve. 


192 


THE   AHTICULATIONS    OF    THE    HORSE 


THE  HIP  JOINT 

This  joint  (Articulatio  coxae)  is  an  enarthrosis  formed  by  the  proximal  end 
of  the  femur  and  the  acetabulum. 

Articular  Surfaces. — The  head  of  the  femur  presents  an  almost  hemispherical 
articular  surface,  which  is  continued  a  short  distance  on  the  upper  surface  of  the 
neck.  It  is  more  extensive  than  the  socket  which  receives  it.  Internally  it  is 
cut  into  by  a  deep  notch  for  the  attachment  of  the  round  and  pubo-femoral  liga- 
ments. The  acetabulum  is  a  typical  cotyloid  cavity.  Its  articular  surface  is 
somewhat  crescentic,  being  deeply  cut  into  internally  by  the  acetabular  notch  and 


Fig.  154. — Pelvic  LinAMENT.s  and  Htp  Joint. 
1,  Dorsal  sacro-iliac  ligament;  2,  lateral  sacro-iliac  ligament;  3,  sacro-sciatic  ligament;  j^,  greater  sciatic 
foramen;  5,  les.ser  sciatic  foramen;  ff,  line  of  attachment  of  intermuscular  septum  between  hicefjs  femoris  and  semi- 
tendinosus;  7,  capsule  of  hip  joint;  8,  rectus  parvus  or  capsularis  muscle;  9,  outer  tendon  of  origin  of  biceps 
femoris;  iO,  internal,  //,  external,  angle  of  ilium;  15,  shaft  of  ilium;  7;?,  superior  ischiatic  spine;  i.^,  pubis;  15, 
tuber  ischii;  /5,  trochanter  major;  i7,  semimembranosus;  /5,  fifth  lumbar  spine;  i5,  £0,  first  and  second  coccygeal 
vertebra*. 


fossa.  It  is  increased  and  deepened  by  a  ring  of  fil)ro-cartilage,  the  cotyloid 
ligament  (Labrum  glenoidale),  which  is  attached  to  the  bony  margin;  that  part  of 
the  ligament  which  crosses  the  notch  is  called  the  transverse  ligament  (Fig.  456). 
The  joint  capsule  is  roomy.  It  is  attached  around  the  margin  of  the  acetab- 
ulum and  the  neck  of  the  femur.     It  is  thickest  externally. 

The  attachment  on  the  femur  is  about  1  cm.  from  the  margin  of  the  articular  surface,  except 
above,  where  2  to  3  cm.  of  the  neck  is  intracapsular,  k  thin  oblique  band  corresponding  in  direc- 
tion with  the  rectus  parvus  niu.scle  reinforces  the  antero-cxternal  part  of  the  capsule;  this  appears 
to  be  the  feeble  lioiiiologue  of  the  very  strong  ilio-femoral  ligament  of  man.  The  capsule  is  very 
thin  under  the  ilio-p.soas.  and  is  adherent  to  the  muscle.  Internally,  its  fibrous  part  is  perforated 
by  the  pubo-femoral  and  round  ligaments  and  the  articular  vessels. 


THE    HIP    JOINT 


193 


The  round  ligament  (Ligamontuni  tores)  is  a  strong  hand  which  is  attached 
in  the  subpubic  groove  close  to  the  acetabular  notch,  passes  outward,  and  ends 
in  the  notch  on  the  head  of  the  femur  (Fig.  456). 

The  pubo-femoral  ligament  (Ligamentum  accessoriuin)  does  not  occur  in  the 
domestic  animals  other  than  the  equidiE.  It  is  a  strong  band  detached  from  the 
prepubic  tendon  of  the  abdominal  muscles  (Fig.  456).  It  is  directed  outward, 
backward,  and  upward,  passes  through  the  acetabular  notch  above  the  transverse 
ligament,  and  ends  behind  the  round  ligament  in  the  notch  on  the  head  of  the 
femur.  The  origin  of  the  pectineus  muscle  is  perforated  by  the  ligament,  which 
furnishes  attachment  to  the  greater  part  of  the  fibers  of  the  muscle. 

The  synovial  membrane  is  reflected  over  the  intracapsular  parts  of  these 


External  patellar  Ugnment 
Middle  patellar  ligament 


Tuberositi/  of  tibia 


External  lateral  ligament 
External  condyle  of  tibia 


Shaft  of  fibula 


Fig.  155. — Left  Stifle  Joint  of  Horse,  External  View,  in  Partial  Flexion. 

The  capsules  have  been  removed.     /S,  Femur;   ao,  patella;    2/,  tibia;  a",  internal  patellar  ligament;   (i,  external 

femoro-patellar  ligament;  d,  external  semilunar  cartilage.      (After  EUenberger-Baum,  .\nat.  fiir  Kiinstler.) 


ligaments  and  covers  the  fossa  acetabuli.  A  pouch  also  extends  from  the  acetabular 
notch  for  a  variable  distance  along  the  subpubic  groove  above  the  pubo-femoral 
ligament. 

Movements.— This  joint  is  capable  of  all  the  movements  of  a  ball-and-socket 
joint,  viz.,  flexion,  extension,  abduction,  adduction,  rotation,  and  circumduction. 
The  greatest  range  of  movement  is  displayed  in  flexion  and  extension.  When 
standing  at  rest,  the  joint  is  partially  flexed,  the  articular  angle  (in  front)  being 
about  100°  to  115°.  The  other  movements  occur  to  a  very  limited  extent  in  normal 
action. 

Abduction  appears  to  be  checked  by  tension  of  the  round  ligament.     The  pubo-femoral 
ligament  is  tensed  most  promptly  by  inward  rotation  of  the  thigh. 
13 


194 


THE    ARTICULATIONS    OF   THE    HORSE 


THE  STIFLE  JOINT 

This  joint  (Articulatio  genu),  which  corresponds  to  the  knee-joint  of  man, 
is  the  largest  and  most  elaborate  of  all  the  articulations.  Taken  as  a  whole,  it 
may  be  classed  as  a  ginglymus,  although  it  is  not  a  typical  example  of  the  group. 
In  reality  it  consists  of  two  joints — the  femoro-patellar  and  the  femoro-tibial. 

The  femoro-patellar  articulation  (Articulatio  fenioro-patellaris)  is  formed 
between  the  trochlea  of  the  femur  and  the  articular  surface  of  the  patella. 

Articular  Surfaces. — The  trochlea  consists  of  two  slightly  oblique  ridges, 
with  a  wide  and  deep  groove  between  them.  The  inner  ridge  is  much  the  larger 
of  the  two,  especially  at  its  upper  part,  which  is  wide  and  rounded.     The  outer 

Proximal  //art  of  fcmoro- patellar  capsule 


Patella 


Middle  patellar  ligament 

Distal  part  of  femoro- 
patellar  capsule 
Tendon  of  origin,  of  long  ex- 
tensor and  pironciiK  tertiiis 

Pouch  of  femoro-tibial 
capsule 


External  femoro-patellar 
ligament 


Femoro-tibial  capsule 


External  lateral  ligament 
Semilunar  cartilage 


External  condyle  of  tibia 


Fir,,  15fi. — Left  Stifle  Joint  of  Horse,  Laterai,  Vie 
The  oai)suies  arn  distended  and  the  external  patellar  ligament  is  ri 


ridge  is  much  narrower,  and  is  more  regularly  curved;  its  upper  part  lies  about 
an  inch  behind  a  frontal  plane  tangent  to  the  inner  ridge.  The  articular  surface 
of  the  patella  is  much  smaller  than  that  of  the  trochlea.  It  is  completed  internally 
by  a  supplementary  plate  of  fibro-cartilage  (Fibrocartilago  patellae),  which  curves 
over  the  internal  surface  of  the  inner  lip  of  the  trochlea.  A  narrow  strip  of  cartilage 
is  found  along  the  outer  border  also.  The  articular  cartilage  on  the  trochlea 
completely  covers  both  surfaces  of  the  inner  ridge,  Ijut  only  a  narrow  marginal  area 
on  the  external  surface  of  the  outer  ridge. 

Joint  Capsule. — This  is  thin  and  is  very  capacious.  On  the  patella  it  is 
attached  around  the  margin  of  the  articular  surface,  but  on  the  femur  the  line  of 
attachment  is  at  a  varying  distance  from  the  articular  surface.  On  the  inner  side 
it  is  an  inch  or  more  from  the  articular  cartilage;    on  tlu>  outer  side  and  aliove, 


THE    STIFLE    JOINT 


195 


about  half  an  inch.  It  pouches  upward  under  the  quadriceps  femoris  for  a  distance 
of  two  or  three  inches,  a  pad  of  fat  separating  the  capsule  from  the  muscle. 
Below  the  patella  it  is  separated  from  the  straight  ligaments  by  a  thick  pad  of 
fat,  but  inferiority  it  is  in  contact  with  the  femoro-patellar  capsules.  The  joint 
cavity  is  the  most  extensive  in  the  body.  It  usually  communicates  with  the 
inner  feraoro-tibial  joint  cavity  by  a  sht-like  opening  situated  at  the  lowest  part 
of  the  inner  ridge  of  the  trochlea.  A  similar,  but  smaller,  communication  with  the 
outer  femoro-patellar  capsule  is  often  found  at  the  lowest  part  of  the  outer  ridge. 

The  inner  communication  appears  to  be  constant  in  adult  horses,  but  is  liable  to  be  over- 
looked on  account  of  the  fact  that  it  is  covered  by  a  valvular  fold  of  the  synovial  membrane.  It 
is  about  half  an  inch  wide,  and  lies  under  the  narrow  articular  area  which  connects  the  trochlea 
and  internal  condyle.  The  outer  communication  occurs  in  18  to  2.5  per  cent,  of  cases,  according 
to  Baum.  It  is  instructive  to  distend  this  capsule  and  thus  obtain  an  idea  of  its  potential  capa- 
city and  relations  (Fig.  laOj. 


Accessory  cartilage  of  patella- 
Inlernal  ridge  of  trochlea  of  femur - 
Middle  patellar  ligament 

Internal  semilunar  cartilage - 
Internal  patellar  ligament- 


Tuberosity  of  tibia  _ 


External  fcmoro-patcllnr  ligament 

-  External  patellar  ligament 

-  External  femoro-tibial  ligament 

-  External  semilunar  cartilage 

-  External  condyle  of  tibia 


Fig.  157. — Left  Stifle  Joint  of  Horse,  Front  View,  in  Extension. 
I  are  removed.     iS,  Femur;    20,  patella;    2/,  tibia,     (.\fter  EUenberger-Baum, -\naf .  fiir  Kiinstle 


Ligaments. — The  lateral  femoro-patellar  ligaments,  external  and  internal 
(Ligamentum  femoro-patellare  fibulare,  tibiale),  are  two  thin  bands  which  reinforce 
the  capsule  on  either  side.  The  external  ligament  is  fairly  distinct;  it  ari.ses  from 
the  external  epicondyle  of  the  femur  just  above  the  lateral  femoro-tibial  ligament, 
and  ends  on  the  external  l)order  of  the  patella.  The  internal  ligament  is  thinner 
and  is  not  distinct  from  the  capsule;  it  arises  above  the  internal  epicondyle,  and 
ends  on  the  patellar  fibro-cartilage. 

The  patellar  ligaments  (Ligamcnta  patellse),  also  called  the  straight  ligaments 
of  the  patella,  are  three  very  strong  l)ands  which  attach  the  patella  to  the  tuberosity 
of  the  tibia.  The  external  patellar  ligament  is  attached  above  to  the  outer  part 
of  the  anterior  surface  of  the  patella,  and  below  to  the  outer  part  of  the  tulicrosity. 
It  receives  a  strong  tendon  from  the  liiceps  femoris  muscle.  The  middle  patellar 
ligament  extends  from  the  front  of  the  apex  of  the  patella  to  the  lower  part  of 


196 


THE    ARTICULATIONS    OF   THE    HORSE 


the  groove  on  the  tuhciHjsity  of  the  tibia,  a  bursa  l)eins  interposed  between  the 
Hgament  and  the  upper  i)art  of  the  groove.  The  internal  patellar  ligament  is 
attached  above  to  the  patellar  fibro-cartilage,  and  ends  on  the  tuberosity  of  the 
tibia,  internally  to  the  groove.  It  is  joined  by  the  common  aponeurosis  of  the 
gracilis  and  sartorius.  These  so-called  ligaments  are,  in  reality,  the  tendons  of 
insertion  of  the  quadriceps  fenioris  nuiscle,  and  transmit  the  action  of  the  latter 

to  the  tibia;  they  also  func- 
l-nirrii,r  crtirial       tiou    similarly    for   the    other 
muscles  attached  to  them  as 
noted  above. 

It  will  lie  notico<l  that  the 
upper  attachments  arc  furtlicr  apart 
than  the  lower  ones,  so  that  the  liga- 
ments converge  below.  The  inner 
ligament  is  especially  oblique.  The 
middle  ligament  is  more  deeply 
placed  than  the  others,  and  there- 
fore cannot  usually  be  felt  distinctly 
in  the  living  animal. 

l.'jS. — Skmii.un.vr  Cartilages  and  Crucial  Ligaments   of 

The  femoro-tibial  articu- 
lation     (Articulatit)      femoro- 
tibialis)  is  formed  between  the 
condyles   of    the    femur,    the 
]iroximal  end  of  the  tibia,  and  the  interposed  semilunar  cartilages. 

Articular  Surfaces. — The  condyles  of  the  femur  are  slightly  oblique  in  direc- 
tion. The  articular  surface  of  the  outer  one  is  more  strongly  curved  than  that  of 
the  inner  one;  the  latter  is  confluent  below  with  the  inner  ritlge  of  the  trochlea, 
while  the  narrow  ridge  which  connects  the  external  condyle  with  the  trochlea  is 
usually  non-articular.  The  saddle-shaped  surfaces  of  the  condyles  of  the  tibia  are 
not  adapted  to  the  femoral  condyles,  and 


lUcriur  ligaments 
of  semilunar  car- 
tilages 


UNAR  Cartilages  and  Crucial  Ligame: 
Right  Stifle  of  Horse. 
Femoral  ligament  of  e.xternal  cartilage,     (.\fter  Schmaltz 
d.  Anat.  tl.  Pferdes.) 


Anterior  crucial  ligament 


Posterior  crucial 
ligiuncnl 


are  in  contact  with  only  a  small  part  of 
them. 

The  semilunar  cartilages  (Meniscus 
lateralis,  medialis)  are  two  C-shajied  or 
crescentic  discs  of  fibro-cartilage  which 
produce  congruence  in  the  articular  sur- 
faces. Each  has  an  upper  concave  sur- 
face adaptetl  to  the  condyle  of  the  femur, 
and  a  lower  surface  which  fits  the  cor- 
responding condyle  of  the  tiliia.  Tlie 
external  cartilage  does  not  cover  the 
outer  and  posterior  part  of  the  condyle, 
over  which  the  tendon  of  origin  of  the 
popliteus  muscle  plays.  The  peripheral 
Ijorder  is  thick  and  con\-ex,  the  central 
one  very  thin  and  concave.  The  fil^rous 
ends  or  comua  are  attached  to  the  tibia 
in  front  of  and  behind  the  spine.     The 

external  cartilage  has  a  third  attachment  by  means  of  an  oliliiiuc  baml  (l.iga- 
mentmn  femorale  menisci  lateralis)  which  passes  from  the  posterior  cornu  to  the 
posterior  part  of  the  iiitercondyloid  fossa  of  the  femur. 

The  comua  of  the  internal  cartilage  (Ligameiil:i  tibi:r  .■micrius  et  posterius  menisci  medialis) 

arc  attached  in  front  of  and  behinil  the  inner  eminci if  the  s])ine.     The  anterior  cornu  of  the 

external  cartilage  fLig.amcntuin  tibiic  anterius  menisci  l.-itcralis)  is  attached  in  front  of  the  outer 
eminence  of  the  spine.    The  posterior  cornu  bifurcates;    the  lower  branch  (Ligamentum  tibise 


ISfl.— PROXI^ 

lAL   Em«   of   Right  Tii 

Fibula    of 

Horse,    with    Semii.ilnv 

tilages    an 

D    Crucial    Ligaments, 

NAL  View. 

(After  Schmaltz,  Atlas  i 

d.  Pferdes.) 

THE    STIFLE   JOINT 


197 


posterius  menisci  lateralis)  is  inserted  at  tiie  popliteal  notch,  the  upper  (Ligamentuni  fenioralc 
menisci  lateralis)  in  a  small  fossa  in  the  extreme  posterior  part  of  the  iutercondyloid  fossa. 

Tlie  joint  capsule  is  attached  to  the  margin  of  the  tibial  articular  surface, 
hut  on  the  femur  the  line  of  attachment  is  for  the  greater  part  about  half  an  inch 
from  the  articular  margin.  It  is  also  attached  to  the  convex  borders  of  the  semi- 
lunar cartilages  and  to  the  crucial  ligaments.  It  is  strong  posteriorly,  but  in  front 
it  practically  consists  only  of  the  synovial  layer.  There  are  two  synovial  sacs, 
corresponding  to  the  double  nature  of  the  articular  surfaces;  they  do  not  usually 
comnmnicate,  and  each  is  partially  divided  into  an  upper  and  a  lower  compartment 
by  the  semilunar  cartilage.  The  inner  sac  pouches  upward  about  half  an  inch 
over  the  condyle  of  the  femur.  The  external  sac  invests  the  tendon  of  origin  of  the 
popliteus  muscle,  and  also  pouches  downward  about  three  or  four  inches  (ca.  8 
to  10  cm.)  beneath  the  peroneus  tertius  and  long  extensor  muscles  (Fig.  156). 


Internal  femoro-pateUni 
ligament 


Internal  lateral  (femora- 
tibial)  ligament 


-  Aecessory  cartilage  of  patella 


Internal  ridge  of  trochlea  of 
Internal  patellar  ligament 


Middle  patellar  ligament 


-  Tuberosity  of  tibia. 


Fig.  160. — Left  Stifle  Joint  of  Horse,  Internal  View  in  Extreme  Extension.' 
18,  Femur;    30,  patella  (base);  21,  tibia;  d,  internal  semilunar  cartilage.    (After  Ellenberger-Baum.  .Anat.  fur 

Kunstler.) 


As  stated  above,  the  outer  sac  sometimes  communicates  with  the  femoro-patellar 
joint  cavity,  and  the  inner  sac  usually,  if  not  always,  does  so  in  the  adult. 

Ligaments. — There  are  four  of  these — two  lateral  and  two  crucial. 

The  internal  lateral  ligament  (Ligamentuni  collaterale  tibiale)  is  attached 
above  to  the  prominent  internal  epicoiul>-le  of  the  femur,  and  below  to  a  rough 
area  below  the  margin  of  the  internal  condyle  of  the  tibia. 

The  external  lateral  ligament  (Ligamentuni  collaterale  fibulare)  is  somewhat 
thicker;  it  arises  from  the  upper  depression  on  the  external  epicondyle,  and  ends 
on  the  head  of  the  fibula.  It  covers  the  tendon  of  the  origin  of  the  popliteus 
muscle,  and  a  bursa  is  interposed  between  the  lower  part  of  the  ligament  and  the 
margin  of  the  external  condyle  of  the  tibia. 

'In  this  figure  the  patella  is  pushed  up  above  the  trochlea— a  position  which  it  does  not 
occupy  normally. 


198 


THE    ARTICULATION'S    OF   THE    HORSE 


The  crucial  ligaments  are  two  strong  rounded  bands  situated  mainly  in  the 
intercondyloid  fossa  of  the  femur,  between  the  two  synovial  sacs.  They  cross 
each  other  somewhat  in  the  form  of  an  X,  and  are  named  according  to  their  tibial 
attachments.  The  anterior  crucial  ligament  (Ligamentum  cruciatum  anterius) 
arises  in  the  central  fossa  on  the  tibial  spine,  extends  upward  and  backward, 
and  ends  on  tlie  u]iper  jiart  of  the  inner  surface  of  the  external  condyle  of  the  femur. 
The  posterior  crucial  ligament  (Ligamentum  cruciatum  posterius)  is  internal  to 
the  preceding,  and  is  somewhat  larger.  It  is  attached  to  an  eminence  at  the 
popliteal  notch  of  the  tibia,  is  directed  upward  and  forward,  and  ends  in  the  an- 
terior part  of  the  intercondyloid  fossa  of  the  femur. 


Vastus  inlcrmedius 


Semimemlirnnosii.'s 


'  Terr,  on  ^ 


4Km^  * 


y^J  J  lector     ^eiri- 


Fio.  Ifil 


rPa 


Stifle  Joint  of  Horse;    Sagittal  Section  Passing  Throtjg 
OF  Trochlea  and  Intercondyloid  Fossa. 
1,  .-Vnterior  crucial  lic.irnetit;    2,  posterior  crucial  ligament;    3,  posterior    cornu    of    internal  semilu 
4,  femoral  ligament  of  external  semilunar  cartilage;   5,  articular  artery;   G,  part  of  vastus  int 


It  may  be  added  that  these  ligaments  do  not  lie  in  a  sagittal  plane,  but  are  somewhat  twisted 
across  each  other;   outward  rotation  of  the  leg  untwists  and  slacliens  them. 

Movements. — The  principal  movements  of  the  stifle  joint  as  a  whole  are 
flexion  and  extension.  In  the  ordinary  standing  position  the  articular  angle 
(behind)  is  about  140°  to  150°.  Flexion  is  limited  only  by  contact  of  the  leg  with 
the  thigh  if  the  hock  is  also  flexed.  Extension  is  incomplete,  i.  e.,  the  femur 
and  tibia  cannot  be  brought  into  the  same  straight  line.  Rotation  is  limited, 
and  is  freest  during  semiflexion.  The  patella  glides  on  the  femoral  trochlea  up- 
ward in  extension,  downward  in  flexion. 

Extension  is  checked  mainly  by  tension  of  the  crucial  and  lateral  hgaments.  In  extreme 
extension,  which  is  accoinpaniod  In-  .sHfiht  outward  rotation  of  tlie  leg,  (lie  patella  can  l>e  pusliod 
upward  and  inw;ird  so  tlial  its  filiro-cartilase  lioolis  over  the  upper  end  of  the  inner  ridge  of  the 
trochlea,  but  it  will  not  iciiKiin  there  unless  held  in  position.  When  pressure  is  removed,  the  base 
of  the  patella  tips  forward  ;uid  the  cartilage  lies  upon  the  most  prominent  part  of  the  trochlear 


TIBIO-FIBULAR   ARTICULATION — THE    HOCK   JOINT 


199 


riilgo.  During  flexion,  whit-h  is  accompanied  by  sliglit  inward  rotation  of  the  leg,  the  condyles 
of  tlie  femur  and  the  srniilunar  cartilages  glide  backward  on  the  tibia;  the  movement  of  the" ex- 
ternal condyle  ami  carlilagc  is  grcalei-  than  that  of  the  inner  one.  In  extreme  flexion  the  patellar 
and  posterior  crucial  ligauiciils  arc  tense;  the  other  ligaments  are  relaxed.  The  movement  of  the 
patella  is  gliding  with  coaptation,  i.  e.,  different  parts  of  the  opposing  articular  surfaces  come  into 
contact  successively.  Only  a  narrow  transverse  strip  (ca.  1.5  to  2  cm.  wide)  of  the  patella  is  in 
contact  with  the  trochlea  at  a  time. 


TIBIO-FIBULAR  ARTICULATION 

The  heail  of  the  filiula  artirulates  with  a  erescentie  facet  just  lielow  the  outer 
mai-gui  of  the  external  condyle  of  the  tibia.  The  joint  capsule  is  .strong  and  close. 
The  shaft  of  the  fibula  is  attached  to  the  external  Ijorder  of  the  tibia  by  the  inter- 
osseous membrane  of  the  leg  (Membrana  interossea  criu'is);  this  is  perforated 
about  an  inch  from  its  proximal  end  by  an  opening  which  transmits  the  anterior 
tibial  vessels  to  the  front  of  the  tibia.  A  fibrous  cord  usually  extends  from  the 
distal  end  of  the  shaft  of  the  fibula  to  the  external  malleolus.  The  latter  is  the 
distal  end  of  the  fibula  which  has  fused  with  the  tibia.  No  appreciable  movement 
occurs  in  this  joint. 


Fig.   162. — IvEFT  Hock  Joi.nt  of   Horse,  Extern' 


Fic.    163. — Left   Hock   Joint  of   Horse,   In 
View. 

.Tibia;  ^.j,  tuber  ealcis;   3.5,  large  metatarsal  bone;   ^(7,  long  externallateral  ligament;    5/,  long  internal  lateral 
ligament,     (After  EUenberger-Baum,  .\nat.  fur  KuQstler.) 


THE  HOCK  JOINT 

This  is  a  composite  joint  made  up  of  a  number  of  articulations  (Articulationes 
tarsi).  These  are:  (1)  The  tibio-tarsal  articulation;  (2)  the  intertarsal  articula- 
tions; (3)  the  tarso-metatarsal  articulation. 

The  tibio-tarsal  articulation  (Articulatio  talo-cruralis)  is  a  typical  ginglymus 
formed  by  the  trochlea  of  the  tibial  tarsal  bone  (astragalus  or  talus)  and  the  cor- 
responding surface  of  the  distal  end  of  the  tibia.  The  ridges  and  grooves  of  these 
surfaces  are  directed  oliliquely  forward  and  outward  at  an  angle  of  about  12°  to  15°, 
with  a  sagittal  plane.  The  trochlear  surface  is  about  twice  as  extensive  as  that 
on  the  tibia,  and  its  ridges  have  a  spiral  curvature.     The  other  articulations  are 


200  THE    ARTICULATIONS    OF    THE    HORSE 

arthrodia,  which  have  joint  surfaces  and  ligaments  of  such  a  nature  as  to  allow 
only  a  minimal  amount  of  gliding  motion. 

As  in  the  case  of  the  carpal  joints,  it  is  convenient  to  describe  first  the  common 
capsule  and  ligaments,  which  are  the  more  important  practicallj',  and  then  to 
consider  very  briefly  the  special  ligaments. 

The  fibrous  part  of  the  joint  capsule  is  attached  around  the  margin  of  the 
tibial  articular  surface  above  and  the  metatarsal  surfaces  below;  it  is  also  attached 
in  part  to  the  free  surface  of  the  bones  which  it  covers,  and  blends  with  the  lateral 
ligaments.  Its  anterior  part  (anterior  ligament)  is  rather  thin;  in  distention  of  the 
capsule,  as  in  "bog-spavin,"  its  antero-internal  part,  which  is  not  bound  down  by 
the  tendons  passing  over  the  joint,  forms  a  fluctuating  swelling  over  the  inner  ridge 
of  the  trochlea.  The  posterior  part  (posterior  and  tarso-metatarsal  ligaments)  is 
very  thick,  and  is  intimately  attached  to  the  tarsal  bones.  Its  superficial  face  is 
in  part  cartilaginous,  and  forms  a  smooth  surface  for  the  perforans  tendon.  Su- 
periorly, it  pouches  upward  behind  the  distal  end  of  the  tibia  for  a  distance  of  about 


Short  internal  lateral  ligament -US'    f^i^^K 

Long  internal  lateral  ligament -Bk  (*   ^^^'1        ~"- 1 

»n    \W^/^S       _.-\  Extirnal  lateral  ligament 

I nternal  small  metatarsal  bone ■■■ --  r  <         i         n       ,  ,        >  j,     « 

■I  hxternal  small  metatarsal  bone 


Fir,.  164. — Left  Hock  Joint  of  Horse,  Anterior  View. 

SI,  Tibia;  S2,  trochlea  of  tibial  tarsal  bone;  35,  large  metatarsal  bone:  50,  dorsal  or  oblique  ligament.     (After 

Ellenberger-Baum,  Anat.  fur  Kiinstler.) 

two  inches  (ca.  .'i  cm.).  Inferiorly,  it  is  continued  downward,  forming  the  sub- 
tarsal  or  check  ligament,  which  unites  with  the  perforans  tendon  about  the  middle 
of  the  metatarsus. 

There  are  four  synovial  sacs:  1.  The  tibio-tarsal  sac  lubricates  the  proximal 
joint,  and  is  much  the  largest  and  most  important.  It  is  chiefly  involved  in  the 
swelling  produced  by  excess  of  fluid  in  the  joint  cavity,  when  the  capsule  bulges 
antero-internally  and  postero-superiorly.  2.  The  first  intertarsal  sac  lines  the  joints 
formed  by  the  tibial  and  fibular  tarsal  bones  above,  and  the  central  and  fourth 
tarsals  lielow;  it  communicates  in  front  with  the  proximal  synovial  capsule.  3. 
The  second  intertarsal  sac  lubricates  the  joints  formed  between  the  central  tarsal 
and  the  bones  below  and  on  either  side.  4.  The  tarso-metatarsal  sac  lubricates 
the  joints  formed  between  the  tarsal  and  metatarsal  bones,  those  between  the 
proximal  ends  of  the  metatarsal  bones,  and  those  formed  liy  the  third  tarsal  with 
the  bones  on  either  sifle. 

Common  Ligaments. — The  external  lateral  ligament  (Ligamentum  coUaterale 


THE    HOCK    JOINT 


201 


filiularc  longuin  ct  breve)  consists  of  two  distinct  hands  which  cross  eacli  other. 
The  long  (superficial)  ligament  arises  on  the  posterior  part  of  the  external  malleolus, 
is  directed  almost  straight  downward,  and  is  attached  to  the  fibular  and  fourth 
tarsal  bones  and  the  large  and  external  small  metatarsal  bones.  It  forms  a  canal 
for  the  lateral  extensor  tendon.  The  short  (deep)  ligament  arises  on  the  anterior 
part  of  the  external  malleolus,  is  directed  chiefly  backward,  and  ends  on  the  rough 
excavation  on  the  external  surface  of  the  tibial  tarsal  and  the  adjacent  surface  of 
the  fibular  tarsal  bone. 

The  internal  lateral  ligament  (Ligamentum  collaterale  tibiale  longum  et  breve) 
also  consists  of  two  parts  which  cross  each  other.  The  long  ligament  arises  on  the 
posterior  part  of  the  internal  malleolus,  becomes  wider  below,  and  is  attached  on 
the  lower  tuberosity  of  the  tibial  tarsal,  the  large  and  outer  small  metatarsal  bones, 
and  the  inner  surface  of  the  lower  tarsal  bones  which  it  covers.  The  short  ligament 
lies  largely  under  cover  of  the  long  one.  It  extends  from  the  anterior  part  of  the 
internal  malleolus    runs  backward  and  somewhat  downward,  and  divides  into  two 


External  lateral  ligament 
Plantar  ligament 


Stnall  metatarsal  bones 


Large  metatarsal  bone  - 


Long  internal  lateral  ligament 
Short  internal  lateral  ligament 


Suspensory  ligament 


Fig.  165. — Left  Hock  Joint  of  Horse,  Posterior  View. 
et.  Tibia;  S4,  tuber  calcis.     (After  Ellenberger-Baum,  Anat.  ftir  Kiinstler.) 


branches;  one  of  these  ends  on  the  upper  tuberosity  on  the  inner  surface  of  the 
tibial  tarsal  bone,  the  other  on  the  sustentaculum  tali. 

The  plantar  or  calcaneo-metatarsal  ligament  (Ligamentum  tarsi  plantare)  is  a 
very  strong  flat  liand  which  covers  the  outer  part  of  the  posterior  surface  of  the 
tarsus.  It  is  attached  to  the  posterior  surface  of  the  fibular  and  fourth  tarsal 
bones  and  the  proximal  end  of  the  external  metatarsal  bone. 

The  dorsal  or  oblique  ligament  (Ligamentum  tarsi  dorsale)  is  a  triangular 
sheet  which  is  attached  above  to  the  lower  tuberosity  on  the  inner  face  of  the  tibial 
tarsal  bone,  and  spreads  out  below  on  the  central  and  third  tarsal  bones,  and  the 
proximal  ends  of  the  large  and  inner  small  metatarsal  bones,  to  all  of  which  it  is 
attached. 

Special  Ligaments. — A  considerable  number  of  short  bands  which  connect 
adjacent  bones  of  the  tarsus  and  metatarsus  are  described  by  various  authors; 
some  of  these  are  quite  distinct;  others  arc  difficult  to  isolate.  Most  of  them  are 
not  of  sufficient  importance  to  justify  detailed  description. 


202 


THE    ARTICULATIONS    OF    THE    HORSE 


(1)  The  tibial  and  fibular  tarsal  bones  are  united  bj-  four  bands  (astragalo-calcaneal  liga- 
ments). The  internal  ligament" extends  from  the  .sustentaculum  tah  to  tlie  adjacent  part  of  the 
tibia  tarsal,  Ijlending  with  the  short  hitcral  ligament.  The  external  ligament  extencis  from  the 
anterior  process  of  tlie  fibular  tarsal  to  the  adjacent  part  of  the  external  ridge  of  the  trochlea. 
The  superior  ligament  extends  from  the  posterior  margin  of  the  trochlea  to  the  fibular  tarsal. 
The  interosseous  ligament  is  deeply  placed  in  the  sinus  tarsi  between  the  two  bones,  and  is  attached 
in  the  roii^jh  area>  nl  tlio  oppo.sed  surfaces. 

(2)  Tlie  siiiallei-  liunes  are  attached  to  each  other  as  follows:  The  central  and  third  tarsal  are 
united  by  an  interosseous  and  an  oblique  anterior  ligament  (scaphoido-cunean  ligaments). 
The  central  and  fourth  tarsal  are  united  by  an  interosseous  and  a  transverse  external  ligament 
(cuboido-scaphoid  ligament).  The  third  and  fourth  tarsals  are  .similarly  connected  (cuboido- 
cunean  ligaments).     The  third  tarsal  is  joined  by  an  interosseous  (intercunean)  ligament  to  the 


Supi-TJicial  Jtrxor  tendon 

Gastrocncniius  tendon 

Tarsal  tendon  of 
biceps  femoris 

Calcanean  bursa 

Gastrocnemius 
bursa 


Upper  pouch  of 
joint  capsule 


Tibial  tarsal  hone 

Interosseous  liijtuncnt 

Plantar  ligament 

Fourth  tarsal  bone 

Interosseous  liijament 
Large  metatarsal  bone 

Suspensory  ligament 
Check  ligament 


Tibialis  anterior 
Pcroneus  tertius 


Tibio-tarsal  joint  carity 
Joint  capsule 
Central  tarsal  bone 
Third  tarsal  hone 

Distal  annular  ligament 


Fig.  166. — Sagittal  Section  of  Hock  of  Horbe 


(fused)  first  and  .second  tarsals;    the  latter  are  connected  with  the  fourth  tarsal  by  a  transverse 
posterior  ligament. 

(3)  The  smaller  bones  are  connected  with  the  upper  row  as  follows:  The  central  is  attached 
to  the  tibial  tarsal  by  posterior  and  interosseous  (astragalo-scaphoid)  ligaments,  and  to  the  fibular 
tarsal  by  a  short  oblique  (calcaneo-scaphoid)  band.  The  fourth  is  attached  to  the  fibular  tarsal 
by  interosseous  .and  posterior  (calcaneo-cuboid)  ligaments.  The  (fu.sed)  first  and  second  tarsals 
are  connected  with  the  fibular  tarsal  by  a  posterior  (calcaneo-cunean)  ligament. 

(4)  The  lower  tarsal  bones  are  coimected  with  the  metatarsus  by  tarso-metatarsal  ligaments, 
which  are  not  distinct  from  the  common  ligaments,  except  in  the  case  of  the  interosseous  ligament 
between  the  third  tarsal  and  metatarsal  bones. 

Movements. — These  are  flexion  and  extension,  which  take  place  at  the  tibio- 
tarsal  joint.  The  movements  between  the  tarsal  bones,  and  lietween  the  latter 
and  the  metatarsus,  are  so  limited  as  to  be  negligible  so  far  as  tlie  action  of  the  joint 
as  a  whole  is  concerned.  In  the  standing  position  the  articular  angle  (in  front) 
is  about  1.50°  to  160°.  Complete  extension  is  prevented  b.v  tension  of  the  lateral 
ligaments.     P'lexion  is  checked  only  by  contact  of  the  metatarsus  with  the  leg, 


JOINTS   AND    LIGAMENTS    OF    THE    VERTEBRA 


203 


provided  the  stifle  joint  is  also  flexed.  Owins  to  the  fact  that  the  axis  of  motion 
is  shghtly  obli(iue,  the  lower  jiart  of  the  linih  deviates  somewhat  outward  during 
flexion. 

The  movements  of  the  hock  joint  must  correspond  witli  those  of  the  stifle  on  account  of  the 
tendinous  bands  in  front  and  behind  (peroneus  tertius  and  flexor  perforatus),  which  extend  from 
the  lower  part  of  the  femur  to  the  tarsus  and  metatarsus. 

The  remaining  joints  differ  in  no  material  respect  from  those  of  the  thoracic 
limh. 


COMPARATIVE  ARTHROLOGY' 

JOINTS  AND  LIGAMENTS  OF  THE  VERTEBRA 
Ox. — The  ligaineutum  nuchte  is  better  developed  than  in  the  horse.  The 
funicular  part  is  clearly  divided  into  two  lateral  halves,  which  are  round  at  their 
occipital  attachment,  l>ut  from  the  axis  backward  become  rapidly  wider  and  flat. 
This  wide  portion  is  almost  sagittal,  lies  on  either  side  of  the  vertebral  spines,  and 
is  covered  by  the  trapezius  and  rhomboideus  muscles.     From  the  highest  part  of 


,  Funicular  part;  b,  wide  porti* 


Fig.  167. — Ligamentum  Nuch.e  op  Ox. 
c.  d,  lamellar  part;  e,  interspinous  ligaments;  1,  spin 
:    1.  axis.     (EllenherKer-Baum,  .\nat.  il.  llaustiere. 


i  process  of  first  thoracic 


the  withers  (third  thoracic  spine)  it  gradually  diminishes  in  size  and  fades  out  in 
the  lumbar  region.  The  lamellar  part  is  thick,  and  consists  of  anterior  and  pos- 
terior parts.  The  anterior  part  is  double;  its  fibers  proceed  from  the  funicular 
part  to  the  second,  third,  and  fourth  cervical  spines.  The  posterior  part  is  single; 
its  fibers  extend  from  the  first  thoracic  spine  to  the  fifth,  sixth,  and  seventh  cervical 
spines. 

The  inferior  common  ligament  is  very  strong  in  the  lumbar  region. 

The  intervertebral  fibro-cartilages  are  thicker  than  in  the  horse. 

The  interspinous  ligaments  of  the  back  and  loins  consist  largely  of  elastic 
tissue. 

'This  section  consists  necessarily  only  of  a  brief  statement  of  the  most  important  differences 
in  the  joints  of  the  other  animals. 


204  COMPARATIVE  ARTHROLOGY 

There  are  no  intertransverse  joints  in  the  lumljar  region. 

Pig. — The  ligamentuni  nuchse  is  represented  by  a  fibrous  raph6  and  thin 
layers  of  elastic  tissue  which  extend  between  the  cervical  spines. 

The  atlanto-occipital  and  atlanto-axial  joints  resemble  those  of  the  dog. 

The  interspinous  ligaments  of  the  neck  arc  clastic. 

Dog. — The  ligamentum  nuchae  consists  of  a  small  fibrous  band  which  extends 
from  the  spine  of  the  axis  to  the  anterior  thoracic  spines;  it  may  be  regarded  as  a 
mere  fibrous  raphe  between  the  right  and  left  muscles. 

There  are  interspinous  muscles  instead  of  ligaments  in  the  neck. 

There  are  three  ligaments  in  connection  with  the  odontoid  process.  The  two 
alar  ligaments  (Ligamenta  alaria)  arise  on  either  side  of  the  odontoid  process, 
diverge,  and  end  on  either  side  of  the  foramen  magnum.  The  transverse  ligament 
of  the  atlas  (Ligamentum  transversum  atlantis)  stretches  across  the  dorsal  surface 
of  the  odontoid  process  and  binds  it  down  on  the  ventral  arch  of  the  atlas,  a  bursa 
being  interposed.     It  is  attached  on  either  side  to  the  lateral  masses  of  the  atlas. 

The  two  capsules  of  the  atlanto-occipital  joint  communicate  with  each  other, 
and  usually  with  the  capsule  of  the  atlanto-axial  joint  also. 


Articulations  of  the  Thorax 

Ox. — The  second  to  the  eleventh  costo-chondral  joints  inclusive  are  diarthroses 
with  close  capsules,  reinforced  externally.  (They  are  synchondroses  in  the  sheep.) 
The  upper  parts  of  the  cartilages  are  attached  to  each  other  b}'  distinct  elastic 
ligaments  (Ligamenta  intercostalia). 

The  first  pair  of  chondro-sternal  joints  are  separate  from  each  other;  inter- 
crossing fibers  unite  the  costo-chondral  junctions  above  the  joints. 

The  first  segment  of  the  sternum  forms  a  diarthrosis  with  the  body.  The 
anterior  joint  surface  is  concave,  the  posterior  convex.  The  joint  (Articulatio 
intersternalis)  is  surrounded  by  a  close  capsule,  and  the  joint  surfaces  are  attached 
to  each  by  a  small  intra-articular  ligament.  Limited  lateral  movement  is  possible. 
(In  the  sheep  the  joint  is  a  synchondrosis.) 

Both  surfaces  of  the  sternum  are  covered  by  a  layer  of  fibrous  tissue. 

Pig. — The  second  to  the  fifth  or  sixth  costo-chondral  joints  are  diarthroses. 
The  intersternal  articulation  and  the  sternal  ligaments  resemble  those  of  the  ox. 

Dog. — The  first  chondro-sternal  joints  do  not  coalesce. 

The  internal  sternal  ligament  divides  into  three  bands. 


temporo-mandibular  articulation 

Ox. — The  articular  surfaces  are  of  such  a  character  as  to  permit  more  extensive 
lateral  movement  than  in  the  horse. 

The  condyle  of  the  mandible  is  relatively  small  and  is  concave  transversely.  The  temporal 
articular  surface  is  extensive  and  is  convex  in  both  directions.     The  postglenoid  process  is  small. 

Pig. — The  considerable  longitudinal  diameter  of  the  temporal  articular  sur- 
faces and  the  very  small  size  of  the  postglenoid  process  allow  great  freedom  of 
protraction  and  retraction  of  the  lower  jaw.  Lateral  movement  is  limited.  The 
posterior  ligament  is  absent. 

Dog. — The  articular  surfaces  allow  extremely  little  lateral  or  gliding  movement. 
They  are  cylindrical  in  curvature,  and  the  interarticular  disc  is  very  thin.  The 
posterior  ligament  is  absent. 

The  other  articulations  of  the  skull  are  sufficiently  described  in  the  Osteology. 


ARTICULATIONS    OF   THE    THORACIC    LIMB — THE    CARPAL   JOINTS  205 

Articulations  of  the  Thoracic  Limb 

SHOULDER  joint 

Ox. — The  articular  angle  is  about  100°. 

Pig  and  Dog. — The  joint  capsule  communicates  freely  with  the  bicipital  bursa. 
There  is  a  rudimentary  marginal  cartilage  around  the  rim  of  the  glenoid  cavity. 
In  the  dog  there  is  usually  a  strong  band  extending  from  the  acromion  to  the  outer 
part  of  the  capsule;  another  band  (Ligamentum  coraco-acromiale)  often  stretches 
between  the  scapular  tuberosity  and  the  acromion. 


ELBOW  JOINT 

Ox. — Xo  important  differences  exist.  The  upper  part  of  the  interosseous 
radio-ulnar  ligament  is  commonly  ossified  in  the  adult. 

Pig. — There  are  no  important  differences.  The  radius  and  ulna  are  so  firmly 
united  by  the  interosseous  ligament  as  to  prevent  any  appreciable  movement 
between  them. 

Dog. — The  joint  capsule  is  reinforced  in  front  by  an  oblique  ligament  which 
arises  on  the  front  of  the  external  condyle  of  the  humerus  above  the  joint  surface, 
and  joins  the  terminal  part  of  the  biceps  and  In-achialis  below.  The  external 
lateral  ligament  is  thick  and  divides  into  two  parts;  the  anterior  part  is  attached 
to  the  radius  and  blends  with  the  annular  ligament;  the  posterior  part  widens 
below,  forming  a  sort  of  cap,  and  is  attached  to  the  ulna.  The  internal  lateral 
ligament  also  divides  into  two  branches;  the  anterior  branch  ends  on  the  inner 
surface  of  the  neck  of  the  radius;  the  posterior  enters  the  interosseous  space  and 
is  attached  to  both  bones.  An  elastic  band  (Ligamentum  olecrani)  extends  from 
the  outer  surface  of  the  internal  epicondyle  to  the  anterior  border  of  the  ulna. 

There  are  two  radio-ulnar  joints.  The  proximal  radio-ulnar  joint  is  included 
in  the  capsule  of  the  elbow,  but  is  provided  with  an  annular  ligament  which  extends 
from  the  lower  part  of  the  external  ligament  across  the  front  of  the  proximal  end 
of  the  radius  to  the  ulna,  blending  with  the  biceps  and  brachialis  tendons.  The 
distal  joint  is  formed  by  a  concave  facet  on  the  radius  and  a  convex  one  on  the 
radius,  and  is  surrounded  bj-  a  tight  capsule.  The  interosseous  membrane  unites 
the  shafts  of  the  two  bones.  The  movements  consist  of  limited  rotation  of  the 
radius  (ca.  20°),  carrying  the  paw  with  it.  The  ordinary  position  is  termed  prona- 
tion:  outward  rotation  is  supination.' 


THE  CARPAL  JOINTS 

These  have  the  same  general  arrangement  as  in  the  horse.  Numerous  minor 
differences  naturally  exist,  but  must  be  excluded  from  this  brief  account,  which 
contains  only  important  special  features. 

The  lateral  movements  are  freer,  especially  in  the  dog,  but  flexion  is  not  so 
complete:  the  anatomical  explanation  of  these  facts  lies  in  the  nature  of  the  articu- 
lar surfaces  and  certain  ligamentous  differences.  The  lateral  ligaments  are  much 
weaker,  the  long  external  one  being  especially  small  in  the  ox.  Two  oblique, 
somewhat  elastic,  bands  cross  the  front  of  the  radio-carpal  and  intercarpal  joints. 
The  proximal  one  is  attached  to  the  distal  end  of  the  radius  and  passes  downward 
and  outward  to  the  ulnar  carpal  bone;  the  other  one  connects  the  radial  and  fourth 
carpal  bones  in  a  similar  fashion. 

In  the  ox  the  short  lateral  ligaments  are  well  defined,  a  ligament  connects 

'These  movements  are  best  seen  in  man,  in  whom  the  back  of  the  hand  may  be  turned  for- 
ward (pronation)  or  backward  (supination). 


206 


COMPARATIVE    ARTHROLOGY 


the  accessory  carpal  with  the  distal  end  of  the  ulna,  and  strong  bands  connect 

the    distal     bones     with    the 
metacarpus. 

The  interosseous  and  in- 
terordinal  ligaments  vary  with 
the  number  of  carpal  bones 
present  in  the  different  species. 


INTERMETACARPAL  JOINTS 
In  the  ox  the  small  (fifth) 
metacarpal  bone  articulates 
with  the  large  metacarpal,  but 
not  with  the  carpus.  The  joint 
cavity  is  connected  with  that 
of  the  carpo-metacarpal  sac. 
The  proximal  end  of  the  small 
metacarpal  bone  is  attached 
by  a  ligament  to  the  fourth 
carpal,  and  another  band  ex- 
tends from  its  distal  part  to 
the  side  of  the  large  metacar- 
pal. There  is  also  an  inter- 
osseous ligament,  which  is  per- 
manent and  allows  a  small 
amount  of  movement. 

The  chief  metacarpal 
bones  of  the  pig,  and  the  second 
to  the  fifth  of  the  dog,  articu- 
late with  each  other  at  their 
proximal  ends,  and  are  connect- 
ed by  interosseous  ligaments, 
which  do  not,  however,  unite 
them  closely,  as  in  the  horse. 


METACARPO-PHALANGEAL 
JOINTS 

Ox. — There  are  two 
joints,  one  for  each  digit.  The 
two  capsules  communicate 
posteriorly.  The  two  inter- 
digital  lateral  ligaments  (Liga- 
menta  collatcralia  interdigi- 
talia)  result  from  the  bifurca- 
tion of  a  band  which  arises  in 
the  furrow  between  the  divi- 
sions of  the  distal  end  of  the 
large  metacarpal  bone;  they 
spread  out  and  end  on  the 
])roximal  ends  of  the  first 
l)halangos.     A  strong  superior 

consisting  of  short  intercrossing 

es  of  the  first  jihalanges. 


—Distal  Part  of  Limb  of  Ox,  Showing 
AND  Tkndons.  One  Digit  and  Corresponding  Articu- 
lar Part  of  Metacarpal  Bone  are  Removed. 
a,  Suspensory  liEament;  a',  branch  of  a  to  superficial  flexor 
tendon;  a",  o'",  lateral  and  central  branches  of  a;  b,  deep  flexor 
tendon;  6',  branch  of  b  to  digit  removed;  c,  c,  superficial  flexor 
tendon;  d,  d' ,  intersesamoid  ligament  (cut);  e,  interdigital  lateral 
ligament  of  fetlock  joint;  /.  tendon  of  common  extensor;  o,  pro.xi- 
mal  interdigital  ligament;  A,  digital  annular  ligament;  i,  posterior 
annular  ligament  of  fetlock;  A*,  lateral  ligament  of  pastern  joint; 
I,  distal  interdigital  ligament;  m,  crucial  interdigital  ligament 
(cut);  m',  7«",  attachments  of  m  to  second  phalanx  and  distal 
sesamoid  bone;  h.  suspensory  ligament  of  distal  sesamoid;  o,  an- 
terior elastic  ligament;  p,  lateral  volar  ligament  of  pastern  joint; 
1,  metacarjJus,  sawn  off  at  /';  2,  first  phalanx;  3.  second  phalanx; 
4,  third  phalanx.     (Ellenberger-Baum,  .\nat.  d-  Haustiere.) 

interdigital  ligament  (I^igamentum  interdigitale), 
fillers,  unites  the  middles  of  the  interdigital  surfac 


METACARPO-PHALANGEAL   JOINTS 


207 


Crucial  ligaments  (Ligamenta  phalango-sesamoideae)  connect  the  sesamoids 
with  the  proximal  end  of  the  opposite  first  phalanx. 

The  intersesamoid  ligament  connects  all  four  sesamoids,  and  extends  upward 
much  less  than  in  the  horse. 

The  lateral  sesamoidean  ligaments  end  almost  entirely  on  the  first  phalanges. 

The  superficial  inferior  sesamoidean  ligament  is  absent.  The  midclle  inferior 
sesamoidean  ligaments  of  each  digit  are  two  short  strong  bands  which  extend  from 
the  distal  margins  of  the  sesamoids  to  the  proximal  ends  of  the  first  phalanges. 
The  deep  inferior  sesamoidean  ligaments  are  strong  and  distinctly  crucial. 


Fig.  169. — Ligamknts  and  Tendons  of  Digits  of  Pig, 
Volar  View. 
a.  Superficial  flexor  tendon;  b,  deep  flexor  tendon;  b', 
branches  of  6  to  accessory  digits;  c,  c' ,  annular  ligaments; 
d-d'",  ligaments  of  accessory  digits;  e,  cruciate  interdigital 
ligaments;  /,  /',  si>iral  band  around  the  flexor  tendons  of 
the  accessory-  digits:  g,  abductor  of  accessory  digit.  (Ellen- 
berger-Baum,  .\nat.  d.  Haustiere.) 


Fig.  170. — Ligaments  a.nd  Tendons  of  Paw  of 
Dog,  Hind  Limb,  Volar  View. 
a,  a'.  Superficial  flexor  tendon;  6,  tendon 
to  large  pad;  c,  lumbricales  muscles;  d,  interossei 
muscles;  e,  f,  annular  ligaments  at  metatarso- 
phalangeal joints;  ff,  suspensory  Ugament  of  large 
pad;  h,  digital  annular  ligaments;  i.  deep  flexor 
tendon;  k,  distal  sesamoid;  /,  suspensory  ligament 
of  k;  m,  suspensory  Ugament  of  digital  pad;  n, 
digital  pads.  (Ellenberger-Baum,  .\nat.  d.  Haus- 
tiere.) 


The  suspensory  or  superior  sesamoidean  ligament  is  more  distinctly  muscular 
than  in  the  horse — indeed  in  the  young  animal  it  consists  almost  entirely  of 
muscular  tissue.  At  the  distal  third  of  the  metacarpus  it  divides  into  three 
branches.  These  give  rise  to  five  subdivisions,  either  by  bifurcation  of  the  lateral 
branches  or  trifurcation  of  the  middle  branch.  The  four  lateral  bands  end  on  the 
sesamoid  bones  and  the  distal  end  of  the  large  metacarpal  bone,  and  detach  slips 
to  the  extensor  tendons.  The  middle  band  passes  through  the  groove  between  the 
two  divisions  of  the  distal  end  of  the  metacarpus,  and  divides  into  two  branches 


208  COMPARATnE    ARTHROLOGY 

wliicli  join  the  tendons  of  the  proper  extensors  of  the  digits;  it  sends  fibers  also  to 
the  interdigital  hiteral  Hgaments  and  to  the  central  sesamoids.  About  the  middle 
of  the  metacarpus  the  suspensory  ligament  detaches  a  band  which  unites  lower 
down  with  the  superficial  flexor  tendon,  thus  inclosing  the  tendon  of  the  deep  flexor 
of  the  digit ;  it  also  blends  with  the  thick  fascia  of  the  region.  The  latter  gives  off 
a  band  on  either  side  to  the  accessory  digits,  and  a  tendinous  band  descends  from 
each  accessory  digit  to  the  third  ])lialanx  and  sesamoid  bone,  blending  with  the 
tendon  of  the  corresponding  proper  extensor. 

Pig. — There  are  four  metacarpo-phalangeal  joints,  each  of  which  has  a  capsule, 
lateral,  intersesamoidean,  and  crucial  sesamoidean  ligaments.  Since  distinct  inter- 
osseous muscles  are  present,  there  are,  of  course,  no  suspensory  ligaments. 

Dog. — There  are  five  metacarpo-phalangeal  joints,  each  having  its  own  capsule 
and  indistinct  lateral  ligaments.  A  small  sesamoid  bone  occurs  in  the  anterior 
part  of  each  ca]isule,  over  which  the  corresponding  extensor  tendon  plays.  The 
intersesamoidean  ligaments  do  not  extend  above  the  sesamoids.  The  cruciate 
ligaments  are  present,  as  well  as  a  fibrous  layer  which  attaches  the  distal  margins 
of  the  sesamoids  to  the  posterior  surface  of  the  proximal  end  of  the  first  phalanx. 


INTERPHALANGEAL  JOINTS 

Ox. — The  two  proximal  joints  have  separate  capsules,  and  broad,  but  rather 
indistinct,  lateral  ligaments.  Each  joint  has  also  two  central  and  two  lateral  volar 
ligaments.  The  central  ligaments  arc  largely  fused  to  form  a  strong  hand.  The 
lateral  ones  extenil  from  the  borders  of  the  first  phalanx  to  the  proximal  end  of  the 
second  phalanx. 

The  distal  interphalangeal  joints  have,  in  addition  to  the  capsules  and  lateral 
ligaments,  bands  which  reinforce  them  on  either  side.  The  central  or  interdigital 
pair  arise  in  the  depressions  on  the  distal  ends  of  the  first  phalanges,  receive  fibers 
from  the  second  phalanges,  and  end  on  the  interdigital  surfaces  of  the  third  phal- 
anges at  the  margin  of  the  articular  surface.  The  lateral  pair  have  a  similar  course, 
but  are  thinner,  and  end  on  the  corresponding  third  sesamoid.  An  elastic  band 
crosses  the  front  of  the  second  phalanx  obliquely,  from  the  distal  end  of  the  first 
phalanx  to  the  extensor  ]iroccss  of  the  tiiird  jilialanx. 

The  crucial  or  inferior  interdigital  ligaments  (Ligamenta  cruciata  interdigitalia) 
are  two  strong  bands  which  limit  the  separation  of  the  digits.  They  are  attached 
above  to  the  lateral  (or  abaxial)  eminences  on  the  proximal  ends  of  the  second 
phalanges  (blending  with  the  lateral  ligaments),  cross  the  deep  flexor  tendon 
obliquely,  and  reach  the  interdigital  space,  where  they  intercross  and  blend.  Most 
of  the  fibers  end  on  the  third  sesamoid  of  the  opposite  side,  but  some  are  attached 
to  the  interdigital  aspect  of  the  second  phalanx  and  the  third  sesamoid  of  the  same 
side.  In  the  sheep  there  is,  instead  of  the  foregoing,  a  transverse  ligament  which 
is  attached  on  either  side  to  the  interdigital  surfaces  of  the  second  and  third  phalanges 
and  the  third  sesamoid  bone.     It  is  related  below  to  the  skin,  above  to  a  pad  of  fat. 

Pig. — The  interphalangeal  joints  of  the  chief  digits  resemble  in  general  those 
of  the  ox.  The  inferior  interdigital  ligament  resembles,  however,  that  of  the  sheep, 
and  is  intimately  adherent  to  the  skin.  There  is,  besides,  a  remarkable  arrange- 
ment of  ligaments  which  connect  the  small  digits  with  each  other  and  with  the 
chief  digits. 

This  nprLiratus  is  somewhat  complox,  hut  its  chief  features  are  as  follows:  A  superior  iiiter- 
(linilal  li«ariic-nl  is  altaelieil  on  cither  side  to  the  third  phalanges  of  tlie  small  digits,  wliili'  centrally 
it  liicn<ls  with  the  aiuuilar  ligaments  of  the  flexor  tendons  lichind  the  metacarpri-plialanfj;cal 
joints  of  tlic  chief  digits.  Two  bands  (central  longitudinal  interdigital  ligaments)  arise  on  the 
bases  of  the  small  digits,  cross  the  flexor  tendons  olili(|uelv  downwar.l  and  inward,  pass  through 
the  superior  interdigital  ligament,  and  blend  below  with  the  inl'crior  irjterdigital  ligament.  Two 
lateral   bands   (lateral   longitudinal   interdigital  ligaments)   are  attached   in   common  with   the 


COMPARATIVE  ARTHROLOGY  209 

superior  interdigital  ligaments  to  tlie  third  plialanges  of  the  small  digits,  and  blend  below  with 
the  outer  part  of  the  inferior  interdigital  ligament. 

Dog.— Each  joint  has  a  capsule  and  two  lateral  ligaments.  The  distal  joints 
have  also  two  elastic  dorsal  ligaments  (Ligamenta  dorsalia),  which  extend  from  the 
l^roximal  end  of  the  second  phalanx  to  the  ridge  at  the  base  of  the  third  phalanx 
(Fig.  133).  They  produce  dorsal  flexion  of  the  joint,  and  thus  raise  or  retract  the 
claws  when  the  flexor  muscles  relax.  The  distal  sesamoids  arc  represented  by 
complementary  cartilages  attached  to  the  volar  margins  of  the  articular  surfaces 
of  the  third  phalanges. 

Three  interdigital  ligaments  restrict  the  spreading  apart  of  the  digits.  Two 
of  these  cross  the  volar  surface  of  the  proximal  parts  of  the  chief  digits,  ?'.  c,  one 
for  the  second  and  third,  the  other  for  the  fourth  and  fifth;  they  blend  with  the 
annular  ligaments  on  either  side.  The  third  ligament  is  attached  on  either  side  to 
the  foregoing  ligaments  and  the  annular  ligaments  of  the  third  and  fourth  digits, 
and  .curves  downward  centrally,  ending  in  the  large  pad  on  the  paw. 


Articulations  of  the  Pelvic  Limb 

SACRO-ILIAC  joint 
This  joi,nt  and  the  pelvic  ligaments  present  no  very  striking  differences  in  the 
other  animals.     The  sacro-sciatic  ligament   in  the  dog  is  a  narrow  but  strong 
band  which  extends  from  the  posterior  part  of  the  lateral  margin  of  the  sacrum  to 
the  tuber  ischii;  it  is  the  homologue  of  the  ligamentum  saero-tuberosum  of  man. 

HIP  JOINT 

Ox. — The  shallowness  of  the  acetabulum  is  compensated  by  the  greater  size 
of  the  marginal  cartilage.  The  head  of  the  femur  has  a  smaller  radius  of  curvature 
than  that  of  the  horse,  and  the  articular  surface  extends  a  considerable  distance 
outwaril  on  the  upper  surface  of  the  neck.  The  round  ligament  is  entirely  intra- 
articular; it  is  small,  and  sometimes  absent.  The  pubo-femoral  or  accessory 
ligament  is  absent. 

There  are  no  important  differences  in  the  other  animals. 

STIFLE  JOINT 

Ox. — There  is  a  considerable  communication  between  the  femoro-patellar 
and  inner  femoro-tibial  joint  cavities;  this  is  situated  as  in  the  horse,  but  is  wider. 
A  small  communication  with  the  external  femoro-tibial  capsule  sometimes  occurs. 
The  two  femoro-tibial  capsules  usually  communicate.  The  middle  patellar  liga- 
ment is  not  sunken,  as  there  is  no  groove  on  the  tuberosity  of  the  tibia  where  it  is 
attached.  The  external  patellar  ligament  fuses  completely  with  the  tendon  of 
insertion  of  the  biceps  femoris,  and  a  synovial  bursa  is  interposed  between  them 
and  the  external  condyle  of  the  femur. 

In  the  other  animals  there  is  a  single  ligamentum  patellae,  and  the  synovial 
sacs  communicate  so  freely  as  to  constitute  a  common  joint  cavity.  In  the  dog 
the  semilunar  cartilages  are  united  anteriorly  by  a  transverse  ligament,  and  the 
posterior  part  of  the  capsule  contains  the  two  Vesalian  sesamoids,  which  articulate 
with  the  condyles  of  the  femur. 

TIBIOFIBULAR  JOINTS 
Ox. — The  proximal  end  of  the  fibula  fuses  with  the  external  condyle  of  the 
tibia.     The  distal  end  remains  separate,  and  forms  an  arthrosis  with  the  distal  end 
14 


210  COMPARATIVE   ARTHROLOGY 

of  the  tibia;  the  movement  here  is  imjierceptible,  as  the  two  hones  are  closely 
united  by  strong  peripheral  fibers. 

Pig. — The  superior  joint  is  provided  with  a  capsule  which  is  reinforced  in 
front  and  behind  by  fibrous  tissue. 

The  interosseous  ligament  attaches  the  shaft  of  the  fibula  to  the  outer  border 
of  the  tibia. 

The  inferior  joint  is  included  in  the  capsule  of  the  hock  joint,  and  is  strength- 
ened by  oblique  anterior  and  posterior  ligaments.  There  is  also  an  interosseus 
ligament. 

Dog. — The  arrangement  is  essentially  the  same  as  in  the  pig,  but  there  is  no 
interosseous  ligament  in  the  inferior  joint. 


HOCK  JOINT 

Ox. — There  is  very  considerable  mobility  at  the  first  intertarsal  joint,  the 
capsule  of  which  is  correspondingly  roomy.  The  short  external  lateral  ligament 
is  attached  below  on  the  tibial  tarsal  only.  A  strong  transverse  ligament  attaches 
the  external  malleolus  (distal  end  of  the  fibula)  to  the  back  of  the  tibial  tarsal  bone. 
The  dorsal  or  oblique  ligament  is  narrow  and  thin. 

Pig. — The  arrangement  in  general  resembles  that  of  the  ox. 

Dog. — The  long  lateral  ligaments  are  very  small,  and  the  short  ones  double. 
The  plantar  ligament  is  weak,  and  ends  on  the  fourth  metacarpal  bone.  No 
distinct  dorsal  (or  oblicjue)  ligament  is  present.  Movement  occurs  almost  ex- 
clusively at  the  tibio-tarsal  joint. 

The  remaining  joints  resemble  those  of  the  thoracic  limb. 


THE  iWUSCULAR  SYSTEM 

MYOLOGY 

The  muscles  (Musculi)  are  the  active  organs  of  motion.  Thej'  are  charac- 
terized by  their  property  of  contracting  when  stimulated.  ^Muscular  tissue  is  of 
three  kinds:  (a)  Striated  or  striped;  (b)  non-striated,  unstriped,  or  smooth;  and 
(c)  cardiac.  Only  the  first  of  these  varieties  will  he  considered  in  this  section.  The 
striped  muscles,  being  for  the  most  part  directly  or  indirectly  connected  with  the 
skeleton,  are  often  termed  skeletal  or  somatic,  while  unstriped  muscle  may  be  spoken 
of  as  visceral  or  splanchnic.  The  former  cover  the  greater  part  of  the  skeleton, 
and  thus  in  a  large  measure  determine  the  form  of  the  animal.  They  are  red  in 
color,  the  shade  varying  in  different  muscles  and  under  various  conditions. 

]\Iuscles  vary  greatly  in  form,  and  may  be  classified  as — (a)  Long;  (b)  short; 
(c)  flat;  (d)  ring-like  or  orbicular.  Long  muscles  are  found  chiefly  in  the  limbs, 
while  the  flat  or  broad  muscles  occur  principally  in  the  trunk,  where  they  assist  in 
forming  the  walls  of  the  body  cavities.  The  ring-like  or  orbicular  muscles  circum- 
scribe orifices  which  the}'  close,  and  are  hence  termed  sphincters. 

Attachments. — The  muscles  are  attached  to  bones,  cartilages,  Ugaments, 
fasciae,  or  the  skin.  In  all  cases  the  attachment  is  by  means  of  fibrous  tissue,  the 
muscle-fibers  not  coming  into  direct  relation  with  the  bone  or  cartilage.  The 
perimysium  of  the  muscle  may  fuse  directly  with  the  periosteum  or  perichondrium 
(fleshy  attachment),  or  the  union  may  be  by  means  of  intermediary  fibrous  struc- 
tures called  tendons  or  aponeuroses  (tendinous  attachment).  Tendons  may  be 
funicular,  ribbon-like,  or  in  the  form  of  membranous  sheets;  to  the  latter  the  term 
aponeurosis  is  commonly  applied. 

In  certain  positions,  especially  where  tendons  play  over  joints  or  are  subjected 
to  great  pressure,  sesamoid  bones  develop  in  the  original  tendon  tissue.  Some 
of  these  are  large  and  constant,  as  the  patella  and  the  great  sesamoids  of  the  fet- 
lock. 

The  accessory  structures  connected  with  the  muscles  are  the  synovial  mem- 
branes and  the  fasciae. 


^eseten^m 


Jubreus  3hea/k. 

'Synovial  sftealh 


sheath 


Fig.  1. 1. — DiAGRA 


Choss-sectioxs  of  Tendok  Sheath  (.\)  axd  Bcbsa  (B):    T.  Tendon 


The  synovial  membranes  are  arranged  in  two  principal  forms:  (n)  Bursal; 
(6)  vaginal.  A  biu-sa  (Bursa  mucosa)  is  a  simple  sac  interposed  between  the  tendon 
or  muscle  and  some  ileeper  seated  structure — most  commonly  a  bony  prominence. 
A  vagina  tendinis  or  tendon  sheath  differs  from  a  bursa  in  the  fact  that  the  synovial 
sac  is  folded  around  the  tendon  more  or  less  completely,  so  that  two  layers  can  be 
distinguished;  of  these,  the  inner  one  adheres  closely  to  the  tendon,  while  the 
outer  lines  the  groove  or  canal  in  which  the  tendon  lies.     The  two  layers  are  con- 

211 


212  THE   MUSCULAR   SYSTEM 

tinuous  along  a  fold  termed  the  mesotendon.  The  arrangement  is  shown  in 
Fig.  171.^  The  articular  synovial  membranes  in  some  places  form  extra-articular 
pouches,  which  facilitate  the  play  of  tendons. 

The  fasciae  are  sheets  of  connective  tissue,  mainly  of  the  white  fibrous  variety, 
with  a  greater  or  less  admixture  of  elastic  fibers  in  certain  cases.  Two  layers  may 
usually  be  recognized.  Of  these,  the  superficial  fascia  (Fascia  subcutanea)  is  com- 
posed of  loose  connective  tissue  which  may  contain  more  or  less  fat  and  is  sub- 
cutaneous. The  deep  fascia  is  composed  of  one  or  more  layers  of  dense  fibrous 
tissue  spread  over  the  surface  of  the  muscles  chiefly.  Its  deep  face  may  be  very 
loosely  attached  to  the  underlying  structures  or  may  fuse  with  the  epimysium, 
tendons,  bones,  or  ligaments.  In  some  parts,  especially  the  limbs,  septal  plates 
pass  between  the  muscles  and  arc  attached  to  the  bones  or  ligaments;  these  are 
termed  intermuscular  septa.  In  this  way  many  muscles  are  inclosed  in  fibrous 
sheaths  wliich  liold  them  in  ]i(isition.  Not  uncommonly  special  bands  stretch 
across  the  grooves  in  which  tendons  jilay,  converting  these  into  canals.  Such 
bands  are  termed  vaginal  or  annular  ligaments.  The  deep  fascia  is  often  so  dis- 
tinctly tendinous  in  structure,  furnishing  attachment  to  special  tensor  muscles, 
as  to  render  the  distinction  between  fascia  and  aponeurosis  quite  arbitrary.  Bursae 
occur  in  certain  situations  between  the  fascia  and  underlying  structures  (subfascial 
l)ursiB),  or  between  the  fascia  and  the  skin  (subcutaneous  bursa). 

It  is  convenient  to  divide  the  description  of  a  muscle  into  seven  heads,  viz.: 
(1)  Name,  followed  by  important  synonyms;  (2)  position  and  form;  (3)  attach- 
ments;   (4)  action;    (5)  structure;   (6)  relations;    (7)  blood  and  nerve  supply. 

1.  The  name  is  determined  by  various  factors,  viz.:  (a)  The  action,  e.  g., 
extensor,  adductor,  etc.;  (6)  the  shape,  e.  g.,  quadratus,  triangularis;  (c)  the  direc- 
tion, e.  g.,  rectus,  obliquus;  (d)  the  position,  e.  g.,  the  subscapularis,  iliacus;  (e) 
the  division  (into  heads,  etc.),  e.  g.,  biceps,  triceps,  etc.;  (J)  the  size,  e.  g.,  major, 
minor,  etc.;  {g)  the  attachments,  e.  g.,  sterno-cephalicus,  mastoido-humeralis; 
{h)  the  structure,  e.  g.,  semitendinosus.  In  most  cases  two  or  more  of  these  factors 
have  combined  to  produce  the  name,  e.  g.,  adductor  magnus,  longus  colli,  obli<iuus 
externus  abdominis. 

2.  The  shape  is,  in  many  cases,  sufficiently  definite  to  allow^  the  use  of  such 
terms  as  triangular,  (luadrilateral,  fan-shaped,  long,  flat,  fusiform,  ring-like,  etc. 

3.  The  attachments  are  in  most  cases  to  bone,  l)ut  many  muscles  are  attached 
to  cartilage,  ligaments,  fascia,  the  skin,  etc.  It  is  usual  to  apply  the  term  origin 
to  the  attachment  which  always  or  more  commonly  remains  fixed  when  the  muscle 
contracts.  The  term  insertion  designates  the  movable  attachment.  Such  a 
distinction  cannot  always  be  made,  as  the  action  may  be  reversible,  or  both  at- 
tachments may  be  freely  movable. 

4.  The  action  belongs  rather  to  physiological  study,  but  is  Itricfly  inilicated 
in  anatomical  descriptions. 

5.  The  structure  includes  the  direction  of  the  muscle-fibers,  the  arrangement 
of  the  tendons,  the  synovial  membranes,  and  any  other  accessory  structures,  e.  g., 
annular  ligaments  and  reinforcing  sheaths  and  bands.  The  relation  of  the  muscle- 
fibers  to  the  tendon  varies,  and  this  fact  has  given  rise  to  special  terms.  Thus  a 
muscle  in  which  the  fibers  converge  to  either  side  of  the  tendon  is  ternietl  bipennate  ; 
while  one  in  which  this  arrangement  exists  only  on  one  side  of  the  tendon  is  called 
unipennate.  The  terms  fleshy  and  tendinous  are  used  to  indicate  the  relative 
amomits  of  muscular  and  tendinous  tissue.  The  muscular  tissue  is  often  spoken  of 
as  the  belly  (Venter)  of  the  muscle.    In  the  case  of  the  long  muscles,  the  origin  is 

'The  student  will  note  in  dissection  that  transition  forms  occur;  also  that  the  same  sheath 
may  belong  to  two  or  more  ti-ndons  in  common,  c.  g.,  the  sheath  of  the  two  flexors  on  the  l)ack  of 
the  carpus.  In  sudi  cases  the  synovial  membrane  is  reflected  from  one  tendon  to  the  other,  and 
may  form  a  secondary  mesotenon. 


MUSCLES    OF   THE    LIPS   AND    CHEEKS  213 

often  termed  the  head  (Caput).  Muscles  having  two  or  more  heads  are  called 
biceps,  triceps,  etc.  Digastric  muscles  are  those  which  have  two  bellies  joined  by 
an  intermediate  tenilon.  Ring-like  muscles  which  circumscribe  openings  are 
termed  sphincters,  on  account  of  their  action. 

6.  The  relations  are,  of  course,  important  on  surgical  grounds. 

7.  The  nerve-supply  is  of  clinical  interest,  and  is  important  for  the  determina- 
tion of  homologies. 


FASCLE  AND  MUSCLES  OF  THE  HORSE 
PANNICULUS  CARNOSUS 
The  panniculus  camosus  (Musculus  cutancus)  is  a  thin  muscular  layer  de- 
veloped in  the  superficial  fascia.  It  is  intimately  adherent  in  great  part  to  the  skin, 
but  has  very  little  attachment  to  the  skeleton.  It  does  not  cover  the  entire  body, 
and  may  be  conveniently  divided  into  facial,  cervical,  thoracic,  and  abdominal 
jiortions,  each  of  which  will  be  described  with  the  muscles  of  the  corresponding 
region. 

The  FAsa^  and  Muscles  of  the  Head 

The  muscles  of  the  head  may  be  divided  into  three  groups,  viz.:  (1)  Superficial 
muscles,  including  the  panniculus  and  those  of  the  lips,  cheeks,  nostrils,  eyelids, 
and  external  ear;   (2)  the  orbital  muscles;    (3)  the  muscles  of  mastication. 

The  superficial  fascia  forms  an  almost  continuous  layer,  but  is  very  scanty 
around  the  natural  orifices.  It  contains  a  number  of  the  thin  superficial  muscles, 
so  that  care  must  be  exercised  in  removing  the  skin.  Over  the  frontal  and  nasal 
bones  the  fascia  blends  with  the  periosteum. 

The  deep  fascia  is  of  special  interest  in  three  regions.  The  temporal  fascia 
covers  the  temporalis  muscle,  and  is  attached  to  the  parietal  and  frontal  crests 
internally,  and  to  the  zygomatic  arch  externally.  The  buccal  fascia  covers  the 
buccinator  muscle  and  the  free  part  of  the  outer  surface  of  the  ramus  of  the  jaw. 
Superiorly  it  is  attached  to  the  facial  crest,  and  posteriorly  it  forms  a  band  (Liga- 
mentum  pterygomandibulare)  which  stretches  from  the  hamulus  of  the  pterygoid 
bone  to  the  mandible  behind  the  last  molar  tooth.  It  is  directly  continuous  with 
the  pharjmgeal  fascia,  which  is  attached  to  the  great  and  thyroid  cornua  of  the 
hyoid  bone,  covers  the  lateral  walls  of  the  pharynx,  and  blends  dorsally  with  the 
median  raphe  of  the  constrictor  muscles  of  the  latter. 


SUPERFICIAL  MUSCLES 
1.  Panniculus  camosus. — The  facial  panniculus  (M.  cutaneus  faciei)  consists 
of  a  thin  and  usually  incomplete  muscular  stratum,  which  covers  the  submaxillary 
space  and  the  masseter  muscle.  A  branch  from  it  passes  forward  to  the  angle  of 
the  mouth  and  blends  with  the  orbicularis  oris;  this  part  (M.  cutaneus  labiorum) 
retracts  the  angle  of  the  mouth.  (A  number  of  the  superficial  muscles  of  the  face 
may  be  considered  modified  parts  of  the  panniculus,  e.  g.,  the  corrugator  supercilii, 
malaris,  zygomaticus,  etc.) 


MUSCLES  OF  THE  LIPS  AND  CHEEKS 
1.  Orbicularis  oris. — This  is  the  sphincter  muscle  of  the  mouth;    it  is  con- 
tinuous with  the  other  muscles  which  converge  to  the  lips.     It  lies  between  the 
skin  and  the  mucous  membrane  of  the  lips,  and  is  intimately  adherent  to  the 


214 


FASCI.E    AXD    MUSCLES    OF   THE    HORSE 


former.     Most  of  the  fibers  run  jiarallel  to  the  free  edges  of  the  U]is  and  have  no 
direct  attachment  to  the  skeleton. 

Action. — It  closes  the  lips. 

Blood-mpply. — Palato-labial,  facial,  and  mental  arteries. 

Nerve-supply. — Facial  nerve. 

2.  Levator  nasolabialis  (Levator    hihii    superioris   ala?que  nasi). — This    thin 


Fig.  172. — Muscles  op  Head  of  Horse,  Lateral  View.  The  Panniculi's  is  Removed. 
a.  Levator  labii  superioris  proprius;  6,  levator  nasolabialis;  c,  mastoido-humeralis;  d,  sterno-cephalicus; 
<f',  tendon  of  d;  e,  omo-hyoideus;  /,  dilatator  naris  laterali-s;  g,  zygomaticus;  h,  buccinator;  /,  depressor  labii 
inferioris;  k,  orbicularis  oris;  /,  dilatator  naris  superior;  wi,  masseter;  n,  parotido-auricularis;  o,  zygoiiiatico- 
auricularis;  ;),  interseutularis;  7/,  fronto-scutularis,  pars  temporalis:  q,  cervico-auricularis  profundus  major; 
r,  cervico-auricularis  superficialis;  a,  oblitiuus  capitis  anterior;  (,  splenius;  v,  styio-ma.xillaris;  y.  mastoid  tendon 
of  mastoido-humeralis;  2,  posterior,  3,  anterior,  border  of  external  ear;  S,  scutiform  cartilage;  9,  zygomatic 
arch;  W,  depression  behind  supraorbital  process;  IS,  temporo-mandibular  articulation;  27.  facial  crest;  30', 
angle  of  jaw;  37,  external  maxillary  vein;  dS.  jugular  vein;  39,  facial  vein;  40,  parotid  duct;  41.  transverse 
facial  vein;  42,  masseteric  vein;  43,  facial  nerve;  44,  parotid  gland;  40,  chin;  jr,  wing  of  atlas.  (After  Ellen- 
berger-Baum,  Anat.  fiir  Kiiusller.) 


muscle  lies  ilinn'tly  under  the  skin,  and  chiefly  on  the  lateral  surface  of  the  nasal 
region. 

Origin. — The  frontal  and  nasal  bones. 

Insertion. — (1)  The  upper  lip  and  the  outer  wing  of  the  nostril;  (2)  th(>  com- 
missure of  the  lips. 

Action. — (1)  To  elevate  the  upper  lip  and  the  connnissure;  (2)  to  dilate  the 
nostril. 


MUSCLES   OF   THE    LIPS    AND    CHEEKS 


215 


Slnicture. — The  muscle  arises  by  a  thin  a]5oneurosis.     The  belly  is  also  thin, 
and  divides  into  two  branches,  between  which  the  lateral  dilator  of  the  nostril 
passes.     The  dorsal  branch  reaches  the  nostril  and  upper  lip,  blending  with  the 
lateral  dilator;  the  ventral  one  is  much 
smaller,  and  blends  at  the  labial  com- 
missure with  the   orliicularis  and  i)uc- 
cinator. 

Relations. — Superficially,  the  skin, 
fascia,  and  lateral  dilator  (in  part); 
deepl.y,  the  levator  labii  superioris  pro- 
prius,  lateral  dilator  (in  part),  buccin- 
ator, branches  of  the  facial  vessels  and 
nerve,  and  the  infraorbital  arterj-  and 
nerve. 

Blood-supply. — Facial  and  palato- 
labial  arteries. 

Xerve-supply. — Facial  nerve. 

3.  Levator  labii  superioris  pro- 
prius. — This  lies  on  the  dorso-lateral 
aspect  of  the  face,  partly  covered  bj' 
the  preceding  muscle. 

Origin. — The  lacrimal,  malar,  and 
maxillary  bones  at  their  junction. 

Insertion. — The  upper  lip,  by  a 
common  tendon,  with  its  fellow. 

Action. — Acting  with  its  fellow,  to 
elevate  the  upper  lip.  This  action,  if 
carried  to  the  fullest  extent,  results  in 
eversion.  In  unilateral  action  the  lip 
is  drawn  upward  and  to  the  side  of  the 
muscle  acting. 

Structure. — The  muscle  has  a 
short,  thin  tendon  of  origin.  The 
belly  is  at  first  flattened,  but  be- 
comes narrower  and  thicker,  then 
tapers  over  the  false  nostril,  to  termin- 
ate in  a  tendon.  The  tendons  of  the 
two  muscles  unite  over  the  alar  car- 
tilages of  the  nostrils,  forming  an  ex- 
pansion which  spreads  out  in  the  sub- 
stance of  the  upper  lip. 

iJeZaiions.-^uperficially,  the  skin, 
the  levator  nasolabialis,  and  the  angu- 
lar vessels  of  the  eye;  deeply,  the 
superior  and  transverse  dilators  of 
the  nostril  and  the  infraorbital  artery 
and  nerve. 

Blood-supply. — Facial  artery. 

Neri'e-supphj. — Facial  nerve. 

4.  Zygomaticus.— This  very  thin  muscle  lies  immediately  under  the  skin  of 
the  cheek. 

Origin. — The  fascia  covering  the  masseter  muscle  below  the  facial  crest. 
Insertion.— The  commissure  of  the  lips,  blending  with  the  buccinator. 
Action.— To  retract  and  raise  the  angle  of  the  mouth. 


Fig.  173. — Muscles  of  Head  of  Horse,  Dorsal  View. 
The  Pax.mcclus  is  Removed. 
a.  Levator  labii  superioris  proprius;  a',  common 
tendon  of  a  with  opposite  muscle;  6,  levator  nasolabialis; 
/,  dilatator  naris  lateralis;  a,  zygomaticus;  /,  dilatator 
nans  superior;  ii,  parotido-auricularis;  o" ,  scutulo-auricu- 
laris  superficialis  superior;  p.  interscutularis;  p',  fronto- 
scutularis,  pars  temporalis;  r,  cer\'ico-auricularis  superfici- 
alis; u,  corrugator  supercilii;  x,  trausversus  nasi;  2,  poste- 
rior, 3,  anterior,  border  of  external  ear;  8,  scutiform  carti- 
lage; 9,  zygomatic  arch;  /O,  suijraorbital  depression;  .:J.5, 
inner  wing  of  nostril,  containing  lamina  of  alar  cartilage; 
39.  facial  vein.  (After  EUeuberger-Baum,  Anat.  fiir 
Kunstler.) 


216  FASCIA    AND    MUSCLES    OF   THE    HORSE 

Structure. — Fleshy,  with  a  thin  aponeurotic  origin. 
Relations. — Superficially,  the  skin;   deeply,  the  buccinator. 
Blood-supply. — Facial  artery. 
Nerve-supply. — Facial  nerve. 

5.  Incisivus  superior  (Depressor  labii  superioris). — This  lies  under  the 
mucous  membrane  of  the  upper  lip. 

Origin. — The  alveolar  border  of  the  premaxilla  from  the  second  incisor  to  the 
first  cheek  tooth. 

Insertion. — The  upper  lip. 
Action. — To  depress  the  upper  lip. 

6.  Incisivus  inferior. — This  is  arranged  in  the  lower  lip  like  the  preceding 
muscle  in  the  upper  one. 

Origin. — The  alveolar  border  of  the  mandible  from  the  second  incisor  to  a 
point  near  the  first  cheek  tooth. 

Insertion. — The  skin  of  the  lower  lip  and  the  ])rominence  of  the  chin. 
Action. — To  raise  the  lower  lip. 

7.  Mentalis  (Levator  menti). — This  is  situated  in  the  prominence  of  the  chin. 
Its  fibers  arise  from  each  side  of  the  body  of  the  mandible  and  are  inserted  into  the 
skin  of  the  chin.  It  is  mingled  with  fat  and  strands  of  connective  tissue,  in  which 
the  roots  of  the  tactile  hairs  are  embedded.  It  raises  and  corrugates  the  skin  to 
which  it  is  attached. 

8.  Depressor  labii  inferioris. — This  muscle  lies  on  the  outer  surface  of  the 
ramus  of  the  mandible,  along  the  ventral  border  of  the  buccinator. 

Origin. — The  alveolar  border  of  the  mandible  near  the  coronoid  process  and 
the  maxillary  tuberosity,  in  common  with  the  buccinator. 

Insertion. — The  lower  lip. 

Action. — To  depress  and  retract  the  lower  lip. 

Structure. — The  tendon  of  origin  and  the  belly  are  fused  with  the  buccinator 
as  far  forward  as  the  first  cheek  tooth.  From  this  point  forward  the  belly  is  dis- 
tinct and  rounded,  terminating  in  a  tendon  which  spreads  out  in  the  lower  lip, 
blending  with  the  orbicularis  and  the  muscle  of  the  opposite  side. 

Relations. — Superficially,  the  skin,  masseter,  facial  vessels,  and  jiarotid  duct; 
deeply,  the  mandible  and  inferior  laliial  artery. 

Blood-supply. — Facial  artery. 

Nerve-supply. — Facial  nerve. 

9.  Buccinator. — This  muscle  lies  in  the  lateral  wall  of  the  mouth,  extending 
from  the  angle  of  the  mouth  to  the  maxillary  tuberosity'. 

Origin. — The  external  surface  of  the  maxilla  above  the  interdental  space  and 
the  molar  teeth;  the  alveolar  border  of  the  mandible  at  the  interdental  space  and 
also  posteriorly  where  it  turns  upward  to  the  coronoid  process;  the  pterygo-mandib- 
ular  ligament. 

Insertion. — The  angle  of  the  mouth,  blending  with  the  orbicularis  oris. 

Action. — To  flatten  the  cheeks,  thus  pressing  the  food  between  the  teeth; 
also  to  retract  the  angle  of  the  mouth. 

Structure. — Two  layers  may  be  recognized.  The  superficial  layer  (Pars  buc- 
calis)  extends  from  the  angle  of  the  mouth  to  the  masseter.  It  is  incompletely 
pennate,  having  a  longitudinal  raph6  on  which  most  of  tlie  muscle-fibers  converge. 
The  upper  fibers  are  directed  chiefly  downward  and  backward,  the  lower  ones  up- 
ward and  backward.  The  deep  layer  (Pars  molaris)  consists  mainly  of  longitudinal 
fibers.  It  blends  in  part  with  the  .superficial  layer  of  the  orbicularis;  it  has  a 
small  tendinous  attachment  to  the  coronoid  process  behind,  and  is  united  below 
with  the  depressor  labii  inferioris. 

Relations. — Superficially,  the  skin  and  fascia,  the  zygomaticiis,  levator  naso- 
labialis,  lateral  dilator  of  the  nostril,  the  superior  Ijuccal  glands,  thi^  parotid  duct, 


MUSCLES    OF   THE    NOSTRILS  217 

the  facial  vessels,  and  branches  of  the  facial  nerve;  deeply,  the  mucous  membrane 
of  the  mouth  and  the  inferior  buccal  glands. 

Blood-supplij. — Facial  and  buccinator  arteries. 

Nerve-supply. — Facial  nerve. 


MUSCLES  OF   THE  NOSTRILS 

1.  Levator  nasolabialis. — This  has  been  described  (p.  214). 

2.  Dilatator  naris  lateralis  (M.  caninus). — This  thin,  triangular  muscle  lies 
on  the  lateral  nasal  region,  and  passes  between  the  two  branches  of  the  levator 
nasolabialis. 

Origin. — The  maxilla,  close  to  the  anterior  extremity  of  the  facial  crest. 
Insertion. — The  outer  wing  of  the  nostril. 


Fig.  174. — Nasal  and  Superior  Labial  Mcscles  of  Horse. 

a,  a'.  Dilatator  naris  transversus;   b,  levator  labii  superioris  proprius;  b',  tendon  of  b;  b" ,  common  temion  of 

two  levatores  labii  superioris  proprii;    c,  d .  dilatator  naris  inferior;  d,  e.  dilatator  naris  superior;  /,  orbicularis  oris; 

g,  levator  nasolabialis.  a  portion  of  which  is  removed;    li.  dilatator  naris  lateralis  fcut);    i,  cornu  of  alar  cartilage: 

i-,  nostril;  t',  false  nostril;  (,  nasal  diverticulum;  m,  nasal  bone,     (.\fter  Ellenberger-Baum,  Top.  .\nat.  d.  Pferdes.) 

Action. — To  dilate  the  nostril. 

Structure. — The  muscle  lias  a  flat  tendon  of  origin,  passes  between  the  two 
branches  of  the  levator  nasolabialis,  and  si)reads  out  in  the  external  wing  of  the 
nostril.     The  lower  fibers  blend  with  the  orbicularis  oris. 

Relations. — Superficially,  the  skin,  fascia,  and  tlie  labial  branch  of  the  levator 
nasolabialis;   deeply,  the  maxilla  and  the  nasal  branch  of  the  levator  nasolabialis. 

Blood-supply. — Facial  artery. 

Nerve-supply. — Facial  ner^•e. 

3.  Dilatator  naris  transversus  (M.  transversus  nasi). — This  is  an  unpaired, 
cjuadrilateral  muscle,  which  lies  between  the  nostrils.     It  consists  of  two  layers. 

Attachments. — Superficial  laj-er,  the  superficial  faces  of  the  laminsE  of  the  alar 
cartilages;  deep  layer,  the  convex  edges  of  the  cornua  of  the  same. 

Action. — To  dilate  the  nostrils. 


218  FASCIA    AND    MUSCLES   OF   THE    HORSE 

Structure. — It  is  composed  of  transverse  fleshy  fibers,  which  blend  below  with 
the  orbicularis. 

Relations. — Superficially,  the  skin,  fascia,  and  tendinous  expansion  of  the 
levator  labii  superioris  proprius;  deeply,  the  alar  cartilages,  the  extremity  of  the 
septum  nasi,  and  the  palato-labial  arterj'. 

Blood-.suppli/. — Palato-labial  artery. 

Nerve-xupply. — Facial  nerve. 

4.  Dilatator  naris  superior  (Pars  dorsalis  m.  lateralis  nasi). — This  very  thin 
muscle  occupies  the  angle  between  the  nasal  process  of  the  premaxilla  and  the 
nasal  bone. 

Origin. — The  lateral  border  of  the  nasal  bone. 

Insertion. — The  inner  wall  of  the  false  nostril  and  the  parietal  lamina  of  the 
septal  cartilage. 

Action. — To  dilate  the  vestibule  of  the  nasal  cavity. 

Structure. — Fleshy. 

Relations. — Superficially,  the  skin,  fascia,  and  levator  labii  superioris  proprius; 
deeply,  the  parietal  cartilage  and  false  nostril. 

Blood-supply. — Facial  artery. 

Nerre-.'nipply. — Facial  nerve. 

5.  Dilatator  naris  inferior  (Pars  ventralis  m.  lateralis  nasi). — This  is  a  similar 
but  thicker  muscle,  which  lies  on  the  nasal  process  of  the  premaxilla. 

Origin. — The  maxilla  and  the  nasal  process  of  the  premaxilla. 

Insertion. — The  cartilaginous  prolongations  of  the  turbinal  bones  and  the 
inner  wall  of  the  false  nostril. 

Action. — To  rotate  the  turbinal  outward  and  dilate  the  nostril  and  the  vestibule 
of  the  nasal  cavity. 

Structure. — Fleshy.  A  division  into  two  or  more  parts  may  be  recognized. 
A  small  part  posteriorly  is  inserted  into  the  cartilage  of  the  dorsal  turbinal  bone, 
while  the  bulk  of  the  muscle  is  inserted  into  the  cartilage  of  the  ventral  turbinal 
bone.  A  few  fibers  also  pass  between  the  cornu  of  the  alar  cartilage  and  the  outer 
wing  of  the  nostril. 

Relations. — Superficially,  the  levator  labii  superioris  proprius,  the  levator 
nasolabialis,  and  the  lateral  nasal  artery;  deeply,  the  maxilla,  the  premaxilla,  and 
the  anterior  nasal  branch  of  the  infraorbital  nerve. 

Blood-supply. — Facial  artery. 

Nerve-supply. — Facial  nerve. 


MUSCLES  OF  THE  EYELIDS 

1.  Orbicularis  oculi. — This  is  a  flat,  elliptical,  sphincter  muscle,  situated  in  and 
around  the  eyelids,  the  portion  in  the  upper  lid  being  much  broader  than  that  in 
the  lower.  The  chief  attachment  is  to  the  skin  of  the  lids,  but  .some  bundles  are 
attached  to  the  palpebral  ligament  at  the  inner  canthus  and  to  the  lacrimal  bone. 
Its  action  is  to  close  the  lids. 

2.  Corrugator  supercilii. — This  is  a  very  thin,  small  muscle,  which  arises  over 
the  root  of  the  supraorbital  ])rocess  and  spreads  out  in  the  upper  eyelid,  blending 
with  the  orbicularis.  Its  action  is  to  assist  in  raising  the  upper  lid  or,  especially 
in  pathological  conditions,  to  wrinkle  the  skin. 

3.  Malaris. — This  is  a  very  thin  muscle,  which  varies  much  in  different  sub- 
jects. It  extends  from  the  fascia  in  front  of  the  orbit  to  the  lower  lid.  Its  action 
is  to  depress  the  lower  lid. 

The  foregoing  muscles  receive  their  blood-sup])ly  from  the  facial,  transverse 
facial,  supraorbital,  and  infraorbital  arteries;  the  nerve-supply  is  derived  from  the 
facial  nerve. 


MUSCLES   OF   MASTICATION  219 

4.  Levator  palpebrae  superioris. — This  slender,  flat  inusclo  is  almost  entirely 
within  the  orbital  cavity.  It  arises  on  the  pterygoiil  crest,  passes  forward  above  the 
rectus  oculi  sui)eri()r  and  below  the  lacrimal  gland,  and  terminates  in  a  thin  tendon 
in  the  uii]iin-  lid. 

Actiiin. — To  elevate  the  U])per  lid. 

Blood-supply. — Ophthalmic  artery. 

Nerve-supply. — Oculomotor  nerve. 


MUSCLES  OF  MASTICATION 
The  muscles  of  this  group  are  six  in  number  in  the  horse.     They  arise  chiefly 
from  the  upper  jaw  and  the  base  of  the  cranium,  and  are  all  inserted  into  the  man- 
dible. 

1.  Masseter. — This  muscle  extends  from  the  zygomatic  arch  ami  facial  crest 
over  the  broad  part  of  the  mandibular  ramus.     It  is  semi-elliptical  in  outline. 

Origin. — B,y  a  strong  tendon  from  the  zygomatic  arch  and  the  facial  crest. 

Insertion. — The  outer  surface  of  the  broad  part  of  the  ramus  of  the  mandible. 

Action. — Its  action  is  to  bring  the  jaws  together.  Acting  singly,  it  also  carries 
the  lower  jaw  toward  the  side  of  the  contracting  muscle. 

Structure. — The  superficial  face  of  the  muscle  in  its  upper  jiart  is  covered  liy  a 
strong,  glistening  aponeurosis,  and  several  tendinous  intersections  partially  divide 
the  muscle  into  layers.  The  fibers  of  the  superficial  layer  take  origin  from  the 
malar  and  maxilla  only,  and  diverge  somewhat  to  their  insertion  close  to  the  thick 
ventral  border  of  the  lower  jaw.  The  fibers  of  the  deep  layer  arise  from  the  entire 
area  of  origin,  and  pass  straight  to  the  border  of  the  mandible;  it  ^"ill  lie  noted  that 
a  small  part,  near  the  temporo-maxillary  joint,  is  not  covered  by  the  superficial  layer. 
The  two  laj'ers  are  separable  onlj'  above  and  behind;   elsewhere  they  are  fused. 

Relations. — Superficially,  the  skin  and  panniculus,  the  parotid  gland,  the 
transverse  facial  and  masseteric  vessels,  and  the  facial  nerve;  deeply,  the  ramus  of 
the  mandible,  the  buccinator,  depressor  labii  inferioris,  and  mylo-hyoideus  muscles, 
the  superior  buccal  glands,  the  buccinator  nerve,  and  two  large  varicose  veins  which 
join  the  facial  vein  at  the  anterior  edge  of  the  muscle.  The  facial  vessels  and  parotid 
duct  run  along  the  anterior  edge  of  the  muscle;  the  duct,  however,  bends  forward 
about  the  mitldle  of  the  border  and  leaves  the  muscle. 

Blood-supply. — Transverse  facial  and  masseteric  arteries. 

A'erre-supply. — ^Mandibular  nerve. 

2.  Temporalis. — This  muscle  occupies  the  temporal  fossa. 

Origin. — The  rough  part  of  the  temporal  fossa  and  the  crests  which  surround  it. 

Insertion. — The  coronoid  process  of  the  mandible,  which  it  envelops. 

Action. — Chiefly  to  raise  the  lower  jaw,  acting  with  the  masseter  and  internal 
pterygoid  muscles. 

Structure. — The  surface  of  the  muscle  is  covered  with  a  glistening  aponeurosis, 
and  strong  tendinous  intersections  are  found  in  its  substance.  The  inner  edge  of 
the  muscle  is  quite  thin,  but  as  the  fibers  converge  toward  the  much  smaller  area 
of  insertion,  the  muscle  becomes  nearly  an  inch  thick.  It  fuses  somewhat  \dth  the 
masseter. 

Relations. — Superficially,  the  scutiform  cartilage  and  anterior  muscles  of  the 
external  ear  and  the  orbital  fat;  deeply,  the  temporal  fossa  antl  the  tleep  temporal 
vessels  and  nerves. 

Blood-supply. — Superficial  and  deep  temporal,  and  mastoid  arteries. 

Nerve-supply. — ^Mandibular  nerve. 

3.  Pterygoideus  intemus  (s.  medialis). — This  muscle  occupies  a  position  on 
the  inner  surface  of  the  ramus  of  the  mandible  similar  to  that  of  the  masseter  on  the 
outside. 


220 


FASCI.E    AND    MUSCLES    OF   THE    HORSE 


Origin. — The  crest  formed  by  the  pterygoid  process  of  the  sphenoid  and  the 
palate  bone. 

Insertion. — The  concave  inner  surface  of  the  broad  portion  of  the  ramus  of  the 
mandible,  and  the  inner  lip  of  the  lower  border. 

Action. — Acting  together,  to  raise  the  lower  jaw;  acting  singly,  to  produce  also 
lateral  movement  of  the  jaw. 

Structure. — The  muscle  is  capable  of  division  into  two  parts.  The  principal 
part  is  superficial  (internal),  and  its  fibers  are,  for  the  most  part,  vertical  in  direc- 
tion. It  contains  much  tendinous  tissue  (septa).  The  smaller  portion  is  external 
to  the  foregoing,  and  its  fibers  are  directed  downward  and  backward. 

Relations. — Externally,  the  ramus  of  the  mandible,  the  external  pterygoid 
muscle,  the  inferior  alveolar  vessels  and  nerve,  and  the  lingual  and  mylo-hyoid 
nerves;    internally,  the  great  cornu  of  the  hyoid  bone,  the  tensor  palati,  pterygo- 


Ethmo-  Septum  of 

turbinals      frontal  sinuses 
Superior  meatus 
Superior  turbinal 
Middle  meatus 
Inferior  turbinal 
Inferior  meatus 


Fin. 


Section  of  He 


OF  Horse,  Showing  Deep  Pterygo-maxillary 
AND  Cranial  Cavities. 
1,  Cerebral  compartment  of  cranial  cavity;    5,  cerebellar  compartment  of  same; 
4.  tentorium  cerebelli;    6,  sphenoidal  sinus;  6,  hamulus  of  pterygoid  bone-tendon  of  tensor 
anterior  border  of  hamulus;   7,  mylo-glossus.     The  olfactory  mucous  membrane  is  shadetl. 


3,  tentorium  osseum; 
palati  cut  off  short  at 


pharyngeus,  palato-pharyngeus,  mylo-hyoideus,  digastricus,  and  stylo-hyoideus 
muscles,  the  guttural  jiouch,  the  external  maxillary  vessels,  the  ninth  and  twelfth 
nerves,  the  submaxillary  salivary  gland,  the  submaxillary  and  parotid  ducts,  and 
the  submaxillary  and  pharyngeal  lymph-glands, 

Blood-supphj. — Internal  maxillary,  masseteric,  and  inferior  alveolar  arteries. 

Nervf-supph/. — Mandibular  nerve. 

■i.  Pterygoideus  extemus  (s.  lateralis). — This  muscle  is  consideraljly  smaller 
than  the  preceding  one,  and  is  situated  external  to  its  upper  part. 

Origin. — The  external  surface  of  the  pterygoid  process  of  the  sphenoid 
bone. 

Insertion. — The  iimer  surface  of  the  neck  and  the  inner  jiart  of  the  anterior 
border  of  the  cond.yle  of  the  mandible. 

Action. — Acting  together,  to  draw  the  lower  jaw  forward:  acting  singly,  to 
move  the  jaw  laterally,  ('.  e.,  toward  the  side  opposite  to  the  muscle  acting.     The 


MUSCLES    OF    MASTICATION 


221 


latter  action  is  due  to  the  I'aet  that  the  origin  is  nearer  to  the  median  plane  than  the 
insertion. 

Structure. — The  muscle  is  almost  entirely  fleshy,  and  the  fibers  are  almost 


Fig.  176. — Submaxillary  and  Laryngeal  Regions  of  Hor.se,    after  Re.moval  op  Skin  and  Pannii 

c,  Mastoiflo-humeralis;  d,  sterno-cephalicus;  e,  oniO-hyoicieus  and  sterno-hyoideus;  h,  buccinator;  i, 
depressor  labii  inferioris;  m,  masseter;  r,  stylo-maxillaris;  w,  mylo-hyoideus;  ^,  posterior,  S,  anterior,  border 
of  external  ear;  50',  angle  of  jaw;  36,  submaxillary  lymph-glands;  rf7,  external  maxillary  vein;  ci9,  facial  continua- 
tion of  37:  40,  parotid  duct;  44,  parotid  gland;  4S,  prominence  of  chin;  x,  wing  of  atlas.  (.■Vfter  Ellenberger- 
liaum,  Anat.  fiir   Kunstler.) 


longitudinal  in  direction.     Some  of  them  are  inserted  into  the  edge  of  the  inter- 
articular  meniscus. 

Relations. — Externally,  the  temporo-maxillary  articulation  and  the  temporalis 
muscle;  internally,  the  internal  pterygoid  and  tensor  palati  muscles.     The  internal 


222  FASCIA    AND    MUSCLES    OF   THE    HORSE 

maxillary  artery  crosses  the  lower  face  of  the  muscle  and  dips  in  between  it  and  the 
tensor  palati.  The  mandibular  nerve  lies  on  the  ventral  surface,  and  the  buccinator 
nerve  perforates  the  origin  of  the  muscle. 

Blood-supply. — Internal  maxillary  and  inferior  alveolar  arteries. 

Nerre-suppb/. — Mandibular  nerve. 

5.  Stylo-maxillaris  (s.-mandibularis)  (M.  jugulomandibularis). — This  is  a  short 
muscle  extending  from  the  paramastoid  or  styloid  process  of  the  occipital  bone  to 
the  posterior  border  of  the  lower  jaw;  it  is  covered  by  the  parotid  gland. 

Origin. — The  ])aramastoid  or  styloid  process  of  the  occipital  bone,  in  common 
with  the  posterior  belly  of  the  digastricus. 

Insertion. — The  posterior  border  of  the  ramus  of  the  mandible. 

Action. — To  depress  the  lower  jaw  and  open  the  mouth. 

Structure. — The  muscle  contains  a  good  deal  of  tendinous  tissue.  It  blends 
with  the  posterior  belly  of  the  digastricus. 

Relations. — Superficially,  the  parotid  gland,  the  tendon  of  the  stcrno-cephalicus, 
and  the  fibrous  expansion  which  connects  it  with  the  tendon  of  the  mastoido- 
humeralis;  deeply,  the  guttural  pouch,  the  external  carotid  artery,  the  ninth  and 
twelfth  nerves,  the  pharynx,  and  the  submaxillary  gland. 

Blood-supply. — External  carotid  artery. 

Nerve-supphj. — Facial  nerve. 

6.  Digastricus. — This  muscle  is  composed  of  two  fusiform,  flattened  l>ellies, 
united  by  a  round  tendon. 

Origin. — The  paramastoid  or  styloid  process  of  the  occipital  bone,  in  common 
with  the  preceding  muscle. 

Insertion. — The  inner  surface  of  the  lower  border  of  the  mandible  behind  the 
symphysis. 

Action. — It  assists  in  depressing  the  lower  jaw  and  opening  the  mouth.  If  the 
mandible  be  fixed  and  both  bellies  contract,  the  hyoid  bone  and  the  base  of  the 
tongue  are  raised,  as  in  the  first  phase  of  deglutition. 

Structure. — The  posterior  belly  has  the  appearance  of  a  branch  detached  from 
the  inner  surface  of  the  stylo-maxillaris.  It  passes  do^^^lward  and  forward,  and  is 
succeeded  by  a  small  rounded  tendon.  The  latter  perforates  the  tendon  of  in- 
sertion of  the  stylo-hyoideus,  and  is  provided  with  a  synovial  sheath.  The  anterior 
belly  is  larger  and  terminates  by  thin  tendinous  bimdles. 

Relations. — The  posterior  belly  has  practically  the  same  relations  as  the  stylo- 
maxillaris.  The  intermediate  tendon  is  in  contact  externally  with  the  internal 
pterygoid  muscle,  the  submaxillary  gland  and  duct,  and  the  (>xternal  maxillary 
artery.  The  anterior  belly  lies  in  the  submaxillary  space  between  the  ramus  of  the 
jaw  and  the  mylo-hyoideus  muscle;  the  sublingual  vessels  run  along  its  upper  border. 

Blood-supply. — External  carotid  and  sublingual  arteries. 

Nerve-supply. — Facial  and  mandibular  nerves. 


THE  HYOID  MUSCLES 

This  group  consists  of  eight  muscles,  one  of  which,  the  hyoideus  transversus, 
is  unpaired. 

1.  Mylo-hyoideus. — This  muscle,  together  with  its  fellow,  forms  a  sort  of 
sling  between  the  two  rami  of  the  lower  jaw,  in  which  the  tongue  is  supported. 

Origin. — The  inner  surface  of  the  alveolar  l)order  of  the  mandible. 

Insertion. — (1)  A  median  fibrous  raphe  extending  from  the  symphysis  to  the 
hyoid  bone;    (2)  the  lingual  process  and  body  of  th(^  hyoid  bone. 

Action. — It  raises  the  floor  of  the  mouth,  the  tongue,  and  the  hyoid  bone. 

Structure. — Each  muscle  consists  of  a  thin  curved  sheet,  the  fibers  passing 
downward  from  their  origin  and  then  curving  toward  the  median  raphd.     It  is 


THE  inoiD  MUSCLES  223 

chiefly  fleshy,  and  is  thickest  hchiiul.  The  anterior  superficial  part  of  the  muscle 
is  termeil  the  mylo-glossus. 

Relations. — On  the  superficial  surface  of  the  muscles  are  the  ramus,  the  in- 
ternal pterygoid  and  digastricus  muscles,  and  the  submaxillary  lymph-glands.  The 
deep  surface  is  in  contact  with  the  mucous  membrane  of  the  mouth,  the  stylo- 
glossus, hyo-glossus.  and  genio-hyoideus  muscles,  the  sublingual  gland  ami  vessels, 
the  submaxillary  duct,  and  the  lingual  and  hypo-glossal  nerves. 

Blood -sup  ply. — Sublingual  artery. 

\erve-.mpply. — Mylo-hyoid  branch  of  the  mandibular  nerve. 

2.  Stylo-hyoideus. — This  is  a  slender,  fusiform  muscle,  having  a  direction 
nearly  parallel  to  that  of  the  great  cornu  of  the  hyoid  bone  (Fig.  43G). 

Origi)}. — The  heel-like  prominence  on  the  proximal  extremity  of  the  great 
cornu  of  the  hyoid  bone. 

Insertion. — The  anterior  part  of  the  thyroid  cornu  of  the  hyoid  bone. 

Action. — It  draws  the  base  of  the  tongue  and  the  larynx  upward  and  backward. 

Structure. — It  arises  by  a  thin,  short  tendon,  and  has  a  fusiform  belly.  The 
tendon  of  insertion  is  perforated  for  the  passage  of  the  intermediate  tendon  of  the 
digastricus.  and  at  this  point  there  is  a  small  synovial  sheath. 

Relations. — Superficially,  the  internal  pterygoid  muscle  and  the  parotid  gland; 
deeply,  the  guttural  pouch,  the  pharynx,  the  external  carotid  and  maxillary  arteries, 
and  the  hypoglossal  nerve. 

Blood-supply. — External  carotid  artery. 

Nerve-supply. — Facial  nerve  (stylo-hyoid  branch). 

3.  Occipito-hyoideus  (M.  jugulo-hyoideus ;  occipito-styloideus). — This  is  a 
small  triangular  muscle,  which  lies  in  the  space  between  the  paramastoid  process 
and  the  great  cornu  of  the  hyoid  bone. 

Origin. — The  paramastoid  (styloid)  process  of  the  occipital  bone. 

Insertion. — The  proximal  extremity  and  ventral  edge  of  the  great  cornu  of 
the  hyoid  bone. 

Action. — It  carries  the  distal  extremity  of  the  great  cornu  backward  and  up- 
ward. Acting  with  the  genio-hyoideus  and  digastricus,  it  raises  the  hyoid  bone 
and  the  larynx. 

Structure. — The  muscle  is  somewhat  triangular,  its  fibers  being  longer  as  the 
ventral  border  is  approached.     It  blends  with  the  posterior  belly  of  the  digastricus. 

Relations. — Superficially,  the  parotid  gland;  deeply,  the  guttural  pouch. 

Blood-supply. — Occipital  artery. 

Nerve-supply. — Facial  nerve. 

4.  Genio-hyoideus. — This  is  a  long,  spindle-shaped  muscle,  which  lies  under 
the  tongue  in  contact  with  its  fellow  of  the  opposite  side  (Fig.  243). 

Origin. — The  angle  of  union  of  the  rami  of  the  mandible. 

Insertion. — The  extremity  of  the  lingual  process  of  the  hyoid  bone. 

Action. — It  draws  the  hyoid  bone  and  tongue  forward. 

Structure.—The  muscle  arises  by  a  short  tendon,  which  is  succeeded  by  the 
belly,  composed  of  long  bundles  of  parallel  fibers. 

Relations.— Be\o\\;  the  mylo-hyoideus :  above,  the  hyo-glossus,  stylo-glossus, 
genio-glossus,  the  sublingual  gland,  submaxillary  duct,  and  the  lingual  nerve. 

Blood-supply. — Sublingual  artery. 

Nerve-supply. — Hypoglossal  nerve. 

5.  Kerato-hyoideus.— This  small  triangular  muscle  lies  in  the  space  between 
the  thyroid  and  small  cornu.  under  cover  of  the  hyo-glossus  (Fig.  243). 

Origin.— The  posterior  edge  of  the  small  cornu  and  the  adjacent  part  of  the 
ventral  border  of  the  great  cornu. 

Insertion.— The  dorsal  edge  of  the  thyroid  cornu. 
Action.— It  raises  the  thyroid  cornu  and  the  larjTix. 


224  FASCIA    AND    MUSCLES    OF   THE    HORSE 

Relaiium. — The  muscle  is  crossed  outwardly  by  the  lingual  artery. 
Bloods  up  ply. — Lingual  artery. 
Nerve-supply. — Glosso-pharyngeal  nerve. 

6.  Hyoideus  Transversus. — This  is  a  thin,  unpaired  muscle,  which  extends 
transversely  between  the  two  small  cornua  of  the  hyoid  bone. 

.4/toc/(wen^s.— The  small  cornua  close  to  the  junction  with  the  great  cornua. 
Action. — When  relaxed,  its  upper  surface  is  concave;    when  it  contracts,  it 
elevates  the  root  of  the  tongue. 

Structure. — Fleshy,  composed  of  parallel  transverse  bundles. 
Blood-snpphj. — Lingual  artery. 
Nerrr-.'iiipj)!!/. — Glosso-iiharyngeal  nerve. 

7.  Stemo-thyro-hyoideus,  and 

8.  Omo-hyoideus. — These   are   described   with   the   muscles   on   the   ventral 
surface  of  the  neck. 


The  Fasci.(E  and  Muscles  of  the  Neck 

It  is  convenient  to  divide  the  muscles  of  the  neck  into  ventral  and  lateral 
groups,  the  two  lateral  grou]3s  being  separated  from  each  other  by  the  ligamentum 
nuchse. 

THE  FASCIA  OF  THE  NECK 

The  superficial  fascia  is  in  part  two-layered,  and  contains  the  cervical  portion 
of  the  panniculus.  The  fascice  of  the  right  and  left  sides  are  attached  along  the 
dorsal  line  of  the  neck  to  the  ligamentum  nuchte,  while  along  the  ventral  line  they 
meet  in  a  fibrous  raphe.  A  deep  layer  is  detached  which  passes  underneath  the 
panniculus,  bridges  over  the  jugular  furrow,  and  crosses  over  the  deep  face  of  the 
mastoido-humeralis  and  omo-hyoideus  to  join  the  superficial  layer.  It  again  sepa- 
rates to  pass  under  the  cervical  trapezius,  and  become  attached  to  the  ligamentum 
nuchae.  Along  the  ventral  line  a  septum  is  detached  which  separates  the  sterno- 
cephalici.  Two  other  layers  in  front  of  the  shoulder  inclose  the  prescapular  lymph- 
glands. 

The  deep  fascia  also  forms  two  layers.  The  superficial  layer  is  attached  to 
the  wing  of  the  atlas  and  the  lower  edge  of  the  trachelo-mastoideus  and  scalenus. 
Passing  downward,  it  incloses  the  trachea,  and,  together  with  the  deep  layer, 
furnishes  sheaths  for  the  vagus  and  sympathetic  nerves  and  the  carotid  artery. 
Passing  upward  it  detaches  septa  between  the  extensor  muscles  of  the  spine.  An- 
teriorly it  covers  the  thyroid  gland,  the  guttural  pouch,  the  adjacent  vessels  and 
nerves  and  the  larynx,  and  is  attached  to  the  mastoid  process  of  the  temporal  bone 
and  the  thyroid  cornu  of  the  hyoid  bone.  Posteriorly,  it  is  attached  to  the  first 
rib  and  the  cariniform  cartilage  of  the  sternum.  The  deep  layer  (prevertebral 
fascia)  covers  the  ventral  surface  of  the  longus  colli,  and  incloses  the  trachea  and 
CEsophagus.  Anteriorly,  it  forms,  with  the  corresponding  layer  of  the  opposite 
side,  a  septum  between  the  guttural  pouches;  posteriorly,  it  becomes  continuous 
with  the  endothoracic  fascia.  A  fascia  propria  forms  a  tulailar  sheath  around  the 
trachea,  inclosing  also  the  recurrent  nerves. 


VENTRAL  MUSCLES 

This  group  consists  of  eleven  ]iairs  of  muscles  which  lie  almost  entirely 
ventral  to  the  Ycrtebne. 

1.  Panniculus  carnosus. — The  cervical  panniculus  (platysma  myoides  of 
man)  has  a  fleshy  origin  on  the  cariniform  cartilage  (manubrium)  of  the  sternum. 


VENTRAL    MUSCLES    OF   NECK  225 

It  passes  forward,  outward,  and  upward,  crossing  over  the  storno-cephalicus  and 
jugular  furrow  obliquely.  On  reaching  the  surface  of  the  mastoido-hunieralis 
it  adheres  closely  to  this  muscle,  and  soon  thins  out,  to  be  continued  over  the 
splenius  and  trapezius  by  an  aponeurosis  which  is  difficult  to  remove  from  the  latter 
muscle.     Scattered  bundles  may  be  traced  on  the  ventral  surface  of  the  neck  to 


Fig.  177. — Antero-latkrai.  View  of  Musci-f.s  axd  Skeleton  of  Horse. 
a.  Trapezius;  c,  mastoido-humeralis;  d,  sterno-cephaliciLs;  /,  long  head  of  triceps;  /'.  external  liead  of 
triceps;  g,  anterior  superficial  pectoral  muscle;  g' ,  posterior  superficial  pectoral:  k',  anterior  deep  pectoral:  r, 
cervical  panniculus:  z,  supraspinalus:  39.  omo-hyoideus:  SO,  slerno-thyro-hyoideus;  31,  jugular  vein;  32, 
cephalic  vein;  I,  scapula;  1',  cartilage  of  scapula:  3,  spine  of  scapula:  4.  shaft  of  humerus;  4',  external  epi- 
condyle;  5,  external  tuberosity  of  humerus;  5,  deltoid  tuberosity:  /4,  ventral  border  ("keel ")  of  sternum;  14', 
cariniform  cartilage:    I.E.,  first  rib.     C.\fter  Ellenberger-Baum,  Anat.  fiir  Kilnstler.) 


the  facial  portion.     The  right  and  left  muscles  meet  at  a  ventral  median  raph^  in 
peanate  fashion. 

2.  Mastoido-humeralis. — This  is  described  on  p.  2.52. 

3.  Stemo-cephalicus  (Sterno-maxillaris  s.-mandibularis).' — This  is  a  long,  nar- 

'This  mu.scle  is  probably  the  homologue  of  the  sternal  portion  of  the  .^terno-cleido-mastoid 
of  man.     On  account  of  the  differences  in  its  insertion  in  the  various  animals,  it  seems  desirable 
to  adopt  the  name  stemo-cephalicus. 
1.5 


22G  FASCIiE    AND    MUSCLES    OF   THE    HORSE 

row  muscle,  extending  along  the  ventral  and  lateral  aspects  of  the  trachea  from  the 
sternum  to  the  angle  of  the  jaw.   It  forms  the  ventral  boundary  of  the  jugular  furrow. 

Origin. — The  cariniform  cartilage  of  the  sternum. 

Insertion. — The  posterior  border  of  the  lower  jaw. 

Action. — Acting  together,  to  flex  the  head  and  neck;  acting  singly,  to  incline 
the  head  and  neck  to  the  side  of  the  muscle  contracting. 

Structure. — The  two  muscles  are  fused  at  their  origin,  which  is  fleshy.  Near 
the  middle  of  the  neck  they  separate,  and,  becoming  thinner,  each  muscle  passes 
under  the  parotid  gland  and  terminates  in  a  fiat  tendon. 

Relations. — Superficially,  the  cervical  panniculus;  deeply,  the  stcrno-thjTO- 
hyoideus  and  omo-hyoideus  muscles.  The  uiijxn-  edge  of  the  muscle  is  related  to 
the  jugular  vein,  which  lies  in  the  jugular  furrow.  The  carotid  artery,  the  vagus, 
sympathetic,  and  recurrent  nerves  also  lie  along  the  upper  edge  at  the  root  of  the 
neck.  The  tendon  passes  under  the  submaxillary  vein  and  the  parotid  gland,  hav- 
ing the  submaxillary  gland  and  stylo-maxillaris  muscle  on  its  inner  side. 

Blood-supply. — -Carotid  artery. 

Nerve-supphj. ^Ventral  branches  of  the  spinal  accessory  and  first  cervical 
nerves. 

4.  Stemo-thyro-hyoideus  (Sterno-thyroideus  et  sterno-hyoidcus). — This  is  a 
long,  slender,  digastric  muscle,  applied  to  the  ventral  surface  of  the  trachea  and 
its  fellow  of  the  opposite  side. 

Origin. — The  cariniform  cartilage  of  the  sternmii. 

Insertion. — (1)  The  external  surface  of  the  thjroid  cartilage  of  the  larynx; 
(2)  the  body  of  the  hyoid  bone. 

Action. — To  depress  and  retract  the  hyoid  bone,  the  base  of  the  tongue,  and 
the  larynx,  as  in  deglutition.  It  may  also  fix  the  hyoid  lione  when  the  depressors 
of  the  tongue  are  acting,  as  in  suction. 

Structure. — The  origin  of  the  muscle  is  fleshy,  and  as  far  as  the  middle  of  the 
neck  it  blends  with  its  fellow.  The  common  belly  is  then  interrupted  by  a  tendon, 
or  sometimes  two  tendons,  from  which  arise  three  or  four  fleshy  bands.  The  lateral 
bands  diverge  to  reach  their  insertion  into  the  thyroid  cartilage;  while  the  inner 
bands,  closely  applied  to  each  other  and  blending  with  the  omo-hyoideus,  pass 
straight  forward  to  reach  the  ventral  surface  of  the  hyoid  bone. 

Relations. — At  the  root  of  the  neck  the  common  l)elly  has  the  sterno-ce]ihalicus 
below,  and  the  carotid  arteries  and  recurrent  nerves  above.  Further  forward  the 
trachea  becomes  the  upper  relation,  and  near  the  head  the  skin  and  fascia,  the  lower 
one. 

Blood-supphj. — -Carotid  artery. 

A^e?'(ic-s(//j/)///.  -Ventral  branch  of  the  first  cervical  nerve. 

5.  Omo-hyoideus  (vSubscapulo-hyoideus).  —  This  is  a  thin,  riMion-like  muscle, 
almost  entirely  fleshy,  which  crosses  the  trachea  very  obli(iuel\-  under  cover  of  the 
mastoido-humeralis. 

Origin. — The  subscapular  fascia  close  to  the  shoulder  joint. 

Insertion. — The  body  of  the  hyoid  bone,  in  common  with  the  hyoid  branch  of 
the  preceding  muscle. 

Action. — To  depress  the  hyoid  bono. 

Structure. — The  muscle  is  composed  of  iwralU-l  fleshy  fibers,  exce])t  at  its  iirigin, 
where  it  has  a  thin  tendon. 

Relations.-  -In  the  first  part  of  its  course  the  muscle  passes  forward  between 
the  supraspinatus.  anterior  deep  pectoral,  mastoido-humeralis  (outwardly),  and 
the  scalenus  (inwardly).  It  is  intimately  adherent  to  the  mastoido-humeralis. 
In  the  middle  of  the  neck  it  is  related  superficially  to  the  mastoido-humeralis, 
sterno-cephalicus,  and  the  jugular  vein;  deeply,  to  the  rectus  capitis  anterior  major, 
the  carotid  artery,  the  vagus,  sympathetic,  and  recurrent  nerves,  the  trachea,  and, 


VENTRAL    MUSCLES    OF   NECK  227 

on  the  left  side,  the  oesophagus.  In  its  anterior  part  the  muscle  blends  with  the 
hyoid  part  of  the  stcrno-thyro-hj-oideus,  the  two  covering  the  thyroid  portion  of  the 
latter  muscle,  the  thyroid  glaml,  and  the  ventral  face  of  the  larj-nx. 

Blood-supply. — Carotid  and  inferior  cervical  arteries. 

Nerrc-siipphj. — Ventral  branches  of  the  cervical  nerves. 

0.  Scalenus  (M.  scalenus  primse  costae). — This  muscle  is  deeply  situated  on 
the  side  of  the  posterior  half  of  the  neck.  It  is  composed  of  two  parts,  between 
which  the  roots  of  the  brachial  plexus  of  nerves  emerge. 

Origin. — The  anterior  liorder  and  outer  surface  of  the  first  rib. 

Insertion. — (1)  The  dorsal  (smaller)  portion  is  attached  to  the  transverse 
process  of  the  seventh  cervical  verteljra;  (2)  the  ventral  portion  is  attached  to  the 
transverse  processes  of  the  sixth,  fifth,  and  fourth  cervical  vertebrae. 

Action. — The  neck  is  flexed  or  inclined  laterally,  according  as  the  muscles  act 
together  or  singly.  If  the  neck  l)e  the  fixed  point,  the  muscle  may  have  a  respira- 
tory action  by  pulling  forward  or  fixing  the  first  rib. 

Structure. — The  dorsal  portion  is  composed  of  three  or  four  fleshy  bundles.' 
The  ventral  portion,  which  is  much  larger,  is  almost  entirely  fleshy,  and  not  so 
divided. 

Relations. — Superficially,  the  anterior  deep  pectoral,  mastoido-humeralis,  and 
omo-hyoideus  muscles,  the  phrenic  nerve,  and  the  other  branches  of  the  brachial 
plexus;  deeply,  the  vertebrte,  the  longus  colli  and  intertransvcrsales  muscles,  the 
oesophagus  (on  the  left  side),  the  trachea  (on  the  right  side),  the  vertebral  vessels, 
the  vagus,  sympathetic,  and  recurrent  nerves.  The  roots  of  the  brachial  plexus 
form  a  flat  anastomosis,  which  lies  between  the  two  portions  of  the  muscle.  The 
brachial  vessels  cross  the  ventral  edge  close  to  the  first  rib. 

Blood-supply. — Carotid,  vertebral,  and  inferior  cervical  arteries. 

Nerve-supply. — Ventral  branches  of  the  cervical  nerves. 

7.  Rectus  capitis  anterior  major  (M.  longus  capitis). — This  is  the  largest 
of  the  three  special  flexors  of  the  head,  and  lies  along  the  ventro-lateral  surface 
of  the  anterior  cervical  vertebrae  and  the  base  of  the  cranium. 

Origin. — The  transverse  processes  of  the  fifth,  fourth,  and  third  cervical  ver- 
tebrae. 

Insertion. — The  tubercles  at  the  junction  of  the  basilar  process  of  the  occipital 
bone  with  the  body  of  the  sphenoid. 

Action. — Acting  together,  to  flex  the  head;  acting  singlj',  to  incline  it  to  the 
same  side  also. 

Structure. — The  origin  of  the  muscle  is  ])y  fleshy  digitations.  The  belly  in- 
creases in  size  by  the  union  of  these  digitations,  reaching  its  maximum  at  the  axis. 
It  then  diminishes,  passes  toward  the  median  plane,  and  terminates  on  a  rounded 
tendon. 

Relations. — Superficially,  the  mastoido-humeralis.  omo-hyoideus,  and  rectus 
capitis  anticus  minor,  the  submaxillary  gland,  the  carotid  arterj-  (which  lies  along 
the  lower  border),  the  occipital  and  internal  carotid  arteries,  and  the  tenth,  eleventh, 
and  sympathetic  nerves;  deeply,  the  vertebrae,  the  longus  colli,  intertransvcrsales, 
and  the  small  straight  muscle.  The  terminal  part  of  the  muscle  lies  in  contact 
with  its  fellow  at)ove  the  pharynx  and  between  the  guttural  pouches. 

Blood-supply. — Carotid,  verteliral,  and  occipital  arteries. 

Nerve-supply. — Ventral  branches  of  the  cervical  nerves. 

8.  Rectus  capitis  anterior  minor  (AI.  rectus  capitis  ventralis). — This  is  a  small 
muscle  which  lies  under  cover  of  the  preceding  one. 

Origin. — The  ventral  arcli  of  the  atlas. 

'  The  upper  part  of  this  may  be  separated  from  the  scalenus  proper,  and  is  then  termed  the 
cervicaUs  ascendcns  or  iho-costalis  cervicis — a  continuation  in  the  neck  of  the  transversalis  cos- 
tarum. 


228  FASCI.E    AND    MUSCLES    OF    THE    HORSE 

Insertion. — The  liasilar  process,  close  to  the  preceding  muscle. 

Action. — To  flex  the  occipito-atlantal  articulation. 

Structure. — Flesh  j-. 

Relations. — Below,  to  the  preceding  muscle;  above,  to  the  atlas,  occipito- 
atlantal  articulation,  and  the  liasilar  process;  externally,  to  the  rectus  capitis 
lateralis  and  the  guttural  pouch. 

Blood-supply. — Occipital  artery. 

Nerve-supphj. — ^'entral  branch  of  the  first  cervical  nerve. 

9.  Rectus  capitis  lateralis. — This  is  a  still  smaller,  entirely  fleshy  muscle, 
which  lies  for  the  most  part  under  the  small  oblique  muscle. 

Origin. — The  atlas,  external  to  the  preceding  muscle. 
Insertion. — The  paramastoid  or  styloid  process  of  the  occipital  bone. 
Action. — The  same  as  the  preceding  muscle. 
Structure. — Fleshy. 

Relations. — Superficially,  the  small  oblique  muscle,  the  occipital  vessels,  and 
the  ventral  branch  of  the  first  cervical  nerve. 
Blood-supphj . — Occipital  artery. 
Nerve-supply. — Ventral  branch  of  the  first  cervical  nerve. 

10.  Longus  colli. — This  muscle  covers  the  ventral  surface  of  the  vertebrae, 
from  the  sixth  thoracic  to  the  atlas,  and  is  united  with  its  fellow.  It  consists  of 
two  portions,  thoracic  and  cervical. 

Origin. — (1)  Thoracic  portion,  the  bodies  of  the  first  six  thoracic  vertebrae; 
(2)  cervical  portion,  the  transverse  processes  of  the  cervical  vertebra;. 

Insertion. — (1)  Thoracic  portion,  the  bodies  and  transverse  processes  of  the 
last  two  cervical  vertebrae;  (2)  cervical  portion,  the  bodies  of  the  cervical  vertebrae 
and  the  tubercle  on  the  ventral  surface  of  the  atlas. 

Action. — -To  flex  the  neck. 

Structure. — The  muscle  is  composed  of  a  succession  of  bundles.  The  largest 
of  these  constitute  the  thoracic  part  of  the  muscle,  which  has  a  strong  tendon  in- 
serted into  the  last  two  cervical  vertebrae.  A  bursa  is  interposed  between  the  tendon 
and  the  spine  at  the  first  cost o- vertebral  articulation.  The  cervical  portion  con- 
sists of  a  number  of  smaller  bundles,  each  of  which  passes  from  its  origin  on  the 
transverse  process  of  one  vertebra  forward  antl  inward  to  its  insertion  into  a  vertebra 
further  forward.  The  most  anterior  bundle  is  inserted  by  a  strong  tendon  into 
the  ventral  tubercle  of  the  atlas. 

Relations. — The  principal  relations  of  the  two  muscles  in  the  thorax  are: 
ventrally,  the  pleura,  and,  further  forward,  the  trachea  and  oesophagus;  dorsally, 
the  vertebrae  and  the  costo- vertebral  joints;  laterally,  the  dorsal,  superior  cervical, 
and  vertebral  vessels,  the  sympathetic  nerve,  and  the  thoracic  roots  of  the  brachial 
plexus.  In  the  neck,  important  relations  are:  ventrally,  the  trachea  and  a?sophagus, 
the  carotid  artery,  the  vagus,  sympathetic  and  recurrent  nerves;  dorsally,  the 
vertebrae  and,  in  the  middle  third  of  the  neck,  the  iutcrtransversales  muscles; 
laterally,  the  scalenus,  the  rectus  capitis  anticus  major,  and  the  intertransversales 
(in  the  anterior  third).  The  terminal  part  of  the  muscle  is  separated  from  the 
trachea  by  the  cesophagus,  which  is  here  median  in  position. 

Blood-supply. — Subcostal  and  vertebral  arteries. 

Nerve-supply. — Ventral  liranches  of  the  spinal  nerves. 

11.  Intertransversales  colli  (Mm.  intertransversarii  cervicis). — These  are  six 
fasciculi  which  occu])y  the  spaces  between  the  lateral  aspects  of  the  vertebrae  and 
the  transvers(!  and  articular  processes.  There  is  thus  a  bundle  for  each  inter- 
vertel)ral  articulation  except  the  first.  Each  bundle  consists  of  a  dorsal  and 
ventral  portion. 

Attachments. — The  dorsal  bundles  pass  from  transverse  process  to  articular 
process;   the  ventral  l)undlcs  extend  between  adjacent  transverse  processes. 


LATERAL    MUSCLES    OF    NECK  229 

Action. — To  bend  the  neck  laterally. 

Structure. — They  contain  strong  tendinous  intersections. 

Relation.'!. — Superficially,  the  mastoido-humeralis,  rectus  capitis  anterior  major, 
complexus,  trachelo-mastoideus,  splenius,  scalenus,  and  longissimus  muscles; 
deeply,  the  vertebrae,  the  longus  colli  muscle,  and  the  vertebral  vessels.  The 
muscles  are  perforated  by  branches  of  these  vessels  and  by  the  primary  branches  of 
the  cervical  nerves. 

Blood-supply. — Vertebral  artery. 

Nerve-supply. — The  cervical  nerves. 


LATERAL  MUSCLES 
This  group  consists  of  twelve  pairs  of  muscles  arranged  in  layers. 

First  Layer 

1.  Trapezius  cervicalis. — Described  on  p.  2.50. 

Second  Layer 

2.  Rhomboideus  cervicalis. — Described  on  p.  251. 

.3.  Serratus  magnus  (M.  .serratus  cervicis). — Described  with  the  thoracic  part 
on  p.  254. 

Third  Layer 

4.  Splenius. — This  is  an  extensive,  flat,  triangular  muscle,  partly  covered  by 
the  preceding  three  muscles. 

Origin. — The  second,  third,  and  fourth  thoracic  spines  by  means  of  the  dorso- 
scapular  ligament,  and  the  funicular  portion  of  the  ligamentum  nuchse. 

Insertion. — The  occipital  crest,  the  mastoid  process,  the  wing  of  the  atlas, 
and  the  transverse  processes  of  the  third,  fourth,  and  fifth  cervical  vertebra. 

Action. — Acting  together,  to  elevate  the  head  and  neck;  acting  singly,  to 
incline  the  head  and  neck  to  the  side  of  the  muscle  acting. 

Structure. — The  muscle  arises  in  the  withers  from  the  anterior  part  of  the 
dorso-scapular  ligament,  which  also  affords  attachment  to  the  rhomboideus, 
serratus  anticus,  and  complexus  muscles.  The  fibers  pass  upward  and  forward 
toward  the  head  and  the  first  cervical  vertebra.  The  insertion  on  the  occipital 
bone  and  the  mastoid  process  is  by  means  of  a  thin  aponeurosis  common  to  the 
splenius,  trachelo-mastoideus,  and  mastoido-humeralis.  The  atlantal  insertion 
is  by  a  strong,  fiat  tendon,  also  in  common  with  these  muscles.  The  remaining 
insertions  are  fleshy  digitations. 

Relations. — Superficially,  the  skin  and  fascia,  the  trapezius  rhomboideus, 
cer\ncalis,  serratus  magnus,  and  posterior  auricular  muscles;  deeply,  the  com- 
plexus, trachelo-mastoideus,  and  longissimus  muscles. 

Blood-Supply. — Deep  cervical  and  dorsal  arteries. 

Nerve-supply. — Dorsal  branches  of  the  last  six  cervical  nerves. 

Fourth  Layer 

5.  Trachelo-mastoideus  (M.  longissimus  capitis  et  atlantis). — This  muscle 
consists  of  two  parallel,  fusiform  portions.  It  lies  Ijetween  the  deep  face  of  the 
splenius  and  the  ventral  part  of  the  complexus. 

Origin.— (!)  The  transverse  processes  of  the  first  two  thoracic  vertebra;  (2) 
the  articular  processes  of  the  cervical  vertebrie. 

Insertion.— {I )  The  mastoid  process;    (2)  the  wing  of  the  atlas. 


230 


FASCI.E    AND    MUSCLES    OF    THE    HORSE 


u     ?*    n 


■»  ^4.S  ■=- 


LATERAL   MUSCLES  OF   NECK  231 

Action. — Acting  together,  to  extend  the  head  and  neck; 
acting  singly,  to  flex  the  head  and  neck  laterally  or  to  rotate 
the  atlas. 

Structure. — The  origin  from  the  thoracic  vertebrae  is  by 
aponeurotic  slips  which  blend  with  the  complexus.  The  suc- 
ceeding fleshy  portion,  in  passing  along  the  neck,  receives 
fasciculi  from  each  of  the  cervical  vertebrae  except  the  first 
two.  The  dorsal  division  of  the  muscle  is  inserted  into  the 
mastoid  process  by  a  flat  tendon  which  fuses  with  that  of  the 
splenius;  the  ventral  division  is  inserted  into  the  wing  of  the 
atlas  by  a  ribbon-like  tendon  in  common  with  the  splenius  and 
mastoido-humeralis. 

Relations. — Superficially,  the  splenius  muscle  and  dorsal 
branches  of  the  cervical  nerves;  deeply,  the  complexus,  the 
spinalis  colli,  and  the  oblique  muscles  of  the  head.  The  superior 
cervical  vessels  cross  the  deep  face  of  the  muscle  obliquely  at 
the  level  of  the  sixth  and  seventh  cervical  vertebrae. 

Blood-S}ipphj . — Vertebral  and  superior  cervical  arteries. 

Nerve-supply. — Dorsal  branches  of  the  last  six  cervical 
nerves. 

6.  Complexus  (jM.  semispinalis  capitis).  —  This  is  a 
large  triangular  muscle  which  lies  chiefly  on  the  ligamentum 
nuchse,  under  cover  of  the  splenius  and  trachelo-mastoideus 
muscles. 

Origin. — (1)  The  second,  third,  and  fourth  thoracic  spines, 
in  common  with  the  splenius  and  serratus  anticus;  (2)  the 
transverse  processes  of  the  first  six  or  seven  thoracic  vertebrae; 
(3)  the  articular  processes  of  the  cer\'ical  vertebrae. 

Insertion. — The  posterior  surface  of  the  occipital  bone, 
external  to  the  funicular  portion  of  the  Hgamentum  nuchae. 

Action. — It  is  the  chief  extensor  of  the  head  and  neck.  Act- 
ing singly,  the  muscle  inclines  the  head  to  the  same  side. 

Structure. — The  origin  of  the  muscle  at  the  withers  is  apo- 
neurotic. In  the  neck  the  bundles  arising  from  the  articular 
processes  run  obliquely  upward  and  forward,  giving  the  lower 
part  of  the  muscle  a  distinct  pennate  character.  The  upper 
part  of  the  belly  is  crossed  obliquely  by  four  or  five  tendinous 
intersections.     The  insertion  is  hy  a  strong  tendon. 

Relations. — Superficially,  the  rhomboideus,  serratus  magnus, 
splenius,  and  trachelo-mastoideus  muscles;  deeply,  the  liga- 
mentum nuchae,  the  multifidus  cervicis,  longissimus,  and  the 
oblique  and  posterior  straight  muscles  of  the  head,  the  deep 
or  superior  cervical  vessels,  and  the  dorsal  cutaneous  branches 
of  the  cervical  nerves. 

Blood-supply. — Deep  cervical,  vertebral,  and  occipital 
arteries. 

Nerve-supply. — Dorsal  branches  of  the  last  six  cervical 
nerves. 

7.  Multifidus  cervicis  {'SI.  semispinalis  colli;  transverse 
spinous  muscle  of  neck). — This  muscle  lies  on  the  arches  of  the 
last  five  cervical  vertebrae.     It  consists  of  five  or  six  segments. 

Origin. — The  articular  processes  of  the  last  five  (or  four) 
cervical  and  the  first  thoracic  vertebrae. 

Insertion. — The  spinous  processes  of  the  cervical  vertebrae. 


232 


FASCIA    AND    MUSCLES    OF    THE    HORSE 


a  t  -  ■§ 


LATERAL    MUSCLES  OF   NECK  233 

I  s  ■°'  I  2  3  Action. — Acting  together,  to  extend  the  neck;  acting  singly, 

g  I  ^'  I  °  I  to  flex  and  rotate  the  neck  to  the  opposite  side. 

^  g  §•  ft  Ss  I  Structure. — The  muscle  is  composed  of  two  sets  of  Innidles. 

S  i  -^  5  I  f  The    superficial    bundles    arc    directed    obliciuely    forward   and 

g  £•  2  J  I  I  inward,    each    passing   from    an  articular   process  to  the  spine 

>»"  §  &  ^-  ~  I  of  the  preceding  vertebra.     The  deep  bundles  are  shorter  and 

I"  I  '^^  I  o  run  straight  from  an  articular  process  to  that  of  the  preceding 

o  "■  3  ;!  I  2  vertebra. 

S»&2||  Relations. — Superficially,    the    complexus,  longissimus,  tra- 

il ■3.2  ""I  chelo-mastoideus,     and    great    oblique    muscles;     deeply,    the 

y  I  a  I'  ^-  ^.  spinalis  muscle,  the  ligamentum  nuchse,  and  the  arches  of  the 

vertebrae. 

Blood-supply. — Deep  cervical  and  vertebral  arteries. 

Nerve-supply. — Dorsal  branches  of  the  last  six  cervical 
nerves. 

8.  Spinalis. — DcscrilDed  with  the  longissimus  on  p.  237. 

9.  Obliquus  capitis  posterior  (s.  caudalis)  (great  oblique 
muscle  of  the  head).— This  is  a  strong,  quadrilateral  muscle, 
which  covers  the  dorso-lateral  aspect  of  the  atlas  and  axis. 

Origin. — The  side  of  the  spine  and  the  posterior  articular 
process  of  the  axis. 

Insertion. — The  dorsal  surface  of  the  wing  of  the  atlas. 

Action. — Chiefly  to  rotate  the  atlas,  and  with  it  the  head, 
to  the  same  side;  also  to  assist  in  extending  and  fixing  the 
atlanto-axial  joint. 

Structure. — The  muscle  is  composed  almost  entirely  of 
parallel  fleshy  fibers  directed  oliliquely  forward  and  outward. 

/2c?ai)'ons.— Superficially,  the  skin,  the  splenius,  complexus, 
trachelo-mastoideus,  and  mastoido-humeralis  muscles;  deeply, 
the  arch  and  spine  of  the  axis,  the  wing  of  the  atlas,  the 
atlanto-axial  joint,  the  multifidus  cervicis,  the  posterior 
straight  muscles,  the  occipital  and  vertebral  vessels,  and  the 
first  and  second  cervical  nerves.  The  terminal  part  of  the 
vertebral  artery  joins  the  posterior  branch  of  the  occipital 
artery  under  cover  of  the  muscle. 

Blood-supply. — Occipital  and  vertebral  arteries. 

Nerve-supply.— Dorsal  branch  of  the  second  cervical  nerve. 

10.  Obliquus  capitis  anterior  (s.  cranialis)  (small  oblique 
muscle  of  the  head).— A  short,  thick,  quadrilateral  muscle  which 
lies  on  the  side  of  the  occipito-atlantal  articulation. 

Origin.— The  anterior  edge  of  the  wing  of  the  atlas  and  the 
fossa  atlantis. 

Insertion.— The  styloid  process  and  crest  of  the  occipital 
bone,  and  the  mastoid  process. 

.■Ic^io/).— Acting  together,  to  extend  the  head  on  the  atlas; 
acting  singly,  to  flex  the  head  laterally. 

Structure.— The  muscle  contains  a  good  deal  of  tendinous 
tissue.     The  direction  of  its  fibers  is  forward,  upward,  and  inward. 

Relations.— SuperhciaWy,  the  posterior  auricular  muscles, 
artery,  and  nerve,  the  aponeurosis  of  the  splenius,  trachelo- 
mastoideus  and  mastoido-humeralis,  and  the  parotid  gland; 
deeply,  the  straight  muscles,  the  complexus,  the  occipito- 
hyoideus,  the  occipito-atlantal  articulation,  branches  of  the 
occipital  artery,  and  a  branch  of  the  occipital  nerve. 


i:i~^-3|%! 


o  J;   *  — 


S   a  2P  ■= 


■^  -^   3  t: 


234 


FASCLE    AND    MUSCLES    OF   THE    HORSE 


Blood-supply. — Occipital  artery. 

N^erre-suppli/. — Dorsal  branch  of  the  first  cervical  nerve. 

11.  Rectus  capitis  posterior  major  (s.  dorsalis  major)  (great  posterior  straight 
muscle  of  the  head). — This  muscle  extends  from  the  axis  to  the  occipital  bone, 
in  contact  with  the  ligamentum  nuchae. 

Origin. — The  edge  of  the  spinous  process  of  the  axis. 

Iihscrtion. — The  occipital  bone,  below  and  external  to  the  complexus  and 
ligamentum  nuchse. 

Action. — To  extend  the  head. 

Structure. — The  muscle  is  fleshy  and  may  be  divided  into  two  parallel  portions, 


YiG.  180. — Deepest  Later  of  Muscles  of  Neck  of  Horse. 
a,  Obliciuus capitis  anterior;  b,  obliquus  capitis  posterior;  c,  rectus  capitis  lateralis;  d,  rectus  capitis  anterior 
minor;  c,  rectus  capitis  anterior  major;  /.  longus  colli;  g,  g' ,  scalenus:  h,  transversalis  costarum;  j,  longissinius 
dorsi;  k,  spinalis  et  semispinalis;  /,  multifitius  dorsi;  m,  multifi<lus  cervicis;  n,  intertransversales;  o,  o',  rectus 
capitis  posterior  major;  p,  rectus  capiti.s  posterior  minor;  q.  ten<lon  of  insertion  of  complexus:  1,  lamellar  part, 
V .  funicular  part  of  ligamentum  nuchae;  2,  occipital  crest;  S,  paraniastoid  process;  4.  edge  of  wing  of  atlas;  6, 
transverse,  and  ff,  articular,  processes  of  cervical  vertebra?;  7.  nerves  of  brachial  plexus  (cut);  8,  first  rib. 
(Ellenberger-Baum,  Anat.  d.  Haustiere.) 


suj)(>rficial  and  deep.  The  former  blends  somewhat  with  the  terminal  part  of  the 
complexus.     The  tleep  portion  may  be  termed  the  rectus  capitis  posterior  medius. 

Relations. — Superficially,  the  anterior  oblique,  splenius,  and  complexus; 
internally,  the  ligamentum  nuchae;  deeply,  the  atlas,  the  occipito-atlantal  articula- 
tion, and  the  rectus  capitis  posterior  minor.  The  dorsal  branch  of  the  first  cervical 
nerve  appears  between  this  muscle  and  the  small  oblique. 

Blood-supply. — Occipital  artery. 

Nerve-supply. — Dorsal  branch  of  the  first  cervical  nerve. 

12.  Rectus  capitis  posterior  minor  (s.  dorsalis  minor)  (small  posterior  straight 
muscle  of  the  head). — This  small  muscle  lies  under  cover  of  the  preceding. 


THE    FASCIiE   AND    MUSCLES    OF    THE    BACK    AND    LOINS  235 

Oritjin. — The  dorsal  surface  of  the  atlas. 

Insertion. — The  occipital  bone  beneath  the  ])rececling  muscle. 

Action. — To  assist  the  preceding  muscle. 

Structure. — It  is  fleshy  and  varies  a  good  deal  in  volume,  being  sometimes 
small  and  difficult  to  recognize.'     On  the  other  hand,  it  is  sometimes  double. 

Relations. — Superficially,  the  preceding  muscle  and  the  small  ol)liciue;  deeply, 
the  atlas  and  the  occipito-atlantal  articulation. 

Blood-supply. — Occipital  artery. 

Nerve-supply. — Dorsal  branch  of  the  first  cervical  nerve. 


The  FascijE  and  Muscles  of  the  Back  and  Loins 

The  superficial  fascia  ]iresents  no  special  features.  The  lumbo-dorsal  fascia 
(Fascia  lumbo-dorsalis)  closely  invests  the  muscles,  but  is  easily  stripped  off  the 
longissimus.  It  is  attached  medially  to  the  supraspinous  ligament  and  the  spinous 
processes  of  the  vertebraj;  laterally,  it  divides  into  two  layers.  The  superficial 
layer  is  practically  the  aponeurosis  of  the  latissimus  dorsi.  The  deep  layer  gives 
origin  to  the  serratus  anticus  and  posticus,  the  lumbar  part  of  the  obliquus  ex- 
ternus  abdominis,  the  transversus  abdominis,  and  the  retractor  costae.  Its  lateral 
edge  curves  under  the  longissimus  and  is  attached  to  the  ribs  and  lumbar  transverse 
processes.  Posteriorly,  it  is  continuous  with  the  gluteal  fascia.  At  the  withers  it 
forms  an  important  structure,  the  dorso-scapular  ligament.  This  is  a  strong 
tendinous  sheet,  attached  to  the  third,  fourth,  and  fifth  thoracic  spines.  Its  upper 
part  is  very  thick  and  gives  origin  by  its  superficial  surface  to  the  rhomboideus  dorsi, 
by  its  anterior  part  to  the  splenius.  The  lower  part  is  thin  and  elastic,  and  furnishes 
numerous  lamellte  which  intersect  the  scapular  part  of  the  serratus  and  are  at- 
tached with  it  to  the  scapula.  Three  lamella?  are  detached  from  the  deep  face  of 
the  ligament.  The  deepest  of  these  passes  between  the  longissimus  and  spinalis 
and  is  attached  to  the  transverse  processes  of  the  first  seven  thoracic  vertebrae; 
it  gives  attachment  to  the  complexus.  The  middle  one  dips  in  between  the  longis- 
simus and  transversalis  costarum.  The  superficial  one  gives  origin  to  the  serratus 
anticus.  A  strong  fascial  layer,  the  ilio-lumbar  ligament,  extends  from  the  last 
rib  to  the  external  angle  of  the  ilium. 

There  are  nine  pairs  of  muscles  in  this  region,  arranged  in  four   layers. 


First  Layer 


1.  Trapezius  thoracalis. 

2.  Latissimus  dorsi. 


Second  Layer 
3.  Rhomboideus  thoracalis. 

The  foregoing  are  described  with  the  other  muscles  which  attach  the  thoracic 
limb  to  the  trunk  (p.  251). 

■i.  Serratus  anticus  (M.  serratus  dorsalis  inspiratorius). — This  is  a  thin  quadri- 
lateral muscle,  named  from  its  toothed  ventral  border.  It  lies  beneath  the  rhom- 
boideus, serratus  magnus,  and  latissimus  dorsi. 

Origin. — The  lumbo-dorsal  fascia  and  dorso-scapular  ligament. 

Insertion. — The  external  surfaces  of  the  fifth  to  the  eleventh  or  twelfth  ribs 
inclusive. 

Action. — To  draw  the  ribs  on  which  it  is  inserted  forward  and  outward,  thus 
assisting  in  inspiration. 

'This  seems  due  to  pressure  produced  liy  pathological  changes  in  the  supra-atloid  bursa, 
which  are  frequently  extensive  in  dissecting-room  subjects. 


236  FASCIAE    AND    MUSCLES    OF   THE    HORSE 

Stntciure. — The  muscle  arises  by  means  of  a  thin  aponeurosis  which  iilends 
with  the  lumbo-dorsal  fascia  and  the  aponeurosis  of  the  latissimus  dorsi.  The 
muscle-fibers  pass  downward  and  backward  to  be  attached  to  the  ribs  by  seven  or 
eight  digitations  below  the  outer  edge  of  the  transversalis  costarum. 

Relations. — Superficially,  the  rhomboideus,  serratus  magnus,  latissimus  dorsi, 
and  serratus  posticus;  deeply,  the  longissimus  dorsi,  transversalis  costarum,  ex- 
ternal intercostal  muscles,  and  the  ribs. 

Blood-supply. — Intercostal  arteries. 

Nerve-supply. — Thoracic  nerves. 

5.  Serratus  posticus  (M.  serratus  dorsalis  cxspiratorius). — Tliis  muscle  re- 
semliles  the  preceding  one,  which  it  partly  covers. 

Origin. — The  lumbo-florsal  fascia. 

Insertion. — The  outer  surfaces  of  the  last  seven  or  eight  ribs. 

Action. — To  draw  the  ribs  backward,  thus  assisting  in  expiration. 

Structure. — Similar  to  the  preceding  muscle.  The  fibers  are  directed  downward 
and  forward  and  terminate  in  seven  or  eight  digitations,  one  or  two  of  which  cover 
the  posterior  teeth  of  the  anticus.  The  aponeurosis  blends  with  that  of  the  latissi- 
mus dorsi. 

Relations. — Superficially,  the  latissinms  dorsi  and  external  oblique;  d(>eply, 
the  longissimus  dorsi,  transversalis  costarum,  external  intercostals,  serratus  anti- 
cus, and  the  ribs. 

Blood-supply. — Intercostal  and  lumljar  arteries. 

Nerve-supply. — Thoracic  nerves. 

Third  Layer 

G.  Transversalis  costarum  (M.  ilio-costalis). — This  long,  segmental  muscle 
extends,  as  its  name  indicates,  across  the  series  of  ribs,  in  contact  with  the  outer 
edge  of  the  longissimus  dorsi. 

Origin. — (1)  The  transverse  processes  of  the  second  and  third  lumbar  verte- 
bra ancl  the  deep  layer  of  the  lumbo-dorsal  fascia.  (2)  The  anterior  liordcrs  and 
external  surface  of  the  last  fifteen  ribs.' 

Insertion. — The  posterior  borders  of  tlie  ribs  and  the  transverse  processes  of 
the  last  two  or  three  cervical  vertebrae. 

Action. — Chiefly  to  depress  and  retract  the  ribs  and  so  help  in  expiration. 
Acting  together,  they  may  assist  in  extending  this  spine,  acting  singly  in  inclining 
it  laterally. 

Structure. — This  muscle  presents  a  distinct  segmental  arrangement.  It  is 
composed  of  a  series  of  bundles,  the  fibers  of  which  are  directed  forward  and  a  little 
downward  and  outward.  From  these  are  detached  two  sets  of  tendons.  The 
superficitd  tendons  spring  from  the  outer  edge  of  the  muscle.  They  are  flat  anil  are 
about  lialf  an  iuch  in  width.  Each  crosses  two  or  three  intercostal  spaces, 
to  be  inserted  on  the  posterior  border  of  a  rib.  The  deep  tendons  are  detached 
from  the  dorsal  part  of  the  deep  face  of  the  muscle.  Each  passes  backward  across 
one  or  two  intercostal  spaces  to  its  origin  on  the  anterior  border  or  outer  surface 
of  a  rib.     Small  bursse  may  be  found  between  the  ribs  and  tendons. 

Relations. — Superficially,  the  dorsal  serrati  and  the  complexus;  deeply,  the  ex- 
ternal intercostals  and  the  ribs.  The  lumbar  origin  is  covered  by  the  longissimus. 
The  superior  (deep)  cervical  and  dorsal  vessels  cross  the  surface  of  the  muscle  at 
the  first  and  second  intercostal  spaces  respectively,  and  branches  of  the  intercostal 
vessels  and  nerves  emerge  between  the  transversalis  and  longissimus;  here  a  fascial 
layer  dips  in  between  the  two. 

'  The  liiml);ir  part  of  this  muscle  i.s  subject  to  variation.  It  may,  in  quite  exceptional  cases, 
extend  as  far  as  tlie  ilium. 


THE    FASCIA    AND    MUSCLES    OF    THE    BACK    AND    LOINS 


237 


Blood-suppbj. — Intercostal  arteries. 

Merve-supply. — Dorsal  branches  of  the  thoracic  nerves. 

7.  Longissimus.' — This  is  the  largest  antl  longest  nuiscle  in  the  body.  It 
extends  from  the  sacrum  and  ilium  to  the  neck,  filling  up  the  space  between  the 
spinous  processes  mediall.v  and  the  lumljar  transverse  jiroccsses  and  the  upper 
ends  of  the  ribs  below;   consequently  it  has  the  form  of  a  three-sided  prism. 

Origin.— (I)  The  internal  angle,  crest,  and  adjacent  part  of  the  ventral  surface 
of  the  ilium;  (2)  the  first  three  sacral  spines;  (3)  the  lumbar  and  thoracic  spines 
and  the  supraspinous  ligament. 

Insertion. — (1)  The  lumbar  transverse  and  articular  jirocesses;   (2)  the  thoracic 
transverse  processes;     (3)   the  spinous  and  transverse  processes  of  the  last  four 
cervical  vertebrae ;  (4)  the  outer  surfaces  of 
the  ribs,  except  the  first. 

Action. — -Acting  with  its  fellow,  it  is 
the  most  powerful  extensor  of  the  back 
and  loins;  by  its  cervical  attachment  it 
assists  in  extending  the  neck.  By  its 
costal  attachment  it  may  also  assist  in 
expiration.  Acting  singly,  it  flexes  the 
spine  laterally. 

Structure. — This  is  quite  complex.  The 
posterior  part  of  the  muscle  is  greatly  de- 
veloped and  constitutes  the  common  mass 
of  the  loins.  This  is  covered  by  a  strong 
aponeurosis  which  blends  with  the  supra- 
spinous and  sacro-iliac  ligaments,  and  is 
attached  to  the  crest  and  inner  (sacral) 
angle  of  the  ilium  and  the  first  and  second 
sacral  spines;  it  furnishes  origin  to  the  lum- 
bar portion  of  the  middle  gluteus.  In  its 
course  further  forward  the  muscle  receives 
fasciculi  from  the  lumbar  and  thoracic 
spines,  but  diminishes  somewhat  in  vol- 
ume. At  the  withers  it  divides  into  two 
parts.  The  dorsal  division  (spinalis  et 
semispinalis),  reinforced  by  bundles  from 
the  first  four  thoracic  spines,  passes  for- 
ward under  the  complexus  to  be  inserted 
into  the  spines  of  the  last  four  cervical 
vertebrae.  The  ventral  division  passes 
forward  and  downward  underneath  the 
serratus  magnus  to  be  inserted  into  the 
ribs   and   the   transverse    processes    of   the 

last  four  cervical  vertebrce.  Three  sets  of  fasciculi  may  be  distinguished,  viz.:  (1) 
spinal,  which  are  superficial  and  internal;  (2)  transverse,  attached  to  the  transverse 
and  articular  processes,  which  are  internal  and  deep;   (3)  costal,  which  are  external. 

i?eia<tOfts.— Superficially,  the  middle  gluteus,  the  lumbo-dorsal  fascia,  the 
latissimus  dorsi,  dorsal  serrati,  serratus  magnus,  and  complexus;  deeply,  the 
multifidus,  intertransversales,  external  intercostals,  levatores  costarum,  the  liga- 
mentum  nuchae,  and  its  fellow  of  the  opposite  side  (in  the  neck). 

Blood-supply. — Dorsal,  superior  cervical,  intercostal,  and  lumbar  arteries. 

Nerve-supply. — Dorsal  branches  of  the  thoracic  and  lumbar  nerves. 

'The  muscle  as  here  described  includes  the  spinalis  and  semispinaUs  components,  as  the 
separation  of  these  is  largely  artificial  in  the  horse. 


Fig.  181. — Right  Portiox  of  Cross-section  of 
Back  op  Horse.  Section  is  Cut  Through 
Seventh  Thoracic  Vertebra. 
a,  Ligamentum  nuchae;  b.  trapezius  mus- 
cle; c,  cartilage  of  scapula;  d,  latissimus  dorsi;  e, 
panniculus  carnosus;  /,  rhomboideus  dorsi;  g,  ser- 
ratus magnus;  h,  serratus  anticus;  h',  lumbo- 
dorsal  fascia,  whicli  divides  below  into  three 
layers;  ;',  transversalis  costarum;  /:,  levator  costse; 
k' ,  internal  intercostal  muscle;  /,  longissimus  dor- 
si; m,  w',  seventh  thoracic  vertebra;  n,  head  of 
eighth  thoracic  vertebra;  o,  head  of  eighth  rib; 
p,  seventli  rib;  r,  intercostal  arter>-  and  ner\'e;  s, 
skin.  The  fascia?  are  indicated  liy  dotted  lines. 
CAfter  Ellenberger,  in  Leisering's  Atlas.) 


238  FASCI.E   AND    MUSCLES    OF   THE    HORSE 

8.  Multifidus  dorsi  (scniispinalis  of  the  back  and  loins). — This  is  a  long 
segmental  muscle  whicli  covers  the  siiles  of  the  spinous  processes  of  the  vertebrtB 
from  the  sacrum  to  the  neck. 

Origin. — (1)  The  lateral  portion  of  the  sacrum;  (2)  the  articular  processes  of 
the  lumbar  vertebnr;    (3)  the  transverse  processes  of  the  thoracic  vertelira^. 

Insertion. — The  spinous  processes  of  the  first  two  .sacral,  the  lumbar,  thoracic, 
and  last  cervical  vertebrae. 

Action. — Acting  with  its  fellow,  it  is  an  extensor  of  the  spine;  acting  singly, 
it  flexes  it  laterally. 

Structure. — It  is  composed  of  a  series  of  liundles  which  are  directed  obliquely 
forward  and  upward.  Each  fasciculus  passes  over  several  vertebrae  to  its  insertion. 
In  the  posterior  part  of  the  series  the  bundles  cross  two  or  three  vertebrae  and  are 
inserted  into  the  summits  of  the  spines.  Anteriorly,  the  bundles  have  a  more 
horizontal  direction,  cross  three  to  five  vertebrae,  and  are  inserted  into  the  sides 
of  the  spines  considerably  below  their  summits.  A  further  complication  consists 
in  the  fusion  of  several  bundles  into  a  common  insertion. 

Relations. — Superficially,  the  longissimus;    deeply,  the  vertel)ral  sjjines. 

Blood-supply. — Intercostal  and  lumbar  arteries. 

Nerve-supply. — Dorsal  branches  of  the  thoracic  and  lumbar  nerves. 

9.  Intertransversales  lumbonun. — These  are  very  thin  muscular  and  tendin- 
ous strata,  which  occupy  the  spaces  between  the  transverse  processes  of  the  lumbar 
vertebrae  except  the  fifth  and  sixth. 

Action. — To  assist  in  flexing  the  loins  laterally. 

Relations. — Superficially,  the  longissimus;    deeply,  the  cjuadratus  lumborum. 

Blood-supply. — Lumbar  arteries. 

Nerve-supply. — Lumbar  nerves. 

The  Fascia  and  Muscles  of  the  Tail 

The  muscles  of  the  tail  are  inclosed  in  the  strong  coccygeal  fascia,  which  is 
continuous  in  front  with  the  gluteal  fascia  and  blends  with  the  lateral  sacro- 
iliac ligament.  At  the  root  of  the  tail  it  is  loosely  attached  to  the  subjacent  muscles, 
but  further  back  it  is  intimately  adherent  to  them.  From  its  deep  face  are  de- 
tached septa  which  pass  between  the  muscles  to  become  attached  to  the  vertebrae. 

1.  Coccygeus  (Compressor  coccygis;  ischio-coccygeus) . — This  is  a  'flat, 
triangular  muscle  which  lies  chiefly  between  the  sacro-sciatic  ligament  and  the 
rectum. 

Origin. — The  pelvic  surface  of  the  sacro-sciatic  ligament  near  the  ischiatic 
spine. 

Insertion. — The  first  four  coccygeal  vertebrae  and  the  coccygeal  fascia. 

Action. — Acting  together,  to  depress  (flex)  the  tail,  compressing  it  over  the 
perineum;  acting  singly,  to  depress  and  incline  it  to  the  same  side. 

Structure. — The  origin  of  the  muscle  is  aponeurotic.  Becoming  fleshy,  its 
fibers  pass  upward  and  backward  and  divide  into  two  layers.  The  outer  layer  is 
attached  to  the  vertebrae,  the  inner  to  the  fascia;  included  between  the  two  lie 
the  intertransversales.  When  the  tail  is  raised,  the  ventral  edges  of  the  muscles 
produce  a  distinct  ridge  at  either  side  of  the  anus. 

Relations. — Outwardly,  the  sacro-sciatic  ligament  and  the  semimembranosus; 
inwardly,  the  rectum  and  the  sacro-coccygeus  ventralis  muscle.  The  internal 
pudic  artery  crosses  the  outer  face  of  the  origin  of  the  muscle. 

2.  Sacro-coccygeus  superior  (M.  sacrococcygeus  dorsalis  medialis;  erector 
s.  extensor  coccygis). — This  muscle  lies  along  the  dorso-median  aspect  of  the 
tail,  in  contact  with  its  fellow. 

Origin. — The  last  three  sacral  spines  and  some  of  the  coccygeal  spines. 


THE    FASCLE    AND    MUSCLES    OF    THE    TAIL 


239 


Insertion. — Tlie  dorsal  surface  of  the  eoecyseal  vertehni'. 

Action. — Acting  together,  to  elevate  (extend)  the  tail;  acting  singly,  to  elevate 
and  incline  it  laterally. 

Structure. — The  muscle  has  a  strong  rounded  l)elly.     It  is  inserted  by  means  of 
short  tendons  wliich  fuse  with  those  of  the  next  muscle. 

RcldtionK. — Superficially,  the  coccygeal  fascia;    internally,  its  fellow;    later- 
ally, the  sacro-corcygeus  lateralis;   deeply,  the  vertehra\ 

3.  Sacro-coccygeus  lateralis  (M.  sacro-eoccygeus  dorsalis  lateralis;  curvator 
coccygis). — This  muscle  lies  im- 
mediately lateral  to  the  preced- 
ing. 

Origin. — The  sides  of  the 
sacral  spines,  with  the  multifi- 
dus,  and  the  transverse  processes 
of  the  sacral  and  coccygeal  ver- 
tebra*. 

Insertion. — The  lateral  sur- 
face of  the  coccygeal  vertebrae, 
except  the  first  four. 

Action. — Acting  with  its  fel- 
low, to  assist  the  preceding  mus- 
cle in  elevating  the  tail;  acting 
singly,  to  incline  it  to  the  same 
side. 

Structure. — This  muscle  ap- 
pears to  be  a  direct  continuation 
of  the  multifidus  dorsi .    The  belly 


Fig.  1S2. — Cross-section'  of  Tail  of  H 
Close  to  .\xus. 
34,  Coccygeal  vertebra;  35,  sacro 
cygeus  superior;  36,  intertransversalis; 
sacro-coccygeus  inferior;  3S,  coccygeus 
recto-coccygeus;  40,  coccygeal  fascia.  (.\fti 
Ellenberger-Baum,  Anat.  fijr  Kiinstler.) 


39, 


Fig.  183. — Muscles  of  Perinei'm  of  Horse. 
a,  Coccygeus;  b,  retractor  ani;  c,  c',  spiiincter  ani  exter- 
nus;  d,  recto-coccygeus;  e,  sacro-coccygeus  inferior  lateralis; 
/.  retractor  penis;  g,  bulbo-cavernosus;  h,  iscliio-cavernosus; 
I.  internal  puilic  artery:  k,  anus;  I,  penis,  (.\ftcr  Ellenberger- 
Baum,  Top.  Anat.  (1.  Pferdes.) 


is  fusiform  and  receives  reinforcing  fasciculi  from  the  transverse  processes  of  the 
sacrum.  This  is  succeeded  by  bundles  of  tendons,  as  many  as  four  lying  alongside 
of  each  other. 

Relations. — Superficially,  the  lateral  sacro-iliac  ligament  and  the  coccygeal 
fascia;  dorsally,  the  sacro-coccygeus  superior;  ventrally,  the  intertransversales; 
deeply,  the  vertebra:^  and  a  branch  of  the  lateral  coccygeal  artery  and  accompanying 
vein  and  ner\'e. 

4.  Intertransversales  caudse  (Mm.  intertransversarii  cauda>). — These  con- 
sist of  muscular  bundles  which  lie  on  the  lateral  aspect  of  the  tail,  between  the 
preceding  muscle  and  the  sacro-coccygeus  inferior.     They  begin  on  the  lateral  edge 


240  FASCLE   AND    MUSCLES    OF   THE    HORSE 

of  the  sacrum  and  occupy  the  spaces  between  the  transverse  processes,  to  which 
thej-  are  attached.     They  are,  however,  not  arranged  in  a  strict  segmental  manner. 

Adion. — Acting  together,  to  fix  the  coccygeal  vertebrae;  acting  singly,  to 
assist  in  lateral  flexion. 

.5.  Sacro-coccygeus  inferior  (^Im.  sacro-coccygei  ventrales;  depressor 
coccygis). — This  muscle  lies  on  the  ventral  aspect  of  the  sacrum  and  coccyx. 
It  is  composed  of  two  portions,  described  bj*  Bourgelat  and  the  German  anatomists 
as  separate  muscles. 

(a)  The  outer  portion  (il.  coccygeus  ventralis  lateralis)  is  much  the  larger 
of  the  two.  It  arises  from  the  outer  jiart  of  the  ventral  surface  of  the  sacrum,  about 
as  far  forward  as  the  third  foramen,  and  is  inserted  into  the  transverse  processes 
and  ventral  surface  of  the  coccygeal  vertebrse. 

(6)  The  inner  portion  (M.  sacro-coccygeus  ventralis  medialis)  arises  from 
the  ventral  surface  of  the  sacrum  internal  to  the  preceding  muscle  and  the  first 
eight  coccygeal  vertebrae,  and  is  inserted  into  the  ventral  surfaces  of  the  coccygeal 
vertebra. 

Action. — Acting  together,  to  depress  (flex)  the  tail;  acting  singly,  to  incline 
it  laterally  also. 

Structure. — The  outer  portion  has  a  somewhat  compressed  belly,  and  receives 
bundles  from  the  transverse  processes  of  the  coccygeal  vertebrae.  The  inner  por- 
tion is  much  smaller  and  shorter,  reaching  only  about  to  the  middle  of  the  tail. 

Relations. — Ventrally,  the  pelvic  and  coccygeal  fasciae;  dorsally,  the  sacrum, 
coccygeal  vertebrae,  and  the  intertransversales ;  laterally,  the  sacro-sciatic  liga- 
ment, the  coccygeus,  and  the  coccj'geal  fascia;  medially,  its  fellow,  the  recto- 
coccygeus,  and  the  middle  coccygeal  vessels.  Branches  of  the  lateral  coccygeal 
vessels  and  nerves  lie  between  the  outer  division  of  the  muscle  and  the  intertrans- 
versales. 

Blood-supply. — Middle  and  lateral  coccygeal  arteries. 

Nerve-supply. — Coccygeal  nerves. 

The  Muscles  of  the  Thorax 

These  consist  of  seven  muscles  or  sets  of  muscles,  which  are  attached  to  the 
thoracic  vertebrae,  to  the  ribs  and  their  cartilages,  and  to  the  sternum.  Func- 
tionall}',  they  are  muscles  of  respiration. 

1.  Levatores  costarum. — These constituteaseriesofsmalhnuscles  which  occupy 
and  overlie  the  upper  ends  of  the  intercostal  spaces. 

Origin. — The  transverse  processes  of  the  thoracic  vertebrae. 

Insertion. — The  external  surfaces  of  the  upper  ends  of  the  ribs  posterior  to  the 
vertebral  origin. 

Action. — ^To  draw  the  rilis  forward  in  inspiration. 

Structure. — Arising  by  tendinous  fibers,  each  muscle  passes  backward  and  out- 
ward and  expands  at  its  insertion.  Some  fibers  pass  over  one  rib  and  are  inserted 
on  a  succeeding  one.  At  the  first  and  last  spaces  the  muscle  cannot  be  distin- 
guished from  the  external  intercostal,  of  which  it  is  in  reality  only  a  specially  de- 
veloped part. 

Relations. — Superficially,  the  longissimus  dorsi;  deeply,  the  ribs,  internal 
intercostal  muscles,  and  the  intercostal  vessels  and  nerves. 

Blood-supply. — Intercostal  arteries. 

Nerve-s)ipphi. — Intercostal  nerves. 

2.  External  intercostals  (Mm.  intercostales  externi). — Each  of  these  oc- 
cupies an  intercostal  space,  from  the  levatores  to  the  sternal  extremity  of  the  rib. 
They  do  not  occupy  the  intercartilaginous  spaces. 

Origin. — The  posterior  borders  of  the  ribs. 


THE  MUSCLES  OF  THE  THOUAX 


241 


Insertion. — The  anterior  borders;  and  external  surfaces  of  the  succeeding  ribs. 

Action. — To  draw  the  ribs  forward  in  inspiration. 

Structure. — The  fibers  are  directed  downward  and  backward.  There  is  a 
considerable  admixture  of  tendinous  tissue.  Tlie  thickness  of  the  muscles  grad- 
ually diminishes  toward  the  lower  ends  of  the  spaces. 


Seventh  cerincal  vcrtchra- 
Firsl  thoracic  vertebra 


Section  of  scapula 


hitertrarisversalcs 


Levatorcs  coslarum 


Retractor  co^I't:  '       ~~-^i' 
Intertransverse  ligaments    , 
Ilio-lumbar  ligament.._  ^ 


Fig.  184.— Dorsal  ,ixd  Lumbar  Regions  of  Horse,  Dorsal  View.     (After  Schni.-iltz,  Atlas  <1.  Anat.  d.  Pferdes.) 


Relations. — Superficially,  the  serratus  magnus,  latissimus  dorsi,  serratus  anticus 
and  posticus,  longissiraus  dorsi,  transversalis  costarum,  rectus  thoracis,  deep 
pectorals,  obliquus  abdominis  externus.  and  panniculus;  deeply,  the  internal  mter- 
costals  and  (in  the  upper  part  of  the  spaces)  the  intercostal  vessels  and  nerves. 

Blood-siipphj. — Intercostal  and  internal  thoracic  arteries. 

Xerve-supply. — Intercostal  nerves. 
16 


242  FASCIA    AND    MUSCLES    OF   THE    HORSE 

3.  Internal  intercostals  (Mm.  intcrcostali's  interni). — These  occupy  the 
entire  length  of  the  intercostal  spaces,  including  their  interchondral  portion. 

Origin. — The  anterior  borders  of  the  ril)s  and  their  cartilages. 

Insertion. — The  posterior  borders  of  the  preceding  ribs  and  cartilages. 

Action. — To  draw  the  ribs  backward  in  expiration.  It  seems  probable,  how- 
ever, that  the  intcrcartilaginous  portion  is  inspiratory.' 

Structure. — The  direction  of  the  fibers  is  oblique  downward  and  forward. 
There  is  a  smaller  amount  of  tendinous  tissvie  than  in  the  external  set,  and  the 
thickness  diminishes  from  below  upward.  In  the  upper  part  of  the  spaces  fibers 
sometimes  cross  a  rib  in  a  fashion  similar  to  the  sulicostals  of  man.  A  thin 
aponeurosis  separates  the  internal  from  the  external  intercostal  muscle  in  each 
space. 

Relations. — Superficially,  the  levatores  costarum  and  the  external  intercostals; 
deeply,  the  endothoracic  fascia  and  pleura,  the  transversus  thoracis,  diaphragm, 
transversus  abdominis,  and  the  internal  thoracic  and  asternal  vessels.  In  the 
upper  ijart  of  the  intercostal  spaces  the  int(>rcostal  vessels  and  nerves  lie  between 
the  internal  and  external  intercostal  muscle,  but  below  they  lie  chiefly  on  the  deep 
face  of  the  inner  muscle. 

Blood-supphj. — Intercostal  and  internal  thoracic  arteries. 

Nerrr-siipply. — Intercostal  nerves. 

4.  Retractor  costae. — This  is  a  small  triangular  muscle  which  lies  liehind  the 
last  rib,  chiefiy  under  cover  of  the  serratus  posticus. 

Origin. — The  transverse  processes  of  the  first  three  or  four  lumbar  vertebrae 
by  means  of  the  lumbar  fascia. 

Insertion. — The  posterior  border  of  the  last  rib. 

Action. — To  retract  the  last  rib. 

Structure. — The  muscle  arises  by  a  thin  ajioneurosis.  Its  fibers  are  parallel 
to  those  of  the  adjacent  internal  oblique. 

Relations. — Superficially,  the  serratus  posticus  and  external  oblique;  deeply, 
the  transversus  abdominis. 

Blood-supply. — Lumbar  arteries. 

Nerve-supply. — Lumbar  nerves. 

5.  Rectus  thoracis  (M.  tranisversus  costarum;  lateralis  sterni). — This  is  a 
thin  muscle  which  lies  under  cover  of  the  deep  pectoral  muscles.  It  is  directed 
oliliquely  backward  and  downward,  and  crosses  the  lower  part  of  the  first 
three  intercostal  spaces. 

Origin. — The  outer  surface  of  the  first  rib,  below  the  scalenus. 

Insertion. — The  cartilage  of  the  third  or  fourth  rib.  The  aponeurosis  usually 
joins  the  rectus  abdominis.     It  may  reach  the  sternum. 

Action. — It  may  assist  in  inspiration  or  concur  with  the  rectus  abdominis. 

Relations. — Superficially,  the  deep  pectoral  muscles;  deeply,  the  intercostal 
muscles  and  the  rilis. 

6.  Transversus  thoracis  (Triangularis  sterni). — This  is  a  fiat  mu.scle  situated 
on  the  thoracic  surface  of  the  sternum  and  the  cartilages  of  the  sternal  ribs. 

Origin. — The  sternal  ligament. 

Insertion. — The  cartilages  of  the  ribs,  from  the  second  to  the  eighth  inclusive. 

Action. — It  draws  the  costal  cartilages  inward  and  backward,  thus  assisting 
in  expiration. 

Structure. — Each  muscle  has  the  form  of  a  scalene  triangle,  of  which  the  base 
is  the  strongly  serrated  external  border.  The  muscle  contains  a  good  deal  of  tend- 
inous tissue.  The  anterior  bundles  are  directed  forward  and  outward;  the  poste- 
rior liackward  and  outward. 

•  Thp  function  of  tho  intorco.stal  mu.scles  is  stil!  :i  snhjcct  of  iiiucli  ilisciission.  The  statements 
made  above  seem  to  represent  the  view  most  commonly  lield  in  rcgunl  to  their  action. 


THE  MUSCLES  OF  THE  THORAX  243 

Relations. — Superiorly,  the  cndothoracic  fascia  ami  jileura:  inferiorly,  the 
costal  cartilages,  the  internal  intercostal  muscles,  and  the  internal  thoracic  vessels. 

Blood-suppb/. — Internal  thoracic  artery. 

Nerrc-supplij. — The  intercostal  nerves. 

7.  Diaphragm. — This  is  a  broad,  unpaired  muscle  which  forms  a  partition  be- 
tween the  thoracic  and  abdominal  cavities.'  In  outline  it  has  some  resemblance  to 
a  palm-leaf  fan.  In  form  it  is  dome-shaped,  comi^ressed  laterally.  On  a  median 
section  it  is  seen  to  have  a  general  direction  downward  and  forward  from  the  lumbar 
vertebrie  to  the  xiphoid  cartilage.  The  thoracic  surface  is  strongly  convex,  and 
is  covered  by  the  pleura.  The  abdominal  surface  is  deeply  concave,  and  is  covered 
for  the  most  part  by  the  peritoneum.  The  muscle  consists  of  a  peripheral  fleshy 
portion,  two  muscular  crura,  and  a  tendinous  center. 

Attachments. — (1)  Costal  part:  The  cartilages  of  the  ninth  to  the  fifteenth 
ribs,  and  the  last  three  ribs  at  an  increasing  distance  from  their  sternal  ends. 

(2)  Sternal  part:  The  upper    surface  of  the  xiphoid  cartilage. 

(3)  Lumbar  part:  (a)  The  right  cms  is  attached  to  the  inferior  common 
ligament,  and  by  this  means  to  the  first  four  or  five  lumbar  vertebrae.  (6)  The  left 
crus  is  attached  in  a  similar  fashion  to  the  first  and  second  lumbar  vertebrae. 

Action. — ^It  is  the  principal  muscle  of  inspiration  and  increases  the  longi- 
tudinal diameter  of  the  chest.  The  contraction  produces  a  general  lessening 
of  the  curvature  of  the  diaphragm.  In  the  expiratory  phase  the  costal  part 
and  crura  lie  directly  on  the  body  walls,  so  that  the  bases  of  the  lungs  are  in 
contact  with  the  tendinous  center  and  sternal  portion  only.  In  ordinary  inspira- 
tion the  fleshy  rim  recedes  from  the  chest -wall,  so  that  the  bases  of  the  lungs  move 
backward  to  a  line  about  parallel  with  the  curve  formed  by  the  cartilages  of  the 
asternal  ribs,  and  about  four  or  five  inches  (ca.  10  to  12  cm.)  therefrom.  It  is 
stated  that  the  inspiratory  movement  affects  the  tendinous  center  much  less  than 
the  fleshy  part,  since  the  posterior  vena  cava  is  finnly  attached  to  the  former.  It 
should  be  noted,  however,  that  the  direction  of  the  thoracic  part  of  the  vena  cava 
in  the  expiratory  phase  is  oblique  upward  and  backward.  Thus  it  would  seem 
that  there  is  no  anatomical  reason  why  the  diaphragm  should  not  move  as  a  whole 
in  ordinary  inspiration  at  least. 

Structure.^The  costal  part  (Pars  costalis)  consists  of  a  series  of  digitations 
which  meet,  or  are  separated  by  a  very  narrow  interval  from,  the  transversus  ab- 
dominis; between  the  two  are  the  asternal  vessels.  From  the  tenth  rib  backward 
the  attachments  are  to  the  ribs  at  an  increasing  distance  above  the  costo-chondral 
junctions.  Thus  at  the  last  rib  the  attachment  is  four  to  five  inches  (10  to  12  cm.) 
from  the  lower  end.  Anteriorly,  the  origin  extends  along  the  ninth  costal  cartilage 
to  the  xiphoid  cartilage.  From  these  points  of  origin  the  fibers  curve  inward  and 
forward  to  join  the  tendinous  center.  The  right  crus  (Crus  dextrum)  is  about  twice 
as  thick  as  the  left  one  and  is  also  longer.  It  arises  by  a  strong  tendon  from  the 
lumbar  vertebra  (by  means  of  the  inferior  common  ligament).  The  tendon  is 
succeeded  by  a  rounded  belly  which  leaves  the  vertebral  column,  at  the  last  thoracic 
vertebra.  Passing  downward  and  forward,  its  fibers  spread  out  and  join  the  tend- 
inous center.  The  left  crus  (Crus  sinistrum)  arises  by  a  thin  tendon  from  the 
inferior  common  ligament  at  the  first  and  second  lumbar  vertebrae.  This  is  suc- 
ceeded by  a  triangular  belly  which  joins  the  central  tendon.  Between  the 
crura  and  the  attachment  to  the  last  rib  the  edge  of  the  muscle  crosses  the  ventral 
surface  of  the  psoas  muscles  without  attachment,  forming  the  so-called  limibo- 
costal  arch;  here  the  thoracic  and  abdominal  cavities  are  separated  only  by  the 
serous  membranes  and  some  areolar  tissue.  The  tendinous  center  (Centrum 
tendineum)  resembles  the  periphery  in  outline,  but  is  more  elongated.     It  is  par- 

1  It  should  be  noted,  liowever,  th.at  in  the  embryo  the  diapliragm  appears  as  a  paired  struc- 
ture, extending  from  the  lateral  walls  of  the  ca?loni  to  fuse  with  the  septum  transversum. 


244 


FASCI.E    AND    MUSCLES    OF    THE    HORSE 


tially  ilivided  into  right  and  left  halves  by  the  tlescent  of  the  crura  into  it.  It  is 
composed  largely  of  radiating  fibers,  but  many  interlace  in  various  directions; 
this  is  specially  evident  around  the  foramen  vense  cavse,  which  is  encircled  by  fibers. 
A  strong  tendinous  layer  extends  across  below  the  hiatus  asophageus. 


Longusimus  dorsi 

Lumbar  iransverae 
process 


Coital  (trch 
AsliiiKil  mil  1 1/ 

ahdnniiHis  (,  lit 
ulyo 
Xiphoid  cnrldage 
(diprei^&cd) 


FlO.    ISo. — DiAPMRiCM    OF    H 

1,  Inferior  common  ligament;  3,  2' ,  tendonsof  crura;  S,  lumbar  symj>athetic  trunks;  Jt,  external  spermatic 
nerve;  5,  5,  great  splanchnic  nerves;  6,  cisterna  chyli  (opened);  7,  7,  oesophageal  continuations  of  vagus  nerves; 
8.  lymph-gland;  9,  coronary  ligament  of  liver  (cut);  10.  right  lateral  ligament  of  liver  (cut);  /;,  left  lateral  liga- 
ment of  liver  (cut);  12,  falciform  li'^ament  of  liver  (cut);  A.L,  lumbo-costal  arch;  .V.('.,  intercostal  nerve;  (\d., 
right  crus;  C'.s..  left  crus;  4,  aorta;  Co.  coeliac  artery;  Oc,  oesophagus;  I'. c,  posterior  vena  cava;  I'.p.,  i>hrenic 
veins,     {.\fter  Schmaltz,  Atl.is  d.  Anat.  d.  Pferde.s.) 


The  diaphragm  is  pierced  by  three  foramina.  (1)  The  hiatus  aorticus  is  an 
interval  between  the  two  crura  and  below  the  last  thoracic  vortelira.  It  contains 
the  posteridr  aorta,  vena  azygos,  and  cisterna  chyli.  (2)  The  hiatus  oesophageus 
(or  foramen  sinistrum)  perforates  the  right  crus  near  its  junction  with  the  tendinous 


THE    ABDOMINAL    MUSCLES  245 

center.  It  is  situated  a  little  to  the  left  of  the  median  \i\ane  and  two  or  three 
inches  below  tiie  thirteenth  thoracic  vertebra  (in  expiration).  It  transmits  the 
a?sophagus,  the  vagus  nerves,  and  the  a?sophageal  branch  of  the  gastric  arterj-. 
(3)  The  foramen  venae  cavse  (s.  dextruni)  pierces  the  tendinous  center  about  an 
inch  to  the  right  of  the  median  plane,  and  about  six  inches  below  the  twelfth 
thoracic  vertebra  (in  expiration).  The  vena  cava  is  firmly  attached  to  the 
margin  of  the  opening.' 

Relations. — The  thoracic  surface  is  related  to  the  endothoracic  fascia,  pleurse, 
pericardium,  the  bases  of  the  lungs,  and  the  ribs  in  part.  The  abdominal  surface 
is  in  great  part  covered  by  the  peritoneum,  and  is  related  chiefly  to  the  liver,  stom- 
ach, spleen,  pancreas,  kidneys  and  adrenals,  and  the  anterior  flexures  of  the  colon. 
The  sympathetic  and  sj^lanchnic  nerves  pass  between  the  crus  and  the  psoas  muscles 
on  each  side.  The  asternal  vessels  perforate  the  edge  of  the  muscle  at  the  ninth 
costo-chondral  joint. 

Blood-supply. — Phrenic  and  asternal  arteries. 

Xerre-supply. — Phrenic  nerves  (from  the  fifth,  sixth,  and  seventh  cervical 
nerves). 


The  Abdominal  Muscles 

The  superficial  fascia  covering  the  lateral  and  ventral  walls  of  the  abdomen  is 
continuous  dorsally  with  the  lumbo-dorsal  fascia,  in  front  with  the  thoracic  fascia, 
and  behind  with  the  gluteal  fascia.  In  the  inguinal  region  it  forms  part  ofthe 
fascia  of  the  penis  or  of  the  mammary  glands.  At  the  lower  part  of  the  flank  it 
forms  a  fold  which  is  continuous  with  the  fascia  of  the  thigh  near  the  stifle  joint. 
In  this  fold  are  the  precrural  lymph-glands.  ^Medially  it  blends  with  the  linea  alba. 
It  contains  the  abdominal  portion  of  the  panniculus  carnosus. 

The  abdominal  panniculus  (^I.  cutaneus  maxinius)  covers  a  large  part  of 
the  lateral  surface  of  the  abdomen  and  thorax.  The  general  direction  of  its 
fibers  is  longitudinal.  Its  posterior  extremity  forms  the  basis  of  the  fold  of  the 
flank.  Its  anterior  extremity  is  inserted  by  a  thin  tendon  into  the  internal  tuber- 
osity of  the  humerus,  with  the  posterior  deep  pectoral  muscle.  Its  dorsal  edge  may 
be  indicated  by  a  line  drawn  from  the  upper  end  of  the  thirteenth  rib  to  the  fold  of 
the  flank.  Its  ventral  limit  corresponds  to  a  line  drawii  from  the  fold  to  a  point 
about  a  hand-breadth  external  to  the  umbilicus,  and  from  here  to  a  point  a  little 
above  the  level  of  the  elbow.  Behind  the  shoulder  the  fibers  become  oblique  and 
blend  with  the  scapular  portion.  The  aponeurosis  extends  ventrally  to  the  linea 
alba,  dorsally  to  the  supraspinous  ligament.  The  muscle  is  intimately  adherent 
to  the  skin,  so  that  special  care  is  necessary  in  removing  the  latter.  Its  deep  face, 
on  the  other  hand,  is  loosel}'-  attached  to  the  underlying  structures  by  a  ciuantity  of 
areolar  tissue  which  is  more  or  less  loaded  with  fat  (panniculus  adiposus)  in  animals 
in  good  condition.  The  large  external  thoracic  ("  spur  ")  vein  is  partially  embedded 
in  the  lower  part  of  the  muscle.     Its  action  is  to  twitch  the  skin. 

The  deep  fascia  is  represented  chiefly  by  the  abdominal  timic  (Tunica  flava 
abdominis).  This  is  a  sheet  of  elastic  tissue  which  assists  the  muscles  in  supporting 
the  great  weight  of  the  abdominal  viscera.  It  is  practically  coextensive  with  the 
obliquus  externus,  which  it  covers.  Ventrally  it  is  thick,  and  is  intimately  ad- 
herent to  the  aponeurosis  of  the  muscle.  Laterally  it  becomes  thinner  and  is 
more  easih'  separated,  although  fibers  from  it  dip  in  between  the  muscle-bundles. 
It  is  continued  for  some  distance  upon  the  intercostals  and  serratus  magnus. 

'  In  order  to  get  a  clear  idea  of  the  relative  positions  of  these  foramina  and  of  the  form  of 
the  diaphragm,  the  thoracic  surface  of  the  latter  should  be  examined  while  the  abdominal  viscera 
remain  in  sUu. 


246  FASCLE   AND    MUSCLES    OF   THE    HORSE 

Traced  forward,  it  passes  as  a  thin  layer  Ijeneath  the  posterior  deep  pectoral 
muscle.  Posteriorly  it  is  attached  to  the  external  angle  of  the  ilium.  In  the  in- 
guinal region  it  forms  the  deep  fascia  of  the  prepuce  or  of  the  mammary  glands. 

The  linea  alba  is  a  median  fibrous  raphe  which  extends  from  the  xiphoid 
cartilage  to  the  .symphysis  pubis.  It  is  formed  chiefly  by  the  junction  of  the  apo- 
neuroses of  t  he  ol  ilifiue  and  transverse  muscles,  but  partly  by  longitudinal  fibers.  A 
little  behind  its  middle  is  a  cicatrix  which  indicates  the  position  of  the  umbilical 
opening  of  the  foetus. 

1.  Obliquus  abdominis  extemus  (great  obhque;  external  oblique  of  the 
abdomen). — This  is  the  most  extensive  of  the  abdominal  muscles.  It  is  a  broad 
sheet,  irregularly  triangular  in  shape,  widest  behind.  Its  fibers  arc  directed  chiefly 
downward  and  backward. 

Origin. — (1)  The  outer  surfaces  of  the  last  fourteen  ribs,  and  the  fascia 
over  the  external  intercostal  muscles;    (2)  the  lumbo-dorsal  fascia. 

Insertion. — (1)  The  linea  alba  and  the  prepubic  tendon;  (2)  the  external 
angle  and  shaft  of  the  ilium;    (3)  the  internal  femoral  fascia. 

Action. — (1)  To  compress  the  abdominal  viscera,  as  in  defecation,  micturition, 
parturition,  and  expiration;  (2)  to  flex  the  trunk  (arch  the  back);  (3)  acting 
singly,  to  flex  the  trunk  laterally. 

Structure. — The  muscle  is  composed  of  a  fleshy  portion  and  an  aponeurosis. 
The  muscular  portion  lies  on  the  lateral  wall  of  the  thorax  and  abdomen.  It 
arises  by  a  series  of  digitations,  the  anterior  four  of  which  alternate  with  those  of  the 
serratus  magnus.  The  origin  may  be  indicated  l)y  a  slightly  curved  line  (concave 
above)  drawn  from  the  lower  part  of  the  fifth  rib  to  the  external  angle  of  the  ilium. 
The  fibers  are  directed  downward  and  backward  and  terminate  on  the  aponeurosis, 
except  in  the  fiank,  where  they  are  almost  horizontal  in  direction.  The  line  of 
junction  is  a  curve  (concave  above)  extending  from  the  upper  edge  of  the  po.sterior 
deep  pectoral  muscle  toward  the  external  angle  of  the  ilium.  The  aponeurosis 
is  intimately  attached  to  the  abdominal  tunic,  and  its  fibers  are  largely  interwoven 
ventrally  with  those  of  the  aponeurosis  of  the  internal  oblique.  By  this  fusion  is 
formed  the  outer  sheath  of  the  rectus  abdominis,  which  blends  at  the  linea  alba 
with  thai;  of  the  opposite  side.  In  the  inguinal  region  the  aponeurosis  divides  into 
two  chief  layers;  one  of  these  curves  upward  and  backward  and  is  inserted  into 
the  external  angle  of  the  ilium  and  the  prepubic  tendon.  Between  these  points 
the  aponeurosis  is  much  strengthened  and  is  called  the  inguinal  (Poupart's)  liga- 
ment (Ligamentum  inguinale).  This  curves  upward  and  somcwliat  forward,  be- 
comes thin,  and  blends  with  the  iliac  fascia.  It  forms  the  posterior  wall  of  the 
inguinal  canal.  About  an  inch  (ca.  2  to  3  cm.)  in  front  of  the  pubis  and  about  two 
inches  (ca.  4  to  5  cm.)  from  the  median  plane  the  aponeurosis  is  pierced  by  a  slit-like 
opening,'  the  external  inguinal  ring  (Annulus  inguinalis  subcutaneus).  This  is  the 
external  orifice  of  the  inguinal  canal.  Its  long  axis  is  directed  outward  and  forward, 
and  is  about  four  inches  (ca.  10  cm.)  in  length.  The  inner  angle  is  rounded  and  is 
well  defined  by  the  junction  of  the  inguinal  ligament  with  the  prepubic  tendon,  but 
the  outer  angle  is  not  so  sharply  defined.  The  borders  or  pillars  are  constituted  by 
arciform  fibers  of  the  aponeurosis  of  the  external  oblique  (Crus  mediale,  laterale). 
The  femoral  layer  of  the  aponeurosis  (Lamina  femoralis)  passes  on  to  the  inner  sur- 
face of  tlic  thigii,  where  it  blends  with  the  femoral  fascia.  A  thin  iliac  layer  ( Lamina 
iliaca)  passes  over  the  outer  margin  of  the  iliacus  to  the  external  liorder  of  the  ilium. 

Relations. — Superficially,  the  skin,  the  panniculus  carnosus,  the  abdominal 
tunic,  and  the  posterior  deep  pectoral  muscle;  deeply,  the  ribs  and  their  cartilages, 
the  intercostal  muscles,  the  internal  obli(iue,  the  contents  of  the  inguinal  canal, 
and  the  sartorius  and  gracilis. 

'It  is  narrow  and  slit-like  in  the  natural  condition,  but  may  appear  oval  in  the  dissecting- 
room,  especially  if  the  hind  limb  is  drawn  back  and  abducted. 


THE    ABDOMINAL    Ml'SCLES 

Blood-supply.— Intercostal  and  lumliar  arteries. 
Nerve-supply.— Intercostal  aud  lumbar  nerves. 


247 


2.  ObUquus  abdominis  interaus  fsmall  oblique;  internal  oblique  of  the 
abdomen).— This  muscle  is  situated  under  the  preceding  one.  Its  fibers  are 
directed  downward,  forward,  and  inward.  It  forms  a  triangular  curved  sheet  with 
the  base  behind. 


248  FASCI.E    AND    MrSCLES    OF   THE    HORSE 

Origin. — The  external  angle  of  the  ilium  and  the  adjacent  part  of  the  iiiKuiual 
(Poupart's)  ligament. 

Insertion. — (1)  The  cartilages  of  the  last  four  or  five  ribs;  (2)  the  linea  alba 
and  the  prepubic  tendon. 

Action. — Similar  to  that  of  the  preceding  muscle. 

Structure. — Like  the  external  oblique,  it  is  composed  of  a  fleshy  jiortion 
and  an  aponeurosis.  The  fleshy  portion  is  fan-shaped,  and  is  situated  chiefly  in 
the  flank.  At  its  iliac  origin  it  is  covered  by  a  glistening  aponeurosis.  Traced 
inward  and  downward  along  the  abdominal  surface  of  the  inguinal  ligament, 
the  muscular  origin  is  found  to  become  much  thinner,  and  also  becomes  loosely 
attached  to  the  ligament.  About  four  or  five  inches  (ca.  10  to  12  cm.)  from  the 
linea  alba  the  muscle  separates  from  the  ligament  and  forms  the  anterior  wall 
of  the  inguinal  canal.  The  abdominal  orifice  of  the  canal,  the  internal  inguinal 
ring'  (Annulus  inguinalis  abdominalis),  is  found  here.  It  is  normally  a  narrow 
slit,  hounded  in  front  by  the  edge  of  the  internal  oblique,  and  behintl  liy  tlie  in- 
guinal ligament.  The  aponeurosis  is  to  a  great  extent  blended  with  that  of 
the  external  oblique,  being,  indeed,  consiilerably  interwo^'en  with  it  ventrally. 
Where  it  covers  the  rectus  abdominis  it  is  attached  to  the  tendinous  inscriptions 
of  that  muscle. 

Relations. — Superficially,  the  external  oblique;  deeply,  the  rectus  abdominis, 
transversus  abdominis,  and  the  peritoneum. 

Blood-supply. — Circumflex  iliac,  lumbar,  and  intercostal  arteries. 

Nerve-supply. — Ventral  branches  of  the  lumbar  nerves. 

3.  Rectus  Abdominis. — This  muscle  is  confined  to  the  ventral  part  of  the 
abdominal  wall;   it  extends  from  the  lower  part  of  the  chest -wall  to  the  pubis. 

Origin. — The  cartilages  of  the  fifth  to  the  ninth  ribs  inclusive,  and  the  adja- 
cent surface  of  the  sternum. 

Insertion. — The  pubis,  by  means  of  the  jirepubic  tendon. 

Action. — Similar  to  that  of  the  oblique  muscles.  It  is  specially  adapted  to 
flex  the  lumbo-sacral  joints  and  the  lumliar  and  thoracic  parts  of  the  spine. 

Structure. — The  fibers  of  the  muscle  are  directed  longitudinally.  Nine  to 
eleven  transverse  bands  of  fibrous  tissue  extend  in  an  irregular  manner  across 
the  muscle.  These  are  termed  inscriptiones  tendineae.  They  strengthen  the 
muscle  and  serve  to  prevent  separation  of  its  fillers.  The  width  of  the  nniscle  is 
greatest  about  its  middle. 

Relations. — Superficially,  the  aponeuroses  of  the  oblique  muscles  (which 
constitute  the  external  rectus  sheath),  and  the  posterior  deep  pectoral;  deeply, 
the  transversus,  intercostals,  the  cartilages  of  the  ribs,  and  the  stermmi.  The 
posterior  abdominal  artery  runs  along  the  outer  edge  of  the  muscle  posteriorly, 
and  the  anterior  abdominal  artery  on  or  in  its  anterior  part. 

Blooil-siipplj/. — Anterior  and  posterior  abdominal  arteries. 

Nerre-siippli/.  -Intercostal  and  lumbar  nerves. 

4.  Transversus  abdominis. — This  muscle,  named  from  the  general  direction 
of  its  fibers,  is  a  triangular  curved  sheet.  Its  lateral  jiart  is  muscular,  its  ventral 
aponeurotic. 

Origin.— (i)  The  inner  surfaces  of  the  distal  ends  or  the  cartilages  of  the 
asternal  ribs,  meeting  the  costal  attachment  of  the  diaphragm;  (2)  the  transverse 
processes  of  the  lumbar  vertebrae,  by  means  of  the  deep  layer  of  the  lumlio-dorsal 
fascia. 

Insertion. — The  xiphoid  cartilage  and  the  linea  alba. 

'  It.  must  1)0  admitted  that  the  term  "ring"  is  ratlier  misleading  as  applied  to  the  abdomi- 
nal opening  of  the  eanal,  since  normally  it  is  a  mere  dilatable  slit.  The  ring-like  eonstriotion 
which  exists  liere  in  the  male  is  constit'uleil  liv  the  peritoneum,  whieh  descends  into  the  canal 
to  form  the  tunica  vaginalis.  This  peritoneal  ring  is  termed  the  vaginal  ring  (Annulus  vagmalis), 
and  must  not  be  confused  with  the  subperitoneal  ring,  i.  c,  the  internal  inguinal  ring. 


THE    ABDOMINAL    MISCLES  249 

Action. — Similar  to  tliat  of  the  olilique  inusclos. 

Strufture. — The  muscular  part  is  a  sheet  of  parallel  liundlcs  of  fibers,  directed 
downward  and  inward.  It  is  thickest  over  the  cartilages  of  the  ribs,  and  from 
here  it  thins  out  srcatly  toward  the  aponeurosis  and  the  lumbar  region.  The 
fibers  of  the  aponeurosis  directly  continue  those  of  the  fleshy  part.  Posteriorly 
it  becomes  extremely  thin  and  blends  with  the  aponeuroses  of  the  oblique  muscles. 
It  covers  the  deep  face  of  the  rectus,  so  forming  the  internal  rectus  sheath. 

Relations. — Superficially,  the  oblique  and  straight  muscles,  the  retractor 
costse,  the  cartilages  of  the  asternal  ribs,  and  the  internal  intercostal  muscles; 
deeply,  the  transversalis  fascia  and  the  peritoneum.  The  transversalis  fascia  is 
little  developed  in  the  horse,  and  is  very  thin  in  emaciated  subjects,  but  in  animals 
in  good  condition  it  contains  a  good  deal  of  fat.  It  blends  with  the  iliac  fascia 
and  descends  into  the  inguinal  canal.  The  asternal  artery  runs  along  the  inter- 
val between  the  origin  of  the  transversus  and  the  costal  part  of  the  diaphragm. 
The  intercostal  nerves  pass  down  over  the  external  surface  of  the  muscle,  to 
which  they  give  branches.  Branches  of  the  first  three  lumbar  nerves  are  simi- 
larly disposed  further  back. 

Blood-supply. — Intercostal,  lumbar,  and  asternal  arteries. 

Nervc-supply. — Intercostal  and  lumbar  nerves. 

5.  Cremaster  extemus. — This  small  muscle  may  be  regarded  as  a  detached 
portion  of  the  internal  oblique,  with  which  it  blends  at  its  origin  (Figs.  272,  450). 

Origin. — The  iliac  fascia,  near  the  origin  of  the  sartorius. 

Insertion. — The  tunica  vaginalis  communis. 

Action. — To  raise  the  tunica  vaginalis,  and  with  it  the  testicle. 

Structure. — The  muscle  arises  by  a  thin  aponeurosis  which  is  succeeded  by 
a  flat  muscular  belly  about  one  and  a  half  to  two  inches  (ca.  4  to  5  cm.)  in  width.' 
It  passes  doum  the  inguinal  canal  on  the  postero-external  surface  of  the  tunica 
vaginalis,  to  which  it  is  rather  loosely  attached.  On  reaching  the  point  where 
the  tunic  is  reflected  on  to  the  tail  of  the  epididymis,  the  muscle  is  firmly  attached 
to  the  outer  surface  of  the  tunic  by  short  tendinous  fibers. 

Relations. — The  muscle  lies  between  the  peritoneum  and  the  fascia  trans- 
versalis in  front  and  the  iliac  fascia  and  inguinal  ligament  behind.  On  reaching 
the  internal  ring  it  descends  the  inguinal  canal  on  the  postero-external  surface  of 
the  tunica  vaginalis  communis. 

Blood-supply. — External  spermatic  or  cremasteric  arterj'. 

Nerve-supply. — External  spermatic  nerve. 

The  Inguinal  Canal. — This  term  (Canalis  inguinalis)  is  applied  to  an  oblique 
passage  through  the  posterior  part  of  the  abdominal  wall."  It  begins  at  the 
internal  inguinal  or  abdominal  ring,  and  extends  obliquely  downward,  inward, 
and  somewhat  forward,  to  end  at  the  external  inguinal  or  subcutaneous  ring. 
Its  anterior  wall  is  formed  by  the  fleshy  posterior  part  of  the  internal  oblique 
muscle,  and  the  posterior  wall  by  the  strong  tendinous  inguinal  (Poupart's)  liga- 
ment. The  average  length  of  the  canal,  measured  along  the  spermatic  cord, 
is  about  four  inches  (ca.  10  cm.).  The  internal  inguinal  ring  (Annulus  inguinalis 
abdominalis)  is  bounded  in  front  by  the  thin  margin  of  the  internal  oblique  muscle, 
and  behind  by  the  inguinal  ligament.  It  is  directed  approximately  from  the  edge 
of  the  prepubic  tendon  toward  the  external  angle  of  the  ilium.  Its  length  is  about 
four  or  five  inches  (ca.  10  to  12  cm.).     The  edge  of  the  muscle  is  attached  to  the 

'  As  might  be  expected,  the  cremaster  usualh'  undergoes  more  or  less  atrophy,  and  is  paler 
in  the  castrated  subject.  In  the  mare  tlie  muscle  is  small,  and  ends  in  the  connective  tissue  in 
the  lower  part  of  the  inguinal  canal. 

'  The  term  canal  is  somewhat  misleading;  it  is  rather  a  slit-like  passage  or  space  between 
the  two  oblique  muscles,  since  the  inguinal  hgament  is  that  part  of  the  aponeurosis  of  the  exter- 
nal oblique  muscle  which  stretches  between  the  external  angle  of  the  ilium  and  the  prepubic 
tendon. 


250  FASCIA    AND    MUSCLES    OF    THE    HORSE 

surface  of  the  ligament  here  by  tlelicate  connective  tissue,  except  where  structures 
intervene  between  the  walls  of  the  canal.  Conseciucntly  the  limits  of  the  ring 
are  not  very  clearly  defined.  The  external  inguinal  ring  (Annulus  inguinalis 
subcutaneus)  is  a  well  defined  slit  in  the  aponeurosis  of  the  external  oblique 
muscle,  situated  lateral  to  the  prepubic  tendon.  Its  long  axis  is  directed  from  the 
edge  of  the  prepubic  tendon  outward  and  forward,  and  its  average  length  is  about 
four  inches  (ca.  10  cm.).  The  canal  contains  in  the  male  the  spermatic  cord, 
the  tunica  vaginalis,  the  external  cremaster  muscle,  the  external  pudic  artery 
and  a  small  satellite  vein,  and  the  inguinal  lymph-vessels  and  nerves.  In  the 
female  it  contains  the  mammary  vessels  and  nerves;  in  the  bitch  it  also  lodges 
the  round  ligament  of  the  uterus,  inclosed  in  a  tubular  process  of  peritoneum. 

The  two  rings  do  not  correspond  in  direction,  so  that  tlie  length  of  the  canal  varies  greatly 
when  measured  at  difTerent  points.  The  inner  angle  of  the  internal  ring  lies  almost  immediately 
above  that  of  the  external  ring,  but  the  outer  angle  is  situated  five  to  six  inches  (ca.  12  to  15  cm.) 
from  that  of  the  external  ring.  The  inner  angles  of  the  external  rings  are  well  defined  and  dis- 
tinctly palpable  in  the  living  subject;    they  are  about  three  to  four  inches  (ca.  8  to  10  cm.)  apart. 

The  Prepubic  Tendon. — The  prepubic  tendon  is  essentially  the  tendon  of 
insertion  of  the  two  recti  abdominis,  but  also  furnishes  attachment  to  the  obliqui, 
the  graciles,  and  the  pectinei.  It  is  attached  to  the  anterior  borders  of  the  pubic 
bones,  including  the  ilio-pectineal  eminences.  It  has  the  form  of  a  very  strong 
thick  band,  with  concave  lateral  borders  which  form  the  inner  boundaries  of  the 
external  inguinal  rings.  Its  direction  is  oblique  upward  and  backward.'  Its 
structure  is  somewhat  complex.  Most  of  the  fibers  of  the  posterior  part  extend 
from  one  ilio-pectineal  eminence  to  the  other.  The  fibers  which  belong  to  the 
recti  curve  in  to  the  median  line.  The  aponeuroses  of  the  internal  obliciue  muscles 
are  inserted  into  its  abdominal  surface,  and  the  inguinal  ligaments  are  attached 
to  and  continue  across  it  in  arciforra  fashion.  The  anterior  part  of  the  tendon  of 
origin  of  the  gracilis  is  fused  with  it  ventrally,  and  many  of  the  fibers  of  the  pectineus 
arise  from  it.  It  gives  off  on  either  side  a  strong  round  band,  the  so-called  pubo- 
femoral or  accessory  ligament,  which  is  inserted  into  the  fossa  of  the  head  of  the 
femur  with  the  round  ligament  {ride  hip  joint). 


Muscles  of  the  Thoracic  Limb 

I.  THE  MUSCLES  OF  THE  SHOULDER  GIRDLE  (Figs.  177,  178,  179,  186) 

Tliis  grou]i  consists  of  those  muscles  Avhich  connect  the  thoracic  limb  with 
the  head,  neck,  and  trunk.  The  group  naturally  falls  into  two  divisions — dorsal 
and  ventral. ■ 

A.  Dorsal  Division 

This  division  consists  of  two  la>(M-s  which  overlie  the  ])ro]ier  muscles  of  the 
neck  and  back. 

First  Layer 

1.  Trapezius. — This  is  a  flat,  triangular  muscle,  the  base  of  the  triangle 
corresponding  with  the  spine.  It  is  divided  liy  an  ai)oneiirotic  portion  into  two 
divisions: 

(a)  Trapezius  cervicalis. — Origin. — The  funicular  portion  of  the  ligamentum 
nuchcB,  from  the  second  cervical  to  the  third  thoracic  vertebra. 

Insertion. — The  spine  of  the  scapula  and  the  fascia  of  the  shoulder  and  arm. 

1  The  obliquity  of  the  tendon  and  the  angle  which  it  forms  with  the  pelvic  floor  are  of  clinical 
importance  in  regard  to  manipulation  of  the  foetus  in  obstetrical  cases.  The  slope  varies  in 
different  subjects.     In  some  ca.ses  the  tendon  forms  about  a  right  angle  with  the  pubic  bones. 

•The  terms  dorsal  and  ventral  are  here  used  in  the  topographic  and  not  in  the  morpho- 
logical sense.     All  the  muscles  of  the  group  are  ventral  in  the  latter  sen.se. 


THE    .MUSCLES    OF    THE    SHOULDER    GIRDLE  251 

(b)  Trapezius  thoracalis  s.  dorsalis.—O?- /<///(. — The  supraspinous  ligament, 
from  the  third  to  the  tentii  thoraeic  vertebra. 

Insertion. — The  tubercle  of  the  spine  of  the  scapula. 

Action. — Acting  as  a  whole,  to  elevate  the  shoulder;  the  cervical  portion 
draws  the  scapula  forward  and  upward  and  the  thoracic  portion  draws  it  backward 
and  upward. 

Structure. — The  muscle  arises  by  a  short,  thin  aponeurosis,  from  which  the 
fibers  of  the  fiat  fleshy  portion  converge  to  the  spine  of  the  scapula  and  the  apo- 
neurosis which  separates  the  two  portions.  The  cervical  fascia  joins  the  ventral 
edge  of  the  cervical  portion  to  the  mastoido-humeralis,  or  the  two  muscles  may 
unite  here. 

Relations. — Superficially,  the  skin  and  fascia;  deeply,  the  rhomboideus, 
latissimus  dorsi,  supraspinatus,  infraspinatus,  deltoid,  splenius,  serratus  niagnus, 
ami  anterior  deep  pectoral  muscles,  and  the  cartilage  of  the  scapula. 

Blood-supply. — Deep  cervical  and  intercostal  arteries. 

Nerve-supply. — Spinal  accessory  nerve. 

Second  Lai-er 

This  consists  of  two  muscles — the  rhomboideus  and  the  latissimus  dorsi. 

2.  Rhomboideus. — This  consists  of  two  portions: 

(a)  Rhomboideus  cervicalis  s.  cervicis. — Origin. — The  funicular  portion  of 
the  ligainentum  nuchiP,  from  the  second  cervical  to  the  second  thoracic  vertebra. 

Insertion. — The  internal  surface  of  the  cartilage  of  the  scapula. 

(b)  Rhomboideus  thoracalis  s.  dorsalis. — Origin. — The  spinous  processes 
of  the  second  to  the  seventh  thoracic  vertebra  by  means  of  the  dorso-scapular 
ligament. 

Insertion. — The  inner  surface  of  the  cartilage  of  the  scapula. 

Action. — To  draw  the  scapula  upward  and  forward.  When  the  limb  is 
fixed  the  cervical  portion  will  elevate  the  neck. 

Structure. — The  cervical  portion  is  narrow,  pointed  at  its  anterior  extremity, 
and  lies  along  the  funicular  part  of  the  ligamentum  nuchse,  to  which  it  is  attached 
by  short  tendon  bundles.  The  fibers  are  directed  for  the  most  part  longitudinally. 
The  thoracic  portion  is  quadrilateral  in  shape,  and  its  fibers  are  nearly  vertical. 
Its  deep  face  is  intimately  attached  to  the  dorso-scapular  ligament. 

Relations. — Superficially,  the  skin  and  fascia  (over  a  small  area),  the  trape- 
zius, and  the  cartilage  of  the  scapula;  deeply,  the  dorso-scapular  ligament,  the 
splenius,  complexus,  longissimus  dorsi,  and  serratus  anticus. 

Blood-supply. — Dorsal  and  superior  cervical  arteries. 

Nerve-supply. — Sixth  cervical  nerve. 

3.  Latissimus  Dorsi. — This  is  a  wide  nmscle  which  has  the  form  of  a  right- 
angled  triangle.  It  lies  for  the  most  part  under  the  skin  and  panniculus,  on  the 
lateral  wall  of  the  thorax,  from  the  spine  to  the  arm. 

Origin. — The  lumbo-dorsal  fascia — and  by  this  means  from  the  lum])ar  and 
thoracic  spines  as  far  forward  as  the  highest  point  of  the  withers. 

Insertion. — The  internal  tubercle  of  the  humerus,  in  common  with  the  teres 
major. 

Action. — To  draw  the  humerus  upward  and  backward  and  flex  the  shoulder- 
joint.     If  the  limb  is  advanced  and  fixed,  it  draws  the  trunk  forward. 

Structure. — The  muscle  arises  by  a  wide  aponeurosis,  which  fuses  with  that 
of  the  serratus  posticus  and  with  the  lumbo-dorsal  fascia.  The  muscular  portion 
is  at  first  rather  thin,  but  by  the  convergence  of  its  fibers  becomes  thicker  as  it 
approaches  the  arm.  The  anterior  fibers  pass  almost  vertically  downward  over 
the  dorsal  angle  of  the  scapula  and  its  cartilage.     The  posterior  fibers  are  directed 


252  FASCI.E    AND    MUSCLES    OF    THE    HORSE 

downward  and  forward.  Tlie  thick  belly  formed  by  the  convergence  of  these 
passes  under  the  triceps  to  end  on  the  fiat  tcntlon  of  insertion,  which  is  common 
to  this  muscle  and  the  teres  major. 

Blood-supply. — Subscapular,  intercostal,  and  lumbar  arteries. 

Nerve-supply. — Brachial  plexus  (eighth  cervical  and  dorsal  roots). 

B.  Ventral  Division 

1.  Mastoido-humeralis  {M.  brachiocephalicus;  levator  humeri). — This 
muscle  extends  along  the  side  of  the  neck  from  the  head  to  the  arm.  It  is 
incompletely  divisil)le  into  two  portions. 

Origin. — (1)  The  mastoid  process  of  the  petrous  temporal  bone  and  the 
occipital  crest;  (2)  the  wing  of  the  atlas  and  the  transverse  processes  of  the  second, 
third,  and  fourth  cervical  vertebrse. 

Insertion. — The  deltoid  tuberosity  and  the  curved  rough  line  which  extends 
from  this  to  the  distal  extremity  of  the  humerus. 

Action. — When  the  head  and  neck  are  fixed,  to  draw  the  limb  forward,  ex- 
tending the  shoulder  joint.  When  the  limb  is  fixed,  to  extend  the  head  and  neck, 
if  the  muscles  act  together;  acting  separately,  to  incline  the  head  and  neck  to 
the  same  side. 

Structure. — As  already  mentioned,  the  muscle  is  capable  of  incomplete 
division  into  two  parts,  the  line  of  division  being  indicated  by  the  emergence  of 
superficial  branches  of  the  ventral  divisions  of  the  cervical  nerves.  The 
mastoid  portion  (M.  cleido-mastoideus)  partly  overlaps  the  other  portion  (M. 
cleido-transversarius),  which  lies  dorsal  to  it.  The  former  is  attached  to  the 
mastoid  process  and  the  occipital  bone  by  a  broad  tendon  which  fuses  with  that 
of  the  splenius  and  trachelo-mastoideus;  it  is  also  attached  to  the  tendon  of  in- 
sertion of  the  sterno-cephalicus  by  aponeurosis.  The  dorsal  portion  is  attached 
to  the  transverse  processes  by  four  fleshy  digitations.  The  belly  of  the  muscle 
is  adherent  superficially  to  the  cervical  fascia  and  the  panniculus,  and  deeply 
to  the  subscapulo-hyoideus.  In  front  of  the  shoulder  its  deep  face  is  marked 
by  a  tendinous  intersection  of  variable  development.'  Here  the  muscle  becomes 
wider,  covers  the  shoulder  joint,  passes  between  the  brachialis  and  biceps,  and  is 
inserted  by  means  of  a  wide  tendon  which  it  shares  with  the  superficial  pectoral 
muscle. 

Relations. — Superficially,  the  skin,  cervical  fascia,  the  parotid  gland,  the  pan- 
niculus, brachialis,  and  branches  of  the  cervical  nerves;  deeply,  the  splenius, 
trachelo-mastoideus,  rectus  capitis  anterior  major,  omo-hyoideus,  serratus  mag- 
nus,  anterior  deep  pectoral  and  biceps  muscles,  the  inferior  cervical  artery,  the 
prescapular  lymph-glands,  and  branches  of  the  cervical  nerves.  The  ventral 
edge  of  the  muscle  forms  the  dorsal  boundary  of  the  jugular  furrow.  The  dorsal 
border  may  be  in  contact  with  the  cervical  trapezius,  or  separated  from  it  by  a 
variable  interval. 

Blood-supply. — Inferior  cervical,  carotid,  and  vertebral  arteries. 

Nerve-supply. — Spinal  accessory  and  cervical  nerves. 

The  pectoral  fascia  is  a  thin  membrane  covering  the  surface  of  the  pectoral 
muscles,  to  which  it  is,  for  the  most  part,  pretty  intimately  attached.  It  de- 
taches a  layer  which  passes  between  the  superficial  and  deep  pectorals.  At  the 
posterior  edge  of  the  triceps  another  layer  is  given  off,  which  passes  on  the  outer 
surface  of  this  muscle  to  blend  with  the  scapular  fascia;  the  deeper  layer  becomes 
continuous  with  the  subscapular  and  cervical  fasciis. 

The  pectoral  muscles  form  a  large  fleshy  mass  which   occupies  the  space 

'  This  is  regartied  as  a  vestige  of  the  clavicle.  On  this  basis  tlie  portion  of  the  muscle  from 
the  vestige  to  the  arm  represents  the  clavicular  part  of  the  deltoid  of  man. 


VENTRAL    DIVISION  253 

between  the  ventral  part  of  the  chest-wall  and  the  shoulder  and  arm.  They  are 
clearly  divisible  into  a  superficial  and  a  deep  layer.  The  superficial  layer  may  be 
subdivided  into  two  portions  by  careful  dissection;  the  deep  layer  is  clearly  made 
up  of  two  muscles. 

2.  Superficial  pectoral   (M.  pectoralis  superficialis). 

(a)  Anterior  superficial  pectoral  (portio  clavicularis  s.  descendens;  pectoralis 
anticus). — This  is  a  short,  thick,  somewhat  rounded  muscle,  which  extends  between 
the  anterior  part  of  the  sternum  and  the  front  of  the  arm.  It  forms  a  distinct  pro- 
minence on  the  front  of  the  breast,  which  is  easily  recognized  in  the  living  animal. 

Origin. — The  cariniform  cartilage  of  the  sternum. 

Insertion. — (1)  The  curved  line  of  the  humerus  with  the  mastoido-humeralis; 
(2)  the  fascia  of  the  arm. 

Action. — To  adduct  and  advance  the  limb. 

Structure. — The  belly  of  the  muscle  is  convex  on  its  superficial  face,  but 
deeply  it  is  flattened  where  it  overlaps  the  posterior  superficial  pectoral.  Here 
the  two  muscles  are  usually  pretty  intimately  attached  to  each  other,  and  care 
must  be  exercised  in  making  the  separation.  The  tendon  of  insertion  blends  with 
that  of  the  mastoido-humeralis  and  with  the  fascia  of  the  arm.  At  the  middle 
line  of  the  breast  a  furrow  occurs  between  the  two  muscles;  lateralh',  another 
furrow,  containing  the  cephalic  vein,  lies  between  the  muscle  and  the  mastoido- 
humeralis. 

Relations. — Superficially,  the  skin,  fascia,  and  panniculus;  deeply,  the  pos- 
terior division,  the  deep  pectoral,  and  the  biceps.  The  cephalic  vein  lies  in  the 
groove  between  this  muscle  and  the  mastoido-humeralis. 

(b)  Posterior  superficial  pectoral  (portio  sternocostalis;  pectoralis  trans- 
versus). — This  is  a  ^\ide  muscular  sheet  which  extends  from  the  ventral  edge  of 
the  sternum  to  the  fascia  on  the  inner  surface  of  the  forearm. 

Origin. — (1)  The  ventral  edge  of  the  sternum  as  far  back  as  the  sixth  car- 
tilage;  (2)  a  fibrous  raphe  common  to  the  two  muscles. 

Insertion. — (1)  The  fascia  on  the  proximal  third  of  the  forearm;  (2)  the 
curved  line  of  the  humerus  with  the  preceding  muscle. 

Action. — To  adduct  the  limb  and  to  tense  the  fascia  of  the  forearm. 

Structure. — It  is  thin  and  pale,  and  mixed  with  a  good  deal  of  fibrous  tissue. 
The  right  and  left  muscles  fuse  at  a  median  fibrous  raphe.  The  tendon  of  inser- 
tion unites  with  the  fascia  on  the  inner  side  of  the  forearm  for  the  most  part; 
only  a  small  part  in  front,  about  an  inch  in  width,  is  attached  to  the  humerus. 

Relations. — Superficially,  the  skin,  fascia,  and  the  preceding  muscle;  deeply, 
the  deep  pectoral,  the  biceps,  and  the  brachialis;  at  the  elbow,  the  posterior 
radial  vessels,  the  median  nerve,  and  the  inner  and  middle  flexors  of  the  carpus. 

.3.  Deep  pectoral  (M.  pectoralis  profundus). — This  muscle  is  much  thicker 
and  more  extensive  in  the  horse  than  the  superficial  pectoral.  It  consists  of 
two  distinct  portions. 

(a)  Anterior  deep  pectoral  (portio  prescapularis;  pectoralis  parvus). — 
This  division  is  prismatic  and  extends  from  the  anterior  part  of  the  lateral  sur- 
face of  the  sternum  to  the  cervical  angle  of  the  scapula. 

Origin. — The  anterior  half  of  the  lateral  surface  of  the  sternum  and  the 
cartilages  of  the  first  four  ribs. 

Insertion. — The  aponeurosis  which  covers  the  supraspinatus  at  its  dorsal 
end,  and  the  scapular  fascia. 

Action. — To  adduct  and  retract  the  limb;  when  the  limb  is  advanced  and 
fixed,  to  draw  the  trunk  forward. 

Structure. — The  muscle  is  almost  entirely  fleshy.  It  describes  a  curve  (con- 
vex anteriorly),  passing  at  first  forward,  then  upward  over  the  front  of  the  shoulder, 
a  little  to  its  inner  side,  and  finally  upward  and  backward  along  the  anterior 


254  FASCLE    AND    MUSCLES    OF    THE    HORSE 

liorder  of  the  supraspinatus.  It  is  loosely  attached  to  the  latter  muscle,  and 
terminates  in  a  pointed  end  which  becomes  more  firmly  attached  near  the  cer- 
vical angle  of  the  scapula. 

Relations. — Superficially,  the  skin  and  fascia,  the  panniculus,  superficial  pec- 
toral, trapezius,  and  mastoido-humeralis  muscles,  the  cephalic  vein,  and  the 
inferior  cervical  artery;  deeply,  the  posterior  deep  pectoral,  biceps,  supraspi- 
natus, omo-hyoideus,  and  serratus  magnus  muscles,  the  brachial  vessels,  and  the 
branches  of  the  brachial  plexus  of  nerves. 

(b)  Posterior  deep  pectoral  (portio  humeralis  s.  ascendens;  pectoralis 
magnus). — This  is  much  the  largest  of  the  pectoral  group  in  the  horse.  It  is 
somewhat  triangular  or  fan-shaped. 

Origin. — (1)  The  abdominal  tunic;  (2)  the  xiphoid  cartilage  and  ventral 
aspect  of  the  sternum;   (3)  the  cartilages  of  the  fourth  to  the  ninth  ribs. 

Insertion. — (1)  The  internal  tuberosity  of  the  humerus;  (2)  the  external  lip 
of  the  bicipital  groove;    (3)  the  tendon  of  origin  of  the  coraco-brachialis. 

Action. — To  adduct  and  retract  the  limb;  if  the  limb  is  advanced  and  fixed, 
to  draw  the  trunk  forward. 

Structure. — This  muscle  is  also  almost  entirely  fleshy.  Its  posterior  part  is 
wide  and  thin,  but  as  the  muscle  is  traced  forward,  it  becomes  narrower  and  much 
thicker.  It  passes  forward  and  slightly  upward  in  a  gentle  curve  to  its  insertion. 
The  humeral  insertion  is  just  below  that  of  the  inner  division  of  the  supraspi- 
natus. Part  of  the  fibers  are  inserted  by  means  of  a  tendinous  band  which  binds 
down  the  tendon  of  the  biceps  and  is  attached  to  the  external  lip  of  the  bici]>ital 
groove,  and  a  small  part  is  attached  to  the  tendon  of  origin  of  the  coraco-brachialis. 

Relations. — Superficially,  the  skin,  panniculus,  and  superficial  pectoral; 
deeply,  the  abdominal  tunic,  the  external  oblique,  the  rectus  abdominis  et  thoracis, 
the  brachial  vessels,  and  branches  of  the  brachial  plexus  of  nerves.  The  external 
thoracic  vein  lies  along  the  outer  or  upper  border. 

Blond-supply. — Internal  and  external  thoracic,  inferior  cervical,  anterior 
circumflex,  and  intercostal  arteries. 

Nervc-supplij. — Pectoral  (or  thoracic)  nerves,  from  the  brachial  plexus. 

4.  Serratus  magnus  (AI.  serratus  ventralis). — This  is  a  large,  fan-shaped 
muscle,  situated  on  the  lateral  surface  of  the  neck  and  thorax.  It  derives  its 
name  from  the  serrated  ventral  edge  of  its  thoracic  portion.  It  consists  of  a 
cervical  and  a  thoracic   portion. 

(a)  Cervical  part  (M.  serratus  cervicis;  levator  scapulae  hominis). 
Origin. — The  transverse  processes  of  the  last  four  or  five  cervical  vertebrae. 
Insertion. — The  anterior  triangular  area  on  the  costal  surface  of  the  scapula 

and  the  adjacent  iiart  of  the  cartilage. 

(b)  Thoracic    part    (M.  serratus  thoracis;   serratus  anterior  hom.inis). 
Origin. — The  external  surfaces  of  the  first  eight  or  nine  ribs. 

Insertion. — The  posterior  triangular  area  on  the  costal  surface  of  the  scapula 
and  the  adjacent  part  of  the  cartilage. 

Action. — The  two  muscles  form  a  sort  of  sling  in  which  the  trunk  is  sus- 
pended. (Contracting  together,  they  raise  the  thorax;  contracting  singly,  the 
weight  is  shifted  to  the  limb  on  the  side  of  the  muscle  acting.  The  two  parts 
can  contract  separately  and  are  antagonistic  in  their  action  on  the  scapula. 
The  cervical  part  draws  the  base  of  the  scapula  toward  the  neck,  while  the  thoracic 
part  has  the  opposite  action;  these  effects  concur  in  the  backward  and  for- 
ward swing  of  the  limb  respectively.  With  the  limb  fixed,  the  cervical  part 
extends  (raises)  the  neck  or  inclines  it  laterally.  The  thoracic  part  may  act  as  a 
muscle  of  forced  inspiration. 

Structure.  —  In  the  domesticated  animals  there  is  no  such  clear  division  of 
the  muscle  as  is  found  in  man  and  the  apes.     On  account  of  the  difference  in 


THE    MUSCLES    OF    THE    SHOULDER — -EXTERNAL    GROUP  255 

action,  however,  it  seems  desirable  to  distinguish  the  two  portions.  The  cer- 
vical part  is  thick  and  almost  entirely  fleshy.  The  thoracic  part  has  on  its 
superficial  face  a  thick,  tendinous  layer  which  may  sustain  the  weight  of  the 
trunk  when  the  muscle  substance  relaxes.  The  ventral  edge  presents  distinct 
digitations,  the  last  four  of  which  alternate  with  those  of  the  obliquus  externus 
abdominis,  and  are  covered  by  the  abdominal  tunic.  The  fourth,  fifth,  and  sixth 
digitations  extend  nearly  to  the  distal  ends  of  the  ribs.  The  last  digitation  is 
small  and  may  be  absent.  Exceptionally  additional  digitations  may  be  attached 
to  the  tenth  or  eleventh  rib  or  to  the  fascia  over  the  intercostal  muscles.  The 
fibers  converge  to  the  insertion,  which  is  thick  and  is  intersected  by  elastic  1am- 
elliP  derived  from  the  dorso-scapular  ligament. 

Relations. — Superficially,  the  mastoido-humeralis,  trapezius,  deep  pectoral, 
subscapularis,  teres  major,  latissimus  clorsi,  panniculus  carnosus,  the  abdominal 
tunic,  the  brachial  vessels,  and  .the  long  thoracic  nerve;  deeply,  the  splenius, 
eomplexus,  longissimus.  transversalis  costarum,  the  ribs  and  external  intercostal 
muscles,  and  branches  of  the  superior  cervical  and  dorsal  arteries. 

Blood-supply. — Superior  cervical,  dorsal,  vertebral,  and  intercostal  arteries. 

Nerve-supply. — Brachial  plexus. 


II.  THE  MUSCLES  OF  THE  SHOULDER 

Under  this  head  will  be  described  those  muscles  which  arise  on  the  scapula 
and  end  on  the  arm;  they  may  be  divided  into  two  groups — one  covering  the 
dorsum,  the  other  the  venter  of  the  scapula. 

The  superficial  fascia  of  the  shoulder  and  arm  contains  the  panniculus  carno- 
sus of  this  region,  and  may  be  considered  to  be  continued  on  the  inner  side  of  the 
limb  by  the  subscapular  fascia. 

The  thoracic  or  scapulo-humeral  portion  of  the  panniculus  CSl.  cutaneus 
scapulse  et  humeri)  arises  by  a  thin  aponeurosis  from  the  ligamentum  nuchae  at 
the  withers.  The  fleshy  portion  begins  over  the  upper  part  of  the  scapula  and 
extends  to  the  elbow.  Its  fibers  have  in  general  a  dorso-ventral  direction.  It  is 
continuous  behind  with  the  abdominal  portion. 

The  deep  fascia  of  the  shoulder  and  arm  (Fa.scia  omobrachialis)  is  much  more 
developed  and  important.  It  is  strong  and  tendinous,  and  is  intimately  adherent 
to  the  muscles  on  the  outer  surface  of  the  scapula,  between  which  it  detaches 
intermuscular  septa,  which  are  attached  to  the  spine  and  borders  of  the  scapula. 
The  brachial  portion  is,  for  the  most  part,  only  loosely  attached  to  the  underly- 
ing muscles,  for  which  it  forms  sheaths;  it  is  attached  to  the  humerus,  especially 
to  the  lips  of  the  bicipital  groove  and  the  deltoid  tuberosity.  It  blends  distally 
with  the  tendon  of  insertion  of  the  biceps,  and  is  continued  by  the  antibrachial 
fascia. 

A.  External  Group   Figs.  «78,  179^ 

1.  Deltoid  CSl.  deltoideus;  long  abductor  of  the  arm;  scapular  portion  of 
the  deltoid  of  man).— This  lies  partly  on  the  triceps  in  the  angle  between  the 
scapula  and  humerus,  partly  on  the  infraspinatus  and  teres  minor. 

Origin.— (1)  The  upper  part  of  the  posterior  border  of  the  scapula:  (2)  the 
spine  of  the  scapula,  by  means  of  the  strong  aponeurosis  which  covers  the  infra- 
spinatus. 

/«.se/-((on.— The  deltoid  tuberosity  of  the  humerus. 

Action.— To  flex  the  shoulder  joint  and  abduct  the  arm. 

Structure.— The  origin  of  the  muscle  is  partly  aponeurotic,  partly  fleshy. 
The  aponeurosis  fuses  with  that  of  the  infraspinatus;  the  posterior  part  is 
attached  to  the  scapula  immediately  in  front  of  the  origin  of  the  long  head  of  the 


256  FASCI.B    AND    MUSCLES    OF    THE    HORSE 

triceps.  The  belly  of  the  mviscle  lies  for  the  most  part  in  a  cavity  formed  in 
the  triceps.     It  is  widest  about  its  middle. 

Relations. — Superficially,  the  skin,  fascia,  pannieulus,  and  mastoido-humoralis; 
deeply,  the  infraspinatus,  teres  minor,  triceps,  and  brachialis  muscles,  and 
branches  of  the  posterior  circumflex  artery  and  axillary  nerve. 

Blood-supply. — Subscapular  artery  (chiefly  through  the  posterior  circumflex). 

Nerve-supph/. — Suprascapular  and  axillary  nerves. 

2.  Supraspinatus. — This  muscle  occupies  the  supraspinous  fossa,  which  it 
fills,  and  beyond  which  it  extends,  thus  coming  in  contact  with  the  subscapularis. 

Origin. — The  supraspinous  fossa,  the  spine,  and  the  lower  part  of  the  car- 
tilage of  the  scapula. 

Insertion. — The  inner  and  outer  lips  of  the  bicipital  groove. 

Action. — To  extend  the  shoulder  joint.  It  also  assists  in  preventing  dis- 
location. 

Structure. — The  surface  of  the  muscle  is  covered  by  a  strong  aponeurosis, 
from  the  deep  face  of  which  many  fibers  arise.  The  muscle  is  thin  at  its  origin 
from  the  cartilage,  but  becomes  considerably  thicker  below.  At  the  neck  of  the 
scapula  it  divides  into  two  branches,  between  which  the  tendon  of  origin  of  the 
biceps  emerges.  These  branches,  fleshy  superficially,  tendinous  deeply,  are 
inserted  into  the  lips  of  the  bicipital  groove.  They  are  united  by  a  fibrous  mem- 
brane already  mentioned  in  connection  with  the  deep  pectoral  muscle;  some 
fibers  are  attached  to  this  membrane  and  the  capsule  of  the  shoulder  joint. 

Relations. — Superficially,  the  skin,  fascia,  pannieulus,  trapezius,  and  mas- 
toido-humeralis;  deeply,  the  scapula  and  its  cartilage,  the  subscapularis  muscle, 
and  the  suprascapular  vessels  and  nerve;  in  front,  the  anterior  deep  pectoral 
muscle;   behind,  the  spine  of  the  scapula  and  infraspinatus  muscle. 

Blood-supphj. — Suprascapular  and  posterior  circumflex  arteries. 

Nerve-supply. — Suprascapular  nerve. 

3.  Infraspinatus. — This  muscle  occupies  the  greater  part  of  the  infraspinous 
fossa. 

Origin. — The  infraspinous  fossa  and  the  scapular  cartilage. 

Insertion. — (1)  The  outer  tuberosity  of  the  humerus,  distal  to  the  outer 
insertion  of  the  supraspinatus;    (2)  the  posterior  eminence  of  the  outer  tuberosity. 

Action. — To  abduct  the  arm  and  rotate  it  outward.'  It  also  plays  the  part 
of  a  lateral  ligament. 

Structure. — This  muscle  is  also  covered  by  a  strong  aponeurosis,  from  which 
many  fibers  arise,  and  by  means  of  which  the  deltoid  is  attached  to  the  spine  of 
the  scapula.  A  thick  tendinous  layer  partially  divides  the  muscle  into  two  strata, 
and,  coming  to  the  surface  at  the  shoulder  joint,  constitutes  the  chief  means  of 
insertion.  This  tendon,  an  inch  or  more  (3  cm.)  in  width,  passes  over  the  posterior 
eminence  of  the  external  tuberosity  of  the  humerus;  it  is  bound  down  by  a  fibrous 
sheet,  and  a  synovial  bursa  is  interposed  between  the  tendon  and  the  lione.  When 
the  long  insertion  is  cut  and  reflected,  the  short  insertion,  partly  tendinous,  partly 
fleshy,  is  exposed. 

Relations. — Superficially,  the  skin,  fascia,  pannieulus,  trapezius,  and  deltoid; 
deeply,  the  scapula  and  its  cartilage,  the  shoulder  joint  and  capsule,  the  long 
head  of  the  triceps,  the  teres  minor,  and  the  nutrient  artery  of  the  scapula. 

Blood-supply. — Subscapular  artery. 

Nerve-supply. — Suprascapular  and  axillarj^  nerves. 

4.  Teres  minor. — This  is  a  much  smaller  muscle  than  the  foregoing.  It 
lies  chiefly  on  the  triceps,  under  cover  of  the  deltoid  and  infraspinatus. 

Origin. — (1)  The  rough  lines  on  the  distal  and  posterior  part  of  the  infra- 

'  Giinther  states  that  this  muscle  assists  in  extension  or  flexion  according  to  tlie  position 
of  the  head  of  the  humerus  relative  to  the  glenoid  cavity. 


INTERNAL    GROUP 


257 


#/•/ 


spinous  fossa;    (2)  a  small  part  of  the  posterior  border  of  the  scapula,  about  its 
middle;    (3)  a  tubercle  near  the  rim  of  the  glenoid  artery. 

Insertion. — The  deltoid  tuberosity  and  a  small  area  just  above  it. 

Action. — To  flex  the 
shoulder  joint  and  to  ab- 
duct the  arm;  also  to  assist 
in  outward  rotation. 

Structure. — The  muscle 
is  not  rounded  in  the  horse 
and  ox,  but  flat  and  triangu- 
lar. Its  origin  from  the  pos- 
terior border  of  the  scapula 
is  by  means  of  an  aponeu- 
rosis which  also  gives  origin 
to  fibers  of  the  infraspinatus 
and  triceps.  A  bursa  is 
commonly  found  between 
the  terminal  part  of  the 
muscle  and  the  capsule  of 
the  shoulder  joint,  and  is 
often  continuous  with  that 
of  the  infraspinatus. 

Relations.  —  Superfici- 
ally, the  deltoid  and  infra- 
spinatus muscles;  deejjly, 
the  scapula,  the  shoulder 
joint,  and  the  triceps  mus- 
cle. 

Blood-supphj.  —  Sub- 
scapular artery  (circumflex 
branches). 

Xerve-supphj.  —  Axil- 
lary nerve. 


Coraco-brachialis- 
Biceps  brachii 

Brack  talis  ■ 
Exhnsor  carpi  radicdis 


..Tendon  of  tensor 
fascia'  antibrachii 


Flexor  carpi  me- 
diiis 

..Flexor  carpi  in- 
tern us 


Tendon  of  extensor  carpi — ! 
obligtius 


Deep  flexor  tendon 
■  Check  ligament 


Suspensory  ligament-..^ 

Anterior  extensor  tendon — - 
Branch  of  suspensory  ligament- 


Superficial  flexor 
tendon 


( 


B.  Internal  Group 

1.  Subscapularis. — 
This  muscle  occupies  the 
subscapular  fossa,  beyond 
which,  however,  it  extends 
both  before  and  behind. 

Origin. — The  subscap- 
ular fossa. 

Insertion. — The  poste- 
rior eminence  of  the  internal 
tuberosity  of  the  humerus. 

Action. — To  adduct  the 
humerus. 

Structure. — The  muscle 
is  flat  and  triangular,  with 

the  base  upward.  The  latter  is  thin  and  interdigitates  with  the  scapular  attach- 
ments of  the  serratus.  Below  this  the  belly  thickens  and  becomes  narrower.  It 
is  covered  by  an  aponeurosis,  and  contains  a  considerable  amount  of  tendinous 
tissue.  The  tendon  of  insertion  is  crossed  by  the  tendon  of  origin  of  the  coraco- 
brachialis;  it  is  intimately  adherent  to  the  capsule  of  the  shoulder  joint,  and 
17 


Fig. 


MrscLES  OF  Thoracic  Limb  of  Horse,  Ixtehnai.  View. 
S,  4.  Rhomboideus;  5,  latissimus  dorsi;  S,  posterior  deep  pecto- 
ral; 9,  anterior  deep  pectoral;  11,  supraspinatus;  13,  subscapularis;  16, 
teres  major;  20.  long  head  of  triceps;  33a.  3£b,  tensor  fascia?  antibrachii; 
33.  internal  head  of  triceps.     (After  EUenberger,  in  Leisering's  .\tla3.) 


258  FASCI.'E    AND    MUSCLES    OF    THE    HORSE 

may  be  regarded  as  replaeing  the  internal  ligament  of  the  latter.  A  small  bursa 
may  occur  here. 

Relations. — Superficially,  the  scapula  and  shoulder  joint,  the  supraspinatus, 
triceps,  and  teres  major  muscles;  deeply,  the  serratus  magnus  muscle,  the  bra- 
chial vessels,  and  the  chief  branches  of  the  brachial  plexus.  The  subscapular 
vessels  run  along  or  near  the  posterior  edge  of  the  muscle. 

Blnod-supply. — Subscapular  artery. 

Ncrpc-mipplji. — Subscapular  nerves  (from  the  brachial  plexus). 

2.  Teres  major  (Teres  internus;  adductor  of  the  arm). — This  muscle  is  flat, 
widest  about  its  middle,  and  lies  chiefly  on  the  deep  face  of  the  triceps. 

Origin. — The  dorsal  angle  and  the  adjacent  part  of  the  posterior  border  of 
the  scapula. 

Insertion. — The  tubercle  on  the  inner  surface  of  the  shaft  of  the  humerus,  in 
common  with  the  latissimus  dorsi. 

Action. — To  flex  the  shoulder  joint  and  adduct  the  arm. 

Structure. — It  is  for  the  most  part  fleshy,  but  the  origin  consists  of  an  apo- 
neurosis which  blends  with  that  of  the  tensor  fasciie  antibrachii.  The  insertion 
is  by  a  flat  tendon  which  fuses  with  that  of  the  latissimus  dorsi. 

Relations. — Superficially,  the  triceps,  infra.spinatus,  and  deltoid  muscles; 
deeply,  the  serratus  magnus  muscle.  The  suliscapular  vessels  lie  in  a  groove 
between  the  anterior  edge  of  this  muscle  and  the  posterior  border  of  the  subscapu- 
laris;  near  the  shoulder  joint  the  posterior  circumflex  artery  and  the  axillary 
nerve  emerge  between  the  two  muscles.  The  deep  face  of  the  muscle  is  crossed 
by  the  thoracic  branches  of  the  brachial  plexus,  and  by  the  branch  of  the  subscap- 
ular artery  which  supplies  the  latissimus  dorsi. 

Blood-supply. — Subscapular  artery. 

Nerve-supply. — Axillary  nerve. 

3.  Coraco-brachialis  (Coraco-humeralis). — This  muscle  lies  on  the  inner  sur- 
face of  the  shoulder  joint  and  the  arm. 

Origin. — The  coracoid  process  of  the  scapula. 

Insertion. — (1)  A  small  area  above  the  internal  tubercle  of  the  humerus; 
(2)  the  middle  third  of  the  anterior  surface  of  the  humerus. 

Action. — To  adduct  the  arm  antl  to  flex  the  shoulder  joint. 

Structure. — The  long  tendon  of  origin  emerges  between  the  subscapularis 
and  the  inner  branch  of  the  supraspinatus.  It  ]iasses  over  the  terminal  part  of 
the  subscapularis  and  is  provided  with  a  synovial  sheath.  The  muscular  part 
spreads  out  and  divides  into  two  portions.  The  smaller  and  shorter  portion  is 
inserted  into  the  proximal  third  of  the  shaft  of  the  humerus,  close  to  the  origin 
of  the  lateral  head  of  the  triceps;  the  larger  and  longer  portion  is  inserted  into  the 
middle  third  of  the  humerus,  in  front  of  the  internal  tubercle  and  the  inner  head 
of  the  triceps. 

Relations. — Externally,  the  subscapularis  muscle  and  the  humerus;  inter- 
nally, the  deep  pectoral  and  brachialis  muscles.  The  anterior  circumflex  artery 
and  the  nerve  to  the  biceps  usually  emerge  between  the  two  insertions,  and  the 
l)rachial  vessels  lie  along  the  posterior  border  of  the  muscle. 

Blood-supply. — Anterior  circumflex  artery. 

A^eri'e-supply. — Musculo-cutaneous  nerve. 

4.  Capsularis  (Scapulo-humeralis  posticus  s.  gracilis). — This  is  a  very  small 
muscle,  which  lies  on  the  back  of  the  capsule  of  the  shoulder  joint. 

Origin. — The  scapula,  close  to  the  rim  of  the  glenoid  cavity. 

Insertion. — The  posterior  surface  of  the  shaft  of  the  humerus,  a  short  ilistance 
below  the  head. 

Action. — It  may  perhaps  tense  the  capsule  of  the  shoulder  joint  and  prevent 
its  being  pinched  during  flexion. 


THE    MUSCLES    OF   THE    ARM 


259 


Structure. — It  is  fleshy  and  usually  about  the  breadth  of  a  finger.  It  may, 
however,  consist  of  only  a  few  bundles  of  fibers;  sometimes  it  is  double.  Its 
attachment  to  the  joint  capsule  is  slight.  It  passes  through  the  brachialis  muscle 
to  reach  its  insertion. 

Relations. — Superficially,  the  teres  minor  and  triceps  muscles;  deeplj',  the 
teres  major  and  subscapularis  muscles,  and  the  capsule  of  the  joint. 

Blood-supply. — Posterior  circumflex  artery. 

Nerve-supply. — Axillary  nerve. 


III.    THE  MUSCLES  OF  THE  ARM 
This  group  consists  of  five  muscles  which  are  grouped  around  the  humerus. 
They  arise  from  the  scapula  and  the  humerus,  and  are  inserted  into  the  forearm. 
They  act  on  the  elbow  joint  and  the  fascia  of  the  forearm. 


Spine  of  scapula 

External  tuberosity  of  humerus  -    /' 

Deltoid  tuberosity  - 
Biceps  brachii  ' 


Infraspinous  fossa 


'  Brachialis 

.  -  Musculo-spiral 


Olecranon 


Fig.  ISS.— Bi. 


„,,,,.  ,    »/  "  ^  ■  External  lateral  ligament  of  clhoic  joint 

Shaft  of  radius  '    "  ' 

"    "/'-  If -~^ 

■  ■  -  -  Shaft  of  ulna 

AND  Bhachiaus  Misci.ES  OF  HoHSE.      (.\fter  Ellenberger-Baum,  Anat.  fiir  Kiinstler.) 


1.  Biceps  brachii  (Coraco-radialis;  flexor  brachii). — This  is  a  strong,  some- 
what rounded  muscle,  which  lies  on  the  anterior  surface  of  the  humerus. 

Origin. — The  tuberosity  of  the  scapula. 

Insertion.— il)  The  bicipital  tuberosity  of  the  radius;  (2)  the  internal  lat- 
eral ligament  of  the  elbow  joint ;  (3)  the  fascia  of  the  forearm  and  the  tendon  of  the 
extensor  carpi  radialis. 

Action.— To  flex  the  elbow  joint,  to  fix  the  shoulder,  elbow,  and  carpus  in 
standing,  and  to  tense  the  fascia  of  the  forearm. 

Structure.— The  muscle  is  inclosed  in  a  double  sheath  of  fascia,  which  is 
attached  to  the  lips  of  the  bicipital  groove  and  the  deltoid  ridge  of  the  humerus. 
The  tendon  of  origin  is  moulded  on  the  bicipital  groove;  it  is  very  strong  and  dense 
and  is  partlv  cartilaginous.  Its  play  over  the  groove  is  facilitated  by  the  large 
bicipital  bursa  (Bursa  intertubercularis).  The  synovial  membrane  covers  not 
only  the  deep  face  of  the  tendon,  but  extends  somewhat  over  the  edges  to  the 
superficial  face.  A  well-marked  tendinous  intersection  runs  through  the  belly 
of  the  muscle  and  divides  distally  into  two  portions.  Of  these,  the  short,  thick 
one  is  inserted  into  the  bicipital  tuberosity  and  detaches  fibers  to  the  mternal 


2G0  FASCLE    AXD    MUSCLKS    OK    THE    HORSE 

lateral  ligament.  The  long  tendon  (Lacertus  fibrosus)  is  thinner,  blonds  with  the 
fascia  of  the  forearm,  and  ends  by  fusing  with  the  tendon  of  the  extensor  carjii 
radial  is. 

Relations. — Externally,  the  mastoido-humeralis  and  brachialis  muscles;  in- 
ternally, the  posterior  deep  pectoral  and  the  superficial  pectoral  muscles;  in  front, 
the  anterior  deep  pectoral  muscle;  liehind,  the  humerus,  the  coraco-brachialis  mus- 
cle, the  anterior  circumflex  and  anterior  radial  vessels,  and  the  musculo-cutaneous 
nerve. 

Blood-supply . — Branches  of  the  brachial  and  anterior  radial  arteries. 

Nerve-supply. — Musculo-cutaneous  nerv(>. 

2.  Brachialis  (Humeralis  obliquus  s.  externus;  brachialis  anticus). — This 
muscle  occupies  the  musculo-spiral  groove  of  the  humerus. 

Origin. — The  proximal  third  of  the  posterior  surface  of  the  humerus. 

Insertion. — The  inner  surface  of  the  neck  of  the  radius  (under  cover  of  the 
lateral  ligament)  and  the  arciform  ligament. 

Action. — To  flex  the  elbow  joint. 

Structure. — The  peculiar  spiral  course  of  this  muscle  gave  rise  to  the  name 
often  applied  to  it — humeralis  obliquus.  Beginning  on  the  posterior  surface  of  the 
shaft,  close  to  the  head  of  the  humerus,  it  winds  over  the  lateral  surface,  crosses  the 
biceps  verj'-  obliquely,  and  finally  reaches  the  inner  side  of  the  forearm  by  passing 
between  the  biceps  and  the  extensor  carpi.  It  is  entirely  fleshy,  with  the  exception 
of  its  relatively  slender  tendon  of  insertion. 

Relations. — Externally  the  skin  and  fascia,  the  teres  minor,  deltoid,  triceps 
(lateral  head),  biceps,  and  mastoido-humeralis  muscles.  The  anterior  radial  artery 
crosses  the  deep  face  of  the  muscle  in  its  distal  third,  and  the  radial  nerve  accom- 
panies the  muscle  in  the  distal  half  of  the  musculo-spiral  groove. 

Blood-supply. — Brachial  artery. 

Xerve-supply. — Radial  nerve. 

3.  Tensor  fasciae  antibrachii  (Fig.  187)'  (Scapulo-ulnaris ;  long  extensor 
of  the  forearm;  accessory  anconeus  of  the  latissimus  dorsi). — This  is  a  thin 
muscle  which  lies  on  the  inner  surface  of  the  triceps. 

Origin. — The  tendon  of  insertion  of  the  latissimus  dorsi  and  the  posterior 
border  of  the  scapula. 

Insertion. — (1)  The  fascia  of  the  forearm ;  (2)  a  small  eminence  on  the  posterior 
border  of  the  olecranon. 

Action. — (1)  To  tense  the  fascia  of  the  forearm  and  to  extend  the  elbow 
joint. 

Structure. — The  origin  consists  of  a  very  thin  ajioneurosis  which  l)lends  with 
those  of  the  caput  longum  and  the  latissimus  dorsi.  The  muscular  portion  is 
quite  thin  in  its  anterior  part,  somewhat  thicker  liehind,  and  is  narrower  than  the 
aponeurotic  origin.  It  is  succeeded  by  an  aponeurotic  insertion,  which  ends  chiefly 
by  l)lending  with  the  fascia  of  the  forearm  a  little  below  the  elbow.  There  is,  how- 
ever, a  small  but  constant  tendinous  attachment  to  the  olecranon. 

Relations. — Externally,  the  panniculus,  triceps  (long  and  internal  heads), 
the  inner  and  middle  flexors  of  the  carpus,  and  the  ulnar  vessels  and  nerve;  in- 
ternall.y,  the  latissimus  dorsi,  serratus  magnus,  and  posterior  pectoral  muscles. 

Blood-supply. — Subscapular,  ulnar,  and  deep  brachial  arteries. 

Nervc-supj)ly. — Radial  nerve. 

4.  Triceps  brachii  (Figs.  178,  179,  187)  (Brachial  triceps;  triceps  extensor 
cubiti). — This,  together  with  the  preceding  muscle,  constitutes  the  large  muscular 

'■  M'Fatlycan  and  ^'auglian  term  this  muscle  the  sca])ulo-ulnaris,  while  .^rloing  and  Lesbre 
term  it  "Ancone  accessoire  du  grand  dorsal."  The  above  name  seems  to  agree  best  witli  tlie 
chief  insertion  and  action,  although  it  certainly  arises  largely  from  the  tendon  of  insertion  of 
the  latissimus  dorsi. 


THE    MUSCLES    OF   THE    ARM  261 

mass  which  fills  the  angle  between  the  posterior  border  of  the  scapula  and  the 
humerus.     It  is  clearly  divisible  into  three  heads,  as  described  below. 

(a)  Long  head  (Caput  iongum  tricipitis;  anconeus  longus;  caput  magnum). 
— This,  the  largest  and  longest  of  the  three  heads,  is  a  powerful,  thick,  triangular 
muscle,  which  extends  from  the  posterior  border  of  the  scapula  to  the  olecranon. 

Origin. — The  posterior  border  of  the  scapula. 

Insertion. — The  outer  and  posterior  part  of  the  summit  of  the  olecranon. 

Action. — (1)  To  extend  the  elbow  joint;   (2)  to  flex  the  shoulder  joint. 

Structure. — The  muscle  arises  by  a  wide,  strong  aponeurosis  from  the  posterior 
border  of  the  scapula.  From  this  the  bundles  of  the  fleshy  portion  converge  to 
the  short,  strong  tendon  of  insertion.  A  careful  examination  will  show  that  the 
muscle  is  penetrated  by  a  tendinous  intersection  from  which  many  fibers  take  origin 
obhquelj-.  The  superficial  face  is  covered  by  an  aponeurosis  which  is  specially 
developed  at  its  distal  part.     A  small  bursa  occurs  under  the  tendon  of  insertion. 

Relations. — Externally,  the  panniculus,  deltoid,  infraspinatus,  teres  minor, 
and  the  external  head;  internally,  the  tensor  fasciae  antibrachii,  teres  major, 
latissimus  dorsi,  and  posterior  deep  pectoral  muscles,  and  the  subscapular  vessels; 
in  front,  the  brachialis,  and  the  inner  head,  the  deep  brachial  and  posterior  circum- 
flex vessels,  and  the  axillary  and  radial  nerves;   behind,  the  skin  and  fascia. 

Blood-supply. — Subscapular  and  deep  brachial  arteries. 

Nerve-supply. — Radial  nerve. 

(b>  External  head  (Caput  laterale  tricipitis  s.  anconeus  laterahs  s.  externus; 
caput  medium). — This  is  a  strong,  quadrilateral  muscle,  which  lies  on  the  outer 
surface  of  the  arm.  Its  proximal  third  is  covered  by  the  deltoid  and  teres  minor 
muscles;    the  remainder  only  bj^  the  thin  panniculus  and  the  skin. 

Origin. — The  deltoid  tuberosity  and  the  curved  rough  line  which  extends  from 
it  to  the  neck  of  the  humerus. 

Insertion. — (1)  A  small  prominent  area  on  the  outer  surface  of  the  olecranon; 
(2)  the  tendon  of  the  long  head. 

Action. — To  extend  the  elbow  joint. 

Structure. — The  origin  consists  of  short  tendinous  fibers.  The  belly  is  thick, 
and  is  composed  of  parallel  bundles  which  are  directed  obliquely  downward  and 
backward.  They  are  inserted  partly  into  the  tendon  of  the  long  head  and  partly 
into  the  olecranon  below  and  in  front  of  that  tendon. 

Relations. — Externally,  the  deltoid,  teres  minor,  and  panniculus  muscles; 
internally,  the  long  and  inner  heads  and  the  brachialis  muscle.  Branches  of  the 
circumflex  vessels  and  axillarj'  nerve  emerge  between  the  posterior  edge  of  the 
muscle  and  the  long  head.  The  deep  face  of  the  muscle  is  related  to  the  branches 
of  the  deep  brachial  artery  and  of  the  radial  nerve. 

Blood-supply. — Posterior  circumflex  and  deep  brachial  arteries. 

N'erve-supply. — Radial  nerve. 

(c)  Internal  head  (Fig.  193)  (Caput  mediale  tricipitis;  anconeus  medialis  s. 
internus;  caput  parvum). — This  is  much  the  smallest  of  the  three  heads.  It  is 
situated  on  the  inner  surface  of  the  arm,  and  extends  from  the  middle  third  of  the 
humerus  to  the  olecranon. 

Origin. — The  middle  third  of  the  inner  surface  of  the  shaft  of  the  humerus, 
behind  and  below  the  internal  tubercle. 

Insertion. — The  inner  and  fore  part  of  the  summit  of  the  olecranon,  between  the 
insertion  of  the  long  head  and  the  origin  of  the  ulnar  head  of  the  flexor  perforans. 

Action. — To  extend  the  elbow  joint. 

Structure. — The  muscle  is  fleshy  except  at  its  insertion,  where  it  has  a  flat 
tendon,  under  which  a  small  bursa  may  be  found. 

Relations. — Externally,  the  humerus,  brachialis,  anconeus,  and  the  cx-tcrnal 
head;    internally,   the   posterior   deep   pectoral,   coraco-brachialis,   teres  major, 


262 


FASCI.E   AND    MUSCLES    OF   THE    HORSE 


latissimus  dorsi,  and  tensor  fasciae  antibrachii  muscles,  the  brachial  and  deep 
brachial  vessels,  and  the  median  and  ulnar  nerves;  behind,  the  long  head,  branches 
of  the  deep  brachial  vessels,  and  the  radial  nerve. 

Blood-supply. — Deep  brachial  and  ulnar  arteries. 
Nerve-supply. — Radial  nerve. 

5.  Anconeus  (M.  anconeus  parvus  s.  subanconeus). — This  is  a  small  fleshy 
muscle  which  covers  the  olecranon  fossa  and  is  covered  by  the  triceps.  It  is  some- 
what difficult  to  separate  from  the  outer  head. 

Origin. — The  distal  third  of  the  posterior  surface  of  the  humerus. 

Insertion. — The  outer 
surface  of  the  olecranon. 

Action. — To  extend  the 
elbow  joint,  and  to  raise  the 
capsule  of  the  joint  and 
prevent  its  being  pinched 
during  extension. 

Structure. — It  is  almost 
entirely  fleshy,  and  is  ad- 
herent by  its  deep  face  to 
the  joint  capsule. 

Relatio7is.  —  Superfici- 
ally, the  triceps  muscle; 
deeply,  the  humerus  and 
the  elbow  joint. 

Blood-supply.  —  Deep 
brachial  arter.y. 

Nerve-supply.  —  Radial 
nerve. 


Deep  flexor  tendon 


Distal  end  of  smalt  metacarpal  bone 


Suspensory  ligament 


Branch  of  superficial  flexor  tendon 
Di.'ital  digital  annular  ligament 
-  Upper  border  of  lateral  cartilage 


Fig.  1S9. — Digit  of  Horse,  Posterior  View. 
14.  Deep  flexor  teiuion:  15.  superficial  flexor  tendon;  16,  posterior 
annular  ligament  of  fetlock;  17,  proximal  annular  or  vaginal  ligament 
of  digit;-//,  lateral  cartilage;  ^.4,  plantar  cushion.     (After  EUenberger- 
Bauni,  .\nat.  fiir  Kiinstler.) 


IV.  FASCIiE  AND  MUSCLES 

OF  THE  FOREARM 

AND  MANUS 

The  forearm  is  covered 
on  three  sides  by  the  mus- 
cles of  this  group,  leaving 
the  inner  surface  of  the  radi- 
us for  the  most  part  subcu- 
taneous. The  extensors  of 
the  carpus  and  digit  lie  on  the  anterior  (dorsal)  and  external  part  of  the  region, 
while  the  flexors  occupy  the  posterior  (volar)  surface. 

The  fascia  of  the  forearm  (Fascia  antibrachii)  forms  a  very  strong  and  complete 
investment  for  all  the  muscles  of  the  region.  The  superficial  fascia  is  thin,  and 
disappears  at  the  carpus  by  fusing  with  the  deep  fascia.  The  deep  fascia  is  very 
strong  and  tendinous  in  character.  It  furnishes  insertion  at  its  upper  antl  inner 
part  to  the  tensor  fascia;  antibrachii  and  posterior  superficial  pectoral  muscles; 
at  its  upper  anterior  and  outer  part,  to  aponeuroses  from  the  mastoido-humeralis 
and  biceps.  It  is  attached  at  the  elbow  by  its  deep  face  to  the  outer  tuberosities  of 
the  humerus  and  radius,  to  the  ulna,  and  to  the  lateral  ligaments.  On  the  inner 
surface  of  the  forearm  it  blends  with  the  periosteum  on  the  subcutaneous  surface 
of  the  radius.  It  is  closely  adherent  to  the  surface  of  the  extensor  muscles,  but  is 
rather  loosely  attached  to  the  flexors.  From  its  deep  face  are  detached  inter- 
muscular septa,  which  form  sheaths  for  the  muscles  and  are  attached  to  the  under- 
lying lioiies.     The  principal  septa  are:   (a)  One  which  passes  between  the  common 


FASCI.E    AND    MUSCLES    OF   THE    FOREARM    AND    MANUS  263 

extensor  (in  front)  and  the  lateral  extensor  and  flexor  carpi  cxternus  (behind); 
(6)  one  between  the  common  extensor  and  the  extensor  carpi  radialis;  (c)  one  be- 
tween the  inner  and  middle  flexors  of  the  carpus. 

The  carpal  fascia  (Fascia  carpi)  is  a  direct  continuation  of  that  of  the  forearm. 
It  is  attached  chiefly  to  the  tuberosities  at  the  distal  end  of  the  radius,  to  the  ac- 
cessory carpal  (]iisiform)  bone,  and  to  the  lateral  ligaments.  In  front  it  forms  the 
so-called  anterior  annular  ligament  (Ligamentum  carpi  dorsale),  bridging  over  the 
grooves  and  binding  tlown  the  extensor  tendons  and  their  synovial  sheaths.  Be- 
hind it  is  greatly  thickened  and  forms  the  posterior  annular  or  transverse  liga- 
ment of  the  carpus  (Ligamentum  carpi  transversum).  This  stretches  across  from 
the  accessory  carpal  bone  to  the  internal  lateral  ligament  and  the  proximal 
extremity  of  the  inner  metacarpal  bone.  It  thus  completes  the  carpal  canal,  in 
which  lie  the  flexor  tendons,  their  synovial  sheath,  and  the  principal  vessels  and 
nerves  of  the  region. 

The  fascia  of  the  metacarpus  and  digit  (Fascia  metacarpea  et  digitalis)  is,  in 
general,  thinner  than  the  preceding.  It  is  attached  to  the  tendons,  ligaments,  and 
the  exposed  bony  prominences — especially  to  the  small  metacarpal  bones.  On  the 
flexion  surface  of  the  fetlock  joint  it  is  much  thickened  by  fibers  passing  transversely 
from  one  sesamoid  bone  to  the  other,  forming  an  annular  ligament  which  binds  down 
the  flexor  tendons  in  the  sesamoid  groove  or  canal.  Distal  to  this  is  a  second  thick 
quadrilateral  sheet  (Ligamentum  vaginale)  which  covers  and  is  adherent  to  the 
tendon  of  the  flexor  perforatus.  It  is  attached  on  either  side  by  two  bands  to  the 
borders  of  the  first  phalanx,  thus  firmly  binding  down  the  flexor  tendons.  A  little 
further  down  a  crescentic  fibro-elastic  sheet  covers  the  terminal  expansion  of 
the  deep  flexor  tendon.  It  is  attached  on  either  side  by  a  strong  band  to  the 
side  of  the  first  phalanx  about  its  middle. 

A.  Extensor  DrvisioN 

1.  Extensor  carpi  radialis  (M.  extensor  carpi  radialis  s.  radialis  dorsalis;  ex- 
tensor metacarpi  magnus;  anterior  extensor  of  the  metacarpus). — This  is  the 
largest  muscle  of  the  extensor  division,  and  lies  on  the  anterior  (dorsal)  surface  of 
the  radius. 

Origin. — (1)  The  external  condyloid  crest  of  the  humerus;  (2)  the  coronoid 
fossa. 

Insertion. — The  tuberosity  on  the  anterior  (dorsal)  surface  of  the  proximal 
extremity  of  the  large  (third)  metacarpal  bone. 

Action. — To  extend  and  fix  the  carpal  joint  and  to  flex  the  elbow  joint. 

Structure. — The  belly  of  the  muscle  is  rounded,  and  runs  out  to  a  point  at  the 
distal  third  of  the  forearm.  The  tendon,  which  runs  nearly  the  whole  length  of  the 
fleshy  portion,  appears  on  the  surface  of  the  latter  about  its  middle;  here  the  muscle 
shows  a  distinctly  pennate  arrangement.  The  tendon  passes  through  the  middle 
groove  at  the  distal  extremity  of  the  radius  and  over  the  capsule  of  the  carpal 
joint,  bound  down  by  the  anterior  annular  ligament  and  invested  with  a  synovial 
sheath.  The  ktter  begins  three  to  four  inches  (ca.  8  to  10  cm.)  above  the  carpus 
and  extends  almost  to  the  insertion  of  the  tendon.  In  the  lower  half  of  the  forearm 
the  deep  fascia  blends  with  the  tendon,  and  here  the  latter  is  joined  by  the  long 
tendon  of  the  biceps. 

Relations. — Superficially,  the  skin,  fascia,  and  the  oblique  extensor;  deeply, 
the  capsule  of  the  elbow  joint,  the  biceps  tendon,  the  radius,  the  carpal  joint  capsule, 
the  anterior  radial  artery,  and  the  radial  nerve;  externally,  the  anterior  or  com- 
mon extensor;  internally,  at  the  elbow,  the  brachialis  and  biceps. 

Blood-supph/. — Anterior  radial  artery. 

Nerve-supplij. — Radial  nerve. 

2.  Anterior  or  common  digital   extensor    (M.  extensor  digitalis  communis; 


264 


FASCI.E    AND    MUSCLES    OF    THE    HORSE 


anterior  extensor  of  the  phalanges;  extensor  pedis). — This  muscle  lies  external  to 
the  foregoing,  which  it  resembles  in  general  form,  although  less  bulky. 

Origin. — (1)  The  front  of  the  distal  extremity  of  the  humerus,  just  external  to 
the  coronoid  fossa;  (2)  the  external  tuberosity  on  the  proximal  extremity  of  the 
radius,  the  external  lateral  ligament  of  the  elbow,  and  the  external  border  of  the 


Brachialis 


Cephalic  nin 
Flexor  carpi  internus 


Anterior  or  common  extensor  of  digit 


Extensor  carpi  obliquus 


Metacarpal  tuberosity 


Tendon  of  anterior  extensor 
Tendon  of  lateral  extensor 


Branch  of  suspensory  ligament  to  extensor 
tendon 


Lateral  cartilage 


Fig.  190. — Muscles  of  Left  Thoracic  Limb  of  Horse,  from  Elbow  downward,  Anterior  View. 
a.  Extensor  carpi  radialis;    g'.  superficial  pectoral  muscle,     (.\fter  Ellenberger-Baura,  Anat.  fur  Kiinstler.) 

radius  at  the  junction  of  its  proximal  and  middle  thirds;  (3)  the  external  surface 
of  the  shaft  of  the  ulna;   (4)  the  fascia  of  the  forearm. 

Insertion.— (1)  The  extensor  (or  pyramidal)  process  of  the  [third  phalanx;  (2) 
the  anterior  surface  of  the  proximal  extremities  of  the  first  and  second  phalanges. 

Action.— To  extend  the  digital  and  carpal  joints,  and  to  flex  the  elbow  joint. 

Structure. — The  muscle  is  a  compound  one,  representing  the  common  extensor, 


EXTENSOR    DIVISION  265 

together  with  vestiges  of  the  proper  extensors  of  the  digits.  Usually  at  least 
two  heads  may  be  distinguished.  The  principal  or  humeral  head  (Caput 
iuimerale)  arises  from  the  front  of  the  extensor  epicondyle  of  the  humerus  in 
common  with  the  extensor  carpi.  Its  belly  is  fusiform,  and  terminates  in  a 
point  near  the  distal  third  of  the  radius.  The  tendon  appears  on  the  surface 
of  the  muscle  about  the  middle  of  the  belly,  the  arrangement  being  pcnnate. 
The  tendon  passes  downwartl  through  the  outer  of  the  two  large  grooves 
on  the  front  of  the  distal  end  of  the  radius,  and  over  the  capsule  of  the  carpal 
joint.  Passing  down  over  the  front  of  the  metacarpus,  it  inclines  gradually 
inward,  reaching  the  middle  line  of  the  limb  near  the  fetlock.  A  little  below 
tlie  middle  of  the  first  phalanx  it  is  joined  by  the  branches  of  the  suspensory  liga- 
ment, and  the  tendon  thus  becomes  much  wider.  Two  synovial  membranes 
facilitate  the  play  of  the  tendon.  The  proximal  one  is  a  sheath  which  begins  about 
three  inches  (ca.  7  to  8  cm.)  above  the  carpus,  and  terminates  at  the  proximal  end 
of  the  metacarpus.  At  the  fetlock  a  bursa  occurs  between  the  tendon  and  the 
joint  capsule,  but  otherwise  the  two  are  adherent.  The  smaller  head,  arising 
chiefly  from  the  radius  and  ulna,  is  often  divisible  into  two  parts  (Fig.  443).  The 
larger  of  these  (Caput  radiale,  muscle  of  Phillips)'  arises  from  the  outer  tuberosity 
and  outer  border  of  the  radius,  and  from  the  lateral  ligament  of  the  elbow  joint. 
The  fiat  belly  is  succeeded  by  a  delicate  tendon,  which  accompanies  the  principal 
tendon  over  the  carpus  (included  in  the  same  sheath),  and  then  passes  outward  to 
fuse  with  the  tendon  of  the  lateral  extensor.  Usually  a  slip  is  detached  which  is 
inserted  on  the  proximal  extremity  of  the  first  phalanx,  or  ends  in  the  fascia  here. 
The  smaller  and  deeper  division  (Caput  ulnare,  muscle  of  Thiernesse)-  is  usually 
somewhat  difficult  to  isolate.  It  arises  from  the  ulna  close  to  the  interosseous 
space.  It  has  a  small  rounded  belly  and  is  provided  with  a  delicate  tendon  which 
may  fuse  with  the  principal  tendon  or  may  be  inserted  into  the  capsule  and  the 
fascia  in  front  of  the  fetlock  joint. 

Relations. — The  chief  relations  of  the  belly  of  the  muscle  are:  superficially,  the 
skin  and  fascia;  deeply,  the  elbow  joint,  the  radius  and  ulna,  the  extensor  carpi 
obliquus,  and  the  anterior  radial  vessels  and  radial  nerve;  in  front  and  internally, 
the  extensor  carpi  radialis;  behind,  the  lateral  extensor  and  the  interosseous  vessels. 

Blood-supply. — Radial  and  interosseous  arteries. 

Nerve-supply. — Radial  nerve. 

3.  Lateral  digital  extensor  (M.  extensor  digitalis  lateralis  s.  digiti  quinti  pro- 
prius;  lateral  extensor  of  the  phalanges;  extensor  sufTraginis).— This  muscle  is 
much  smaller  than  the  preceding,  behind  which  it  is  situated. 

Origin.— The  external  tuberosity  of  the  radius  and  the  lateral  ligament  of  the 
elbow  joint,  the  shaft  of  the  ulna,  the  outer  border  of  the  radius,  and  the  inter- 
muscular septum. 

Insertion.— An  eminence  on  the  front  of  the  proximal  extremity  of  the  first 
phalanx. 

Action. — To  extend  the  digit  and  carpus. 

Structure.— The  muscle  is  pennate,  and  is  inclosed  in  a  sheath  formed  by  the 
deep  fascia,  from  which  many  fibers  arise.  The  belly  is  thin  and  fusiform  and 
terminates  at  the  lower  third  of  the  forearm.  From  here  the  tendon  (at  first 
small  and  round)  passes  downward  through  the  groove  on  the  outer  tuberosity 
of  the  distal  end  of  the  radius,  then  over  the  carpus,  and,  gradually  inclining  toward 
the  front,  but  not  reaching  the  middle  line  of  the  limb,  it  passes  over  the  meta- 
carpus and  fetlock  to  its  insertion.     Two  synovial  membranes  occur  in  connection 

>  This  is  considered  to  represent  the  part  of  the  common  extensor  for  the  fourth  and  fifth 
digits. 

2  Martin  considers  that  this  muscle  represents  the  extensor  indicis  proprius  and  the  part 
of  the  common  extensor  for  the  second  digit. 


266 


FASCLE    AND    MUSCLES    OF    THE    HORSE 


with  the  tendon.  A  sheath  envelops  the  tendon,  beginning  about  three  inches 
(ca.  6  to  8  em.)  above  the  carpus,  and  reaching  to  the  proximal  end  of  the  metacarpus. 
At  the  fetlock  a  small  bursa  lies  between  the  tendon  and  the  joint  capsule,  hut 
otherwise  the  tendon  is  adherent  to  the  capsule.     The  tendon  becomes  flat  and 


Extensor  carpi  obliqmi 


Metacarpal  tuberosity    ~^ 
Tendon  from  anterior  to  lateral  extensor 


External  small  metacarpal  bone 


Branch  of  suspensory  ligament  to 
extensor  tendon 


Olecranon 


Ulnar  head  of  deep  flexor 


Lateral  extensor 
Deep  flexor  {humeral  head) 

Tendon,  of  flexor  carpi  externus 
Acccfsory  carpal  bone 


Check  liynmrnt 

Suspensory  ligament 
Flexor  tendons 


Flexor  leiulons 
Ijitiral  earlilaye 


Fig.  191. — Muscles  of  Left  Thoracic  T.iMn  of  Horse  from  Elbow  Downward;   External  View. 
a,   Extensor  carpi  radialis;    g,  brachialis;    o\  anterior  superficial   pectoral:    c,   anterior  or  common  digital  ex- 
tensor;  e,  flexor  carpi  externus.     (.\fter  Elleiiljerger-Baum,  .\nat.  fiir  Kiinstler.) 


much  larger  below  the  carpus,  having  received  the  tendon  of  the  radial  head  of  the 
anterior  e.xtensor  and  a  strong  band  from  the  accessory  carpal  bone. 

Relations. — Superficially,  the  skin  and  fascia;  deeply,  the  outer  face  of  the 
radius  and  ulna;  in  front,  the  common  extensor,  the  oblique  extensor,  and  the 
interosseous  artery;  behind,  the  external  flexor  of  the  carpus  and  the  deep  flexor  of 
the  digit. 

Blood-suppiy. — Interosseous  artery. 


FLEXOR   DIVISION 


267 


Nerve-supply. — Radial  nerve. 

4.  Extensor  carpi  obliquus  (M.  abductor  pollicis  longiis  et  extensor  pollicis 
brevis:  ol)lique  extrnsor  of  the  metacarpus;  extensor  metacarpi  obliquus). — This 
is  a  small  muscle  which  curves  obliquely  over  the  distal  half  of  the  radius  and  the 
carpus. 

Origin. — The  external  border  and  adjacent  part  of  the  anterior  surface  of  the 
radius  (the  attachment  area  beginning  at  a  point  above  the  middle  of  the  bone  and 
extending  do\^ia  to  its  lower  fourth). 

Insertion. — The  head  of  the  inner  (secontl)  metacarpal  bone. 

Action. — To  extend  the  carpal  joint. 

Structure. — The  muscle  is  pennate  and  has  a  flat  belly  which  curves  downward, 
forward,  and  inward  over  the  distal  part  of  the  radius.  The  tendon  continues  the 
direction  of  the  muscle,  crossing  obliquely  over  the  tendon  of  the  extensor 
carpi  radialis;  it  then  occupies  the  oblique  groove  at  the  distal  end  of  the  radius, 
and  crosses  the  inner  face  of  the  carpus.     It  is  provided  with  a  synovial  sheath. 


I-IG,  192- — Cross-section  of  Middle  of  Right  Forearm  of  Horse 
a.  Accessory  cephalic  vein;  6,  cutaneous  branch  of  median  nerve;  c,  extensor  carpi  obliquus;  rf,  posterior 
radial  artery;  e,  satellite  vein;  /,  median  nerve;  g,  3',  ulnar  vessels;  h,  ulnar  nerve;  (,  cephalic  vein;  k,  tendon  of 
ulnar  head  of  deep  flexor;  /,  interosseous  artery;  m,  extensor  carpi  radialis;  n,  anterior  digital  extensor;  o,  lateral 
digital  extensor:  p,  flexor  carpi  externus;  q,  q,  q,  humeral  heads  of  deep  digital  flexor;  r,  radial  head  of  same;  s, 
superficial  digital  flexor;  ^  flexor  carpi  medius;  u,  flexor  carpi  internus;  c,  radius;  w,  skin;  x,  anterior  radial 
artery.     (After  Ellenberger.  in  Leisering's  .\tlas.) 

Relations. — Superficially,  the  skin  and  fascia,  the  lateral  extensor,  and  the 
common  extensor;  deeply,  the  radius,  the  extensor  carpi  radiaUs,  the  carpal  cap- 
sule, and  the  internal  lateral  ligament. 

Blood-supply. — Interosseous  and  anterior  radial  arteries. 

Nerve-supply. — Radial  nerve. 


B.  Flexor  Division 

1.  Flexor  carpi  internus  (M.  flexor  carpi  radialis  s.  radiaUs  volaris;  internal 
flexor  of  the  metacarpus).— This  muscle  lies  on  the  inner  surface  of  the  forearm, 
immediately  behind  the  inner  border  of  the  radius. 

Origin. — The  flexor  (internal)  epicondyle  of  the  humerus,  below  and  behind 
the  lateral  ligament. 

Insertion. — The  proximal  end  of  the  internal  (second)  metacarpal  bone. 

Action. — To  flex  the  carpal  joint  and  to  extend  the  elbow. 

Structure. — The  muscle  has  a  short  tendon  of  origin,  which  is  succeeded  by  a 
somewhat  flattened,  fusiform  belly.  The  tendon  of  insertion  begins  near  the  distal 
fourth  of  the  radius.     It  is  provided  with  a  synovial  sheath  which  begins  two  or 


268 


FASCIiE   AND    MUSCLES    OF   THE    HORSE 


three  inches  (ea.  5  to  8  cm.)  above  the  carpus  and  extends  almost  to  the  insertion 
of  the  tendon. 

Relatiojis. — Superficially,  the  skin  and  fascia,  the  posterior  superficial  pectoral 
and  the  tensor  fascice  antibrachii;  deeply,  the  elbow  joint,  the  radius,  the  deep 
flexor,  the  flexor  carpi  medius,  the  posterior  radial 
vessels,  and  the  median  nerve.  At  the  elbow  the  artery 
and  nerve  lie  in  front  of  the  muscle,  but  below  they 
dip  beneath  it. 

Blood-supply. — Posterior  radial  artery. 
Nerve-supply. — Median  nerve. 

On  removing  the  deep  fascia  on  the  inner  .surface  of  the  elbow 
the  student  may  notice  a  small  muscle  lying  along  the  lateral  liga- 
ment. This  is  the  pronator  teres,  which  is  usually  not  present  or 
a  mere  vest iiii'  in  the  liorsi'.  It  arises  by  a  small,  flat  tendon  from 
the  flexor  cpiromlylc  of  the  humerus,  and  is  inserted  into  the  in- 
ternal lateral  ligament  of  the  elbow.  On  account  of  its  small  size 
and  the  fact  that  the  forearm  is  fi.xed  in  the  position  of  pronation, 
the  muscle  can  have  no  appreciable  function.  It  is  usually  repre- 
sented by  the  long  portion  of  the  internal  lateral  Ugament. 

2.  Flexor  carpi  medius  (M.  flexor  carpi  ulnaris  s. 
ulnaris  medialis;  oblique  or  middle  flexor  of  the  meta- 
carpus).— This  muscle  lies  on  the  inner  and  posterior 
aspect  of  the  forearm  partly  under,  partly  behind,  the 
preceding  muscle.  It  arises  by  two  heads — humeral 
and  ulnar. 

Origin. — (1)  The  flexor  (internal)  epicondyle  of 
the  humerus  just  behind  the  preceding  muscle; 
(2)  the  inner  surface  and  posterior  border  of  the 
olecranon. 

Insertion. — The  upper  edge  of  the  accessory  carpal 
(pisiform)  bone. 

Action. — To  flex  the  carpal  joint,  and  to  extend  the 
elbow. 

Structure. — The  humeral  head  is  much  the  larger, 
constituting,  in  fact,  the  bulk  of  the  muscle.  It  is 
flattened,  curved,  and  tapers  at  both  ends.  The 
ulnar  head,  much  smaller  and  very  thin,  is  covered 
by  an  aponeurosis  from  which  many  of  its  fibers 
arise.  It  joins  the  large  head  a  little  above  the 
middle  of  the  forearm.  The  tendon  of  insertion  is 
short  and  strong;  it  blends  with  the  posterior  annular 
ligament  of  the  carpus. 

Relations. — Superficially,  the  tensor  fasciae  anti- 
brachii, superficial  pectoral,  and  flexor  carpi  internus, 
the  skin  and  fascia,  and  cutaneous  branches  of  the  ulnar 
nerve;  deeply,  the  superficial  and  deep  flexors  of  the 
digit.  In  the  distal  half  of  the  forearm  the  ulnar  vessels 
and  nerve  lie  between  the  outer  edge  of  this  muscle  and 
the  external  flexor  of  the  carpus. 

Blood-supply. — Ulnar  and  posterior  radial  arteries. 

Nerve-supply. — Ulnar  and  median  nerves. 
3.  Flexor    carpi    extemus    (M.  extensor   carpi   ulnaris'  s.  ulnaris  lateralis; 
external  flexor  of  the  metacarpus). — This  muscle  lies  on  the  outer  face  of  the 
forearm,  behind  the  lateral  extensor  of  the  digit. 

'  In  man  the  muscle  is  an  extensor  of  the  hand. 


Fig.  193. — Deeper  Mdscles  of 
Forearm  of  Horse,  In- 
ternal View. 
S3.  Internal  head  of  triceps; 
30,  flexor  carpi  mediu-s;  31 ,  flexor 
carpi  internus:  31',  tendon  of  31; 
32,  superficial  digital  flexor:  32', 
radial  check  ligament:  32" ,  tendon 
of  superficial  flexor:  33a,  33b,  33c, 
humeral  heads  of  deep  flexor:  33' , 
tleep  flexor  tendon:  33" ,  subcarpal 
check  ligament;  ,94.  ulnar  head  of 
deep  flexor;  36,  radial  head  of  deep 
flexor;  ,9fi,  suspensory  ligament, 
(.^fter  Ellenberger.  in  Leisering's 
Atlas.) 


FLEXOR   DIVISION  269 

Origin. — The  extensor  (external)  epicondyle  of  the  humerus,  behind  and  below 
the  lateral  ligament. 

Insertion. — (1)  The  outer  surface  and  upper  edge  of  the  accessory  carpal 
bone;   (2)  the  proximal  extremity  of  the  outer  (fourth)  metacarpal  bone. 

Action. — To  flex  the  carpal  joint  and  to  extend  the  elbow. 

Structure. — The  belly  of  the  muscle  is  flattened  and  is  intersected  by  a  good 
deal  of  tendinous  tissue.  There  are  two  tendons  of  insertion.  The  short  tendon 
is  inserted  into  the  accessory  carpal  bone.  The  long  tendon  is  detached  just  above 
the  carpus;  it  is  smaller  and  rounded;  it  passes  downward  and  a  little  forward 
through  a  groove  on  the  outer  surface  of  the  accessory  carpal  bone,  enveloped  by 
a  synovial  sheath,  to  reach  its  insertion  on  the  outer  metacarpal  bone.     A  synovial 


For  tendon  of 
anterior  extensor 


For  tendon  o/  ex- 
tensor  carpi  radialis 


Joint  cavity 


For  tendon  of  lateral 
extensor 

External  laternl  liga- 
ment 

For  long  tendon  of 
flexor  carpi  cxternus 


For  tendon  of  extensor 
carpi  obliquus 


Internal  lateral  liga- 
ment 


Posterior  ligame?d  of 
carpus 

For  tendon  of  flexor  carpi 

intcrnus 

Large  metacarpal  artery 


Posterior  anmdar     Internal  meta-     Internal  metacarpal  vein 
ligament  carpal  nerve  in 

carpal  canal 

Fig.  194. — Cross-section-  of  Proximal  Part  of  Left  Carpus  of   Horse. 
The  tendons  have  been  removed  to  show  the  canals  in  which  the>-  lie.     The  joint  cavity  is  black.     By 
an  oversight  the  can^al  canal  for  the  two  flexor  tendons  behind  the  posterior  ligament  of  the  carpus  is  not  marked. 
Cr.  Radial,  Ci,  intermediate,  Cu,  ulnar,  Ca,  accessory  carpal  bones. 


pouch  lies  under  the  origin  of  the  muscle  at  the  elbow  joint,  with  the  cavity  of 
which  it  communicates. 

Relations. — Superficially,  the  skin,  fascia,  and  cutaneous  branches  of  the  ulnar 
nerve;  deeply,  the  elbow  joint,  the  ulna,  and  the  flexors  of  the  digit;  in  front,  the 
lateral  extensor  of  the  digit ;  behind,  the  middle  flexor  of  the  carpus,  the  ulnar  head 
of  the  deep  flexor,  and  the  ulnar  vessels  and  nerve. 

Blood-supply. — Interosseous,  ulnar,  and  median  arteries. 

N'erve-supphi. — Radial  nerve. 

4.  Superficial  digital  flexor  or  flexor  perforatus  (M.  flexor  digitalis  sublimis; 
superficial  flexor  of  the  phalanges). —This  muscle  is  situated  in  the  middle  of  the 
flexor  group,  chiefly  under  cover  of  the  middle  flexor  of  the  carpus. 

Origin.— (1)  The  flexor  epicondyle  of  the  humerus,  between  the  flexor  carpi 
iuternus  and  the  deep  flexor  of  the  digit ;  (2)  a  ridge  on  the  posterior  surface  of  the 
radius,  below  its  middle  and  near  the  internal  border. 

Insertion.~{l}  The  eminences  on  the  proximal  extremity  of  the  second  phalanx 


270 


FASCLE    AND    MUSCLES    OF    THE    HORSE 


lieliind  the  lateral  ligaments:    (2)  the  distal  extremity  of  the  first  phalanx,  also 
behind  the  lateral  ligaments. 

Action. — To  flex  the  digit  and  carpus,  and  to  extend  the  elbow. 


f 


Fio.  195.— Synovi.\l  She.kths  and  Burs.e  of  Lower 
Part  of  Right  Fore  Limb  of  Horse,  Lvtfr- 
NAL  View. 

The  synovial  sheaths  (colored  yellow)  and 
a.  Sheath  of  extensor  carpi  obliquus;  b,  sheath 
of  flexor  carpi  internus;  c,  carpal  sheath;  d,  d\  d",d"', 
digital  sheath;  e,  bursa  under  anterior  extensor  ten- 
don; /,  capsule  of  fetlock  joint;  1,  extensor  carpi 
radialis;  2,  tendon  of  extensor  carpi  obliriuus;  5, 
flexor  carpi  internus;  4.  flexor  carpi  medius;  .5,  superfi- 
cial flexor  tendon;  6,  deep  flexor  tendon;  7,  suspensory 
ligament;  S,  small  metacarpal  bone;  9,  large  meta- 
carpal bone;  10,  posterior  annular  ligament  of  fetlock; 
i/.  proximal  digital  annular  ligament;  12,  radius;  IS, 
radiocarpal  joint;  14,  fetlock  joint;  15,  lateral  cartilage; 
16.  band  from  first  phalanx  to  lateral  cartilage.  (After 
Ellenberger,  in  Leisering's  Atlas.) 


Fig.  196.— Synovial  Sheaths  axi.  I5i  rs.k  of  Lower 
Part  of  Right  Fore  Limu  of  Horse,  Exter- 
nal View. 
the  joint  capsules  (colored  pink)  are  injected. 

a.  Sheath  of  extensor  carpi  radialis;  b,  sheath 
of  anterior  extensor;  c,  sheath  oi  lateral  extensor;  d, 
sheath  of  outer  tendon  of  flexor  carpi  externus;  <■,  e', 
carpal  sheath;  /,/'./",  digital  sheath;  (?,  bursa  under 
anterior  extensor  tendon;  h,  bur.sa  under  lateral  ex- 
tensor tendon;  /,  capsule  of  fetlock  joint;  1^  extensor 
carpi  radialis;  3,  anterior  digital  extensor;  S,  lateral 
digital  extensor;  4.  flexor  carpi  externus;  4'f  4"' 
tendons  of  4.'  ^.  superficial  flexor  tendon;  G,  deep 
flexor  tendon;  7,  suspensory  ligament;  5.  external 
metacarpal  bone;  9,  large  metacarpal  bone;  10, 
posterior  annular  ligament  of  fetlock;  7 /.digital  annular 
ligament;  12.  fetlock  joint;  IS,  lateral  cartilage;  14, 
band  from  first  jjhalanx  to  lateral  cartilage.  (After 
Ellenberger,  in  Leisering's  .\tlas.) 


Structure. — The  fleshy  portion  nf  the  musrlo  or  humeral  head  takes  origin 
from  the  humerus.  The  radial  head  (( 'a])ut  tenilineuni)  consists  of  a  strong  fihrous 
band,  usually-  termed  the  radial  or  superior  check  ligament,  v.hieh  fuses  with  the 


FLEXOR   DIVISION 


271 


tendon  near  the  carpus.  The  l)elly  of  the  niusele  is  intersected  by  toiuHnous  strands, 
and  fuses  more  or  less  with  that  of  the  deep  flexor.  Near  the  carpus  it  is  succeeded 
In-  a  strong,  thick  tendon  which  passes  down  through  the  carpal  canal,  formed  by  the 
posterior  ligament  of  the  carpus,  the  accessory  carpal  bone,  and  the  posterior 
annular  ligament  (Ligamentum  carpi  transversum).  Here  it  is  enveloped  by  a 
synovial  sheath,  in  common  with  the  deep  flexor.  This  carpal  sheath  (^'agina 
carpca)  begins  three  or  four  inches  (8  to  10  cm.)  above  the  cai'ijus,  and  extends  down- 
ward nearly  to  the  middle  of  the  metacarpus.  Below  the  carpus  the  tendon  be- 
comes flattened  and  broader.  Near  the  fetlock  it  forms  a  ring  through  which  the 
tendon  of  the  deep  flexor  passes  (Fig.  1.50).  Here  the  two  tendons  are  bound 
down  in  the  sesamoid  groove  by  the  posterior  aimular  ligament,  which  fuses  more 
or  less  with  the  superficial  flexor  tendon.  At  the  distal  end  of  the  first 
phalanx  the  tendon  divides  into  two  branches  which  diverge  to  reach  their  points 
of  insertion,  and  between  these  liranches  the  tendon  of  the  deep  flexor  emerges 
(Fig.    189).     A    second    S5movial    sheath,    the    digital   or   sesamoidean  (Vagina 

Tendon  of  lateral  extensor         Ttndon  of  anterior  extensor 


Upper  pouch  of  joint  capsule 
Branch  of  suspensory  ligament 


Interse^amoid  ligament 


Tendon  of  superficial  flexor         Tendon  of  deep  flexor 
Fig.  197. — Cross-section  of  Dist.vl  P\rt  of  Left  Met.\carpus  of  Horse,  Just  Above  Sesamoids. 


digitalis),  begins  at  the  distal  third  of  the  metacarpus,  three  to  four  inches  (8  to 
10  cm.)  above  the  fetlock,  and  extends  to  the  middle  of  the  second  phalanx. 

Relations. — The  belly  of  the  muscle  is  related  superficially  to  the  ulnar  head 
of  the  deep  flexor,  the  flexor  carpi  medius,  and,  at  its  origin,  to  the  ulnar  vessels 
and  nerve;  deeply  to  the  humeral  head  of  the  deep  flexor.  The  tendon  is  re- 
lated superficially  to  the  skin  and  fascia;  deeply  to  the  deep  flexor  tendon. 

Blood-supph/. — Posterior  radial  artery. 

Xerve-supphj. — ^ledian  nerve. 

.5.  Deep  digital  flexor  or  flexor  perforans  (]M.  flexor  digitalis  profundus; 
deep  flexor  of  the  phalanges). — The  fleshy  part  of  this  muscle  lies  on  the  posterior 
surface  of  the  radius,  under  cover  of  the  preceding  muscles.  It  is  the  largest 
muscle  of  the  flexor  group. 

Origin. — (1)  The  flexor  (internal)  epicondyle  of  the  humerus;  (2)  the  inner 
surface  of  the  olecranon;  (.3)  the  middle  of  the  posterior  surface  of  the  radius 
and  a  small  adjacent  area  of  the  ulna. 

Insertion. — The  semilunar  crest  of  the  third  phalanx,  and  the  adjacent  surface 
of  the  lateral  cartilage. 

Action. — To  flex  the  digit  and  carpus,  and  to  extend  the  elbo^v. 


272 


FASCI.E    AND    MUSCLES    OF    THE    HORSE 


Structure. — This  muscle  consists  of  throe  principal  heads.  The  humeral  head 
(Caput  humerale)  constitutes  the  bulk  of  the  muscle.  It  is  marked  l)y  tendinous 
intersections,  and  is  separable  into  three  secondary  heads.  The  uhiar  head  (Caput 
ulnare,  ulnaris  accessorius)  is  much  smaller,  and  is  at  first  superficially  situated  be- 
tween the  outer  and  middle  flexors  of  the  carpus.  The  radial  head  (Caput  radiale, 
radialis  accessorius)  is  the  smallest,  and  is  not  always  present;  it  is  situated  on  the 
distal  two-thirds  of  the  posterior  surface  of  the  radius,  under  the  humeral  head.  Each 
of  these  heads  is  pro\-ided  with  a  tendon.    The  principal  tendon— that  of  the  humeral 

heacl — begins  about  three  or  four  inches  (8 
to  10  cm.)  above  the  carpus.  It  is  soon 
joined  by  the  small  tendon  of  the  ulnar 
head,  which  begins  about  the  middle  of  the 
forearm.  The  tendon  of  the  radial  head 
fuses  with  the  principal  tendon  close  to 
the  carpus.  The  conjoined  tendon  passes 
downward  through  the  carpal  canal,  lieing 
included  in  the  carpal  synovial  sheath 
with  the  superficial  flexor  tendon,  as 
previously  described.  Continuing  down- 
ward, it  is  joined  about  the  middle  of  the 
metacarpus  by  a  strong  fibrous  band,  the 
so-called  inferior  or  subcarpal  check  liga- 
ment (Caput  tendineum ) .  This  is  a  direct 
continuation  of  the  posterior  ligament  of 
the  carpus.  Below  this  the  tendon  passes 
through  the  ring  formed  by  the  perfor- 
atus,  then  in  succession  over  the  sesamoid 
groove,  the  inferior  sesamoidean  liga- 
ments, and  the  tendon  surface  of  the  third 
sesamoid,  to  its  insertion  (Figs.  150  and 
151).  Its  terminal  part  is  much  widened. 
From  the  distal  third  of  the  metacarpus  to 
the  distal  end  of  the  second  jihalanx  it  is 
inclosed  in  the  digital  synovial  sheath  de- 
scrilied  in  connection  with  the  perforatus. 
The  navicular  bursa  or  bursa  podotroch- 
learis  is  found  between  the  tendon  and 
the  third  sesamoid  or  navicular  l>one. 
The  terminal  part  of  the  tendon  is  bound 
down  by  the  fibrous  sheet  described  with 
the  fascia. 

Relations. — The  belly  of  the  muscle  is 
related  posteriori}^  to  the  perforatus  and 
the  middle  flexor  of  the  carpus;  internally, 
to  the  internal  carpal  flexor,  the  radial 
check  ligament,  and  the  posterior  radial 
vessels  and  median  nerve:  externally,  to  the  externa!  flexor  of  the  carpus;  anteriorly, 
to  the  radius  and  ulna  and  branches  of  the  posterior  radial  artery  and  median  nerve. 
Below  the  carpus  the  tendon  is  accompanied  by  the  vessels  and  nerves  of  the  digit. 
It  may  also  be  noted  that  the  muscle  is  not  entirely  covered  by  the  other  flexors;  it 
comes  in  contact  with  the  skin  and  fascia  on  the  postero-external  aspect  of  the 
proximal  half  of  the  forearm,  and  also  on  the  outer  aspect  of  the  distal  fourth. 
Blood-supphj. — Posterior  radial  and  ulnar  arteries. 
Nerve-supply. — Median  and  ulnar  nerves. 


Fig.  198. — Digit  of  Horse,  Lateral  View. 
I.  Large  metacarpal  bone;  3,  distal  end  of  small 
metacarpal  bone;  S^  fetlock  joint;  5,  first  phalanx;  G, 
pastern  joint;  7.  second  phalanx;  5,  coffin  joint;  9, 
third  phalanx;  ii,  lateral  cartilage:  77', -upper  (sub- 
cutaneous) border  of  cartilage;  12,  suspensory  liga- 
ment; IS,  branch  of  13  to  extensor  tendon;  14,  deep 
flexor  tendon;  75,  superficial  flexor  tendon;  7.5',  branch 
of  lo;  W,  posterior  annular  ligament  of  fetlock;  17, 
proximal  annular  or  vaginal  ligament  of  digit;  75, 
distal  annular  ligament  or  reinforcing  sheath  of  deep 
fle.xor  tendon;  19,  lateral  ligament  of  coffin  joint;  21 , 
tendon  of  common  or  anterior  extensor;  22,  tendon  of 
lateral  extensor;  23,  digital  vein.  (After  Ellenberger- 
Baum,  Anat.  fiir  Kunstler.) 


FASCI/E   AND   MUSCLES   OF  THE    PELVIC   LLMB  273 

METACARPAL  MUSCLES 

The  five  muscles  of  this  group  are  either  reduced  to  vestiges  or  mcxUfied  greatly 
in  structure. 

1,  2.  Lumbricales  (internus  et  externus). — These  are  two  small  muscles  which 
lie  on  either  side  of  the  flexor  tendons  above  the  fetlock.  They  arise  from  the 
deep  flexor  tendon,  and  are  lost  in  the  fibrous  tissue  which  lies  under  the  nodule  of 
horn  or  ergot  at  the  fetlock  (Fig.  447).  Their  action  is  inappreciable.  The  size 
of  these  muscles  is  subject  to  nmch  variation.  Often  very  little  muscular  tissue 
can  be  found,  but  the  small  tendon  is  constantly  present. 

Blood-supply. — Metacarpal  arteries. 

Nerve-supply. — Median  and  ulnar  nerves. 

3,  4,  5.  Interossei. — These  are  three  in  number  in  the  horse,  and  are  situated 
chiefly  in  the  metacarpal  groove.  Two,  the  internus  and  externus,  are  very  small 
muscles,  each  of  which  arises  from  the  corresponding  small  metacarpal  bone  near 
its  proximal  extremity,  and  is  provided  with  a  delicate  tendon  which  is  usually  lost 
in  the  fascia  at  the  fetlock  (Fig.  150).  They  have  no  appreciable  action.  Their 
blood-  and  nerve-supply  is  the  same  as  that  of  the  preceding  muscles. 

The  interosseus  medius  is  so  much  modified  that  it  is  usually  termed  the 
suspensory,  or  superior  sesamoidean  ligament.  It  contains  little  muscular  tissue, 
lieing  transformed  very  largely  into  a  strong  tendinous  band,  bifurcate  below,  and 
having  for  its  chief  function  the  supporting  of  the  fetlock.  It  has  been  described, 
in  deference  to  common  usage,  with  the  ligaments. 


FASa^  AND  MUSCLES  OF  THE  PELVIC  LiMB 

The  FAsa^ 

The  iliac  fascia  (Fascia  iliaca)  covers  the  ventral  surface  of  the  iliacus  and  psoas 
muscles,  over  which  it  is  tightly  stretched  (Fig.  450).  It  is  attached  internally  to 
the  tendon  of  the  psoas  minor,  externally  to  the  inguinal  (Poupart's)  ligament 
and  the  external  angle  of  the  ilium.  Its  anterior  part  is  thin.  Posteriorly,  it  is 
in  part  attached  to  the  ilium,  in  part  becomes  continuous  with  the  pelvic  fascia. 
It  furnishes  surfaces  of  origin  for  the  sartorius,  cremaster  externus,  and  transversus 
abdominis  muscles. 

The  pelvic  fascia  (Fascia  pelvis)  lines  the  cavity  (parietal  layer)  and  is  reflected 
on  the  viscera  at  the  pelvic  outlet  (visceral  layer).  Laminae  are  detached  from  it 
to  strengthen  the  various  peritoneal  folds. 

The  superficial  fascia  of  the  gluteal  region  is  continuous  with  the  aponeurosis 
of  the  panniculus.  It  covers  and  jiartly  blends  with  the  deep  fascia.  The  gluteal 
fascia  (Fascia  glutea)  covers  the  superficial  muscles  of  the  region,  and  detaches 
intermuscular  septa,  which  pass  between  the  muscles.  It  is  attached  to  the  sacral 
spines,  the  dorsal  sacro-iliac  ligament,  and  the  angles  of  the  ilium,  and  is  continuous 
in  front  with  the  lumbo-dorsal  fascia,  l)ehind  with  the  coccygeal  fascia.  Its  deep 
face  gives  origin  to  fibers  of  the  superficial  and  middle  glutei,  the  biceps  femoris, 
and  the  semitendinosus.  so  that  care  is  necessary  in  dissecting  it  off  these  muscles. 
The  chief  intermuscular  septa  are:  (1)  One  which  passes  between  the  superficial 
gluteus  and  the  biceps  femoris;  (2)  one  between  the  bicejis  and  semitendinosus, 
from  which  a  lamella  is  detached  which  passes  between  the  middle  and  posterior 
portions  of  the  biceps  and  is  attached  to  the  tuber  ischii;  (3)  one  between  the 
semitendinosus  and  semimembranosus,  which  is  attached  to  the  sacro-sciatic  liga- 
ment and  tuber  ischii;  it  furnishes  origin  for  fibers  of  the  long  head  of  the  .semi- 
membranosus. 

The  fascia  lata  is  continuous  with  the  preceding,  and  covers  the  muscles  on  the 
18 


274  FASCI.E    AND    MUSCLES    OF   THE    HORSE 

outer  surface  and  front  of  the  thigh.  It  is  tendinous  and  very  strong,  and  for  the 
most  part  easily  separable  from  the  underlying  muscles.  It  furnishes  insertion  to 
the  tensor  fasciae  lata  and  to  the  biceps  femoris  (in  part),  by  both  of  which  it  is 
tensed.  At  the  stifle  it  is  attached  to  the  patella  and  the  inner  and  outer  straight 
ligaments.  Internally  it  is  continuous  with  the  internal  femoral  fascia.  It  fur- 
nishes the  following  intermuscular  septa :  (1)  One  which  passes  between  the  vastus 
externus  and  biceps  femoris  to  l)e  attached  to  the  external  trochanter  of  the  femur; 
(2)  two  which  jiass  lietween  the  three  branches  of  the  biceps  femoris;  (3)  a  fourth 
between  the  biceps  femoris  and  scmitendinosus. 

The  internal  femoral  fascia  (Fascia  femoralis  niedialis)  covers  the  superficial 
muscles  on  the  inner  surface  of  the  thigh.  At  its  upper  part  it  is  joined  by  part  of 
the  aponeurosis  of  the  external  oblique  muscle  (Lamina  femoralis)  (Fig.  450).  The 
posterior  part  is  thin.  It  is  continuous  with  the  fascia  lata  in  front  and  the  crural 
fascia  below.     At  the  stifle  it  fuses  with  the  tendons  of  the  sartorius  and  gracilis. 

The  crural  fascia,  or  fascia  of  the  leg  (Fascia  cruris),  consists  of  three  layers. 
Two  of  these  invest  the  entire  region  and  niaj',  therefore,  be  termed  the  common 
fasciae.  The  superficial  layer  is  a  continuation  of  the  fascite  of  the  thigh,  while  the 
second  layer  may  be  regarded  chiefly  as  a  continuation  of  the  tendons  of  the  super- 
ficial muscles  of  the  hip  and  thigh  (biceps  femoris,  scmitendinosus,  tensor  fascice  latte, 
sartorius,  and  gracilis).  The  two  layers  frequently  fuse,  and  are  attached  chiefly 
to  the  patellar  ligaments  and  the  crest  and  internal  surface  of  the  tibia.  About 
the  middle  of  the  leg  the  two  layers  unite  behind  the  deep  flexor  of  the  digit  and 
form  a  strong  band  which  passes  downward  in  front  of  the  tendons  of  the  gastroc- 
nemius and  superficial  flexor,  to  be  attached  with  the  latter  to  the  anterior  and 
inner  part  of  the  tuber  calcis.  This  may  be  regarded  as  an  accessory  or  tarsal 
tendon  of  insertion  of  the  biceps  femoris  and  scmitendinosus.  The  third  layer 
forms  sheaths  for  the  muscles,  furnishing  origin  in  part  to  their  fibers.  Two  im- 
portant intermuscular  septa  are  detached,  viz.:  (1)  One  which  passes  between  the 
anterior  and  lateral  digital  extensors  to  be  attached  to  the  fibula  and  the  external 
border  of  the  tibia;   (2)  one  between  the  lateral  extensor  and  the  deep  flexor. 

The  tarsal  fascia  (Fascia  tarsi)  fuses  with  the  ligaments  and  bony  prominences 
of  the  region.  It  is  strong  and  tendinous  in  front,  and  joins  the  tendon  of  the  an- 
terior extensor  below  the  joint.  Laterally,  it  is  thin  and  fuses  with  the  ligaments. 
Posteriorly,  it  is  very  thick  and  strong,  forming  an  annular  ligament  which  stretches 
from  the  internal  lateral  ligament  to  the  fibular  tarsal  bone  and  the  plantar  liga- 
ment. This  converts  the  groove  at  the  back  of  the  hock  into  a  canal,  in  which 
are  the  deep  flexor  tendon  with  its  sj'novial  sheath  and  the  plantar  nerves.  In 
front  of  the  tarsus  and  above  and  below  it  there  are  three  annular  ligaments 
(Ligamenta  transversa).  The  proximal  one  binds  down  the  tendons  of  the  anterior 
extensor,  peroneus  tertius,  and  tibialis  anterior  on  the  distal  end  of  the  tibia.  The 
middle  one  stretches  from  the  fibular  tarsal  bone  to  the  outer  tendon  of  the  pero- 
neus tertius,  forming  a  loop  around  the  tendon  of  the  anterior  extensor.  The  distal 
band  stretches  across  the  proximal  extremity  of  the  large  metatarsal  bone  and  in- 
closes the  tendons  (and  sheaths)  of  the  two  extensors  of  the  digit. 

The  metatarsal  and  digital  fasciae  do  not  differ  materially  from  those  of  the 
corresponding  regions  of  the  thoracic  limb. 

The  Muscles 

I.  THE  SUBLUMBAR  MUSCLES  (Figs.  450,  456) 
The  muscles  of  this  group  arc  not  confined  to  the  sublumbar  region,  but  ex- 
tend beyond  it  both  before  and  behind.      Their  chief  function  is  to  flex  the  hip 
joint.     Two,  however, — the  psoas  minor   and    the   quadratus   lumljorum, — have 
not  this  action. 


THE    SUBLUMBAR    MUSCLES  275 

1.  Psoas  minor  (s.  parvus). — This  is  a  fusiform,  flattened,  pennate  muscle, 
which  lies  along  the  ventro-lateral  aspect  of  the  bodies  of  the  last  three  thoracic 
and  the  lumbar  vertebra^. 

Origin. — The  bodies  of  the  last  three  thoracic  and  first  four  or  five  lumbar 
vertebrae,  and  the  vertebral  ends  of  the  sixteenth  and  seventeenth  ribs. 

Insertion. — The  psoas  tubercle  on  the  shaft  of  the  ilium. 

Action. — To  flex  the  pelvis  on  the  loins,  or  to  incline  it  laterally. 

Structure. — The  muscle  arises  by  a  series  of  digitations  which  pass  backward 
and  outward  to  be  inserted  at  an  acute  angle  on  the  tendon.  The  latter  lies  along 
the  outer  border  of  the  fleshy  portion  and  is  flattened.  It  appears  on  the  surface 
of  the  muscle  at  the  third  lumbar  process  and  increases  gradually  in  width  until  it 
reaches  the  pelvic  inlet,  where  it  becomes  narrower. 

Relations. — The  ventral  surface  of  the  thoracic  portion  of  the  muscle  is  related 
to  the  pleura,  crura  of  the  diaphragin,  and  sympathetic  nerve.  In  the  abdomen, 
the  chief  ventral  relations  are  the  peritoneum,  the  vena  cava  (right  side),  the  aorta 
and  left  kidney  (left  side),  the  s\^npathetic  nerves,  and  the  ureters.  Dorsallj-, 
the  chief  relations  are  the  vertebrae,  the  psoas  major,  and  lumbar  nerves.  Near 
its  insertion  the  tendon  is  crossed  internally  by  the  external  iliac  artery,  and  ex- 
ternally by  the  femoral  nerve. 

Blood-supply. — Intercostal  and  lumbar  arteries. 

Nerre-supply. — Lumbar  nerves. 

2.  Psoas  major  (s.  magnus). — This  is  much  larger  than  the  preceding  muscle, 
by  which  it  is  partly  covered.     It  is  triangular,  with  the  base  anterior. 

Origin. — The  ventral  surfaces  of  the  vertebral  ends  of  the  last  two  ribs  and 
the  transverse  processes  of  the  lumbar  vertebrie. 

Insertion. — The  internal  trochanter  of  the  femur,  by  a  common  tendon  with 
the  iliacus. 

Action. — To  flex  the  hip  joint  and  to  rotate  the  thigh  outward. 

Structure. — The  origin  of  the  muscle  is  fleshy,  the  belly  being  in  general 
flattened,  thick  in  its  middle,  thin  at  its  edges.  The  thoracic  portion  is  small, 
the  abdominal  part  much  thicker  and  wider,  extending  laterally  beyond  the  ex- 
tremities of  the  lumbar  transverse  processes.  From  the  lumbo-sacral  articulation 
it  lies  in  a  deep  groove  formed  in  the  iliacus  (with  which  it  is  partly-  united),  be- 
comes smaller  and  rounded,  and  passes  downward  and  backward  to  terminate  by  a 
strong  tendon  common  to  it  and  the  iliacus.' 

Relations. — -Dorsally,  the  last  two  ribs  and  thoracic  vertebrae,  the  lumbar 
vertebriB,  the  internal  intercostals,  quadratus  lumborum,  longissimus  dorsi,  and 
ihacus,  and  the  lumbar  vessels  and  nerves;  ventrally,  the  pleura  and  peritoneimi, 
the  ihac  fascia,  inguinal  ligament,  the  diaphragm,  psoas  minor,  and  sartorius,  the 
kidneys,  the  spleen,  the  intestine  (duodenum,  caecum,  etc.)  and  the  circumflex 
ihac  vessels. 

Blood-supply. — Lumbar  and  circumflex  iliac  arteries. 

A^erve-supply. — Lumbar  and  femoral  ner\-es. 

3.  Iliacus.— This  muscle  covers  the  ventral  surface  of  the  ilium  external  to 
the  sacro-iliac  articulation,  and  ex-tends  outward  beyond  the  ex-ternal  border  of  the 
bone,  underneath  the  middle  gluteus. 

0/-i'3(n.— The  ventral  surface  of  the  ilium  external  to  the  ilio-pectineal  line, 
the  ventral  sacro-iliac  ligament,  the  wing  of  the  sacrum,  and  the  tendon  of  the 
psoas  minor. 

Insertion.— The  internal  trochanter  of  the  femur,  by  a  common  tendon  with 
the  psoas  major. 

>  On  account  of  the  intimate  union  between  the  psoas  major  and  iliacus  they  are  frequently 
considered  a  single  muscle,  to  which  the  name  ilio-psoas  is  applied;  some  anatomists  mcludc  the 
psoas  minor  also  under  this  term. 


276  FASCI.E    AND    MUSCLES    OF    THE    HORSE 

Action. — To  flex  the  hip  joint  and  to  rotate  the  thigh  outward. 

Structure. — The  belly  of  the  muscle  is  so  deeply  grooved  for  the  psoas  major 
as  to  give  the  appearance  of  being  completely  divided  into  outer  and  inner  portions. 
When  the  psoas  is  removed,  it  is  seen,  however,  that  the  two  heads  are  not  entirely 
separated.  The  outer,  larger  head  arises  from  the  wing  of  the  ilium  chiefly;  the 
inner,  smaller  head  arises  chiefly  from  a  small  area  on  the  shaft  of  the  ilium,  be- 
tween the  psoas  tubercle  and  the  depression  for  the  inner  tendon  of  the  rectus 
femoris,  and  from  the  tendon  of  the  psoas  minor.  The  two  portions  inclose 
the  psoas  major  in  front  of  the  hip  joint. 

Relations. — Dorsally,  the  ilium,  sacrum,  sacro-iliac  articulation,  the  gluteus 
medius,  the  ilio-lumbar  and  external  circumflex  vessels;  ventrally,  the  iliac  fascia, 
inguinal  ligament,  the  psoas  major,  sartorius,  and  abdominal  muscles.  At  the 
hip  joint  the  chief  relations  are:  internally,  the  femoral  vessels,  the  femoral  nerve, 
and  the  sartorius  muscle;  externally,  the  rectus  femoris  and  tensor  fasciae  latse;  in 
front,  the  alxlominal  muscles;   behind,  the  hip  joint. 

Blood -.-f  up  ply. — Lumbar,  circumflex  iliac,  and  deep  femoral  arteries. 

A'rrre-supplii. — Lumbar  and  femoral  nerves. 

4.  Quadratus  Inmborum. — This  thin  muscle  lies  on  the  outer  part  of  the 
ventral  surfaces  of  the  lumbar  transverse  processes. 

Origin. — The  ventral  surface  of  the  upper  part  of  the  last  two  ribs  and  the 
lumbar  transverse  processes. 

Insertion. — The  ventral  surface  of  the  wing  of  the  sacrum  and  the  ventral 
sacro-iliac  ligament. 

Action. — Acting  together,  to  fix  the  last  two  ribs  and  the  lumbar  vertebrie; 
acting  singly,  to  produce  lateral  flexion  of  the  loins. 

Structure. — The  muscle  is  pennate,  and  is  curved  with  the  convexity  outward. 
It  is  thin,  largely  mixed  with  tendinous  fibers,  and  is,  in  general,  little  developed  in 
the  horse  in  comparison  with  some  of  the  other  animals  (e.  g.,  dog,  sheep). 

Relations. — Ventrally,  the  psoas  major  and  the  last  intercostal  and  first  three 
lumbar  nerves;  dorsally,  the  last  two  ribs,  the  lumbar  transverse  processes,  and 
the  lateral  branches  of  the  lumbar  arteries. 

Blood-supply. — Lumbar  arteries. 

Ncrre-suppli/. — Lumbar  nerves. 

5.  Intertransversales  lumborum  (^L  intcrtransversarii  lumborum). — These 
are  described  with  the  other  spinal  muscles.     (See  p.  238.) 


II.  THE  EXTERNAL  MUSCLES  OF  THE   HIP  AND  THIGH 

Under  this  head  will  be  described  the  muscles  of  the  outer  surface  of  the  pelvis 
and  thigh,  and  those  which  form  the  posterior  contour  of  the  latter.  They  are 
given  in  tlie  order  in  which  thej'  may  be  conveniently  examined. 

1.  Tensor  fasciae  latae  (Fig.  178). — This  is  the  most  anterior  muscle  of  the 
superficial  layer.  It  is  triangular  in  form,  with  its  apex  at  the  external  angle  of 
the  ilium. 

Origin. — The  external  angle  of  the  ilium. 

Insertion. — The  fascia  lata,  and  thus  indirectly  to  the  patella,  the  external 
straight  ligament,  and  the  crest  of  the  tibia. 

x\ction. — To  tense  the  fascia  lata,  flex  the  hip  joint,  and  extend  the 
stifle  joint. 

Structure. — The  muscle  arises  by  a  rather  small  head,  about  two  inches  (ca. 
5  em.)  wide,  on  the  antoro-inferior  eminence  of  the  external  angle  of  the  ilium. 
Below  this  the  belly  spreads  out  and  terminates  about  midway  between  the  i)oint 
of  the  hip  and  the  stifle  in  the  aponeurosis.  The  belly  fuses  to  a  considerable  ex- 
tent with  the  superficial  gluteus.     The  aponeurosis  fuses  with  the  fascia  lata,  and 


THE    EXTERNAL    MUSCLES    OF   THE    HIP    AND    THIGH  277 

detaches  a  lamina  which  passes  with  the  tendon  of  insertion  of  the  superficial  gluteus 
to  the  external  border  of  the  femur. 

Relations  — Externally,  the  skin  and  fascia;  internally,  the  ohliciuus  abdominis 
externus,  the  iliacus,  superficial  gluteus,  rectus  femoris,  and  vastus  externus, 
branches  of  the  circumflex  iliac,  ilio-lumbar,  and  iliaco-femoral  arteries,  and  the 
anterior  gluteal  nerve;  anteriorly,  the  precrural  lymph-glands.  A  considerable 
quantity  of  connective  tissue  is  found  between  the  deep  face  of  the  muscle  and  the 
abdominal  wall. 

Blood-supply. — Circumflex  iliac,  ilio-lumbar,  and  iliaco-femoral  arteries. 

Xcrrc-supply. — Anterior  gluteal  nerve. 

2.  Gluteus superficialis  (Figs.  178, 199)  (Superficial  gluteus; gluteus  externus). — 
This  muscle  lies  behind  and  partly  underneath  the  tensor  fasciae  latae.  It  is 
triangular  and  consists  of  an  anterior  and  a  posterior  head  united  by  the  gluteal 
fascia. 

Origin. — (1)  The  external  angle  and  the  adjacent  part  of  the  external  border 
of  the  ilium  (anterior  head);    (2)  the  gluteal  fascia  (posterior  head). 

Insertion. — The  third  (external)  trochanter  of  the  femur. 

Action. — To  abduct  the  limb,  flex  the  hip  joint,  and  tense  the  gluteal  fascia. 

Structure. — The  anterior  head  of  the  muscle  is  not  completely  separalile  (ex- 
cept artificially)  from  the  tensor  fascite  latse.  The  attachment  to  the  border  of 
the  ilium  is  by  means  of  an  intermuscular  septum,  which  passes  beneath  the  thick 
outer  border  of  the  gluteus  medius.  The  posterior  head  arises  from  the  deep  face 
of  the  gluteal  fascia,  and  so  indirectly  from  the  dorsal  sacro-iliac  ligament.  The 
two  heads  unite  and  terminate  on  a  strong  flat  tendon,  which  is  inserted  into  the 
edge  of  the  third  trochanter  of  the  femur,  beneath  the  biceps  femoris. 

Relations. — Superficially,  the  skin,  fascia,  and  biceps  femoris;  deeply,  the 
gluteus  medius,  iliacus,  rectus  femoris,  and  branches  of  the  iliaco-femoral  artery; 
in  front,  the  tensor  fascise  latiE;   behind,  the  biceps  femoris. 

Blood-supply. — Gluteal  and  iliaco-femoral  arteries. 

Nerre-supply. — Anterior  gluteal  nerve. 

3.  Gluteus  medius  (Figs.  178,  179)  (^Middle  gluteus;  gluteus  maximus). — 
This  is  a  very  large  muscle  which  covers  the  dorsal  surface  of  the  ilium  and  the 
greater  part  of  the  lateral  wall  of  the  pelvis,  and  extends  forward  also  on  the  lumbar 
part  of  the  longissimus. 

Origin. — (1)  The  aponeurosis  of  the  longissimus,  as  far  forward  as  the  first 
lumbar  vertebra;  (2)  the  gluteal  or  dorsal  surface  and  internal  and  external 
angles  of  the  ilium;  (3)  the  dorsal  and  lateral  sacro-iliac  and  sacro-sciatic  ligaments, 
and  the  gluteal  fascia. 

Insertion. — (1)  The  summit  of  the  trochanter  major  of  the  femur;  (2)  the  crest 
below  the  trochanter;   (3)  the  outer  aspect  of  the  trochanteric  ridge. 

Action. — To  extend  the  hip  joint  and  abduct  the  limb.  By  its  connection 
with  the  longissimus  a  muscular  mass  is  formed  which  is  one  of  the  chief  factors  in 
rearing,  kicking,  and  propulsion. 

Structure. — The  anterior  extremity  of  the  muscle  is  relatively  thin,  and  lies 
in  a  depression  on  the  surface  of  the  longissimus,  from  the  strong  aponeurosis  of 
which  the  fibers  take  origin.  The  pelvic  portion  of  the  muscle  is  very  voluminous, 
and  forms  the  bulk  of  the  muscular  mass  which  gives  the  haunch  its  rounded  con- 
tour. This  part  of  the  muscle  is  intersected  by  several  tendinous  sheets.  One  of 
these  is  particularly  distinct,  and  is  attached  to  the  gluteal  line  on  the  ilium.  This 
divides  the  muscle  incompletely  into  superficial  and  deep  strata.  The  superficial 
part  is  inserted  by  a  strong  tendon  into  the  summit  of  the  great  trochanter,  and 
by  a  pointed  fleshy  mass  with  a  tendinous  border  into  the  trochanteric  ridge.  The 
deep  part  (Clluteus  accessorius)  is  smaller,  and  arises  entirely  from  the  ilium  be- 
tween the  gluteal  line  and  the  external  angle  (Fig.  455j .     It  has  a  strong  flat  tendon 


278  FASCI.E   AND    MUSCLES    OF    THE    HORSE 

which  passes  over  the  convexity  of  the  trochanter  to  l)e  inserted  into  the  crest 
below  it.  The  convexity  is  covered  with  cartilage,  and  the  trochanteric  bursa 
(Bursa  trochanterica)  is  interposed  between  the  tendon  and  the  cartilage.' 

Relations. — Superficially,  the  skin,  lunibo-dorsal  and  gluteal  fascia',  the  tensur 
fasciae  latoe,  gluteus  superficialis,  and  biceps  fenioris;  deeply,  the  longissimus,  the 
ilium,  sacro-iliac  and  sacro-sciatic  ligaments,  the  gluteus  jirofundus,  iliacus  and 
rectus  femoris,  the  iliaco-femoral  artery,  the  gluteal  and  internal  pudic  vessels  and 
nerves,  and  the  great  sciatic  nerve. 

Blood-supply.— Glutesil,  ilio-lumbar,  lumbar,  and  iliaco-femoral  arteries. 

Nerve-supply. — Gluteal  nerves. 

4.  Gluteus  profvindus  (Deep  gluteus;  gluteus  internus;  scansorius). — This 
much  smaller,  quadrilateral  muscle  lies  under  the  posterior  part  of  the  preceding 
muscle,  and  extends  over  the  hip  joint,  from  the  superior  iscluatic  spine  to  the 
anterior  part  of  the  great  trochanter  (Fig.  455). 

Origin. — The  superior  ischiatic  spine  and  the  adjacent  part  of  the  shaft  of  the 
ilium. 

Insertion. — The  edge  of  the  anterior  part  or  convexity  of  the  trochanter  major 
of  the  femur. 

Action. — To  abduct  the  thigh  and  to  rotate  it  inward. 

Structure. — The  muscle  is  short  and  thick  and  contains  numerous  tentlinous 
intersections.  The  fibers  are  directed  ahnost  transversely  outward  over  the  capsule 
of  the  hip  joint  and  converge  at  the  convexit.y  of  the  trochanter. 

Relations. — Superficially,  the  gluteus  medius  and  branches  of  the  gluteal  vessels 
and  nerves;  deeply,  the  shaft  of  the  ilium,  the  hip  joint,  and  the  rectus  femoris 
and  capsularis. 

Blood-supply . — Gluteal  artery. 

Nerve-supply. — Anterior  gluteal  nerve. 

5.  Biceps  femoris  (Gluteo-biceps  s.  paramcro-biceps). — This  large  muscle  lies 
behind  and  in  part  upon  the  superficial  and  middle  glutei.  It  extends  in  a  curved 
direction  from  the  sacral  and  coccygeal  spines  to  the  outer  surface  of  the  stifle 
and  leg  (Figs.  178,  199,  200,  201,  202). 

Origin. — -(1)  The  dor.sal  sacro-iliac  ligament,  the  gluteal  and  coccygeal  fasciae, 
and  the  intermuscular  septum  lietween  this  muscle  and  the  semitendinosus;  (2) 
the  tuber  ischii. 

Insertion. — (1)  A  tubercle  on  the  posterior  surface  of  the  femur  near  the  ex- 
ternal trochanter;  (2)  the  anterior  surface  and  external  straight  ligament  of  the 
patella;  (3)  the  tibial  crest;  (4)  the  anterior  and  internal  surface  of  the  tuber 
calcis. 

Action. — The  action  is  somewhat  comjilex,  because  the  muscle  is  composed 
of  three  portions,  has  several  points  of  insertion,  and  acts  on  all  the  joints  of  the 
limb  except  those  of  the  digit.  The  general  action  is  to  extend  the  limb,  as  in  pro- 
pelling the  body,  rearing  or  kicking,  and  to  abduct  it.  The  anterior  part,  by  its 
attachment  to  the  posterior  surface  of  the  femur  and  to  the  patella,  would  extend 
the  stifle  and  hip  joints  and  abduct  the  limb.  The  middle  part,  being  inserted 
chiefly  on  the  tibial  crest  and  the  external  straight  ligament,  would  extend  the 
hip,  and,  with  the  semitendinosus,  flex  the  stifle.  The  posterior  part,  by  virtue 
of  its  attachment  to  the  tuber  calcis,  assists  in  extending  the  hock. 

Structure. — The  muscle  has  two  heads  of  origin:-  The  long  or  vertebral  head 
arises  chiefly  from  the  dorsal  and  lateral  sacro-iliac  ligaments,  the  coccygeal  fascia, 

'  By  some  anatomists  the  portion  inserted  into  the  crest  is  termed  the  gluteus  accessorius, 
but  Lesbro  considers  this  the  deep  gluteus,  homologous  \vith  the  gluteus  minimus  of  man.  The 
portion  in.scrted  into  the  trochanteric  ridge  apparently  represents  the  piriformis  of  man. 

■  .\pparently  the  muscle  represents  the  biceps,  together  with  part  of  the  gluteus  super- 
ficialis of  man.     Hence  the  names  gluteo-biceps  and  paramcro-biceps  liave  been  suggested. 


THE    EXTERNAL    MUSCLES    OF    THE    HIP    AND    THIGH 


279 


and  the  intermuscular  septum.  There  is  often  a  large  bursa  lietween  this  head  and 
the  trochanter  major.  The  short  or  ischiatic  head  arises  by  a  strong  tendon  from 
the  ventral  spine  on  the  tuber  ischii.  They  unite,  and  a  short  tendon  is  detached 
from  the  deep  face  of  the  muscle,  to  be  inserted  into  the  posterior  surface  of  the 


Sacro-coccygui': 


!>ilt'(it  fascia 


External  angle  of  ilium 


^J,~-'  Superficial  gluteus 


Gastrocnemius  tendon 


Superficial  flexor  tendon  — 


Deep  flexor 
-Lateral  extensor 


Deep  flexor  tendon 
Superficial  flexor  tendon 


Suspeyisory  ligament 


VIC  Limb  of   Horse,  Postero-external  View. 
17,  Position  of  tuber  ischii;  o".  superficial  gluteus;  q,  ci .  <t' .  biceps  femoris;  r,  semitendinosus;  /,  sacro-coccygeus 
lateralis;  d,  semimembranosus;  u),  gracilis;  /,  gastrocnemius.     (After  Ellenberger-Baum,  Anat.  f.  Kunstler.) 


Fig.   199. — Muscles 


femur  near  the  third  trochanter  (Fig.  455),  a  bursa  being  interposed  between  the 
tendon  and  the  bone.  The  muscle  then  divides  into  three  portions,  which  termi- 
nate on  a  strong  aponeurosis  over  the  junction  of  the  thigh  and  leg.  The  anterior 
branch  is  directed  toward  the  patella,  the  middle  toward  the  tibial  crest,  while  the 


280  FASCIA    AND    MUSCLES    OF    THE    HOHSE 

posterior  one  assists  in  the  formation  of  the  posterior  contour  of  the  limb.  The 
aponeurosis  blends  with  the  deep  layer  of  the  fascia  cruris,  as  already  described. 
A  synovial  bursa  occurs  under  the  patellar  insertion. 

Ri'latioitfi. — Superficially,  the  skin  and  fascia;  deeply,  the  sacro-iliac  and  sacro- 
sciatic  ligaments,  the  coccygeal  fascia,  the  femur,  the  obturator,  gemellus,  cjuadratus 
femoris,  adductor,  semimembranosus,  vastus  externus,  and  gastrocnemius  muscles, 
branches  of  the  lateral  sacral,  gluteal,  obturator,  femoral  and  deep  femoral  vessels, 
the  great  sciatic,  tibial,  peroneal,  and  posterior  gluteal  nerves;  in  front,  the  super- 
ficial and  middle  glutei ;   behind  and  internally,  the  semitendinosus. 

Blood-supply. — Gluteal,  obturator,  and  femoro-popliteal  arteries. 

Nervr-supphj. — Posterior  gluteal  and  great  sciatic  nerves. 

6.  Semitendinosus  (Biceps  rotator  tibialis) . — This  is  a  long  muscle  which 
extends  from  the  first  two  coccygeal  vertebrae  to  the  proximal  third  of  the  inner 
surface  of  the  tibia.  It  lies  at  first  behind  the  biceps,  then  passes  downward  on  the 
back  of  the  thigh,  between  that  muscle  and  the  semimembranosus  (Figs.  178,  179, 
199).     It  has  two  heads  of  origin. 

Origin. — (1)  The  transverse  processes  of  the  first  and  second  coccygeal  ver- 
tebrifi,  the  coccygeal  fascia,  and  the  intermuscular  septum  between  this  muscle  and 
the  biceps  femoris;    (2)  the  ventral  surface  of  the  tuber  ischii. 

Insertion. — (1)  The  tibial  crest;    (2)  the  crural  fascia  and  the  tuber  calcis. 

Action. — To  flex  the  stifle  and  rotate  the  leg  inward;  also  to  extend  the  hip 
and  hock  joints,  acting  with  the  biceps  and  semimembranosus  in  propulsion  of  the 
trunk,  rearing,  etc. 

Structure. — The  long  or  vertebral  head  is  small  at  its  origin,  but  becomes  larger 
by  the  accession  of  fibers  arising  on  the  intermuscular  septum.  Below  the  tuber 
ischii  it  is  joined  by  the  short  head,  which  arises  partly  by  fleshy  fibers,  partly  by  a 
common  tendon  with  the  biceps.  The  muscle  then  passes  downward  on  the  back 
of  the  thigh,  and  terminates  on  a  wide  tendon  on  the  inner  surface  of  the  proximal 
third  of  the  leg.  A  distinct  band  passes  forward  to  be  inserted  on  the  tibial  crest 
(a  bursa  lying  between  the  tendon  and  the  tibia),  part  fuses  with  the  fascia  of  the 
leg,  while  the  remainder  joins  the  biceps  tendon  and  concurs  in  the  formation  of  the 
tendinous  band,  which,  as  before  described,  terminates  on  the  tuber  calcis  (Fig. 
458).     A  bursa  may  occur  under  the  long  head  where  it  passes  over  the  tuber  ischii. 

Relations. — Externally,  the  skin  and  fascia,  the  biceps,  and  the  internal  head 
of  the  gastrocnemius;  internally,  the  coccygeal  fascia,  the  sacro-sciatic  ligament, 
the  semimembranosus;  anteriorly,  the  biceps  femoris,  branches  of  the  femoral 
artery,  and  the  great  sciatic  nerve. 

Blood-sup  pi  ij. — Posterior  gluteal,  obturator,  and  femoro-popliteal  arteries 

Nerve-supphj. — Posterior  gluteal  and  great  sciatic  nerves. 

7.  Semimembranosus'  (Figs.  179, 186,  199,  451). — This  muscle  lies  on  the  inner 
surface  of  the  preceding  muscle  and  the  gastrocnemius,  and  has  two  heads  of  origin. 

Origin. — (1)  The  posterior  border  of  the  sacro-sciatic  ligament ;  (2)  the  ventral 
surface  of  the  tuber  ischii. 

Insertion. — The  internal  epicondyle  of  the  femur,  behind  the  lateral  ligament. 

Action. — To  extend  the  hip  joint  and  to  atlduct  the  limb. 

Structure. — The  long  head,  small  and  pointed  above,  extends  toward  the  root 
of  the  tail,  fusing  with  the  sacro-sciatic  ligament.  Passing  downward,  it  becomes 
larger  and  covers  in  part  the  posterior  aspect  of  the  tuber  ischii.  A  bursa  may  be 
found  here.  Below  this  it  joins  the  short  head,  which  is  much  larger.  The  large 
belly  so  formed  passes  downward  and  forward,  covered  in  great  part  by  the  gracilis, 
and  terminates  on  a  short,  flat  tendon  of  insertion  at  the  distal  end  of  the  femur. 

Relations. — The  upper  part  of  the  muscle  assists  in  forming  the  lateral  boun- 

'  This  muscle  was  incorrectly  designated  the  adductor  magnus  by  Percivall  and  Strange- 
ways.     Its  name,  however,  is  not  at  all  descriptive  of  its  structure  in  the  domesticated  animals. 


THE    INTERNAL    MUSCLES    OK    THE    THIGH  281 

dary  of  the  pelvic  outlet.  It  is  related  posteriorly  and  externally  to  the  skin  and 
fascia  and  the  semitcndinosus;  internally,  to  the  anus  and  its  muscles,  the  vulva 
in  the  female,  and  the  internal  pudic  artery  and  nerve  (Figs.  452,  453).  Below 
the  pelvis  the  chief  relations  are:  externally,  the  semitcndinosus,  biceps,  and 
gastrocnemius,  branches  of  the  obturator,  femoral,  and  femoro-popliteal  arteries, 
and  the  great  sciatic  nerve  and  its  chief  branches;  internally,  the  crus  penis 
and  ischio-cavernosus  muscle  (in  the  male),  and  the  gracilis;  in  front,  the  adduc- 
tor and  the  femoral  vessels;   behind,  the  skin  and  fascia. 

Blood-supply. — Obturator  and  femoral  arteries. 

Nerve-supply. — Great  sciatic  uerve. 


IV.   THE  INTERNAL  MUSCLES  OF  THE  THIGH 
The  muscles  of  this  group  are  arranged  in  three  layers. 

First  Layer 

1.  Sartorius  (Figs.  186,  202,  203). — This  long  and  rather  narrow  muscle  is  the 
most  anterior  one  of  the  first  layer.  It  extends  from  the  sublumbar  region  to  the 
lower  and  inner  part  of  the  stifle. 

Origin. — The  iliac  fascia  and  the  tendon  of  the  psoas  minor. 

Insertion. — The  internal  straight  ligament  of  the  patella  and  the  adjacent  part 
of  the  tuberosity  of  the  tibia. 

Action. — To  flex  the  hip  joint  and  adduct  the  limb. 

Structure. — The  muscle  is  very  thin  at  its  origin,  but  becomes  thicker  and 
narrower  as  it  passes  downward  and  a  little  backward.  It  terminates  near  the 
stifle  joint  on  an  aponeurosis  which  blends  with  that  of  the  gracilis  and  with  the 
fascia  of  the  leg. 

Relations. — Superficially,  the  inguinal  (Poupart's)  ligament,  the  abdominal 
muscles,  the  skin  and  fascia,  and  the  saphenous  vessels  and  nerve:  deeply,  the 
ilio-psoas,  quadriceps  femoris,  and  adductor.  It  forms  the  anterior  boundary  of 
the  femoral  canal,  in  which  the  femoral  artery  and  vein  and  the  deep  inguinal 
lymph  glands  are  situated  (Fig.  451). 

Blood-supply. — Femoral  artery. 

Nerve-supply. — Femoral  and  saphenous  nerves. 

2.  GraciUs  (Figs.  186,  199,  202,  203).— This  is  a  wide,  flat,  quadrilateral 
muscle,  situated  behind  the  sartorius,  which  it  exceeds  greatl.y  in  extent. 

Origin. — The  middle  third  of  the  pelvic  symphysis,  the  prepubic  tendon  and 
pubo-femoral  ligament,  and  the  ventral  surface  of  the  pubis  behind  the  prepubic 
tendon. 

Insertion. — The  internal  straight  ligament  of  the  patella,  the  internal  surface 
of  the  tibia  in  front  of  the  lateral  ligament  of  the  stifle  joint,  and  the  fascia  of 
the  leg. 

Action. — To  adduct  the  limb.     It  may  also  rotate  it  inward. 

Structure. — The  muscle  arises  by  a  strong  tendon,  chiefly  in  common  with  the 
opposite  muscle.  Its  direct  attachment  to  the  ventral  surface  of  the  pelvis  is  not 
so  extensive  as  a  superficial  inspection  would  suggest.  The  origin  of  the  muscle 
presents  anteriorly  a  rouml  perforation  for  the  passage  of  the  external  pudic  vein. 
The  belly  is  composed  of  parallel  bundles,  and  is  marked  by  a  superficial  furrow 
which,  however,  does  not  indicate  a  muscular  division.  It  terminates  on  the  inner 
surface  of  the  stifle  on  a  thin  wide  tendon  which  blends  in  front  with  that  of  the 
sartorius,  below  with  the  crural  fascia. 

Relations. — Superficially,  the  skin  and  fascia,  the  penis  or  mammary  gland, 
and  the  saphenous  vessels  and  nerve;  deeply,  the  pectineus,  adductor,  semimem- 


282  FASCLE    AND    MUSCLES    OF   THE    HORSE 

branosus  and  scmitendinosus,  and,  at  the  middle  of  the  femur,  the  femoral  vessels; 
anteriorly,  the  sartorius.  In  the  upper  third  of  the  thigh  the  sartorius  and  gracilis 
are  separated  by  a  triangular  interval  (femoral  triangle),  in  which  lie  the  deep 
inguinal  lymph  glands  and  the  femoral  vessels. 

Blood-supply. — Femoral  and  deep  femoral  arteries. 

Nerve-supply. — Obturator  and  saph(>nous  nerves. 

Second  Layer 

1.  Pectineus  (Figs.  186,  451,  456). — This  muscle  is  fusiform  and  extends  from 
the  anterior  border  of  the  pubis  to  the  middle  of  the  inner  border  of  the  femur. 

Origin. — The  prepubic  tendon,  the  pul)o-femoral  ligament,  and  the  anterior 
border  of  the  pubis. 

Insertion. — The  middle  of  the  internal  border  of  the  femur,  near  the  nutrient 
foramen. 

Action. — To  adduct  the  limb  and  flex  the  hip  joint. 

Structure. — The  belly  is  cylindrical  and  contains  little  fibrous  tissue.  Its 
origin  is  perforated  by  the  pubo-femoral  ligament,  and  is  thus  divided  into  two 
unequal  parts.  The  large  upper  part  arises  mainly  from  the  prepubic  tendon 
— only  a  very  small  part  gaining  direct  attachment  to  the  pubis.  The  small  lower 
part  does  not  reach  the  bone.     The  insertion  is  pointed  and  tendinous. 

Relations. — Superficially,  the  gracilis;  deeply,  the  femur,  the  vastus  internus, 
the  terminal  tendon  of  the  psoas  major  and  iliacus,  and  the  deep  femoral  artery; 
anteriorly,  the  sartorius,  the  femoral  vessels,  the  saphenous  nerve,  and  the  deep 
inguinal  lymph  glands;  posteriorly,  the  adductor,  obturator  externus,  and  cjuadra- 
tus  femoris,  and  the  obturator  nerve  (anterior  division). 

Blood-supply. — Femoral  and  deep  femoral  arteries. 

Nerve-supply. — Femoral  and  obturator  nerves. 

The  femoral  canal  is  exposed  in  the  dissection  of  the  preceding  muscles  (Figs.  200,  451). 
It  is  bounded  anteriorly  by  the  sartorius,  posteriorly  by  the  pectineus,  and  externally  by  the 
iliacus  and  vastus  internus.  Its  internal  wall  is  formed  by  the  femoral  fascia  and  the  gracilis. 
Its  upper  or  abdominal  opening  (Lacuna  vasorum)  lirs  briiiml  and  a  little  internal  to  the  inter- 
nal inguinal  ring  and  is  bounded  anteriorly  by  the  iniiuiiuil  ligament,  posteriorly  by  the  ante- 
rior border  of  the  pubis,  and  externally  by  the  tendon  of  the  psoas  minor.  The  canal  termi- 
nates below  at  the  insertion  of  the  pectineus.  It  contains  the  deep  inguinal  lymph  glands,  the 
femoral  artery  and  vein,  and  the  saphenous  nerve. 

2.  Adductor' (Figs.  179,  186,451)  (Great  and  small  adductors  of  the  thigh).— 
This  fleshy,  prismatic  muscle  lies  behind  the  pectineus  and  vastus  internus.  It 
extends  downward  and  forward  from  the  ventral  siulace  of  the  pelvis  to  the  internal 
condyle  of  the  femur. 

Origin. — The  ventral  surface  of  the  pul)is  and  ischium  and  the  tendon  of  the 
gracilis. 

Insertion. — (1)  The  posterior  surface  of  the  femur  from  the  level  of  the  external 
trochanter  to  the  groove  for  the  femoral  vessels;  (2)  the  internal  epicondyle  of  the 
femur  and  the  internal  lateral  ligament  of  the  stifle  joint. 

Action. — To  adduct  the  limb  and  assist  in  extending  the  hip  joint.  It  may 
also  rotate  the  femur  outward. 

Structure. — It  is  almost  entirely  fleshy,  and  is  composed  of  ])arallel  bundles 
united  rather  loosely.  It  is  usually  possible  to  separate  from  the  principal  mass  a 
small  anterior  short  portion,-  which  is  inserted  into  the  femur  behind  the  pectineus. 
The  principal  mass^  is  perforated  below  its  middle  by  the  femoral  vessels,  and  is 

1  It  has  been  customary  to  describe  two  adductors — a  parvus  or  brevis,  and  a  longus  or 
magnus.  This  division  is  largely  artificial,  and  has  been  abandoned  in  the  new  nomenclature — 
a  return  to  the  views  of  Bourgelat  and  Girard. 

'  This  has  been  termed  by  various  authors  the  adductor  parvus  or  brevis. 

'  Termed  by  various  authors  the  adductor  magnus  or  longus. 


THE    INTERNAL    MUSCLES    OF    THE    THIGH  283 

thus  (livuU'il  inti)  two  hrani'hos.  The  outer  hrancli  is  inserted  into  the  haek  (jf  the 
fonmr  with  the  short  portion,  while  the  inner  branch  is  attached  to  the  internal 
epicondyle  and  hiteral  ligament.  There  is  often  a  superficial  slip  which  reaches 
the  internal  straight  patellar  ligament.  Some  fibers  pass  untler  the  lateral  ligament 
anil  end  on  the  tendon  of  the  semimembranosus. 

Relations. — Internally,  the  gracilis,  and  Ijranches  of  tlie  femoral  artery  and  of 
the  obturator  nerve;  externally,  the  femur,  the  obturator  externus,  quadratus 
femoris,  biceps  femoris,  antl  gastrocnemius,  and  the  femoral,  deep  femoral,  and 
obturator  arteries;  anteriorly,  the  pectineus,  vastus  internus,  and  a  large  branch 
of  the  obturator  nerve;  posteriorly,  the  semimembranosus  and  the  great  sciatic 
nerve. 

Blood-supply. — Femoral,  deep  femoral,  and  obturator  arteries. 

Nerve-siipph/. — Obturator  nerve. 

3.  Semimembranosus. — Described  on  p.  280. 

Third  Layer 

1.  Quadratus  femoris  (Ischio-femoralis). — This  is  a  narrow,  flat  muscle, 
which  lies  under  cover  of  the  upper  part  of  the  adductor  (Figs.  455,  456). 

Origin. — The  ventral  surface  of  the  ischium,  just  in  front  of  the  semimembrano- 
sus. 

Insertion. — An  oblique  line  on  the  posterior  surface  of  the  femur,  near  the 
lower  part  of  the  internal  trochanter. 

Action. — ^To  extend  the  hip  joint,  and  to  adduct  the  thigh  and  rotate  it  out- 
ward. 

Structure. — It  is  composed  of  parallel  bundles  of  fibers  directeil  downward, 
forward,  and  outward. 

Relations. — Internally,  the  adductor,  semimembranosus,  and  the  obturator 
vessels;  externally,  the  obturator  externus  and  biceps  femoris,  the  deep  femoral 
artery,  and  the  great  sciatic  nerve. 

Blood-supply. — Deep  femoral  and  obturator  arteries. 

Nerve-supply. — -Great  sciatic  nerve. 

2.  Obtiirator  Externus  (Fig.  456) . — This  is  a  pyramidal  muscle  which  extends 
across  the  back  of  the  hip  joint  from  the  obturator  foramen  to  the  trochanteric 
fossa. 

Origin. — The  ventral  surface  of  the  pubis  and  ischium,  and  the  margin  of  the 
obturator  foramen. 

Insertion. — The  trochanteric  fossa. 

Action. — To  adduct  the  thigh  and  to  rotate  it  outward. 

Structure. — It  is  almost  entirely  fleshy,  the  muscle-bundles  being  rather  loosely 
connected.  The  insertion  is  pointed,  flattened,  and  partly  tendinous.  The  origin 
is  perforated  by  the  obturator  vessels  and  nerve. 

Relations. — Internally,  the  adductor  and  quadratus  femoris  and  the  deep 
femoral  vessels';  externally,  the  gemellus,  the  tendon  of  the  obturator  internus,  the 
biceps  femoris,  and  the  great  sciatic  nerve;  anteriorly,  the  hip  joint,  the  pectineus, 
and  the  external  pudic  vein. 

Blood-supply. — Deep  femoral  and  obturator  arteries. 

Nerve-supply. — Obturator  nerve. 

3.  Obturator  internus  (Fig.  451).— This  arises  by  two  heads  within  the  pelvic 
cavity,  the  tendon  emerging  through  the  lesser  sciatic  foramen. 

Origin.— (l)  The  pelvic  surface  of  the  pubis  and  ischium  around  the  obturator 
foramen ;   (2)  the  pelvic  surface  of  the  shaft  of  the  ilium  and  the  wing  of  the  sacrum. 
Insertion. — The  trochanteric  fossa. 
Action. — To  rotate  the  femur  outward. 


284  FASCIA    AND    MUSCLES    OF    THE    HORSE 

Structure. — The  ischio-pubie  head  Ucs  on  tlic  pelvic  floor  and  covers  the  ob- 
turator foramen.  It  is  thin  and  fan-shaped.  The  iliac  head  extends  along  the 
lateral  wall  of  the  pelvis,  and  is  pennate,  with  a  central  tendon  throughout.  Both 
terminate  on  a  flat  tendon  which  passes  outward  through  the  lesser  sciatic  fora- 
men to  be  inserted  into  the  trochanteric  fossa.  A  synovial  bursa  facilitates  the 
play  of  the  tendon  over  the  external  border  of  the  ischium.' 

Relations. — The  pelvic  surface  is  covered  by  the  pelvic  fascia  and  the  perito- 
neum. The  obturator  vessels  and  nerve  lie  between  the  two  heads,  and  the  internal 
pudic  vessels  and  nerve  lie  along  the  dorsal  edge  of  the  iliac  head. 

Blood-supply. — Obturator  and  internal  pudic  arteries. 

Nerve-supply. — Great  sciatic  nerve. 

4.  Gemellus'"  (Fig.  455). — This  is  a  thin,  triangidar  nuiscle,  which  extends 
from  the  external  bonier  of  the  ischium  to  the  trochanteric  fossa. 

Origin. — ^The  external  border  of  the  ischium  near  the  ischiatic  spine. 

Insertion. — The  trochanteric  fossa. 

Action. — To  rotate  the  femur  outward. 

Structure. — ^Fleshy,  some  fibers  being  inserted  into  the  tendon  of  the  obturator 
internus. 

Relations. — Dorsally,  the  tendon  of  the  obturator  internus  and  the  gluteus 
profundus:   ventrally,  the  obturator  externus. 

Blood-supply. — Obturator  artery. 

Nerve-supply. — Sciatic  nerve. 


III.  ANTERIOR  MUSCLES  OF  THE  THIGH 
This  group  consists  of  the  sartorius,  ciuadriceps  femoris,  and  capsularis. 

1.  Sartorius. — This  is  described  on  p.  281. 

2.  Quadriceps  femoris  (Figs.  179,  186,  200)  (Crural  triceps). — This  con- 
stitutes the  large  muscular  mass  which  covers  the  front  and  sides  of  the  femur.  It 
has  four  heads,  one  of  which,  the  rectus,  arises  from  the  ilium;  the  other  three 
arise  from  the  femur.     All  are  inserted  into  the  patella. 

(1)  Rectus  femoris. — This  is  fusiform  and  rounded.     It  arises  by  two  tendons. 

Origin. — Two  depressions  on  the  shaft  of  the  ilium  above  and  in  front  of  the 
acetabulum. 

Insertion. — The  base  and  anterior  surface  of  the  patella. 

Action.— To  extend  the  stifle  joint  and  to  flex  the  hip  joint. 

Structure. — It  has  two  short  strong  tendons  of  origin ;  beneath  the  outer  one 
is  a  bursa.  The  belly  is  rounded  and  rests  in  a  groove  formed  by  the  other  portions 
of  the  quadriceps.  Its  sides  are  covered  by  a  strong  tendinous  layer  which  fur- 
nishes insertion  to  fibers  of  the  vasti.  The  tendon  of  insertion  is  formed  by  the 
fusion  of  these  tendinous  layers  on  the  lower  part  of  the  muscle.  The  lower  portion 
of  the  muscle  is  pennate,  the  fibers  on  either  side  converging  on  the  tendon  at  an 
acute  angle. 

Relations. — Internally,  the  iliacus,  sartorius,  and  vastus  internus;  externally, 
the  tensor  fascia  latiE,  glutei,  and  vastus  externus;  posteriorly,  the  hip  joint  and 
the  vastus  intcrmedius;    anteriorly,  the  fascia  lata  and  the  skin.     The  anterior 

'  The  iliac  head  is  described  by  some  authors  as  a  separate  muscle,  and  termed  the  pyri- 
formis.  This  does  not  seem  desirable,  especially  since  it  is  at  least  probable  that  the  homo- 
logue  of  the  pyriformis  of  man  is  that  portion  of  the  middle  gluteus  which  is  inserted  into  the 
back  of  the  trochanteric  ridge. 

-The  name  is  based  on  the  arrangement  in  man,  in  whom  the  muscle  consists  of  two 
fasciculi  forming  a  groove  between  them  for  tlie  tendon  of  the  obturator  internus.  In  the  horse 
it  is  undivided,  and  is  grooved  for  tlie  oliturator  tendon,  so  that  at  first  sight  it  appears  to  be 
double.  The  gemellus  may  be  regarded  as  the  exlrapelvic  head  of  the  obturator  internus 
(.Gegenbaur) . 


ANTERIOR   MUSCLES   OF   THE    THIGH 


285 


femoral  artery  and  branches  of  the  femoral  nerve  descend  into  the  interspace  be- 
tween the  upper  part  of  the  rectus  and  the  vastus  internus;  similarly,  the  iliaco- 
femoral  artery  dips  in  between  the  rectus  femoris  and  vastus  externus. 

Blood-supply. — Femoral  and  iliaco-femoral  arteries. 

Nerve-supply. — Femoral  nerve. 

(2)  Vastus  externus  (s.  lateralis). — This  lies  on  the  outer  surface  of  the  thigh, 
extending  from  the  great  trochanter  to  the  patella.  It  is  thick  and  wide  in  its 
upper  part,  and  becomes  much  thinner  and  narrow  below. 


Fold  of  flank 
Tensor  fascia:  lalm 


Fas/ its  iniernus 

Sartorius 

Saphenuus  vein 

Saphenous  nerve 

Femoral  artery 

Gracilis 

Adduclnr 


Vastus  externus 
Vastus  intermedins 


Peroneal  nerve  ■ 
Tibial  nerve 


Semimem- 
branosus 


Semitendinosu 


V 


Fig.  200. — Cross-section  of  Middle  of  Right  Thigh  of  Horse. 


Origin. — The  external  border  and  surface  of  the  femur,  from  the  great  tro- 
chanter to  the  supracondyloid  fossa. 

Insertion. — (1)  The  outer  part  of  the  anterior  surface  of  the  patella;  (2)  the 
tendon  of  the  rectus  femoris. 

Action. — To  extend  the  stifle  joint. 

Structure. — The  fibers  are  directed  dowTiward  and  forward,  many  being  in- 
serted into  the  tendinous  sheet  which  covers  the  side  of  the  rectus.  A  bursa  is 
often  found  between  the  distal  end  and  the  patella. 


286  FASCIA    AND    MUSCLES    OF   THE    HOBSE 

Relations. — Externally,  the  fascia  lata  and  skin,  tensor  fasciae  latse,  superficial 
gluteus,  and  biceps  femoris;  internally,  the  femur  and  femoro-patellar  joint  capsule, 
the  rectus  femoris,  vastus  intermedius,  and  the  iliaco-femoral  artery. 

Blood-supply. — Iliaco-femoral  artery. 

Nerve-supply. — Femoral  nerve. 

(3)  Vastus  intemus  (s.  medialis). — This  is  smaller  than  the  preceding  muscle, 
and  lies  in  a  similar  position  on  the  inner  side  of  the  thigh. 

Origin. — The  internal  surface  of  the  femur,  from  the  neck  to  the  distal  third. 

Insertion. — (1)  The  upper  part  of  the  inner  border  of  the  patella  and  its  carti- 
lage;   (2)  the  tendon  of  the  rectus  femoris. 

Action. — To  extend  the  stifle  joint. 

Structure. — This  is  very  similar  to  that  of  the  vastus  externus.  It  is,  how- 
ever, more  difficult  to  separate  from  the  intermedius,  because  many  fibers  of  the 
latter  arise  on  the  tendinous  sheet  which  covers  the  contact  surface  of  the  inner 
vastus.  Its  insertion  into  the  patella  is  chiefly  by  means  of  a  broad  strong  tendon. 
From  the  deep  face  fleshy  fibers  are  inserted  also  into  the  femoro-patellar  capsule. 

Relations. — Internally,  the  skin  and  fascia  lata,  the  iliacus,  sartorius,  pectineus, 
and  adductor,  the  femoral  vessels  and  saphenous  nerve;  externally,  the  femur, 
femoro-patellar  joint  capsule,  rectus  femoris,  and  vastus  intermedins,  the  anterior 
femoral  artery,  and  branches  of  the  femoral  nerve. 

Blood-supply. — Femoral  and  anterior  femoral  arteries. 

Nervc-.'<upply. — Femoral  nerve. 

(4)  Vastus  intermedius  (C'rureus). — This  muscle  is  deeply  situated  on  the 
anterior  face  of  the  femur,  and  is  entirely  covered  by  the  preceding  heads. 

Origin. — (1)  The  anterior  and  external  surfaces  of  the  femur,  from  the  proximal 
to  the  distal  fourth;   (2)  the  aponeurosis  of  the  vastus  intemus. 

Insertion. — (1)  The  base  of  the  patella;   (2)  the  femoro-patellar  joint  capsule. 

Action. — (1)  To  extend  the  stifle  joint;  (2)  to  tense  (raise)  the  femoro-patellar 
capsule  during  extension  of  the  joint. 

Structure. — The  muscle  is  usually  quite  difficult  to  isolate  from  the  other  vasti, 
so  that  many  since  Giinther  have  declared  it  an  artefact.'  It  is  entirely  fleshy,  and 
is  small  at  its  proximal  end,  but  when  traced  downward  increases  in  bulk  by  the 
accession  of  fibers  arising  on  the  femur  and  the  tendinous  covering  of  the  vastus 
internus.  The  terminal  part  is  intimately  adherent  to  the  femoro-patellar  joint 
capsule,  where  the  latter  bulges  upward  al)0ve  the  level  of  the  patella. 

Relations. — Internally,  the  vastus  internus;  externally,  the  vastus  externus; 
anteriorly,  the  rectus;  posteriorly,  the  femur  and  femoro-patellar  capsule. 

Blood-supply. — Iliaco-femoral  and  anterior  femoral  arteries. 

Nerve-supply. — Femoral  nerve. 

The  straight  ligaments  of  the  patella  are  to  lie  regarded  as  tendons  of  the  quadriceps  which 
communicate  the  action  of  tlie  latter  to  the  tibia,  the  patella  being  intercalated  as  a  sesamoid 
bone. 

3.  Capsularis  (Fig.  154)  (Rectus  parvus). — This  is  a  small  muscle  (scarcely  as 
large  asoii(>'s  finger),  which  arises  on  the  ilium  immediately  above  the  outer  tendon 
of  the  rectus  femoris,  and  passes  down  between  the  vastus  internus  and  externus  to 
be  inserted  into  the  anterior  surface  of  the  femur.  It  passes  over  the  front  of  the 
hip  joint,  to  the  capsule  of  which  some  fibers  are  attached.  Sometimes  the  muscle 
has  two  distinct  heads,  in  which  case  the  additional  head  arises  between  the  two 
tendons  of  origin  of  the  rectus  femoris.  Its  action  may  be  to  raise  the  capsule 
during  flexion  of  the  joint. 

'  While  it  i.s  true  that  the  separation  of  the  intermedius  is  probably  never  entirely  a  natural 
one  in  the  horse,  it  varies  in  individual  cases,  and  is  usually  clear  on  cross-sections.  In  some 
subjects  it  is  possible  to  separate  another  slip  which  may  represent  the  articularis  genu  of  man. 


THE  MUSCLES  OF  THE  LEG  AND  FOOT 


287 


IV.  THE  MUSCLES  OF  THE  LEG  AND  FOOT 

The  muscles  of  this  r(>gioii  cuvcr  ahnost  all  of  the  tiliia  except  its  internal  face, 
which  is  largely  subcutaneous.     As  in  the  forearm,  the  muscles  fall  into  two  groups, 


Crest  of  tibia 

Anterior  or  long  extensor - 
Lateral  extensor  - 


Proximal  annular  ligament 
External  malleolus 


Middle  annular  ligament 

Distal  annular  ligament 

Tendon  of  anterior  extensor 

Tendon  of  lateral  extensor 


Gastrocnemius,  external  head 

Salens 

Tendon  of  gastrocnemius 

Tarsal  tendon  of  biceps  femoris 

Deep  flexor 


Superficial 
flexor  tendon 


Superficial  flexor 
tendon 

Deep  flexor  tendon 


Suspensory 
ligament 


Branch  of  suspensory  ligament  to 
extensor  tendon 


Fig.  201. — MnscLES  of  Lower  P.irt  of  Thigh.  Lf,g,  and  Foot  of  Horse,  Extebn.ii-  View. 

o',  Fa.5cia  lata;    (j,  </ ,  cf ,  biceps  femoris;    r.  semitendinosus;    21',  external  condyle  of  tibia,     (.\fter  Ellenberger- 

Bauin,  .\nat.  fiir  Kiinstler.) 


an  anterior  or  dorso-lateral,  and  a  posterior  or  plantar.  The  muscles  of  the  first 
group  are  extensors  of  the  digit  and  flexors  of  the  hock,  those  of  the  second  have  the 
opposite  action. 


288  FASCIA    AND    MUSCLES    OF    THE    HORSE 

A.  Anterior  Group 

1.  Anterior  or  long  digital  extensor  (M.  extensor  digitalis  longus;  extensor 
pedis;  anterior  extensor  of  tlie  phalanges). — This  muscle  is  situated  superficially 
on  the  antero-external  aspect  of  the  leg,  and  is  provided  with  a  long  tendon  which 
passes  down  over  the  front  of  the  tarsus,  metatarsus,  and  digit. 

Origin. — The  small  fossa  (Fossa  extensoria)  between  the  external  condyle  and 
the  trochlea  of  the  femur. 

Insertion. — (1)  The  extensor  process  of  the  third  phalanx;  (2)  the  anterior 
surface  of  the  proximal  extremities  of  the  first  antl  second  phalanges. 

Action. — To  extend  the  digit  and  flex  the  hock.  It  also  assists  in  fixing  the 
stifle  joint. 

Structure. — The  origin  is  by  means  of  a  strong  tendon  in  common  with  the 
peroneus  tertius,  on  which  also  many  fibers  arise.  The  common  tendon  passes 
downward  in  the  groove  between  the  outer  condyle  and  the  tuberosity  of  the  tibia, 
where  a  pouch  from  the  femoro-tibial  capsule  descends  four  or  five  inches  (ca. 
10  to  12  cm.)  beneath  the  tendon.  The  belly  is  fusiform  and  somewhat  flattened. 
The  long  tendon  of  insertion  begins  in  the  belly  about  its  middle,  and  is  clear  of  the 
fleshy  part  near  the  tarsus.  It  passes  downward  over  the  front  of  the  hock,  bound 
down  by  the  three  annular  ligaments  already  described  (see  crural  fascia),  and 
enveloped  by  a  synovial  sheath  which  begins  a  little  above  the  level  of  the  external 
malleolus,  and  extends  nearly  to  the  junction  with  the  lateral  extensor  tendon. 
This  union  occurs  usually  about  a  hand's  breadth  below  the  tarsus.  In  the  angle 
of  union  the  extensor  brevis  also  joins  the  principal  tendon.  Beyond  this  ]ioint 
the  arrangement  is  the  same  as  in  the  fore  limb. 

Relations. — Superficially,  the  skin  and  fascia;  deeply,  the  femoro-tibial  capsule, 
peroneus  tertius,  and  tibialis  anterior;  behind,  the  lateral  extensor  and  the  super- 
ficial and  deep  peroneal  nerves.  In  front  of  the  tarsus  the  anterior  tibial  artery 
crosses  the  deep  face  of  the  tendon  (Fig.  460). 

Blood-supplij. — .\nterior  tibial  artery. 

Nerve-supplij. — Peroneal  nerve. 

2.  Lateral  digital  extensor  (M.  extensor  digitalis  lateralis;  peroneus;  lateral 
extensor  of  the  phalanges). — This  muscle  lies  on  the  outer  surface  of  the  leg, 
behind  the  preceding  one. 

Origin. — The  external  lateral  ligament  of  the  stifle  joint,  the  fibula,  tlie  ex- 
ternal border  of  the  tibia,  and  the  interosseus  ligament. 

Insertion. — The  tendon  of  the  anterior  extensor,  about  a  third  of  the  way  down 
the  metatarsus. 

Action. — To  assist  the  anterior  extensor. 

Structure. — The  belly  is  fusiform,  fiattened,  and  pennate.  The  tendon  runs 
through  the  entire  length  of  the  belly  and  becomes  free  from  it  at  the  lower  fourth 
of  the  tibia.  It  passes  downward  through  the  groove  on  the  external  malleolus, 
bound  down  by  an  annular  ligament,  and,  inclining  forward,  blends  (usually)  with 
the  tendon  of  the  anterior  extensor.  It  is  provided  with  a  synovial  sheath,  which 
begins  about  one  inch  (ca.  2  to  3  cm.)  above  the  external  malleolus  and  ends  aliout 
one  and  one-half  inches  (ca.  3  to  4  cm.)  above  the  junction.  Sometimes  the  fusion 
does  not  occur,  and  the  tendon  then  passes  down  the  metatarsus,  alongside  of  that 
of  the  long  extensor,  to  be  inserted  into  the  fir.st  phalanx  like  the  corresi)onding 
muscle  of  the  thoracic  limb. 

Relations. — Externally,  the  skin  and  fascia  and  the  superficial  peroneal  nerve; 
internally,  the  tibia  and  fibula;  anteriorly,  the  intermuscular  septum,  the  long 
extensor,  and  the  tibialis  anterior;  posteriorly,  the  deep  flexor  and  the  soleus. 

Blood-supply. — Anterior  tibial  artery. 

Nerve-supply. — Peroneal  nerve. 


THE  MUSCLES  OF  THE  LEG  AND  FOOT 


289 


3.  Peroneus  tertius  (Tendinous  part  of  the  flexor  metatarsi;  tendo  fcmoro- 
tarseus  [Schmaltz]). — This  consists  in  the  horse  of  a  strong  tendon  which  lies  be- 
tween the  anterior  extensor  and  the  tibialis  anterior. 


y    ^i  m--' Biceps  fcmoris,  anterior  -part 
I  it 


Gracilis- 


-- Biceps  fetnoris,  middle  part 


Tuberosity  of  tibia 


External  condyle  of  tibia 


Tibialis  anterior  ■ 


■  Lateral  extensor 
Anterior  or  long  extensor 


Internal  malleolus  - 


■Peroneus  tertius 

■  Proximal  annular  ligament 

'  External  malleolus 


Inner  (cunean)  tendon  of  tibialis  anterior  - 
Metatarsal  tendon  of  tibialis  anterior- 


Anterior  or  long  extensor  tendon - 


■-■  Middle  annular  ligament 

■  Distal  annular  ligament 

■  Lateral  extensor  tendon 


Branch  of  suspensory  ligament .. 


Fig.  202. — Muscles  of  Pelvic  Limb  of  Horse,  An 
y.  Rectus  femoris;    20,  patella.     (After  Ellenberger-Baum,  .\nat.  fiir  Kiinstler.) 


Origin. — The  fossa  extensoria  (between  the  external  condyle  and  the  trochlea 
of  the  femur),  in  common  with  the  anterior  extensor. 

'  It  seems  inadvisable  to  retain  the  old  nomenclature,  since  it  is  inapplicable  to  other  domes- 
ticated animals  in  which  the  muscle  is  well  developed  (e.  g.,  ox,  pig). 
H) 


290  FASCIA   AND    MUSCLES    OF   THE    HORSE 

Insertion. — (1)  The  proximal  extremities  of  the  large  (third)  and  external  small 
(fourth)  metatarsal  bones,  and  the  third  tarsal  bone;  (2)  the  fibular  and  fourth 
tarsal  bones. 

Action. — Mechanically  to  flex  the  hock  when  the  stifle  joint  is  flexed. 

Structure. — This  is  entirely  tendinous.  The  proximal  end  and  the  underlying- 
prolongation  of  the  s.vnovial  membrane  of  the  femoro-tibial  joint  have  been  men- 
tioned in  the  description  of  the  anterior  extensor.  Fibers  of  the  latter  muscle  and 
of  the  tibialis  anterior  arise  on  the  tendon  as  it  passes  downward  to  the  front  of  the 
hock.  At  the  distal  end  of  the  tiliia  the  tendon  divides  into  two  branches,  between 
which  the  tendon  of  the  tibialis  anterior  emerges.  The  anterior  branch  is  attached 
to  the  third  tarsal  and  third  and  fourth  metatarsal  bones,  while  the  outer  one  curves 
outward,  bifurcates,  andis  inserted  into  the  fibular  and  fourth  tarsal  bones  (Fig.  460). 

Relations. — Superficially,  the  anterior  extensor;  deeply,  the  tibialis  anterior. 
The  anterior  tibial  vessels  cross  the  deep  face  of  the  outer  branch. 

4.  Tibialis  anterior  (Muscular  portion  of  the  flexor  metatarsi). — This  lies 
on  the  antero-external  face  of  the  tibia;  it  is  wide  and  flattened  above,  pointed 
below. 

Origin. — The  external  condyle  and  border  of  the  tibia  and  a  small  area  on  the 
external  surface  of  the  tuberosity. 

Insertion. — (1)  The  metatarsal  tuberosity;  (2)  the  first  and  second  tarsal 
bones. 

Action. — To  flex  the  hock  joint. 

Structure. — The  origin  is  fleshy,  and  is  divided  by  the  groove  in  which  lie 
the  common  tendon  of  the  long  extensor  and  peroneus  tertius  and  a  synovial 
pouch.  Passing  downward  on  the  tibia,  the  belly  is  united  by  tendinous  and  fleshy 
fibers  with  the  peroneus  tertius,  and  terminates  close  to  the  tarsus  in  a  point  on 
the  tendon  of  insertion.  The  latter  emerges  between  the  branches  of  the  peroneus 
tertius  and  bifurcates,  the  anterior  branch  being  inserted  into  the  metatarsal 
tuberosity,  the  inner  one  (cunean  tendon)  into  the  fused  first  and  second  tarsal 
bones  (cuneiform  parvum).  The  tendon  is  provided  with  a  S3movial  sheath  at 
its  emergence,  and  a  bursa  (cunean  bursa)  is  interposed  between  the  inner  branch 
and  the  internal  lateral  ligament. 

Relations. — Superficially,  the  anterior  and  lateral  extensors,  the  peroneus 
tertius,  and  the  deep  peroneal  nerve;  deeply,  the  tibia,  the  deep  flexor,  and  the 
anterior  tibial  vessels. 

Blood-supply. — Anterior  tibial  artery. 

Nerve-supply. — Peroneal  nerve. 

B.  Posterior  Group 

1.  Gastrocnemius  (Figs.  179,  201,  203). — This  muscle  extends  from  the  lower 
third  of  the  femur  to  the  point  of  the  hock.     It  arises  by  two  heads. 

Origin.. — (Ij  Outer  head,  from  the  external  rough  margin  of  the  supracondy- 
loid  fossa  (Fossa  plantaris);    (2)  inner  head,  from  the  supracondyloid  crest. 

Insertion. — The  posterior  part  of  the  tuber  calcis. 

Action. — To  extend  the  hock. 

Structure. — The  two  bellies  are  thick,  fusiform,  and  somewhat  flattened. 
They  are  covered  by  a  strong  aponeurosis  and  contain  tendinous  intersections. 
They  terminate  toward  the  middle  of  the  leg  on  a  common  tendon  (Tendo  calcaneus 
s.  Achillis),  which  at  first  lies  posterior  to  that  of  the  superficial  flexor,  but,  by  a 
twist  in  both,  comes  to  lie  in  front  of  the  latter.  The  deep  fascia  blends  with  the 
tendon  throughout  its  length,  and  the  soleus  muscle  is  inserted  into  its  anterior  edge. 
A  small  bursa  (Bursa  tendinis  calcanei)  lies  in  front  of  the  insertion  on  the  tuber 
calcis,  and  a  large  bursa  is  interposed  between  the  two  tentlons  from  the  twist 


THE  MUSCLES  OF  THE  LEG  AND  FOOT 


291 


downward.     The  superficial  flexor  lies  between  the  two  heads  and  is  adherent  to 
the  outer  one  (Fig.  459). 

Relations. — Anteriorly,  the  stifle  joint,  the  superficial  flexor,  popliteus,  deep 
flexor,  popliteal  vessels,  and  tibial  nerve;    internallj'  (above),  the  semitendinosus, 


Semitendinosus 


Gastrocnemius 

Popliteus 

Long  digital  flexor 

Tibialis  posterior 

Gastrocnemius  tendon 


Deep  digital  flexor 
Superficial  flexor  tendon 


Check  ligament 
Superficial  flexor  tendon 

Deep  flexor  tendon 
Suspensory  ligament 


Fir..  203. — Mrsri. 
r*.  Tendon  of  seraitencUnosas;    w,  gracil. 


'atella 


Crest  of  tibia 


Anterior  or  long  digital  extensor 
Tibialis  anterior 


Proximal  annular  ligament 
Internal  malleolus 


"■"  Inner  {cunean)  tendon  of  tibialis  anterior 
Distal  annular  ligament 

Anterior  extensor  tendon 


Branch  of  sjispensory  ligament 
to  extensor  tendon 


sartorius;    y,  vastus  internus.      (.\fter  EUenberger-Baum,  Anat. 
fiir  Kiinstler.) 


semimembranosus,  and  adductor,  (below)  the  fascia  and  skin;  externally  (above), 
the  biceps  femoris  and  peroneal  (anterior  tibial)  nerve,  (below)  the  fascia  and  skin. 

Blood-supphj. — Popliteal  artery. 

Nerve-supply. — Tiljial  nerve. 


292 


FASCIA   AND    MUSCLES    OF   THE    HORSE 


2.  Soleus  (Fig.  201).— This  muscle  is  very  small  in  the  horse.     It  lies  immedi- 
ately under  the  deep  fascia,  on  the  proximal  half  of  the  outer  surface  of  the  leg, 
and  is  directed  obliquely  downward  and  backward. 
Origin. — The  head  of  the  fibula. 

Insertion. — The  tendon  of  the  gastrocnemius,  about  the  middle  of  tlie  leg. 
Action. — To  assist  the  gastrocnemius. 

Structure.— It  is  a  thin,  fleshy  band,  about  an  inch  (ca.  2  to  3  cm.)  in  width, 
terminating  on  a  thin  tendon  which  fuses  with  that  of  the  gastrocnemius.' 

Relations. — Superficially,  the  skin,  fascia,  and  peroneal  nerve;    deeply,  the 

lateral    extensor    and    deep 
flexor. 

Blood-supphj.  —  Poste- 
rior tibial  artery. 

Nerve-supphj. — T  i  b  i  a  1 
nerve. 

3.  Superficial  digital 
flexor  or  flexor  pedis  per- 
foratus  (Fi-s.  199,  201,  203) 
(M.  flexor  digitalis  pedis  sub- 
liniis;  superficial  flexor  of  the 
phalanges). — The  proximal 
part  of  this  muscle  lies  be- 
tween and  under  cover  of  the 
two  heads  of  the  gastrocne- 
mius (Fig.  459).  It  con- 
sists almost  entirely  of  a 
strong  tendon,  the  belly  be- 
ing very  little  developed. 

Origin. — The  supracon- 
dyloid  fossa  (Fossa  plantaris) 
of  the  femur. 

Insertion . — (1)  The  front 
and  sides  of  the  tuber  calcis; 
(2)    the    eminences    on    the 
proximal    extremity   of    the 
second    phalanx,     and     the 
distal  extremity  of  the  first 
phalanx    behind    the   lateral 
ligament . 
Action. — To  flex  the  digit  and  extend  the  hock  joint.     On  account  of  the  ex- 
ceedingly small  amount  of  muscular  tissue  the  action  is  to  be  regarded  chiefly  as  a 
mechanical  effect,  resulting  from  the  action  of  other  muscles  on  the  stifle  joint. 

Structure. — The  origin  is  by  means  of  a  strong  round  tendon  which  is  incom- 
pletely covered  with  fleshy  fibers  as  far  as  the  ujiper  third  of  the  leg.  It  is  pretty 
intimately'  attached  to  the  gastrocnemius,  especially  to  the  outer  head.  At  the 
distal  third  of  the  tibia  it  winds  around  the  inner  surface  of  the  gastrocnemius 
tendon,  and  then  occupies  a  position  behind  the  latter.  At  the  jioint  of  the  hock 
it  widens  out,  forming  a  sort  of  cap  over  the  tuber  calcis,  detaching  on  either  side 
a  strong  band  which  is  inserted  into  the  tuber  calcis  with  the  tarsal  tendon  of  the 
biceps  and  semitendinosus.  It  then  passes  downward  over  the  plantar  (Calcaneo- 
metatarsal)  ligament,  becomes  narrower,  and  is  arranged  below  as  in  the  thoracic 
limb.     A  large  synovial  bursa  lies  under  the  tendon  from  the  distal  fourth  of  the 

'  Tlic  -soleus  may,  therefore,  be  included  with  the  two  heads  of  the  gastrocnemius  under  the 
name  triceps  sura;. 


Fig.  204. — Cross-section  of  Left  Leg  of  Horse;  Section  is  Cut 
A  Little  .\bove  Middle  of  Region. 
a,  Tibia:  b,  fibula;  c,  tibialis  anterior;  d.  peroneus  tertius: 
€,  anterior  or  long  digital  extensor;  /,  lateral  extensor;  g,  deep 
head  of  deep  flexor  (flexor  hatluci.s  longus);  h,  inner  head  of  deep 
flexor  (flexor  accessorius  s.  digitorum  longus);  i,  superficial  head  of 
deep  flexor  (tibialis  posterior);  k,  popliteus;  /,  superficial  flexor 
tendon;  m,  gastrocnemius  tendon;  n,  soleus;  o,  skin;  p.  anterior 
tibial  artery;  q,  superficial  peroneal  ner\'e;  //.  deep  peroneal  nerve: 
r,  branch  of  (/;  s,  posterior  tibial  artery;  (,  cutaneous  nerve;  u, 
tibial  nerve:  v,  recurrent  tibial  vein;  w,  saphenous  artery;  x,  saphe- 
nous vein;  j/,  branches  of  saphenous  nerve,  (.\fter  Llleuberger,  in 
Leisering's  .\tlaa. ) 


THE    MUSCLES    OF   THE    LEG    AND    FOOT 


293 


tibia  to  the  middle  of  the  tarsus.  A  subcutaneous  bursa  is  sometimes  found  on 
the  wide  part  of  the  tendon  at  the  point  of  the  hock.  (Either  or  both  of  these 
bursse  may  be  involved  in  so-called  '* capped  hock.'') 

Relations. — Posteriorly,  the  gastrocnemius,  fascia,  and  skin;  anteriorly,  the 
femoro-patellar  capsule,  the  popHteus,  the  deep  flexor,  and  the  pophteal  vessels; 
internally,  the  tibial  nerve. 

Blood-supply. —  Femoro-pophteal  artery. 

Nerve-suppb/. — Til)ial  nerve. 

4.  Deep  digital  flexor  or  flexor  pedis  perforans  (^I.  flexor  digitalis  pedis  pro- 


FiG.  206. — Injected  SrNonAL  Sheaths  axd  Burs.e 
OF  Tarsal  Rkgiox  of  Horse,  External  View. 
a.  Synovial  sheath  of  anterior  or  long  digital 
extensor;  b,  synovial  sheath  of  lateral  digital  exten- 
sor; c,  c* ,  bursa  under  superficial  flexor  tendon;  rf, 
capsule  of    hock  joint;    1,    anterior  or  long  extensor; 


2,  lateral  extensor;  3 
deep  digital  flexor;  5, 
superficial  flexor  tendoi 
calcis;  10,  metatarsus, 
ing's  Atlas.) 


,   3,   3,   annular   ligaments;     -J. 

tendon   of    gastrocnemius;    ff, 

i;    7,  tibia;    8,  tarsus;    9.  tuber 

(After  Ellenberger,  in  Leiser- 


FiG.  205. — Injected  Stxovial  She.\ths  and  Bcrs.e 
OF  Tarsal  Region  of  Horse,  Inner  View. 
a.  Synovial  sheath  of  peroneus  tertius  and 
tibialis  anterior;  b,  bursa  under  inner  (cunean)  tendon 
of  tibialis  anterior;  c,  synovial  sheath  of  flexor  longus 
s.  accessorius;  d,  tarsal  sheath  of  deep  flexor;  e,  e*. 
bursa  under  superficial  flexor  tendon;  /.  /',  tibio-tarsal 
joint  capsule;  /,  anterior  extensor;  2,  tibialis  anterior; 
2",  inner  (cunean)  tendon  of  2:  3,  flexor  longus;  4, 
deep  digital  flexor;  S,  superficial  flexor  tendon;  6, 
gastrocnemius  tendon;  7.  tibia;  5,  tarsus;  9,  tuber 
calcis;  10,  large  metatarsal  bone;  11,  inner  small 
metatarsal  bone;  12,  12*,  fascial  bands.  (After  Ellen- 
berger. in  Leisering's  Atlas.) 

fundus;  deep  and  oblique  flexors  of  the  phalanges). — The  belly  of  this  muscle  lies 
on  the  posterior  surface  of  the  tibia,  and  is  divisible  into  three  parts  or  heads, 
which,  however,  finally  unite  on  a  common  tendon  of  insertion. 

Origin. — (1)  The  posterior  edge  of  the  external  condyle  of  the  tibia;  (2)  the 
external  border  of  the  external  condyle  of  the  tibia,  just  l^ehind  the  facet  for  the 
fibula;  (3)  the  middle  third  of  the  posterior  surface  and  the  upper  part  of  the  ex- 
ternal border  of  the  tibia,  the  posterior  border  of  the  fibula,  and  the  interosseous 
ligament.* 

^  The  origins  of  these  heads  are  given  in  the  order  in  which  thej'  may  be  most  conveniently 
dissected,  not  in  order  of  size  and  importance. 


294  FASCIA    AND    MUSCLES    OF   THE    HORSE 

Infiertion. — The  semilunar  crest  of  the  third  phalanx  and  the  adjacent  surface 
of  the  lateral  cartilage. 

Action. — To  flex  the  digit  and  to  extentl  the  hoclv  joint. 

Structure. — (1)  The  inner  head  (M.  flexor  digitalis  longus  s.  flexor  accesso- 
rius)  is  easily  i.solated  (Figs.  203,  459).  It  has  a  fusiform  belly,  which  crosses  the 
leg  obliquely  and  lies  in  a  groove  formed  liy  the  other  heads  and  the  popliteus. 
This  terminates  near  the  lower  thirtl  of  the  tibia  on  a  round  tendon  which  passes 
downward,  partly  emljedded  in  the  internal  lateral  ligament  of  the  hock,  and  joins 
the  common  tendon  about  a  third  of  the  way  down  the  metatarsus.  In  its  course 
over  the  inner  surface  of  the  hock  the  tendon  lies  in  a  canal  formed  by  the  strong 
tarsal  fascia,  the  tibia,  and  the  lateral  ligament,  and  is  provided  with  a  synovial 
sheath  which  extends  from  the  distal  fourth  of  the  tibia  to  the  junction  with  the 
principal  tendon.  (2)  The  superficial  head  (M.  tibialis  posterior)  is  only  partially 
separable.  It  has  a  flattened  belly,  terminating  near  the  lower  third  of  the  tibia 
on  a  flat  tendon  which  soon  fuses  with  the  principal  tendon.  (3)  The  deep  head 
(M.  flexor  hallucis  longus)  is  much  the  largest.  It  lies  on  the  posterior  surface  of 
the  tibia,  from  the  jjopliteal  line  outward  and  downward.  The  belly  contains  much 
tendinous  tissue,  and  terminates  behind  the  distal  end  of  the  tibia  on  a  strong 
round  tendon.  The  latter  receives  the  tendon  of  the  tibialis  posterior,  passes 
downward  in  the  tarsal  groove,  bound  down  by  the  strong  tarsal  fascia  (Ligamentum 
laciniatum)  and  enveloped  in  a  synovial  sheath,  receives  the  tendon  of  the  inner 
head  below  the  hock,  and,  a  little  further  down,  the  so-called  check  ligament  (Caput 
tendineum  [Schmaltz] ).  The  tarsal  sheath  (Vagina  tarsea)  begins  about  two  to  three 
inches  (ca.  5  to  7.5  cm.)  above  the  level  of  the  internal  malleolus,  and  extends  about 
one-fourth  of  the  way  down  the  metatarsus.  (Distention  of  the  sheath,  as  in 
"thoroughpin,"  affects  chiefly  its  proximal  end.)  The  check  ligament  resembles 
that  of  the  fore  limb,  except  that  it  is  longer  and  very  much  weaker;  it  may  be 
absent.     The  remainder  of  the  tendon  is  arranged  like  that  of  the  thoracic  limb. 

Relations. — Anteriorly,  the  tibia  and  fibula,  the  popliteus,  lateral  extensor, 
tibialis  anterior,  and  the  tibial  vessels;  posteriorly,  the  gastrocnemius,  superficial 
flexor,  and  the  tibial  nerve;  externally,  the  fascia,  skin,  and  the  soleus;  internally, 
the  fascia  and  skin. 

Blood -supply. — Posterior  tibial  artery. 

Nerve-supply. — Tibial  nerve. 

5.  Popliteus  (Fig.  203). — This  thick  and  triangular  muscle  lies  on  the  posterior 
surface  of  the  femoro-tibial  articulation  and  the  posterior  surface  of  the  tibia  above 
the  popliteal  line. 

Origin. — A  small  depression  on  the  external  epicondyle  of  the  femur,  close  to 
the  articular  surface  and  under  the  lateral  ligament. 

Insertion. — A  triangular  area  on  the  posterior  surface  of  the  tibia,  above  and 
internal  to  the  popliteal  line;  also  the  j^roximal  half  of  the  inner  border  and  a 
narrow  adjacent  part  of  the  internal  surface  of  the  tibia. 

Action. — To  flex  the  femoro-tibial  joint  and  to  rotate  the  leg  inward. 

Structure. — The  strong  tendon  of  origin  lies  at  first  under  the  lateral  ligament, 
and  curves  backward  and  inward  over  the  external  condyle  of  the  tibia  and  its 
semilunar  cartilage,  being  invested  by  a  reflection  of  the  synovial  capsule  of  the 
joint  (Fig.  459).  The  tendon  is  succeeded  by  a  thick  triangular  belly,  the  fibers 
of  which  are  directed  obliquely  downward  and  inward. 

Relations. — Superficially,  the  fascia  and  skin,  semitendinosus,  gastrocnemius, 
superficial  flexor;  deeply,  the  femoro-tibial  joint,  the  tibia,  the  popliteal  vessels 
and  their  divisions.  The  saphenous  vessels  and  nerve  lie  along  the  inner  border 
of  the  muscle,  separated  from  it,  however,  by  the  deep  fascia. 

Blood-supply. — Popliteal  and  posterior  tibial  arteries. 

Nerve-supply. — Tibial  nerve. 


THE    MUSCLES    OF    THE    OX — MUSCLES    OF   THE    FACE  295 

MUSCLES  OF  THE  METATARSUS  AND  DIGIT 

Extensor  pedis  brevis  (IM.  extensor  digitalis  brevis). — This  small  muscle  lies 
in  the  angle  of  union  of  the  long  and  lateral  extensors  of  the  digit.  (Shown  in 
Fig.  201,  but  not  marked.) 

Origin. — The  outer  tendon  of  the  peroneus  tertius,  the  middle  annular  liga- 
ment, and  the  outer  lateral  ligament  of  the  hock. 

Insertion. — The  tendon  of  the  anterior  or  long  extensor. 

Action. — To  assist  the  anterior  or  long  extensor. 

Structure. — It  is  principallj'  fleshy,  having  a  superficial  origin  from  the  annular 
ligament,  and  a  deep  one  (by  a  thin  tendon)  from  the  outer  tendon  of  the  peroneus 
tertius.     The  insertion  is  by  a  thin  tendon. 

Relations. — Superficially,  the  skin  and  fascia  and  the  tendons  of  the  anterior 
and  lateral  extensors;  deeply,  the  joint  capsule,  the  great  metatarsal  artery,  and 
the  deep  peroneal  nerve. 

Blood-supply. —  Great  metatarsal  artery. 

Nerve-supply. — Deep  peroneal  nerve. 

The  interossei  and  lumbricales  are  arranged  like  those  of  the  thoracic  limb, 
the  only  noticeable  difference  being  the  greater  development  of  the  lumbricales  in 
the  pelvic  limb. 


THE  MUSCLES  OF  THE  OX 
HUSCLES  OF  THE  FACE 

The  panniculus  is  much  more  developed  than  in  the  horse,  presenting  as  a 
special  feature  the  extensive  frontalis  muscle,  which  covers  the  frontal  and  nasal 
regions. 

The  orbicularis  oris  does  not  form  a  complete  ring,  the  defect  being  in  the 
middle  of  the  upper  lip. 

The  levator  nasolabialis  is  extensive,  thin,  and  not  very  distinct  from  the 
frontalis;  it  divides  into  two  layers,  between  which  the  levator  labii  superioris 
proprius  and  the  lateral  dilator  of  the  nostril  pass.  The  superficial  layer  ends  in 
the  nostril  and  upper  lip,  the  deep  layer  on  the  accessorj'  (lateral)  nasal  cartilages 
and  on  the  nasal  process  of  the  ]iremaxilla. 

The  levator  labii  superioris  proprius  arises  on  and  before  the  facial  tuberosity 
and  terminates  by  several  tendons  in  the  muzzle.  It  pa.sses  between  the  two 
layers  of  the  preceding  muscle,  blending  in  part  with  the  deep  layer. 

The  zygomaticus  is  much  stronger  than  in  the  horse.  It  arises  on  the  masse- 
teric fascia,  and  ends  chiefly  in  the  upper  lip. 

The  depressor  labii  superioris  does  not  resemble  the  muscle  of  the  same  name 
in  the  horse.  It  arises  just  in  front  of  the  facial  tuberosity,  antl  divides  usually 
into  two  branches,  which  terminate  in  a  number  of  tendons  that  form  a  network 
in  the  muzzle  and  u])per  lip. 

The  incisivus  inferior  is  a  small,  rounded  muscle,  which  arises  on  the  body  of 
the  mandible  below  the  second  and  third  incisors,  and  ends  in  the  lower  lip, 
blending  with  the  orbicularis. 

The  depressor  labii  inferioris  is  thin,  and  does  not  extend  as  far  backward 
as  in  the  horse;    only  the  anterior  end  is  distinct  from  the  buccinator. 

The  buccinator  shows  no  marked  variation,  but  its  superficial  layer  is  well 
developed. 

The  dilatator  naris  lateralis  arises  in  front  of  the  facial  tuberosity,  passes  for- 


296 


THE    MUSCLES    OF   THE    OX 


ward  between  the  branches  of  the  levator  nasolabialis,  and  terminates  in  the  outer 
wing  of  the  nostril. 

The  dilatator  naris  transversus  is  ref)laced  by  the  dilatator  naris  apicalis, 
which  is  situated  in  the  muzzle  and  joins  its  fellow  at  a  median  raphe.  It  arises 
on  the  border  and  upper  surface  of  the  body  of  the  premaxilla,  the  fibers  passing 
obliquely  upward  and  outward  to  the  inner  wing  of  the  nostril. 

The  dilatator  naris  superior  arises  from  the  alar  cartilage  of  the  nostril  and 
ends  in  the  inner  wing  of  the  nostril. 


Fig.  207. — Muscles  of  Head  of  Ox,  Latf.r.^i.  Vif.w. 
a.  Levator  labii  superioris  proprius;  b,  levator  na-soiabialis;  c,  trapezius;  c',  mastoido-humeralis;  d,  d' , 
sterno-cephalicus;  e,  omo-hyoideus;  /,  dilatator  naris  lateralis;  q,  zygomaticus;  (7',  malaris;  A,  buccinator;  2, 
depressor  labii  inferioris;  k,  orbicularis  oris;  m,  masseter;  n,  parotido-auricularis;  o' ,  zygomatico-auricularis  and 
scutulo-auricularis  superficialis  inferior;  o",  scutulo-auricularis  superficialis  superior;  o'",  scutulo-auricularia 
superficialis  accessorius;  v*v\  scutularis;  w.  frontalis:  uj,  mylo-hyoideus;  7,  concha;  ;2,  5,  posterior  and  anterior 
borders  of  I;  S,  scutiforni  cartilage;  9,  zygomatic  arch;  2S' ,  ramus  of  mandible;  S7 ,  external  maxillary  vein; 
SS,  jugular  vein;  ,;;9,  facial  vein;  4.<,  parotid  gland;  50,  SO',  submaxillary  gland;  dotted  line  at  50  indicates  posi- 
tion of  large  lymph  gland,  anil  another  lies  partly  under  parotid  gland,  just  in  front  of  44.'  ^5,  internal  palpebral 
ligament;    55,  laryngeal  prominence.      (.A.fter  EUenberger-Baum,  .\nat.  fiir  Kiin.stler.) 


The  dilatator  naris  inferior  consists  of  two  layers  which  arise  on  the  nasal  pro- 
cess of  the  premaxilla  and  the  lateral  nasal  cartilage  and  end  in  the  outer  wing 
of  the  nostril. 

The  orbicularis  oculi  is  well  developed. 

The  corrugator  supercilii  is  not  present  as  a  separate  muscle,  its  place  and 
function  being  taken  by  the  frontalis. 

The  malaris  is  broad,  and  spreads  out  below  on  the  fascia  over  the  buccinator 
and  masseter;   it  is  divided  into  two  parts. 


MUSCLES    OF    MASTICATION — HYOID    MUSCLES 


297 


MUSCLES  OF  MASTICATION 

The  masseter  is  not  so  large  as  in  the  horse;  a  considerable  part  of  it  arises 
on  the  facial  tuberosity  ami  is  directed  obliquely  backward  and  dowTiward,  so  that 
it  would  ilraw  the  lower  jaw  forwartl  as  well  as  upward. 

The  temporalis  conforms  to  the  temporal  fossa,  and  is  therefore  longer  and 
entirely  lateral  in  jio.sition. 

The  pterygoidei  are  not  quite  clearly  separated;  their  direction  is  more 
oblique,  and  the  origin  of  the  pterygoideus  internus  is  nearer  the  median  plane 
than  in  the  horse. 


Fig.  208. — Muscles  of  He.xd  of  Ox.  Dors.\l  View. 
a,  a',  Levator  labii  superioris  i>roprius;  b,  levator  iiasolabialis;  /,  dilatator  naris  lateralis:  g',  malaris;  o.  zygo- 
matico-auricularis  and  scutulo-auricularis  superficialis  inferior;  o" ,  scutxilo-auricularis  superficialia  superior;  o"\ 
scutulo-auricularis  superficialis  accessorius;  p,  scutularis;  u,  frontalis;  2,  orbicularis  oculi:  i ,  concave  surface  of 
concha;  3,  2,  anterior  and  posterior  borders  of  concha;  S,  scutifonn  cartilage;  34,  parietal  cartilage;  39,  facial 
vein;  49,  muzzle;  oS.  internal  palpebral  ligament.      (After  Ellenberger-Bamn,  Anat.  fur  Kiinstler.) 

The  stylo-mandibularis  is  absent. 

The  digastricus  has  a  tendinous  origin  on  the  paraniastoid  or  styloid  process 
of  the  occipital  bone;  its  bellies  are  short  and  thick.  It  does  not  perforate  the 
stylo-hyoideus.     The  two  digastrici  are  connected  beneath  the  root  of  the  tongue 

by  a  layer  of  transverse  muscle-fibers  (Transversus  mandibulse). 


HYOID  MUSCLES 
The  mylo-hyoideus  is  thicker  and  more  extensive  than  in  the  horse. 
The  stylo-hyoideus  has  a  long  thin  tenchnous  origin  and  is  not  perforated  by 
the  digastricus. 


298 


THE    MUSCLES    OF    THE    OX 


The  genio-hyoideus  is  more  clevcloped. 

The  kerato-hyoideus  has  an  additional  attachment  on  the  middle  cornu  of  the 
hyoid  bone. 

The  hyoideus  transversus  is  bifid. 

The  stemo-thyro-hyoideus  has  no  intermediate  tendon  and  is  thicker. 

The  omo-hyoideus  ari.ses  as  a  thin  band  from  the  fascia  over  the  third  and 
fourth  cervical  vertebra'.  It  blends  here  with  the  rectus  capitis  anterior  major. 
The  occipito-hyoideus  is  thick. 


Fig.  209. — Muscles  of  Head  of  Ox.  Ventral  View. 
d,  d' ,  Sterno-cephalicus;  f,  omo-hyoideus;  g,  zygomaticus;  h,  buccinator:  /,  (lepre.s.sor  labii  inferioria; 
k,  orbicularis  oris;  m,  masseter;  n,  parotido-aui'icularis;  o' ,  zygomatico-auricularis;  w,  mylo-hyoiileus;  /,  concha, 
convex  surface;  2,  anterior  border  of  concha:  SO',  angle  of  jaw;  39,  facial  vein;  A4,  parotid  gland;  J,6,  lower  lip; 
48,  angle  of  mouth;  60,  60',  submaxillary  gland:  59,  larynx;  x,  wing  of  atla:^.  (After  Ellenberger-Baum,  .\nat. 
fur  Kiinstler.) 


Muscles  of  the  Neck 
a.  ventral  group 

The  sterno-cephalicus  consists  of  two  muscles.  They  arise  from  the  manu- 
brium sterni  and  first  rib.  The  superficial  muscle  (Sterno-mandibularis)  is  inserted 
on  the  anterior  border  of  the  masseter,  the  ramus  of  the  mandible,  and  the  buccal 
fascia.  The  deep  muscle  (Sterno-mastoideus)  crosses  under  the  preceding  and  ends 
on  the  mastoid  process,  the  mandible,  and,  in  common  with  the  rectus  capitis 
anterior  major,  on  the  basilar  process  of  the  occipital  bone. 

There  are  two  scaleni.  The  scalenus  ventralis  (s.  prima  costa>)  arises  on  the 
first  rib  and  ends  on  the  transverse  processes  of  the  third  to  the  seventh  cervical 


VENTRAL    GROUP 


299 


°  11  1 1 
<  -2  3  1  s 


i  s  I  i  . 

<!  o  3  =  a 


§ » 2 is 


ill 


300  THE    MUSCLES    OF    THE    OX 

vcrtcbrffi.  It  is  traversed  by  the  roots  of  tlic  lirachial  plexus,  which  partially 
divide  it  into  a  small  dorsal  and  a  large  ventral  part.  The  brachial  vessels  lie 
below  the  latter.  The  scalenus  dorsalis  (s.  supracostalis)  arises  usually  on  the 
second,  third,  and  fourth  ribs,  and  ends  on  the  transverse  processes  of  the  third 
to  the  sixth  cervical  vertebr;p. 

The  rectus  capitis  anterior  major  arises  on  the  third  to  the  sixth  cervical 
transverse  processes,  and  blends  at  its  insertion  with  the  sterno-mastoideus  and 
the  mastoid  portion  of  the  mastoido-humeralis. 

The  rectus  capitis  anterior  minor  is  larger  than  in  the  horse. 

The  rectus  capitis  lateralis  and  longus  colli  resemble  those  of  the  horse. 

The  intertransversales  are  large.  From  the  sixth  cervical  vertebra  forward 
they  form  a  muscular  mass  (M.  intertransversarius  longus)  which  is  inserted  into 
the  wing  of  the  atlas. 

B.  LATERAL  GROUP 
The  splenius  is  thin.  It  arises  directly  from  the  first  three  or  four  thoracic 
spines,  and  ends  by  a  thin  tendon  on  the  occipital  bone,  the  wing  of  the  atlas, 
and  the  transverse  process  of  the  axis,  blending  with  the  mastoido-humeralis, 
trachelo-mastoideus,  and  omo-transversarius.  The  remaining  muscles  present  no 
very  marked  differential  features. 


Muscles  of  the  Thorax 

The  levatores  costarum  number  ten  or  eleven  pairs. 

The  diaphragm  jjresents  several  important  differential  features.  Its  slope  is 
much  steeper  and  its  width  is  greater  than  in  the  horse.  The  costal  attachment 
extends  almost  in  a  straight  line  from  the  upper  fourth  of  the  last  rib  to  the  junc- 
tion of  the  eighth  rilj  with  its  cartilage,  and  along  the  latter  to  the  sternum.  The 
mid-line  slopes  from  the  twelfth  thoracic  vertebra  obliquely  as  far  as  the  vena 
cava,  beyond  which  it  is  almost  vertical.  The  right  crus  divides  into  two  branches, 
which  circumscribe  the  oesophageal  opening,  unite  below-,  and  then  spread  out  in 
the  tendinous  center.  The  left  crus  is  small.  The  oesophageal  opening  is  situated 
about  four  to  five  inches  (10  to  12  cm.)  below  the  eighth  thoracic  vertebra,  a  little 
to  the  left  of  the  median  plane.  The  foramen  vense  cavse  is  a  little  more  ventral 
and  almost  in  the  median  plane.     The  other  muscles  resemble  those  of  the  horse. 


Muscles  of  the  Back  and  Loins 

The  serratus  anticus  is  very  thin.  It  is  inserted  on  the  fifth  to  the  eighth  ribs. 
It  may  be  reduceil  to  two  or  three  digitations  or  may  be  absent.  The  serratus 
posticus  is  usually  inserted  on  the  last  three  or  four  ribs. 

The  transversalis  costarum  (Iliocostalis)  has  a  distinct  lumbar  portion  which 
is  attached  to  the  lumbar  transverse  processes  and  the  ex-ternal  angle  of  the  ilium. 

The  longissimus  resembles  that  of  the  horse,  but  it  is  more  fleshy  anteriorly, 
and  the  spinalis  dorsi  is  clearly  distinguishable  from  the  common  mass.  In  the 
lumbar  region  the  tendons  meet  across  the  summits  of  the  spines. 

Intertransversales  are  present  in  the  back,  and  interspinales  in  the  back  and 
loins. 

MUSCLES  OF  THE  TAIL 

These  resemble  those  of  the  horse;  the  coccygeus  is,  however,  much  more 
developed. 


ABDOMINAL    MUSCLES 


301 


Abdominal  Muscles 

The  obliquus  abdominis  externus  is  somewhat  thinner  and  has  a  less  extensive 
origin,  which  begins  at  the  lower  part  of  the  fifth  intercostal  space  and  ends  on 
the  last  rib  above  its  middle.  The  direction  of  the  fibers  in  the  flank  is  horizontal, 
and  they  do  not  reach  to  tlie  external  angle  of  the  ilium,  nor  as  high  as  the  lumbar 
transverse  processes.  (In  this  region  the  abdominal  tunic  has  a  strong  attachment 
to  the  point  of  the  hip  and  the  lumbo-dorsal  fascia.)  The  aponeurosis  is  intimately 
united  with  the  abdominal  tunic,  and  does  not  detach  a  layer  on  the  inner  surface 
of  the  thigh. 

The  obliquus  abdominis  internus  is  more  developed  and  has  an  additional 


Fig.  211. — Deeper  Muscles  of  Neck,  Shoulder,  and  Thor.\x  of  Ox. 
c",  Cleido-occipitalis  muscle;  d,  sterno-cephalicus;  /,  /',  long  and  external  heads  of  triceps;  s,  superficial 
pectoral  muscle;  h,  h' ,  posterior  and  anterior  deep  pectoral  muscles;  i,  i' ,  serratus  magnus;  k,  latissimus  dorsi; 
/,  obliquus  abdominis  externus:  r',  biceps  brachii;  w,  splenius;  i,  rhomboideus;  \j,  trachelo-mastoideus;  z, 
supraspinatus;  z! ,  infraspinatus;  s",  tendon  of  insertion  of  s';  1\  cartilage  of  scapula;  2,  tuberosity  of  spine  of 
scapula;  S,  acromion;  5,  external  tuberosity  of  humerus;  5,  deltoid  tuberosity;  S,  olecranon;  2Q,  transverse 
processes  of  cervical  vertebrae;  .^7',  posterior  auricular  muscles;  X,  wing  of  atlas.  C-^fter  EUenberger-Baum, 
Anat.  fiir  Kunstler.) 


origin  from  the  lumbo-dorsal  fascia.  The  aponeurosis  blends  with  that  of  the 
external  oblique  near  the  linea  alba,  and  detaches  a  layer  which  assists  in  the  for- 
mation of  the  internal  sheath  of  the  rectus. 

The  rectus  abdominis  arises  on  the  lateral  border  of  the  sternum  as  far 
forward  as  the  third  costal  cartilage.  The  two  muscles  are  separated,  except 
near  the  pelvis,  by  an  interval  varying  from  two  to  four  inches  (ca.  5  to 
10  cm.),  so  that  this  part  of  the  abdominal  wall  is  entirely  fibrous.  (The 
umbilicus  is  in  a  transverse  plane  through  the  third  lumbar  vertebra.)  There 
are  five  tendinous  inscriptions,  on  the  third  of  which  is  a  foramen  for  the 
passage  of  the  subcutaneous  abdominal  vein  (milk  vein).  The  prepubic 
tendon  has,  in  addition  to  branches  inserted  into  the  ilio-pectineal  eminences, 
a  strong  attachment  to  the  median  common  tendon  of  the  adductors  of  the 
thigh,  so  that  the  abdominal  wall  is  strongly  retracted  and  almost  vertical  at 
its  junction  with  the  pelvis. 


302  THE    MUSCLES    OF   THE    OX 

The  transversus  abdominis  presents  no  striking  differential  features.     The 
transversalis  fascia  is  strong  and  distinct  except  over  the  diaphragm. 


Muscles  of  the  Thoraqc  Limb 
i.  muscles  of  the  shoulder  girdle 

The  trapezius  is  much  thicker  and  broader  than  in  the  horse,  and  is  undivided. 
It  arises  on  the  hgamentum  nuchse  and  supraspinous  hgament,  from  the  atlas  to 
the  twelfth  thoracic  vertebra. 

The  omo-transversarius  is  a  muscle  (not  present  in  the  horse)  which  arises 
on  the  wing  of  the  atlas,  and,  inconstantly,  the  transverse  process  of  the  second 
cervical  vertebra,  and  is  inserted  into  the  scapular  spine  and  fascia. 

The  rhomboideus  is  clearly  divided  into  cervical  and  dorsal  portions,  the  latter 
extending  further  than  in  the  horse. 

The  latissimus  dorsi  has  a  broad  tendon  of  origin,  which  blends  with  the 
lumbo-dorsal  fascia;  it  is  also  attached  to  the  eleventh  and  twelfth  ribs,  the  fascia 
over  the  external  intercostal  and  oblique  abdominal  nmscles,  and  by  a  tendinous 
slij)  to  the  deep  pectoral  muscle. 

The  mastoido-humeralis  has  two  distinct  parts.  The  dorsal  division  (M. 
cleido-occipitalis)  arises  on  the  occipital  bone  and  the  Hgamentum  nucha".  The 
ventral  part  (M.  cleido-mastoideus)  is  smaller  and  arises  by  a  round  tendon  on 
the  mastoid  process  and  the  rectus  capitis  anterior  major,  and  by  a  thin  tendon  on 
the  mandible.  At  the  shoulder  a  small  muscle  which  arises  on  the  first  rib  blends 
with  the  deep  face  of  the  mastoido-humeralis.' 

The  superficial  pectoral  muscle  does  not  present  any  striking  difference. 

The  deep  pectoral  arises  as  far  forward  as  the  second  rib  and  is  undivided. 
However,  tlie  scapular  portion  may  be  considered  to  be  represented  by  a  small 
branch  extending  over  the  lower  part  of  the  supraspinatus.  A  tendon  is  detached 
from  the  dorsal  edge,  which  blends  with  the  latissimus  dorsi  and  coraco-brachialis. 

The  serratus  magnus  is  clearly  divided  into  cervical  and  thoracic  portions. 
The  former  is  large  and  extends  from  the  third  (or  second)  cervical  vertebra  to 
the  fifth  rib,  being  overlapped  behind  by  the  thoracic  part.  The  thoracic  part  is 
relatively  thin  and  is  covered  by  a  very  strong  aponeurosis;  it  is  attached  to  the 
fourth  to  the  ninth  ribs  by  six  digitations,  and  is  inserted  by  a  flat  tendon  into  the 
inner  face  of  the  dorsal  angle  of  the  scapula. 


II.  MUSCLES  OF  THE  SHOULDER 

The  deltoid  is  clearly  divided  into  acromial  and  scapular  portions.  The  former 
arises  on  the  acromion,  the  latter  on  the  posterior  border  of  the  scapula  and  the 
aponeurotic  covering  of  the  infraspinatus.  The  scapular  part  of  the  muscle  is 
largely  inserted  into  the  fascia  covering  the  triceps. 

The  supraspinatus,  infraspinatus,  and  teres  minor  do  not  differ  materially 
from  those  of  the  horse. 

The  subscapularis  consists  of  three  portions  with  a  common  tendon  of  inser- 
tion. 

The  teres  major  and  coraco-brachialis  resemble  those  of  the  horse. 


III.  MUSCLES  OF   THE   ARM 
The  biceps  is  smaller  and  less  tendinous,  and  is  situated  more  internally  than 
in  the  horse.     The  tendon  of  origin  is  flat,  and  is  bound  down  in  the  bicipital  groove 

'  This  is  probably  the  homologue  of  the  subclavius  of  man. 


MUSCLES    OF    THE    AKM 


303 


by  a  fibrous  hand.     (In  the  sheep  the  tendon  is  round  and  passes  through  the 
shoulder  joint.) 


Fig.  212. — Muscles  of  Antibra- 

CHIUM    AND    MaXUS   OF  Ox, 

Anterior  View. 

a.  Extensor  carpi  radiaiis; 
6,  extensor  digiti  tertii;  c,  extensor 
digitalis  communis;  d,  extensor 
digiti  quarti  (tendon):  /,  extensor 
carpi  obliquus;  g,  brachialis;  13\ 
metacarpal  tuberosity.  (After 
Eilenberger-Baum.  Anat.  fur 
Kunstler.) 


Fig.  213. — Muscles  of  Antibra- 

CHIUM   AND   MaN'US    OF    Ox, 

External  View. 
a.  Extensor  carpi  radiaiis;  6, 
extensor  digiti  tertii;  c,  common  or 
anterior  digital  extensor;  d,  exten- 
sor digiti  quarti;  e,  flexor  carpi  ex- 
ternus;  /,  extensor  carpi  obliquus; 
/',  ulnar  head  of  flexor  carpi  medi- 
us;  g,  brachialis;  k,  interosseus 
medius  or  suspensory  ligament;  i, 
flexor  tendons;  i',  branch  of  k,  to 
superficial  flexor  tendon;  S,  ole- 
canon;  11 .  accessory  carpal  bone; 
75',  metacarpal  tuberosity.  (After 
Ellenberger-Baum,  Anat.  fur 
Kunstler.) 


Fig.  214. — Muscles  of  Antibra- 

CHIUM    AN'D    MaSUS  OF  Ox, 

Internal  View. 

a,  Extensor  carpi  radiaiis; 
b,  tendon  of  extensor  digiti  tertii; 
/,  tendon  of  extensor  carpi  ob- 
liquus; 9,  brachialis;  A.interosseus 
medius  or  suspensory  ligament;  i, 
flexor  tendons;  i',  branch  of  h;  k, 
flexor  carpi  internus;  /.  flexor 
carpi  medius;  m,  superficial  digital 
flexor.  (After  Ellenberger-Baum, 
Anat.  fur  Kiinstler.) 


The  internal  liead  of  the  triceps  is  more  developed  than  in  the  horse. 
The  tensor  fasciae  antibrachii  is  a  slender  muscle. 


304 


THE    MUSCLES    OF    THE    OX 


IV.    MUSCLES  OF  THE  FOREARM 
A.  Extensor  Division 
The  extensor  carpi  radialis  is  like  that  of  the  horse.     There  is  sometimes  a 
small  muscle  lying  along  its  inner  border,  which  may  represent  the  extensores 
pollicis. 

There  are  three  digital  extensors :  1.  The  common  or  anterior  digital  extensor 
(M.  extensor  digitalis  communis)  arises  by  two  heads  from  the  extensor  epicondyle 
and  the  ulna.  The  heads  fuse  about  the  middle  of  the  forearm,  and  terminate 
soon  on  a  tendon  which  passes  over  the  carpus  and  metacarpus,  gradually  inclining 


Fig.  215. — Right  Carpvs  of  Ox  with  Bubs.e  axd       Fig.  216. — Right  Carpus  of  Ox  with  Bdrs.e  and 
Synovial  Sheaths  Injected,  External  View.  Synovial  Sheaths  Injected,  Internal  View. 

1,  Extensor  carpi  radialis,  with  synovial  sheath  (/')  and  bursa  (i");  2,  extensor  carpi  obliquus,  with  synovial 
sheath  (3')  and  bursa  (5")  :  5,  e-xtensor  digiti  tertii  proprius:  4.  extensor  digitalis  communis;  3',  common  synovial 
sheath  of  3  and  4'>  5,  extensor  digiti  quarti  proprius,  with  synovial  sheath  (5');  6,  6',  flexor  carpi  e.xternus,  with 
bursa  (6");  7,  flexor  carpi  internus,  with  synovial  sheath:  S,  deep  digital  flexor,  with  synovial  sheath  (5');  9, 
flexor  carpi  medius;  10,  superficial  digital  flexor,  with  synovial  sheath  W;  a,  radius;  6,  carpus;  c,  metacarpus; 
d.  cut  edge  of  annular  ligament,     (.\fter  Schmidtchen.) 


forward.  At  the  fetlock  joint  it  divides  into  two  liranrhes,  which  are  inserted 
into  the  third  phalanges.  2.  The  internal  digital  extensor  (M.  extensor  digiti 
tertii  proprius)  arises  on  the  extensor  eiiicondyle,  and  is  inserted  by  two  branches 
into  the  second  and  third  phalanges  of  the  inner  digit.  The  tentlon  receives  two 
reinforcing  slij^s  from  the  suspensory  ligament.  3.  The  lateral  digital  extensor 
(M.  extensor  digitalis  lateralis  s.  digiti  quarti  proprius)  arises  from  the  external 
lateral  ligament  of  the  elbow  joint,  the  external  tuberosity  of  the  radius,  and  the 
ulna.     The  tendon  terminates  like  that  of  the  preceding  muscle. 

The  extensor  carpi  obliquus  resembles  that  of  the  horse. 

The  extensor  tentlons  are  bound  down  at  the  carpus  by  an  annular  ligament, 
and  are  furnished  with  synovial  sheaths  (Figs.  215,  21G). 


METACARPAL    MUSCLES 


305 


B.  Flexor  Division 

The  three  flexors  of  the  carpus  are  like  those  of  the  horse. 

The  superficial  digital  flexor  is  somewhat  blended  at  its  origin  with  the  middle 
flexor  of  the  carpus.  It  divides  into  two  bellies,  superficial  and  deep,  terminating 
on  tendons  at  the  distal  part  of  the  forearm.  The  superficial  tendon  passes  over 
the  posterior  annular  ligament  (Ligamentum  carpi  transvcrsum),  perforates  the 
metacarpal  fascia,  and  joins  the  deep  tendon  about  the  middle  of  the  metacarpus. 
The  deep  belly  is  connected  with  the  deep  flexor  by  a  strong  fibrous  band.  Its 
tendon  passes  under  the  annular  ligament  in  a  groove  on  the  deep  flexor,  from  which 
it  receives  fibers.  The  conjoined  tendon  soon  bifurcates,  each  branch  receiving  a 
reinforcing  band  from  the  suspensory  ligament,  and  forming  near  the  fetlock  a 
ring  for  the  corresponding  branch  of  the  deep  flexor  tendon.  Passing  under  two 
digital  annular  ligaments,  they  are  inserted  into  the  volar  surfaces  of  the  second 
phalanges  by  three  slips. 

The  deep  digital  flexor  has  the  same  heads  as  in  the  horse,  the  humeral  head, 
as  before  mentioned,  being  connected  with  the  deep  portion  of  the  superficial  flexor. 
The  temlon  divides  near  the  distal  end  of  the  metacarpus  into 
two  branches  which  are  inserted  into  the  volar  surfaces  of  tlie  ,.        ^ 

third  phalanges. 

The  synovial  sheaths  at  the  carpus  present  the  follow- 
ing special  features:  One  is  found  in  connection  with  the 
tendon  of  the  superficial  part  of  the  superficial  flexor  of  the 
digits.  There  is  a  common  sheath  for  the  tendons  of  the 
common  extensor  and  the  inner  extensor. 

Bursae  may  occur  under  the  tendons  of  the  proper  exten- 
sors of  the  digits  at  the  fetlock;  they  are  constant  only  in  old 
animals  (Schmidtchen).  The  branches  of  the  tendon  of  the 
common  extensor  are  provided  with  synovial  sheaths  from 
their  origin  to  the  middle  of  the  second  phalanx.  There  are 
two  digital  synovial  sheaths  for  the  flexor  tendons;  they  may 
communicate  at  their  upper  part,  and  extend  from  the  distal 
third  of  the  metacarpus  nearly  to  the  distal  sesamoids. 
Bursffi  occur  between  the  latter  and  the  branches  of  the 
deep  flexor  tendon. 


2 1 7. — Cross-section 
OF  Distal  Third 
OF  Mf.tacarpus  of 


b,  Tendon  of  exten- 
sor (ligiti  tertii;  c.  tendon 
of  common  extensor;  d, 
tendon  of  extensor  digiti 
quarti;  h,  interosseus  medi- 
us  or  suspensory  ligament; 
i,  tendons  of  digital  flexors; 
?*',  branch  of  h;  12,  meta- 
carpal bone,  (.\fter  EUen- 
berger-Baum,  Anat.  fiir 
Kiinstler.) 


METACARPAL  MUSCLES 

The  lumbricales  are  absent,  unless  we  regard  as  such 
the  muscular  bundles  which  arise  on  the  deep  flexor  and  are 
inserted  into  the  sujicrficial  flexor  temlon  at  the  carpus. 

The  interosseus  medius  or  suspensory  ligament  is  somewhat  more  muscular 
than  in  the  horse;  indeed,  in  the  young  subject  it  may  be  almost  entirely  fleshy. 
Its  arrangement  is  somewhat  complex.  Single  at  its  origin,  it  detaches  about  the 
middle  of  the  metacarpus  a  band  which  joins  the  tendon  of  the  superficial  flexor 
and  concurs  near  the  fetlock  in  the  formation  of  the  ring  for  the  deep  flexor  tendon. 
A  little  lower  down  it  divides  into  three  and  then  into  five  branches.  The  lateral 
branches  (two  pairs)  are  attached  to  the  corresponding  sesamoids  and  tendons  of 
the  proper  extensors,  while  the  middle  branch  passes  through  the  sulcus  at  the  distal 
end  of  the  metacarpus  and  bifurcates,  each  division  fusing  with  the  tendon  of  the 
corresponding  proper  extensor. 

It  is  to  be  noted  that  the  fascia  on  the  posterior  face  of  the  metacarpus  and 

digit  is  very  thick.     It  is  continuous  above  with  the  ligamentum  carpi  transversum, 

and  is  attached  on  either  side  to  the  metacarpal  bone.     At  the  fetlock  it  forms  the 

fibrous  basis  for  the  small  claws,  and  below  this  it  detaches  two  strong  bands  which 

20 


306 


THE    MUSCLES    OF    THE    OX 


diverge  to  be  inserted  into  the  second  and  third    phalanges,  blending  with  the 
lateral  ligaments. 


The  Muscles  of  the  Pelvic  Limb 
i,  the  subluhbar  muscles 

The  psoas  minor  begins  at  the  disc  between  the  twelfth  and  thirteenth  thoracic 
vertebrce. 

The  psoas  major  has  a  fleshy  origin  on  the  posterior  border  of  the  last  rib,  and 
a  thin  tendon  attached  to  the  twelfth  rib. 

The  iliacus  begins  under  the  body  of  the  sixth  lumbar  vertebra,  and  is  more 
closely  united  with  the  psoas  major  than  in  the 
horse. 

The  quadratus  lumborum  extends  as  far 

,^f<^-',~\    \    forward   as  the  l)ody  of  the  tenth  or  eleventh 

^  thoracic  vertebra. 

n.  EXTERNAL  MUSCLES  OF  THE   HIP  AND 
THIGH 
The  tensor  fasciae  latse  is  large,  and  the 
fleshy  part  extentls  further  down  than  in  the 
horse. 

The  gluteus  supcrficialis  is  not  present  as 
such;  apparently  its  anterior  part  has  fused 
with  the  tensor  fasciae  latse  and  its  posterior 
with  the  biceps  femoris. 

The  gluteus  medius  is  small,  the  lumbar 
portion  being  insignificant  and  extending  for- 
wartl  only  to  the  fourth  lumbar  vertebra.  Its 
deep  portion  (Gluteus  accessorius)  is  easily 
separable,  and  its  strong  tendon  is  inserted 
into  the  femur  below  the  trochanter  major, 
under  cover  of  the  upper  part  of  the  vastus 
externus. 

The  gluteus  profundus  is  thin,  but  exten- 
sive, arising  as  far  forward  as  the  external 
angle  of  the  ilium,  antl  from  the  lower  part  of 
the  sacro-sciatic  ligament.  The  fibers  converge 
on  a  tendon  which  passes  under  the  upper  part 
of  the  vastus  externus,  and  is  inserted  into  a 
tubercle  a  short  distance  below  the  great  tro- 
chanter. 

The  biceps  femoris  is  very  wide  at  its 
upper  part,  having  apparently  absorbed  the  posterior  part  of  the  superficial 
gluteus.  It  is  divided  in  the  thigh  into  two  portions,  which  end  on  a  wide 
aponeurosis.  There  is  no  femoral  attachment.  A  large  bursa  occurs  between 
the  muscle  and  the  great  trochanter  in  the  adult.  The  part  of  the  tendon  which 
fuses  with  the  external  patellar  ligament  presents  a  fibro-cartilaginous  thicken- 
ing, and  an  extensive  bursa  is  interposed  between  it  and  the  external  condyle  of 
the  femur. 

The  semitendinosus  and  semimembranosus  arise  on  the  ischium  only.     The 
latter  has  a  branch  attached  to  the  internal  condyle  of  the  tibia. 


Fig.  218. — Gluteal  and  Femoral  Regions 
OF  Ox,  After  Removal  of  Super- 
ficial Muscles. 

p,  Gluteus  medius;  r,  semitendinosus; 
w,  coccygeus;  2S,  vastus  externus;  SS' ,  rectus 
femoris;  29,  semimembranosus;  30,  gastroc- 
nemius; 31,  sacro-sciaticligament;  16,  tuber 
coxse;  17,  tuber  ischii;  19,  trochanter  major; 
SO,  patella;  ST,  external  condyle  of  tibia. 
(.\fter  EUenberger-Baum,  ,\nat.  fur  Kiinst- 
ler.) 


ANTERIOR    MUSCLES    OF    THE    THIGH 


307 


III.  ANTERIOR  MUSCLES  OF  THE  THIGH 
The  quadriceps  femoris  resembles  that  of  the  horse;  the  vastus  intermedius  is 
more  clearly  separable,  and  consists  of  two  parts.     Bursee  occur  under  the  insertions 
of  the  internal  and  external  vasti,  and  often  under  the  end  of  the  biceps  in  the  adult. 


Fig.  219  — Muscles  of  Left  Leg  and  Foot  of  Ox, 
Anterior  View. 
a,  Peroneus  tertius;  a',  tibialis  anterior;  b,  an- 
terior or  long  digital  extensor;  b' ,  extensor  digiti  tertii; 
c,  peroneus  longus;  rf,  extensor  digiti  quarti;  i,  (.annular 
ligaments;  fc,  external  lateral  ligament  of  hock  joint;  I, 
branch  of  suspensory-  ligament;  20,  patella;  31\  external 
condyle  of  tibia;  28,  tuberosity  of  tibia.  (After  Ellen- 
berger-Baum,  Anat.  fiir  Kiinstler.) 


Fig.  220. — Muscles  of  Leg  and  Foot  of  Ox,  Ex- 
ternal View. 
a.  Peroneus  tertius;  a',  tibialis  anterior;  6,  ante- 
rior or  long  digital  extensor;  b',  tendon  of  6;  c,  peroneus 
longus;  d,  extensor  digiti  quarti;  e,  deep  digital  flexor; 
c'.  tendon  of  e;  e" ,  branch  of  interosseus  medius  or  sus- 
pensory ligament;  /,  gastrocnemius  (the  soleus  lies  just 
in  front  of  f  r,  /',  tendon  of  /;  g,  tendon  of  superficial 
digital  flexor;  h,  interosseus  medius  or  suspensory  liga- 
ment; /.  i,  annular  ligaments;  20,  patella;  21\  external 
condyle  of  tibia;  28.  crest  of  tibia.  (After  EUenberger- 
Baum,  Anat.  fiir  Kiinstler.) 


The  articularis  genu  or  subcrureus  is  a  small  muscle  which  lies  under  the  lower 
part  of  the  vastus  intermedius,  and  is  inserted  on  the  [suprapatellar  cul-de-sac  of 
the  s\Tiovial  membrane. 

The  capsularis  is  absent. 


308 


THE    MUSCLES    OF    THE    OX 


IV.  INTERNAL  MUSCLES  OF  THE  THIGH 
The  sartorius  arises  by  two  heads,  one  from  the  tendon  of  the  psoas  minor 

and  the  iUac  fascia,  the  other  from  the  shaft  of  the  ihum.     The  femoral  vessels 

pass  between  them. 

The  gracilis  is  more  extensively  united  with  its  fellow  than  in  the  horse. 
The  pectineus  is  large,  and  arises  by  a  single  head  from  the  pubic  crest  and 


Fig.  221. — I.Ki.T  Tarsus  of  Ox  with  Syno- 
vial Sheaths  and  Burs.e  lNji;rTi:iJ. 
External  Vikw. 

1,  PeronevLS  tertius;  1' ,  tendon  of  /  and 
its  sheath,  1" ;  2,  e.Ktensor  digiti  tei-tii  pro- 
prius;  2' ,  tendon  of  2:  2",  common  sheath  of 
tendons  of  extensor  digiti  tertii  aii<l  extensor 
digitalis  longus  (S,  3');  4,  IJeroneu.'i  longus  and 
its  sheath.  4' ;  6,  extensor  digiti  finarti  and  its 
sheath,  S' ;  6,  tendon  of  gastrocnemius;  7, 
superficial  rligital  flexor  and  its  sheath,  7'; 
S,  tendon  of  tibialis  anterior;  «,  tibia;  b,  proxi- 
mal annular  ligament:  c.  tarsus;  rf,  distal  an- 
nular ligament;  c.  metatarsus;  /,  external 
lateral  ligament.     (.Mter  .Schmidtchen.) 


Fin.  222. — Left  Tarsds  of  Ox  with  Synovial  Sheaths  and 
BURS.E  Injected,  Internal  View. 
;,  Peroneus  tertius;  2,  tendon  of  tibialis  anterior  with 
sheath,  3',  and  bursa,  2";  S,  long  digital  flexor  and  5'.  its  sheath; 
4,  tibialis  posterior;  5,  deep  digital  flexor  and  its  sheath,  5';  6, 
tendon  of  gastrocnemius  and  bursa,  6' ;  7,  superficial  digital  flexor 
and  its  sheath,  7',*  S,  subcutaneous  bursa;  a,  tibia;  b,  pro.ximal 
annular  ligament;  c,  tarsus;  d,  metatarsus,     t After  Schmidtchen.) 


prepubic  tendon.  It  divides  into  two  branches,  one  of  which  is  inserted  as  in  the 
horse,  while  the  other  extends  to  the  internal  epicondyle  of  the  femur. 

The  adductor  resembles  that  of  th(>  horse,  Init  iloes  not  reach  to  theinlernal 
condyle. 

The  quadratus  femoris  antl  obturator  externus  resemlile  those  of  the  horse. 

The  obturator  internus  arises  from  the  ischium  only,  and  its  tentlon  passes 
through  the  obturator  foramen. 

The  gemellus  is  large. 


MUSCLES    OF   THE    LEG    AND    FOOT 


309 


V.  MUSCLES  OF  THE  LEG  AND  FOOT 

There  are  four  digital  extensors,  two  of  which  are  fused  with  each  other  and 
the  peroneus  tcrtius  in  the  upper  third  of  the  leg. 

1.  The  anterior  or  long  digital  extensor  (M.  extensor  digitalis  longus)  arises 
by  the  common  tendon  in  the  extensor  fossa  of  the  femur,  and  separates  from  the 
otlier  muscles  near  the  middle  of  the  leg.     At  the  distal  end  of  the  tibia  it  termi- 


FiG.  223. — Muscles  of  Leg  and  Foot  of  Ox,  Inner  View. 
a,  Peroneus  tertius;  b' .  tendon  of  anterior  or  long  extensor;  e.  deep  digital  flexor;  e",  tendon  of  e;  e" .  branch 
of  h  to  superficial  flexor  tendon;  /.  ga.<!trocnemiu.s;  w.  tendon  of  superficial  digital  flexor;    A.  interosseus  medius 
or  suspensory  ligament;  i,  annular  ligaments;  (,  branch  of  h:  m,  long  digital  flexor;  o,  popliteus;  SO,  patella;  iS, 
tuberosity  of  tibia,      (.\fter  EUenberger-Baum.  .\nat.  fiir  Kiinstler.) 


nates  on  a  tendon  which  passes  down  over  the  hock  (bound  down  by  two  annular 
ligaments)  and  einls  like  that  of  the  thoracic  limb. 

2.  The  internal  digital  extensor  (M.  extensor  digiti  tertii  proprius)  arises  in  com- 
mon with  the  preceding  muscle  and  the  peroneus  tertius,  and  is  covered  by  them 
to  the  distal  third  of  the  tibia.  Its  tendon  passes  under  the  annular  ligaments 
between  those  of  its  cogeners  and  ends  on  the  second  phalanx  of  the  inner  digit. 

3.  The  lateral  digital  extensor  (IVI.  extensor  digitalis  lateralis  s.  digiti  quarti 
proprius)  arises  on  the  external  lateral  ligament  of  the  stifle  joint  and  the  external 
condyle  of  the  tibia.  Its  tendon  passes  over  the  outer  surface  of  the  hock,  and 
terminates  on  the  anterior  surface  of  the  second  phalanx  of  the  external  digit. 


310 


THE    MUSCLES    OF   THE    OX 


The  reinforcing  hantls  from  the  suspensory  Hgament  are  arranged  as  in  the 
fore  limlj. 

4.  The  extensor  brevis  resembles  that  of  the  horse,  but  is  inserted  on  the  ten- 
don of  the  anterior  extensor  only. 

The  peroneus  longus  (not  present  in  the  horse)  is  situated  in  front  of  the  lateral 
extensor.  It  arises  on  the  external  condyle  of  the  tibia  and  the  fibrous  band  which 
represents  the  shaft  of  the  fibula.  Its  tendon  passes  downward  and  backward 
over  the  outer  surface  of  the  hock,  crosses  over  that  of  the  lateral  extensor  and  under 


Fig.  224. — Distal  Part  of  Limb  of  Ox  with  Syno- 
vial Sheaths  and  Burs.k  Lvjkcted,  .\n- 
Tpmioii  View. 

1,  Tendon  of  extensor  digiti  tertii,  with  bursa 
(/');  S,  tendon  of  anterior  extensor;  2* ,  branch  of  2, 
with  synovial  sheath  (5");  3,  tendon  of  extensor  digiti 
quarti,  with  bursa  (.5');  a,  metatarsus:  6.  first  phalanx; 
c,  second  phalanx.    (After  Schmidtchen.) 


Fig.  225. — Distal  Part  of  Limb  of  Ox  with  Syno- 
vial .Sheaths  I.njected,  Posterior  View. 
1,  .Superficial  flexor  tendon;  1',  1',  branches  of 
i;  r\  V" ,  upper  part  of  synovial  sheaths  of  /',  1' ;  2, 
deep  flexor  tendon;  £',  5".  branches  of  2;  2",  upper 
part  of  synovial  sheath  of  2' ;  3,  3,  lateral  branches  of 
iiiterosseus  medius  or  suspensor,\'  ligament;  3',  branch 
<;if  same  to  superficial  flexor  tendon;  a,  fetlock  joint; 
/^  pastern  joint;  c.  cofl^n  joint ;  rf.  c,  annular  ligaments; 
/.  cruci.il  interdigital  ligament,      (.\fter  Schmidtchen.) 


the  lateral  ligament,  and  ends  on  the  first  tarsal  bone  (Cuneiform  parvum).  It  is 
enveloped  by  a  synovial  sheath.  It  would  apparently  act  as  an  inward  rotator 
at  the  hock  joint. 

The  peroneus  tertius  is  a  well-developed  muscle  which  arises  on  the  common 
tendon  with  the  long  and  internal  extensors.  It  has  a  large,  fusiform  belly,  which 
is  superficially  situated  on  the  front  of  the  leg.  Close  to  the  tarsus  it  ends  on  a 
flat  tendon,  which  is  perforated  by  that  of  the  tibialis  anterior,  and  ends  on  the 
large  metatarsal  antl  second  and  third  (fused)  tarsal  bones  (Cuneiform  magnum). 

The  tibialis  anterior  is  smaller,  and  arises  by  two  heads.     The  larger  head 


MUSCLES    OF   THE    PIG — MUSCLES    OF    HEAD  311 

springs  from  tlie  outer  surface  of  the  tuljerositj'  of  the  tibia;  the  outer,  smaller 
one  (M.  extensor  luillucis  longus) ,  from  the  upper  part  of  the  external  border  of  the 
tibia  and  the  fibrous  band  which  replaces  the  shaft  of  the  fibula.  The  tendon 
perforates  that  of  the  jjreceding  muscle  anil  cntls  on  the  metatarsal  and  second  and 
third  tarsal  bones. 

B.  Posterior  Group 

The  gastrocnemius  and  soleus  resemble  those  of  the  hor.se.  The  superficial 
flexor  is  more  fleshy  than  in  the  horse.     Its  tendon  terminates  as  in  the  fore  limb. 

The  deep  flexor  iias  in  its  upper  part  a  close  resemblance  to  that  of  the  horse, 
but  the  superficial  head  (tibialis  posterior)  is  larger  and  distinct.  The  tendon  ends 
like  that  on  the  fore  limb. 


MUSCLES  OF  THE  PIG 
Muscles  of  Head 

The  facial  panniculus  is  pale,  thin,  and  difficult  to  separate  from  the  skin. 

The  orbicularis  oris  is  little  developed. 

The  levator  nasolabialis  is  thin  and  pale,  and  is  undivided. 

The  levator  labii  superioris  proprius  may  well  be  termed  the  levator  rostri. 
It  has  a  large  peimiform  belly,  which  arises  in  the  fossa  on  the  lacrimal  bone  and 
maxilla.  The  tendon  ends  on  the  anterior  part  of  the  os  rostri.  A  muscular  slip 
connects  it  with  the  premaxilla. 

The  zygomaticus  arises  on  the  fascia  over  the  masseter  and  ends  at  the  angle 
of  the  mouth. 

The  depressor  labii  inferioris  separates  from  the  buccinator  only  near  the 
angle  of  the  mouth;    it  ends  by  a  number  of  tendinous  branches  in  the  lower  lip. 

The  dilatator  naris  lateralis  is  well  developed.  It  arises  under  the  levator 
rostri  and  ends  l)y  a  tendinous  network  around  the  nostril. 

The  dilatator  naris  transversus  is  represented  onlj'  by  a  few  fibers  which  cross 
over  the  os  rostri. 

The  depressor  rostri  arises  on  the  facial  crest.  It  has  a  long  strong  tendon 
which  passes  below  the  nostril  and  turns  up  and  inward  to  meet  the  tendon  of  the 
opposite  side  and  end  in  the  skin  of  the  snout.  It  depresses  the  snout  and  con- 
tracts the  nostril. 

The  malaris  is  absent,  and  the  other  palpebral  muscles  present  no  special 
features. 

MUSCLES  OF  MASTICATION 
The  digastricus  has  onlj'  one  belly.     It  ends  on  the  inner  and  lower  surface 
of  the  mandible,  in  front  of  the  groove  for  the  facial  vessels. 
The  other  muscles  have  no  important  differential  features. 
The  same  is  true  of  the  oral  hyoid  muscles. 


MUSCLES  OF  THE  NECK 

The  panniculus  camosus  consists  of  two  layers  which  cross  each  other  ob- 
liquely. The  fibers  of  the  superficial  layer  are  directed  nearly  vertically,  those  of 
the  deep  layer  toward  the  face,  on  which  thej'  are  continued  to  form  the  facial 
portion. 

The  mastoido-humeralis  is  described  on  p.  314. 


312 


MUSCLES    OF   THE    PIG 


The  stemo-cephalicus  (Sterno-mastoideus)  arises  on  the  sternum  and  is  m- 
serted  by  a  long  round  tendon  on  the  mastoid  process. 

The  th\Toid  portion  of  the  sterao-thyro-hyoideus  has  a  peculiar  arrangement. 
It  arises  (separately  from  the  opposite  muscle)  on  the  manubrium  sterni.  About 
the  middle  of  the  neck  it  has  an  oblique  tendinous  intersection,  beyond  which  it 
di\-ides  into  two  branches:  one  of  these  is  inserted  in  the  usual  fashion,  the  other 
ends  on  the  laryngeal  i^rominence.     The  hyoid  portion  is  well  developed. 

The  omo-hyoideus  is  thin.  It  arises  as  in  the  horse,  but  has  no  connection 
with  the  mastoido-humeralis  nor  with  the  opposite  muscle. 

The  omo-transversarius  arises  on  the  first  or  second  cervical  vertebra  (under 
cover  of  the  mastoido-humeralis),  and  is  inserted  into  the  lower  part  of  the  scapular 


spme. 

There  are  two  scaleni. 


The  scalenus  ventralis  (s.  prim®  costs)  resembles 


Fig.  226. —  SrpERFici-\L  MrscLEs  of  Pin,  -\fter  Remov.4l  of  P.\xxicm.us  C.^Rxosrs. 
a.  Levator  na^^labiatis;  6.  levator  labii  «uperioris  proprius;  6',  fleshy  slip  of  6  which  comes  from  pre- 
roaxilla;  c.  dilatator  naris  lateralis;  d,  depressor  rostri;  t.  orbicularis  oris:  /,  depressor  labii  inferioris;  g.  lygo- 
maticus;  A.  masseter;  i,  T,  i',  brachio-cephalicus  ( cleido-occipitalis,  cleido-mastoideus.  pars  claii-icularis);  k, 
stemo-cephalicus;  /,  stemo-hyoideus:  m.  omo-transvensarius;  n,  n',  trapezius;  o,  anterior  deep  pectoral;  p, 
latissimus  dorsi;  q,  lumbo-dorsal  fascia;  r.  obUquus  abdominis  extemus;  r*,  aponeurosis  of  r;  s.  serratus  posticus; 
t,  serratus  magnus:  u.  posterior  deep  pectoral;  r.  supraspinatus;  w.  tr*.  deltoideus;  x,  long  head  of  triceps;  tf, 
external  head  of  triceps:  z,  tensor  fascur  antibrachii;  1,  brachialis:  3,  extensor  carpi  radiaUs:  S,  extensor  digiti 
quarti;  4,  extensor  digiti  quinti:  .5.  extensor  carpi  ulnaris:  d,  ulnar  head  of  deep  Qe.xor;  7.  gluteus  medius:  S, 
tensor  fasci:p  latsc:  9,  10,  !(/ .  biceps  femoris:  il,  semitendinosus:  12.  semimembranosus:  IS,  caudal  muscles; 
74.  panniculus  adiposus  in  section.     t.\fter  EUenberger,  in  Leisering's  .\tlas.) 


that  of  the  ox,  is  attached  to  the  last  four  cervical  vcrtebrje,  and  is  perforated  by 
the  nerves  of  the  brachial  plexus.  The  scalenus  dorsalis  (s.  supracostalis)  arises 
on  the  transverse  processes  of  the  third  to  the  sixth  cervical  vertebra,  and  ends  on 
the  third  rib. 

The  straight  muscles  of  the  head  present  no  special  features. 

The  longus  colli  is  separated  from  the  opposite  muscle,  so  that  part  of  the 
bodies  of  tlie  ccrviial  vertebra  is  exposed  as  in  man. 

The  intertransversales  resemble  those  of  the  ox. 

The  splenius  is  tliick  and  extensive.  It  ends  in  three  parts  on  the  occipital, 
the  temporal,  an<l  the  wing  of  the  atlas  (inconstant). 

The  trachelo-mastoideus  is  small,  and  its  atlantal  portion  is  blended  with  the 
longis-simus. 

The  complexus  is  large,  and  is  clearly  di\-ided  into  two  portions:   the  dorsal 


MUSCLES    OF    THE    THORAX MUSCLES    OF    THE    BACK   AND    LOINS  313 

portion  (Biventer  cervicis)  is   marked   bj-  several   tendinous  intersections;   the 
ventral  part  is  the  conijilexus  proper. 

The  obliquus  capitis  posterior  is  relatively  thin. 

The  recti  capitis  are  thick  and  more  or  less  fused. 


Muscles  of  the  Thorax 

The  levatores  costarum  and  rectus  thoracis  present  no  special  features. 

The  external  intercostal  muscles  are  absent  under  the  serratus  anticus  and 
posticus  and  the  diiiitations  of  the  external  oblique. 

The  internal  intercostals  are  thick  l)ct\vecn  the  cartilages  of  the  sternal  ribs. 

The  retractor  costae  and  the  transversus  thoracis  resemble  those  of  the  horse; 
the  latter  extends  back  to  the  eighth  cartilage  and  fuses  with  the  transversus 
abdominis. 

The  diaphragm  has  seven  costal  digitations  on  each  side,  the  posterior  ones 
being  attached  to  the  ribs  at  some  distance  (ca.  one-third  to  one-fourth  of  rib- 
length)  from  the  costo-chondral  junction.  The  line  of  attachment  reaches  the 
latter  at  the  tenth  rib,  and  passes  along  the  eighth  cartilage  to  the  xiphoid  process. 
The  tendinous  center  is  more  rounded  than  in  the  horse.  The  crura  are  well 
developed.  The  right  cms  is  very  large,  and  is  perforated  by  the  ex-tensive  slit- 
like opening  for  the  oesophagus,  which  is  median  in  position,  and  lies  about  two  and 
one-half  to  three  inches  (ca.  6  to  8  cm.)  below  the  twelfth  thoracic  vertebra.  The 
hiatus  aorticus  is  between  the  crura. 


Abdominal  Muscles 

The  abdominal  tunic  is  little  developed. 

The  obUquus  abdominis  extemus  has  an  extensive  fleshy  portion  and  a  cor- 
respondingly narrow  aponeurosis:  the  latter  does  not  detach  a  femoral  lamina, 
but  is  reflected  in  toto  to  form  the  inguinal  (Poupart's)  ligament. 

The  obliquus  abdominis  intemus  resemblessthat  of  the  ox;  a  small  fusiform 
muscle,  which  crosses  the  inguinal  canal  obliquely  and  is  attached  on  the  abdominal 
surface  of  the  inguinal  ligament,  is  apparently  a  detached  slip  of  the  internal 
oblique. 

The  rectus  abdominis  is  extensive  and  thick.  It  has  seven  to  ten  intersections. 
Its  tendon  of  insertion  fuses  largely  -u-ith  the  common  tendon  of  the  gracihs,  and 
does  not  give  off  an  accessory  band  to  the  head  of  the  femur. 

The  fleshy  part  of  the  transversus  abdominis  is  well  developed.  It  blends  in 
front  with  the  transversus  thoracis. 

The  cremaster  extemus  is  present  in  the  female  as  well  as  in  the  male. 


Muscles  of  the  Back  and  Loins 

The  serratus  anticus  is  inserted  into  the  fifth  to  the  eighth  ribs  inclusive,  the 
serratus  posticus  into  the  last  four  or  five  ribs.  There  are  usually  no  digitations 
attached  to  the  ninth  and  tenth  ribs. 

The  transversaUs  costarum  (Iliocostalis)  extends  to  the  wing  of  the  atlas. 

The  spinalis  et  semispinalis  can  be  separated  without  much  difficulty  from  the 
longissimus  dorsi,  the  division  from  the  common  mass  of  the  loins  beginning  about 
the  first  lumbar  vertebra. 

The  multifidus  resembles  that  of  the  horse. 

Interspinales  are  present,  as  well  as  distinct  intertransversales  of  the  back 
and  loins. 


314  MUSCLES    OF   THE    PIG 

Muscles  of  the  Tail 

The  superior  and  lateral  sacro-coccygei  arise  as  far  forward  as  the  last  lumbar 
vertebra.  Gurlt  explains  the  twist  of  the  tail  as  being  due  to  the  spiral  arrangement 
of  the  insertions  of  the  tendons. 

Muscles  of  the  Thoracic  Limb 

MUSCLES  OF  the  SHOULDER  GIRDLE 

The  trapezius  is  very  wide,  its  line  of  origin  extending  from  the  occipital  bone 
to  the  tenth  thoracic  vertebra.  There  is  no  clear  division  between  its  two  parts, 
which  are  both  inserted  into  the  scapular  spine. 

The  omo-transversarius  resembles  that  of  the  ox. 

The  rhomboideus  consists  of  three  portions.  The  cervical  portion  (Rhom- 
boideus  cervicalis)  is  greatly  developed,  its  origin  extending  from  the  second  cervi- 
cal to  the  sixth  thoracic  vertebra.  The  cephalic  portion  (Rhomboideus  capitis) 
arises  with  the  splenius  on  the  occipital  bone,  and  is  inserted  with  the  cervical  part. 
The  dorsal  portion  (Rhomboideus  thoracalis)  extends  as  far  back  as  the  ninth  or 
tenth  thoracic  vertebra. 

The  latissimus  dorsi  is  attached  to  the  four  ribs  preceding  the  last.  It  is 
inserted  into  the  internal  lip  of  the  bicipital  groove. 

The  mastoido-humeralis  divides  into  two  parts,  the  cleido-mastoideus  and 
cleido-occipitalis,  wliicii  arise  on  the  mastoid  process  and  occipital  crest  respectiveh', 
and  unite  at  the  fibrous  vestige  of  the  clavicle. 

The  anterior  superficial  pectoral  is  thin.  The  posterior  superficial  pectoral 
is  divided  into  parts,  one  of  wliich  ends  on  tlie  humerus,  the  other  on  the  fascia 
of  the  forearm. 

The  deep  pectoral  is  clearlj'  divided  into  two  parts.  The  scapular  portion 
resembles  tliat  of  the  horse,  but  its  origin  does  not  extend  Ijehind  the  first  two 
chondro-sternal  joints.     The  posterior  deep  pectoral  is  very  long. 

The  cervical  portion  of  the  serratus  magnus  is  greatly  developed,  its  origin 
extending  from  the  wing  of  the  atlas  to  the  upper  part  of  the  fifth  rib,  and  passing 
under  the  thoracic  portion;   the  latter  resembles  that  of  the  ox. 


MUSCLES  OF  THE  SHOULDER 

The  deltoid  is  undivided;  it  arises  from  the  aponeurosis  covering  the  infra- 
spinatus, and  it  ends  largely  on  the  deltoid  ridge,  but  partly  on  the  fascia  of  the 
arm. 

The  supraspinatus  is  large;  it  ends  chiefl.y  on  the  external  tulierosity  of  the 
humerus. 

The  infraspinatus  is  inserted  into  a  depression  below  the  posterior  division  of 
the  external  tulicrosity. 

The  teres  minor  is  well  developed;  it  ends  on  a  tubercle  jjetween  the  external 
and  deltoid  tuberosities  of  the  humerus. 

Tlie  subscapularis  and  teres  major  have  no  remarkable  features. 

Tlic  coraco-brachialis  is  short  and  undivided. 

The  capsularis  is  very  small  and  frequently  absent. 


MUSCLES  OF  THE  ARM 
The  biceps  brachii  is  fusiform  and  not  greatly  developed.     Its  tendon  of  origin 
is  rounded  and  ])as.ses  through  the  capsule  of  the  shoulder  joint.     The  tendon  of 
insertion  is  bifid,  ending  on  tl\e  radius  and  ulna. 


MUSCLES    OF    THE    FOREARM    AND    DIGITS 


315 


The  brachialis  is  well  developed,  and  also  ends  on  the  radius  and  ulna. 

The  tensor  fasciae  antibrachii  resembles  that  of  the  horse. 

The  long  head  of  the  triceps  is  divided  into  two  parts,  cxcejit  at  its  distal  end, 
under  which  there  is  a  synovial  bursa.     The  external  head  is  inserted  into  a  crest 
on  the  outer  surface  of  the  olecranon  l)y  a  thin  tendon,  under  which  there  is  a 
bursa.     The  internal  head  arises  near  the  head  of  the 
humerus,  beneath  the  coracobrachialis. 

There  are  two  anconei. 


MUSCLES  OF  THE  FOREARM  AND  DIGITS 

The  extensor  carpi  radialis  is  a  strong,  fleshy  muscle, 
the  tendon  of  which  is  inserted  into  the  proximal  end  of 
the  third  metacarpal  bone.  It  may  be  divided  into  two 
parts  (M.  extensor  carpi  radialis  longus,  lirevis). 

The  extensor  carpi  obliquus  is  well  developed ;  it  ends 
on  the  second  metacarpal  bone. 

There  are  three  (or  four)  digital  extensors. 

1.  The  common  or  anterior  digital  extensor  (M.  ex- 
tensor digitalis  communis)  arises  on  the  extensor  epicon- 
dyle  of  the  humerus  and  the  lateral  ligament  of  the  elbow, 
and  divides  into  three  parts.  The  tendon  of  the  inner 
part  divides  into  two  branches  which  end  on  the  second 
and  third  digits ;  the  tendon  to  the  second  digit  is  small 
and  often  alsscnt.  The  tendon  of  the  middle  part  divides 
lower  down  into  two  branches  for  the  third  and  fourth 
(chief)  digits ;  above  this  bifurcation  it  detaches  a  small 
branch  to  the  second  digit,  which  usually  unites  with  the 
tendon  of  the  extensor  indicis.  The  tendon  of  the  deep 
head  divides  into  two  branches,  the  inner  one  joining  the 
tendon  of  the  middle  head,  while  the  outer  one  ends  on 
the  fifth  digit. 

2.  The  extensor  of  the  second  digit  (M.  extensor 
indicis  proprius)  is  covered  by  the  preceding  muscle, 
with  which  it  is  partially  fused.  It  arises  on  the  ulna. 
Its  delicate  tendon  usually  unites  with  the  tendon  of  the 
middle  head  of  the  common  extensor  which  goes  to  the 
second  digit. 

3.  The  lateral  digital  extensor  (M.  extensor  digitalis 
lateralis)  consists  of  two  distinct  parts:  (1)  The  large 
dorsal  (anterior)  muscle  (M.  extensor  digiti  quarti  pro- 
prius) has  a  long  tendon  which  ends  on  the  fourth  digit, 
and  often  sends  a  slip  to  the  fifth  digit.  (2)  The  small 
volar  (posterior)  muscle  (M.  extensor  digiti  quinti  pro- 
prius) ends  by  a  long  tendon  on  the  lateral  aspect  of  the 
fifth  digit. 

The  supinator  has  been  found  liy  Arloing  and  Lesbre, 
but  is  usually  absent  in  the  pig. 

The  pronator  teres  is  a  small  muscle  which  lies  on  the 
internal  lateral  ligament  of  the  elbow.     It  arises  from  the  internal  epicondyle  of 
the  humerus,  and  reaches  about  to  the  middle  of  the  inner  border  of  the  radius. 

The  flexor  carpi  internus  is  well  developed.     It  arises  on  the  flexor  epicondyle 
of  the  humerus,  ami  is  inserted  into  the  third  metacarpal  bone. 

The  flexor  carpi  medius  is  narrow  and  has  no  ulnar  head. 


Fig.  227. — Muscles  of  Anti- 

BRACHIUM    AND    MaNUS 

OF    Pig,     Antero~Ex- 

TERXAL  View. 

a,  a'.  Extensor  carpi 
radialis;  b,  extensor  carpi 
obliquus  (s.  abductor  pollicis 
longus);  c,  d,  e,  common  or 
anterior  digital  extensor;  c', 
c" ,  tendons  of  insertion  of  c; 
d\  d'\  tendons  of  d;  e' ,  e", 
tendons  of  e:  /,  tendon  of 
extensor  indicis:  g,  extensor 
digiti  quarti:  h,  extensor 
digiti  quinti;  h' ,  tendon  of 
li:  i,  tendinous,  and  k,  fleshy 
part  of  flexor  carpi  externus; 
k' ,  tendon  of  k;  I,  ulnar  head  of 
deep  digital  flexor;  m,  superfi- 
cial digital  flexor;  n,  brachialis. 
(Alter  Ellenberger,  in  Leis- 
ering's  Atlas.) 


316  MUSCLES    OF   THE    PIG 

The  flexor  carpi  externus  (M.  extensor  carpi  ulnaris)  is  covered  by  a  thick, 
tendinous  band,  which  extends  from  the  extensor  epicondyle  to  the  accessory  carpal 
bone  and  outer  aspect  of  the  carpus.  The  tendon  of  the  muscle  perforates  this 
band  in  the  distal  part  of  the  forearm  and  ends  on  the  proximal  end  of  the  fifth 
metacarpal  bone. 

The  superficial  digital  flexor  has  two  bellies.  The  tentlou  of  the  superficial 
head  passes  down  behind  the  posterior  annular  ligament  of  the  carpus  (bound 
down  by  a  special  annular  ligament),  forms  a  ring  at  the  fetlock  for  a  tendon  of 
the  deep  flexor,  and  ends  by  two  branches  on  the  second  phalanx  of  the  fourth 
digit.  The  tendon  of  the  deep  head,  after  detaching  a  slip  to  the  tendon  of  the 
deep  flexor,  passes  down  with  the  latter  (for  which  it  forms  a  ring),  and  ends  on 
the  third  digit. 

The  deep  digital  flexor  has  three  heads — humeral,  ulnar,  and  radial.  The 
common  tendon  divides  into  four  branches,  the  larger  central  pair  ending  on 
the  third  phalanges  of  the  principal  digits,  the  smaller  pair  on  the  accessory 
digits.  The  latter  are  bound  down  by  a  peculiar  spiral  band.  There  is  no  check 
ligament. 

The  lumbricales  are  represented  by  bundles  which  extend  from  the  deep  flexor 
tendon  to  the  tendon  of  the  deep  head  of  the  superficial  flexor. 

The  third  and  fourth  interossei  are  present.  Each  sends  two  slips  to  the  cor- 
responding sesamoid  bones  and  extensor  tendon. 

There  are  flexors,  adductors,  and  abductors  of  tlic  second  and  fifth  digits. 


Muscles  of  the  Pelvic  Limb 
sublumbar  muscles 

The  psoas  minor  is  intimately  united  with  the  psoas  major  in  front,  and  has  a 
long  small  tendon  which  ends  on  the  psoas  tubercle.     It  has  no  thoracic  part. 

The  psoas  major  is  large  and  rounded.     It  begins  at  the  last  rib. 

The  quadratus  lumborum  is  well  developed,  and  extends  forward  as  far  as 
the  twelfth  rib. 

MUSCLES  OF  THE  HIP  AND  THIGH 

The  tensor  fasciae  latae  is  broad,  and  its  fleshy  part  reaches  almost  to  the  pa- 
tella. 

The  gluteus  superficiaUs  has  a  sacral  head  only:  it  blends  with  the  biceps 
femoris. 

The  gluteus  medius  has  a  small  lumliar  jiart  which  does  not  extend  so  far 
forward  as  in  the  horse.  The  deep  part  (CJluteus  accessorius)  is  pretty  clearly 
marked. 

The  gluteus  profundus  is  extensive,  reacliinu  nearly  to  the  external  angle  of  the 
ilium. 

The  biceps  femoris  has  a  narrow  origin  from  the  sacro-sciatic  ligament  and 
tuber  ischii.     It  ends  below  like  that  of  the  ox. 

Tlie  semitendinosus  resembles  that  of  the  horse. 

Tlic  semimembranosus  has  two  insertions  as  in  the  ox. 

The  sartorius  has  two  heads  of  origin,  between  which  the  external  iliac  vessels 
are  situat(>d.  The  inner  arises  from  the  tendon  of  the  psoas  minor,  the  outer  one 
from  tlic  iliac  fascia. 

The  graciles  are  united  at  their  origin  even  more  than  in  the  ox. 

The  pectineus  is  well  developed  and  is  flattened  from  before  backward. 

The  adductor  shows  no  division  and  is  partially  fused  with  the  gracilis.  It 
ends  on  the  femur  just  above  the  origin  of  the  gastrocnemius. 


MUSCLES    OF   THE    LEG    AND    FOOT 


317 


The  quadratus  femoris  is  large. 

The  obturator  extemus  resembles  that  of  the  horse. 

The  obturator  intemus  is  extensive  and  strong;  its  tendon  emerges  through 
the  obturator  foramen. 

The  gemellus  is  fused  in  i)art  with  the  obturator  internus. 

The  quadriceps  femoris  is  more  clearly  divided  than  in  the  horse,  and  its 
action  is  transmitted  l)y  a  single  patellar  ligament. 

The  capsularis  is  alisent. 

MUSCLES  OF  THE  LEG  AND  FOOT 

The  peroneus  tertius  rescml)les  that  of  the  ox,  but  its 
tendon  is  not  perforated  by  that  of  the  tibialis  anterior, 
and  ends  on  the  inner  (second)  large  metatarsal  bone,  de- 
taching a  strong  branch  to  the  first  and  second  tarsal 
bones. 

The  tibialis  anterior  arises  on  the  tiliial  crest.  Its 
tendon  passes  over  the  hock  along  the  inner  border  of  the 
tendon  of  the  peroneus  tertius  (both  being  bound  dowTi 
by  an  annular  ligament),  and  is  inserted  into  the  inner 
(second)  metatarsal  and  first  tarsal  bones. 

The  peroneus  longus  lies  partly  on  the  outer  surface 
of  the  peroneus  tertius.  Its  tendon  crosses  those  of  the 
lateral  extensor,  passes  along  a  groove  on  the  plantar 
surface  of  the  fourth  tarsal  bone,  and  ends  on  the  first 
tarsal  and  second  metatarsal  bones. 

The  anterior  or  long  digital  extensor  arises  with  the 
peroneus  tertius  and  is  largely  covered  by  it  and  the  per- 
oneus longus.  It  divides  into  three  parts.  The  tendon 
of  the  inner  division  (M.  extensor  digiti  tertii)  ends  on 
the  inner  chief  (tliird)  digit;  that  of  the  middle  division 
by  two  branches  on  the  principal  digits;  and  that  of  the 
outer  division  by  three  branches  on  the  second,  fourth, 
and  fifth  digits. 

The  lateral  digital  extensor  divides  into  proper  ex- 
tensors of  the  fourth  antl  fifth  digits  (Extensores  digiti 
quarti  et  quinti). 

The  extensor  hallucis  longus  arises  on  the  fibula  and 
ends  on  the  inner  small  (second)  digit. 

The  extensor  digitalis  brevis  is  well  developed  and 
consists  of  three  parts.  The  inner  and  outer  tendons  end 
on  the  first  phalanges  of  the  chief  digits,  the  middle 
one  joins  the  common  extensor  tendon  of  the  same. 

The  gastrocnemius  presents  nothing  special. 

The  soleus  is  wide,  and  is  partly  blended  with  the 
external  head  of  the  gastrocnemius. 

The  superficial  digital  flexor  has  a  large  belly.     Its 
tendon  ends  on  the  two  chief  digits,  and  is  also  connected      '"^'^  -^"'^  ' 
with  the  ligaments  of  the  accessory  digits. 

The  inner  head  of  the  deep  digital  flexor  (flexor  digitalis  longus)  is  relatively 
small.     The  common  tendon  ends  as  in  the  thoracic  limb. 

The  popUteus  jiresents  no  special  features. 

The  plantar  muscles  resemble  their  homologues  of  the  fore  limb,  except  that 
the  adductors  of  the  accessory  digits  and  the  lumbricales  are  absent. 


Fig.   228. — Muscles  of  Leg 
AND  Foot  of  Pig,  An- 

TERO-EXTERXAL  VjEW. 

a.  Tibialis  anterior;  a\ 
tendon  of  preceding;  6,  pero- 
neus tertius;  h' ,  ten<lon  of  b; 
c,  anterior  or  long  digital  ex- 
tensor; d,  e.  f,  /'.  /".  tendons 
of  c;  a,  iieroneus  longus;  g', 
tendon  of  g:  h.  extensor  digiti 
quarti;  h',  tenilon  of  /t.  "which 
receives  A",  from  the  inter- 
osseus  niedius;  i.  extensor 
digiti  quinti;  h.  deep  digital 
flexor;  /,  soleus;  w.  gastroc- 
nemius: ".  extensor  brevis. 
(.\fter  EUenberger,  in   Leiser- 


318 


THE    MUSCLES    OK   THE    DOG 


THE  MUSCLES  OF  THE  DOG 
Muscles  of  the  Face 

The  panniculus  camosus  is  well  developetl  and  presents  two  distinct  bands, 
one  of  whifh  is  inserted  into  the  lower  lip,  the  other  into  the  seutiform  cartilage  of 
the  ear. 

The  orbicularis  oris  is  poorly  developed.  In  the  upper  lip  it  is  divided  cen- 
trally, and  in  the  lower  it  is  distinct  only  near  the  angles  of  the  movith. 

Tiic  levator  nasolabialis  is  wide  and  undivided,  and  ends  in  the  upper  lip. 

The  levator  labii  superioris  proprius  arises  l)ehind  the  infraorbital  foramen, 
runs  forward  under  the  preceding  muscle,  and  ends  in  numerous  small  tendons 
around  the  nostril,  some  blending  with  those  of  the  opposite  side. 

The  zygomaticus,  long  and  narrow,  arises  on  the  seutiform  cartilage,  and 
ends  at  the  angle  of  the  mouth. 


-/ 


Fig.  229. — Muscles  of  Head  op  Dog 
a,  Scutiilaris:  h,  r.  anterior  auricular  muscles;  d.'helicis;  e,  antitragicus;  /.  /.  zygomaticus,  out  of  which 
a  portion  is  cut;  »,  slip  of  panniculus;  h,  parotido-auricularis;  i,  masseter;  k,  malaris;  (,  levator  nasolabialis; 
m,  levator  labii  superioris  proprius;  n,  dilatator  nans  lateralis;  o,  p,  buccinator  (buccalis,  molaris);  q,  retractor 
anguli  oris;  r,  digastricus;  s,  raylo-hyoideus;  /,  base  of  concha;  3,  parotid  gland;  2',  parotid  duct;  5,  submaxil- 
lary gland;  4.  subma-xillary  lymph  glands;  6,  buccal  glands;  G,  zygomatic  arch;  7,  maxilla;  S,  dorsum  nasi; 
9,  parotid  lymph  gland.     (Ellenberger-Baum,  Anat.  d.  Hundes.) 

The  depressor  labii  inferioris  is  absent,  unless  we  recognize  as  such  a  thin 
stratum  arising  on  the  body  of  the  mandible  and  spreading  out  in  the  orbicularis. 

There  are  no  special  nasal  muscles,  the  homologue  of  the  lateral  dilator  ending 
almost  entirely  in  the  upjier  lip. 

The  buccinator  is  wide  and  very  thin,  and  the  two  planes  of  fibers  cross  each 
other. 

The  palpebral  muscles  jjresent  no  very  noteworthy  special  characters. 


MUSCLES  OF  MASTICATION 

The  masseter  is  large.  It  arises  from  the  zygomatic  arch,  and  extends  beyond 
the  branch  of  the  jaw  below  and  behind.  Three  strata  may  be  recognized  in  its 
structure. 

The  temporalis  is  very  large  and  strong,  and  contains  much  tendinous  tissue. 
It  arises  from  the  temporal  fossa  and  the  orbital  ligament. 


HYOID    MUSCLES — MUSCLES    OF    THE    THORACIC    LIMB 


319 


The  digastricus  is  usually  not  digastric,  but  is  a  strong,  round,  fleshy  muscle, 
which  arises  on  the  paramastoid  or  styloid  process  and  is  inserted  into  the  border 
and  inner  surface  of  the  ramus  at  the  level  of  the  last  molar  teeth. 

The  stvlo-ni:uidil)ularis  is  absent. 


HYOID  MUSCLES 
The  mylo-hyoideus  is  well  developeil. 

The  stylo-hyoideus  is  very  slender,  and  is  inserted  into  the  boily  of  the  hyoid 
bone:   it  is  not  i)erf orated  by  the  digastricus. 


Fig.  230. — Superficial  Mcsclks  op  Dog,  After  Removal  of  Panniculds  Carnosus. 
1,  Levator  Dasolabialis;  2,  levator  labii  superioris  proprius;  3,  dilatator  nans  lateralis;  4,  4\  buccinator; 
6,  retractor  anguli  oris  s.  risorius;  6,  zygomaticus:  7.  malaris;  5,  masseter;  5,  digastricus;  10,  scutularis;  11^ 
other  auricular  muscles;  12,  parotido-auricularis;  IS,  mylo-hyoideus;  14.  sterno-hyoideus;  15,  sterno-thyroideus; 
16,  splenius;  17,  lumbo-dorsal  fascia;  IS,  rectus  abdominis;  19,  obliquus  abdominis  externus;  19',  aponeurosis 
of  preceding;  20,  intercostal  muscle;  21,  sacro-coccygeus  accessorius;  22,  sacro-coecygeus  superior;  23,  sacro- 
coccygeus  inferior;  ^.J,  great  trochanter;  ^5,  jugular  vein;  a.  6.  c,  brachio-cephalicus;  rf.  clavicle;  c, /,  trapezius; 
g,  serratus  cervicis;  h,  omo-transversarius;  /,  latissimus  dorsi;  k,  posterior  deep  pectoral:  /,  supraspinatus; 
m,  m' ,  deltoid;  n,  infraspinatus;  o,  triceps,  long  head;  o' ,  triceps,  external  head;  p,  brachialis;  q,  extensor  carpi 
radialis;  r,  gluteus  medius;  s,  gluteus  superficialis;  (,  (',  tensor  fasciae  lata^;  u,  sartorius;  ?•,  biceps  femoris;  i/, 
fascia  lata;  w,  semitendinosus;  x,  semimembranosus;  y,  sartorius;  z,  gracilis;  26,  pronator  teres;  27,  flexor  carpi 
radialis;  2S,  flexor  carpi  ulnaris;  29,  tibialis  anterior;  SO,  popliteus;  31,  SI',  deep  digital  flexor;  33.  superficial 
digital  flexor;  33,  gastrocnemius;  S4,  spine  of  scapula;  a,  parotid  gland,  with  a',  its  duct;  /3,  submaxillary  gland;  8, 
submaxillary  lymph  glands;  n,  parotid  lymph  gland;  i,  inferior  buccal  glands,  (.\fter  Ellenberger,  in  Leisering's 
Atlas. 

The  hyoideus  transversus  and  omo-hyoideus  are  absent. 
The  stemo-th3rro-hyoideus  is  large  and  arises  chiefly  on  the  first  costal  carti- 
lage. 

Muscles  of  the  Thoracic  Limb 

The  trapezius  is  thin,  and  is  not  clearly  divided  into  cervical  and  thoracic 
portions.  Its  line  of  origin  extends  from  about  the  middle  of  the  neck  to  the 
ninth  or  tenth  thoracic  spine,  the  right  and  left  muscles  meeting  on  a  median 
fibrous  raphe. 

The  omo-transversarius  arises  by  a  tendon  on  the  lower  part  of  the  spine  of 
the  scapula  (often  partially  blended  with  the  trapezius),  and  is  inserted  into  the 
wing  of  the  atlas. 


320 


THE    MUSCLES    OF    THE    DOG 


The  rhomboideus  consists  of  three  parts.  Tlie  dorsal  portion  (Rhomboideus 
thoracahs)  is  small;  it  arises  from  the  fourth  to  the  sixth  or  seventh  thoracic 
spine,  and  is  inserted  into  the  inner  surface  (chief!})  of  the  dorsal  angle  of  the  scap- 
ula. The  cervical  portion  (Rhomboideus  ccrvicalis)  arises  from  the  lisamentum 
nuchiE  as  far  forward  as  the  second  or  third  cervical  vertebra,  and  is  inserted  into 
the  inner  surface  of  the  cervical  angle  of  the  scapula.  The  cephalic  portion  (Rhom- 
boideus capitis)  is  a  continuation  of 
the  preceding  which  is  inserted  into 
the  occipital  crest. 

The  latissimus  dorsi  is  extensive, 
and  has  a  fleshy  attachment  to  the 
last  tw^o  ribs.  Its  lower  edge  blends 
near  the  shoulder  with  the  panni- 
culus. 

The  mastoido-humeralis  con- 
tains in  front  of  the  shoulder  a 
fibrous  mass  in  which  the  clavicle  is 
embedded.  Anterior  to  this  it  sepa- 
rates into  two  diverging  portions. 
The  dorsal  portion  (M.  cleido-cervi- 
calis)  is  attached  to  the  median  raphe 
of  the  neck  and  to  the  occipital  lione. 
The  ventral  portion  (M.  cleido-mas- 
toideus)  is  attached  to  the  mastoid 
process.  The  common  mass  posterior 
to  the  clavicle  and  the  fibrous  inter- 
section, which  is  attached  to  the 
humerus,  is  homologous  with  the 
clavicular  portion  of  the  deltoid  of 
man. 

The  superficial  pectoral  muscle 
is  small.  It  arises  on  the  sternum 
from  the  first  to  the  third  costal 
cartilage,  and  is  inserted  into  the 
anterior  surface  of  the  humerus.  A 
superficial  slip  detached  from  it  is 
inserted  into  the  fascia  of  the  fore- 
arm. The  deep  pectoral  has  no  pre- 
scajiular  portion.  It  ai'ises  on  the 
sternum  and  costal  cartilages  from 
the  second  costal  to  the  xiphoid  car- 
tilage. It  is  inserted  chiefly  into  the 
internal  tuberosity  of  the  humerus, 
but  also  by  small  slips  into  the  ex- 
ternal tuberosity  and  the  fascia  of 
the  arm. 

The  serratus  magnus  shows  no 
clear  division  into  cervical  and  thor- 
acic portions.     It  arises  from  the  last  five  cervical  vertebrie  and  the  first  seven 
or  eight  ribs,  and   is   inserted  into  the  upper   part  of  the   costal  surface  of  the 
scapula. 

The  deltoid  is  clearly  divideil  into  scai)ular  and  acromial  parts,  the  former 
arising  on  the  sjjine,  the  latter  on  the  acromion  of  the  scapula.  Both  end  on  the 
deltoid  tuberosity. 


Pig.  231.— Vkntkai,  Miisri.as  or  HE.\n,  Nkck,  and 
Thorax  of  Dog. 
a,  Mylo-hyoi(ieus;  fc,  digastncus;  c,  sterno-hyoideus; 
c*,  sterno-thyroideus;  d,  sterno-cephalicus;  tr,  brachio- 
cephalieus;  /,  subscapulari.s;  j?,  superficial  liectoral;  h, 
deep  pectoral:  /,  rectus  abdominis;  k,  oblifjuus  abdomiais 
e.xternus;  /,  long  head  of  triceps;  wj,  internal  head  of 
triceps;  n,  biceps  brachii;  o,  brachialis;  1,  1',  1" ,  sub- 
maxillary lymph  elands;  S.  thyroid  gland;  S,  external 
jugular  vein.     (Ellenberger-Baum,  .\nat.  d.  Hundes.) 


MUSCLES    OF   THE    THORACIC    LIMB 


321 


Teres  major  ..-. 

Lntissimus  dorsi  _..., 

Long  head  of  triceps  _ l 

Tensor  fascicc  aniibrachii  

Internal  head  of  triceps 

<< 

Flexor  carpi  medius 

Flexor  carpi  intern  us 
Superficial  digital  flexor  ■ 

Deep  digital  flexor  . 


The  supraspinatus  ends  chiefly  on  the  external  tuberosity  of  the  humerus,  l)ut 
has  a  small  attachment  to  the  internal  tuberosity  also. 

The  infraspinatus  is  inserted  into  the  outer  surface  of  the  external  tuberosity 
of  the  humerus. 


,T      .^  Subscapidaris 

I 

—  Supraspinatus 

\  "f^f" Coraco-brachialis 

Accessory  head  of  triceps 

Biceps  bracliii 

I 

Humerus 

— -  Extensor  carpi  radialis 

Pronator  teres 


Radial  head  of  deep 
digital  flexor 


FtG.   232. — MrscLES  of  Thoracic  Limb  of  Dog,  I 


AL  View.     (EUenberger-Baum,  .\nat.  <les  Hundes.) 


The  teres  minor  arises  on  a  tubercle  on  the  posterior  border  of  the  scapula, 
just  above  the  glenoid  cavity,  and  is  inserted  into  the  deltoid  ridge. 

The  subscapularis  is  wide  and  is  somewhat  multipennate  in  structure,  being 
intersected  by  fibrous  septa  which  are  attached  to  the  rough  lines  on  the  costal 
surface  of  the  scapula. 
21 


322 


THE    MUSCLES    OF   THE    DOG 


The  teres  major  is  tliick.     It  arises  on  the  upper  part  of  the  posterior  border 
of  the  scapula  ami  on  the  subscapularis. 

The  coraco-brachialis  is  short  and  undivided,  and  is  inserted  into  the  upper 
part  of  the  postero-internal  surface  of  the  humerus. 

The  capsularis  is  absent. 

The  biceps  brachii  lies  almost  entirelj*  on  the  inner 
surface  of  the  humerus.  It  is  long  and  fusiform.  The 
tendon  of  origin  is  round,  and  passes  through  the  cap- 
sule of  the  shoulder  joint.  The  tendon  of  insertion  is 
bifid,  one  branch  being  attached  to  the  ulnar,  the  other 
to  the  radial  tuberosity. 

The  brachialis  is  very  little  curved,  and  is  inserted 
chiefly  into  the  tuberosity  and  inner  border  of  the  ulna. 

The  tensor  fasciae  antibrachii  is  thin  and  narrow. 
It  arises  on  the  outer  surface  of  the  latissimus  dorsi, 
and  ends  on  the  olecranon  and  the  fascia  of  the  forearm. 

The  triceps  has  an  additional  deep  hcatl  (Caput 
accessorium),  which  arises  just  below  the  heail  of  the 
humerus. 

The  brachio-radialis  is  a  long,  narrow,  delicate 
muscle,  situated  superficially  on  the  anterior  surface  of 
the  forearm.  It  arises  with  the  extensor  carpi  on  the 
crest  above  the  extensor  epicondyle  of  the  humerus, 
and  is  inserted  into  the  distal  part  of  the  inner  border 
of  the  radius.  It  is  often  much  reduced,  and  is  some- 
times absent.  It  rotates  the  forearm  and  paw  out- 
ward. 

The  extensor  carpi  divides  into  two  parts.  The 
larger  outer  part,  the  extensor  carpi  radialis  brevis,  ends 
on  the  proximal  end  of  the  tliird  metacarpal  bone. 
The  inner  and  more  superficial  part,  the  extensor 
carpi  radialis  longus,  ends  on  the  second  metacarpal 
bone.     (A  tendon  to  the  fourth  metacarjial  may  occur.) 

The  extensor  carpi  obliquus  or  abductor  pollicis 
longus  arises  from  the  outer  border  and  anterior 
surface  of  the  ulna,  the  interosseous  ligament,  and 
the  outer  border  of  the  radius.  It  is  inserted  into 
the  first  metacarpal  bone  by  a  tendon  which  contains 
a  small  (sesamoid?)  bone.     It  abducts  the  first  digit. 

There  are  three  (or  four)  extensors  of  the  digits. 

1.  The  common  digital  extensor  (i\I.  extensor  digi- 
talis communis)  arises  on  the  extensor  epicondyle  of 
the  humerus  and  the  lateral  ligament  of  the  elbow 
joint.  It  has  four  bellies,  each  terminating  in  a  tendon. 
These  are  inserted  into  the  thirtl  phalanges  of  the 
second,  third,  fourth,  and  fifth  digits. 

2.  The  extensor  of  the  first  and  second  digits 
M.  extensor  pollicis  longus  et  extensor  indicis  pro- 
prius)  is  small,  and   is  covered  by  the   common   and 

lateral  extensors.  It  arises  on  the  proximal  part  of  the  ulna.  Its  tendon  passes 
down  with  that  of  the  connnon  extensor  and  divides  into  two  branches.  The 
delicate  inner  branch  ends  on  the  first  digit,  while  the  other  blends  with  the  tendon 
of  the  common  extensor  for  the  second  digit. 

3.  The  lateral  digital  extensor  (M.  extensor  digitalis  lateralis)  consists  of  two 


Fig.  233. — Mhsclks  of  Antihra- 

CHIUM  A.\D  MaNUS  OF  DoG, 

Extp:rnal  View. 

a, Triceps  brachii;  b,  brachi- 
alis: c,  extensor  carpi  radialis:  d, 
common  or  anterior  digital  exten- 
sor; rf',  d",  d"\  d"" ,  tendons  of 
preceding;  e.  lateral  digital  exten- 
sor; c',  /,  tendons  of  preceding;  (,■, 
extensor  carpi  ulnaris;  h,  h' ,  flexor 
carpi  ulnaris;  z,  extensor  carpi  ob- 
liquus (a.  abductor  pollicis  longus) ; 
/:, interossei;  /.branches  from  pre- 
ceding to  extensor  tendons;  i,  ole- 
cranon; 2,  radius;  ^,  extensor  epi- 
cond.vle  of  humerus,  (.\fter  Gllen- 
berger,  in  Leisering's  Atlas.) 


MUSCLES    OF    THE    THORACIC    LIMB 


323 


muscles  which  are  not  rarely  fusctl.  They  arise  on  the  extensor  epicondyle  of  the 
humerus  and  the  lateral  ligament  of  the  elbow  joint.  The  larger,  superficial  belly 
(M.  extensor  digiti  tertii  et  quarti)  terminates  on  a  tendon  which  tlividcs  at  or 
near  the  carpus  into  two  branches,  which  are  insertctl  into  the  third  phalanges 
of  the  third  and  fourth  digits,  blending  with  the  corresponding  tendons  of  the  com- 
mon extensor.  The  posterior  belly  (M.  extensor  digiti  quinti)  terminates  by  a 
tendon  which  fuses  witli  that  of  the  common  extensor  for  the  fifth  digit. 

The  ulnaris  lateralis  or  extensor  carpi  ulnaris  corresponds  to  the  flexor  carpi 
externus  of  the  liorse,  but  is  an  extensor  of  the  carpus.     It  is  a  large  flat  muscle 
which  lies  on  the  outer  surface  of  the  ulna.     It  arises  on  the  ex- 
tensor epicondyle  of  the  humerus,  and  is  inserted  into  the  proxi- 
mal end  of  the  fifth  metacarpal  and  the  accessory  carpal  bone. 

The  ulnaris  medialis  or  flexor  carpi  medius  (s.  ulnaris) 
consists  of  two  ((uite  distinct  heads.  The  larger,  humeral 
head  arises  on  tlie  flexor  epicondyle,  while  the  smaller,  su]ier- 
ficial  ulnar  head  arises  on  the  posterior  border  of  the  ulna. 
The  tendons  of  the  two  einl  together  on  the  accessory 
carpal  bone. 

The  radialis  volaris  or  flexor  carpi  internus  (s.  radialis) 
arises  on  the  flexor  epicondyle  of  the  humerus  and  is  inserted 
by  a  bifid  tendon  into  the  second  and  third  metacarpal  Ijones. 

The  tendons  of  the  foregoing  muscles  are  provided  with 
sj-novial  sheaths  at  the  carpus. 

The  pronator  teres  is  a  round  muscle,  which  is  situated 
superficially  on  the  inner  border  of  the  proximal  part  of  the  ra- 
dius. It  arises  on  the  flexor  epicondyle  of  the  humerus,  and  is 
inserted  into  the  internal  border  of  the  radius.  Its  action  is  to 
flex  the  elbow  and  rotate  the  forearm  inward. 

The  superficial  digital  flexor  is  situated  superficially  on  the 
posterior  and  inner  surfaces  of  the  forearm.  It  arises  on  the 
flexor  epicondyle  of  the  humerus  and  terminates  near  the 
carpus  on  a  tendon  which  passes  downward  outside  of  the 
carpal  canal  and  receives  below  the  carpus  two  reinforcing 
bands,  one  from  the  accessory  carpal,  the  other  from  the 
sesamoid  bone  at  the  inner  side  of  the  carpus.  Below  this 
it  divides  into  four  branches,  which  are  inserted  into  the 
second  phalanges  of  the  second,  third,  fourth,  and  fifth  digits. 

The  deep  digital  flexor  has  humeral,  ulnar,  and  radial 
heads,  the  latter  arising  from  the  inner  border  of  the  radius. 
They  unite  on  a  common  tendon  which  passes  down  through 
the  carpal  canal,  gives  off  a  branch  to  the  first  digit,  and 
divides  into  four  branches.  These  perforate  the  tendons  of 
the  superficial  flexor  and  are  inserted  into  the  third  phalanges 
of  the  second  to  the  fifth  digits.  The  tendons  are  provided 
with  synovial  sheaths  from  the  middle  of  the  metacarpus  downward,  and  are 
held  in  place  by  three  digital  annular  ligaments. 

The  palmaris  longus  accessorius  (?)  is  a  small  muscle  which  arises  from  the 
deep  flexor  lielow  the  middle  of  the  forearm  and  ends  by  two  tendons  which  unite 
with  tlicse  of  the  superficial  flexor  for  the  third  and  fourth  tligits. 

The  supinator  is  a  short,  wide  muscle  which  arises  on  the  humerus  beneath  the 
external  lateral  ligament,  crosses  the  anterior  surface  of  the  radius,  and  is  inserted 
into  the  inner  border  of  the  radius.  (A  pouch  of  the  capsule  of  the  elbow  joint 
lies  under  the  tendon  of  origin.)  Its  action  is  to  rotate  the  forearm  outward 
(supination). 


Fig.  234.— Volar  JIub- 
CLEs  OF  Fore 
Paw  of  Dog. 
a,  .\bcluctor  pol- 
licis  brevis  et  opponens 
pollicis;  fe,*  flexor  polli- 
cis  brevis;  c,  adductor 
pollicis;  d,  adductor 
digiti  secundi;  e,  ad- 
ductor digiti  quinti;  /, 
flexor  digiti  quinti 
brevis;  g,  abductor 
(.ligiti  quinti;  A,  in- 
terossei;  /,  accessory 
carpal  bone;  S,  first 
digit ;  S-6,  sesamoids 
of  metacarpo-phalan- 
geal  joints.  (Ellen- 
berger-Baum,  Anat.  d. 
Huodes.) 


324  THE   MUSCLES    OF   THE    DOG 

The  pronator  quadratus  consists  of  fibers  which  cross  the  inner  surface  of  the 
interosseous  hgament  of  the  forearm,  except  at  the  two  extremities  of  the  latter. 
It  is  attached  to  the  inner  border  of  the  ulna  and  the  anterior  surface  of  the  radius. 
It  rotates  the  forearm  inward  (pronation). 

The  palmaris  brevis  (?)  is  a  very  small  muscle,  which  arises  on  the  tendon 
of  the  superficial  digital  flexor  for  the  fifth  digit,  and  is  inserted  at  the  fifth  meta- 
carpo-phalangeal  joint  into  the  sheath  and  annular  ligament  of  the  deep  flexor. 

The  lumbricales  are  three  very  delicate  muscles,  which  arise  on  the  tendons 
of  the  deep  flexor,  and  are  inserted  into  the  first  phalanges  of  the  third,  fourth, 
and  fifth  digits. 

The  abductor  pollicis  brevis  et  opponens  pollicis,  a  very  small  pale  muscle, 
arises  on  the  fibrous  band  which  connects  the  superficial  flexor  tendon  with  the 
inner  carpal  sesamoid,  and  ends  on  the  distal  end  of  the  first  metacarpal  bone  and 
the  first  phalanx  of  the  first  digit.     It  abducts  the  first  digit.' 

The  flexor  pollicis  brevis  arises  on  the  posterior  carpal  ligament  over  the  second 
metacarpal  bone,  and  ends  on  the  volar  sesamoid  of  the  first  digit. 

The  adductor  pollicis,  situated  externally  to  the  preceding,  is  the  largest  of 
the  thumb  muscles.  It  arises  between  the  preceding  and  the  second  interosseous 
muscle,  and  is  inserted  into  the  first  jihalanx  of  the  first  digit. 

The  adductor  digiti  secundi  is  situated  Ijetwcen  the  second  interosseous 
muscle  and  the  adductor  digiti  quinti.  It  arises  on  the  carpal  ligament,  and  ends 
on  the  first  jihalanx  of  the  second  digit. 

The  adductor  digiti  quinti  arises  close  to  the  preceding  muscle,  and  jiasses 
outward  to  end  on  the  first  phalanx  of  the  fifth  digit. 

The  flexor  digiti  quinti  arises  on  the  ligament  connecting  the  accessory  carpal 
to  the  third  and  fourth  metacarpal  bones,  crosses  the  corresponding  interosseous 
muscle,  and  ends  on  the  fifth  digit  with  the  next  muscle. 

The  abductor  digiti  quinti  is  larger  than  the  two  preceding  muscles;  it  arises 
on  the  accessory  carpal  bone,  and  ends  on  the  outer  sesamoid  of  the  fifth  digit  and 
on  the  lateral  ligament. 

There  are  four  interossei  which  lie  on  the  volar  (posterior)  surface  of  the  meta- 
carpus. They  are  well  developed  and  fleshy.  They  arise  on  the  distal  row  of  the 
carpus  and  on  the  proximal  ends  of  the  metacarpals.  Each  divides  distally  into 
two  branches,  which  are  inserted  by  small  tendons  on  the  corresponding  sesamoid 
bones,  and  detach  slips  to  the  extensor  tendons. 


Muscles  of  the  Neck 

The  stemo-cephalicus  is  well  developed.  It  arises  on  the  manubrium  sterni 
and  ends  on  the  mastoid  process,  blending  with  the  cleido-cervicalis. 

The  scalenus  ventralis  (s.  primte  costse)  arises  on  the  last  four  cervical  trans- 
verse i^rocesses,  and  is  inserted  into  the  first  rib. 

The  scalenus  dorsalis  (s.  supracostalis)  is  large.  Anteriorly  it  blends  with  the 
preceding  muscle,  while  posteriorly  it  divides  into  two  parts.  The  upper  ]iart  is 
inserted  on  the  thinl  and  fourth  ribs,  the  lower  part  by  a  long,  thin  tendon  on  the 
eighth  rib. 

The  longus  colli  resembles  that  of  the  horse. 

The  rectus  capitis  anterior  major  arises  on  the  transverse  processes  of  the  second 
to  the  sixth  cervical  vortebne  and  ends  as  in  the  horse.  The  rectus  minor  and 
lateralis  rcscmlile  those  of  the  horse. 

The  intertransversales  resemble  those  of  the  ox. 

The  splenius  is  strong  and  extensive.     It  arises  on  the  first  four  or  five  thoracic 

'  Movements  of  individual  digits  are  specified  with  regard  to  the  axis  of  the  manus  (hand, 
paw),  and  not  to  the  median  plane  of  tlie  body. 


MUSCLES    OF   THE    THORAX MUSCLES   OF   THE    TAIL  325 

spines  and  the  median  raphe  of  the  neck,  and  is  inserted  into  the  occipital  crest  and 
mastoid  process. 

The  complexus  is  composed  of  two  parts — the  biventer  cervieis  and  the  com- 
plexus  major  proper.  The  biventer  cervieis  arises  from  the  transverse  processes 
of  the  fifth  and  sixth,  and  the  spines  of  the  second  to  the  fifth  (or  sixth)  thoracic 
vertebriB,  from  the  ligamentum  mirhie,  and  the  median  raphe.  It  has  four  ten- 
dinous intersections.  The  complexus  major  arises  on  the  transverse  processes  of 
the  first  three  or  four  thoracic  vertebrje  and  the  articular  processes  of  the  last  five 
cervical.  Both  end  on  a  strong  common  tendon  which  is  inserted  into  the  occipital 
crest  and  the  depression  l)elow  it. 

The  trachelo-mastoideus  consists  of  two  unequal  portions.  The  large  dorsal 
part  (I\I.  longissimus  capitis)  arises  on  the  transverse  processes  of  the  first  four  thor- 
acic and  the  articular  process  of  the  last  three  or  four  cervical  vertebra?,  and  ends 
with  the  splenius  on  the  mastoid  process  of  the  temporal  bone.  The  small  ventral 
part  0,1.  longissimus  atlantis)  arises  on  the  articular  processes  of  the  third,  fourth, 
and  fifth  cervical  vertebrae,  and  ends  on  the  wing  of  the  atlas. 

The  other  muscles  present  no  striking  differential  features, but  it  may  be  noted 
that  distinct  interspinales  are  present. 


MUSCLES  OF  THE  THORAX 

There  are  twelve  pairs  of  levatores  costarum. 

The  external  intercostals  do  not  occupy  the  .spaces  between  the  costal  carti- 
lages. 

The  diaphragm  has  a  small  tendinous  center.  The  oesophageal  opening  is 
between  the  pillars.  The  fleshy  rim  is  attached  at  the  costo-chondral  junctions 
from  the  eighth  backward,  and  along  the  thirteenth  rib  nearlj'  its  entire  length. 


Muscles  of  the  Back  and  Loins 

The  serratus  anticus  arises  from  the  median  raphe  of  the  neck  and  the  first 
six  or  seven  thoracic  sjjines,  and  is  inserted  into  the  second  to  the  ninth  ribs. 
It  is  well  developed.  The  serratus  posticus — much  weaker — arises  on  the  lumbo- 
dorsal  fascia,  and  is  inserted  into  the  last  three  or  four  ribs.  Thus  one  or  two  ribs 
intervene  between  the  two. 

The  transversalis  costarum  (Ilio-costalis)  is  well  developed,  and  extends  from 
the  ilium  to  the  sixth,  fifth,  or  fourth  cervical  vertebra. 

The  longissimus  resembles  that  of  the  other  animals,  but  the  spinalis  et 
semispinalis  separates  clearly  at  the  sixth  or  seventh  thoracic  vertebra.  It  is 
inserted  into  the  articular  and  spinous  processes  of  the  last  six  cervical  vertebrae. 
It  has  no  depression  in  the  lumbar  region  for  the  gluteus  medius. 

The  intertransversales  are  fleshy,  as  in  the  ox. 

The  interspinales  are  distinct,  especially  in  the  lumbar  region. 


Muscles  of  the  Tail 

These  present  the  same  general  arrangement  as  in  the  horse.  The  sacro- 
coccygei,  however,  arise  on  the  lumbar  vertebrae  also,  and  the  coccygeus  on  the 
ischiatic  spine.  There  is  found  a  sacro-coccygeus  accessorius,  which  arises  on  the 
internal  border  of  the  ilium,  the  edge  of  the  sacrum,  and  the  transverse  processes 
of  the  first  coccygeal  vertebrae,  and  is  inserted  between  the  superior  and  lateral 
sacro-coccygei.     It  is  homologous  with  the  intertransversales. 


326 


THE    MUSCLES    OF    THE    DOG 


Muscles  of  the  abdomen 

The  ahdominal  tunic  is  practically  aljsent. 

Th(>  obUquus  abdominis  exteraus  has  an  extensive  fleshy  portion.  It  arises 
from  the  last  (>is;ht  or  nine  ribs  and  the  lumbo-dorsal  fascia. 

Th(^  obUquus  abdominis  interaus  arises  from  the  external  angle  of  the  ilium 
and  the  luinho-dorsal  fascia.  The  fibers  have  an  almost  vertical  direction,  and 
there  is  a  fiesliv  attacliment  to  the  last  rib. 

The  rectus  abdominis  is  attached  by  a  long  tendon  on  the  first  five  or  six  costal 
cartilages,  and  by  fleshy  fibers  on  the  xiphoid  cartilage.  It  has  three  to  six  indis- 
tinct tcndiiKius  inscriptions. 

The  transversus  abdominis  presents  no  special  features  except  that  the  poste- 
rior part  of  its  aponeurosis 
i  splits  into  two  layers  which 

include   the    rectus   between 
them. 


Muscles  of  the  Pelvic 
Limb 
The  psoas  minor  arises 
on  the  last  thoracic  antl  first 
four  or  five  lumbar  vertebra", 
and  is  inserted  into  the  ilio- 
pectineal  line. 

The  psoas  major  is 
sliort,  arising  from  the  last 
four  lumbar  vertebra*. 

The  outer  head  of  the 
iliacus  is  small,  while  the 
inner  head  is  large  and  fuses 
with  the  psoas  major. 

The  quadratus  lumbor- 
um  is  well  developed,  and 
extends  laterally  beyond  the 
outer  edge  of  the  ilio-psoas. 
It  arises  from  the  last  four 
ribs  and  the  lumbar  transverse  processes,  and  ends  on  the  pelvic  surface  of  the 
wing  of  the  iliiun. 

The  tensor  fasciae  latae  consists  of  two  i)arts.  The  anterior  part  is  long  ami 
rounded;   the  posterior  is  shorter  and  fan-like. 

The  gluteus  superficialis  is  small.  It  arises  on  the  sacrum,  first  coccygeal 
vertebra,  and  sacro-sciatic  ligament.  It  is  inserted  below  and  behind  the  tro- 
chanter major  of  the  femur,  on  the  outer  branch  of  the  linea  aspera. 

The  gluteus  medius  has  no  lumbar  portion.  It  is  inserted  into  the  trochanter 
major  by  a  strong  tendon. 

The  gluteus  profundus  is  broad  and  fan-shaped.  It  arises  on  the  superior 
ischiatic  spine  and  on  the  ilium  as  far  forwaril  as  the  gluteal  line,  and  is  inserted 
into  the  trochanter  major  below  the  medius. 

The  pyriformis  is  not  lilended  with  the  gluteus  medius.  It  arises  from  the 
border  of  the  sacrum  and  from  the  sacro-sciatic  ligament,  and  ends  on  the  tro- 
chanter major. 

The  biceps  femoris  has  two  heads  of  origin  which  soon  fuse.  The  larger  head 
arises  from  the  sacro-sciatic  ligament  and  tuber  ischii,  the  smaller  one  from  the  tuber 


Fig.  235. — Moscles  of  Tail,  Anus,  and  Genital  Organs  of  Doo. 
1,  Ilium;  3,  femur;  3,  tuber  ischii;  4.  sacro-sciatic  lig. ;  5,  sacral 
region;  6,  tail:  7.  penis;  8,  anus;  9,  rectum;  a,  sacro-coccygeus  supe- 
rior; b,  sacro-coccygeus  accessorius;  c,  coccygeus;  d,  sacro-coccygeus 
inferior;  c.  retractor  ani;  /, /',  spliiocter  ani  externus;  I7,  retractor 
penis;  h,  bulbo-cavernosus;  i,  transversus  perinei  (?);  k,  ni,  ischio- 
urethrales;  /,  ischio-oavernosus;  n,  tendon  of  obturator  internus;  o, 
gemellus;  p,  uretiiral  muscle.      C.\fter  EUenberger,  in  Leisering's  .\tlas.) 


MUSCLES   OF   THE    PELVIC    LIMB 


327 


ischii.  The  aponeurosis  of  insertion  ends  on  the  patella,  the  patellar  ligament, 
and  the  tibial  crest.  There  is  also  a  tendinous  band,  which  comes  from  the  deep 
face  of  the  muscle  and  terminates  at  the  tarsus,  as  in  the  horse. 

The  abductor  cruris  posterior  may  be  regarded  as  an  accessory  head  of  the 
biceps  femoris.  It  is  a  thin,  muscular  band  which  arises  on  the  sacro-sciatic 
ligament,  passes  downward  between  the  biceps  and  semimembranosus,  and  ends  by 
blending  with  the  former. 

The  semitendinosus  arises  from  the  tuber  ischii  only.     It  ends  as  in  the  horse. 


Fig.   236. — Muscles  or  Pki.vic    Limb  of  Don,   Internal 
View. 
a,  Ilio-psoas;  b,  tendon  of  psoas  minor;  c,  sacro-coccy- 
ntralis  lateralis;  rf,  coceygeus;  e,  pyriformis;  /,  obtur- 
g,  origin  of  retractor  ani;  h,  h' ,  sartorius;  i,  ree- 
ls femoris;   k,  vastus  internus;   /,  pectineus;  m,  adductor: 
,  gracilis;    o,  semitendinosus;  p,  semimembranosus;  q,  gas- 
ocnemius.  inner  head;  (/.  tendon  of  gastrocnemius;  r,  super- 
(?ial  digital  fle.vor;   r',  tendon  of  r;  s,  tarsal  tendon  of  biceps 
;  t.  popliteus;  u.  deep  digital  flexor,  outer  head  (flexor 
s  longus);  u',  long  digital  flexor;  u",  common  tendon  of 
u  and  It';   v,  tendon  of  tibialis  posterior;   w,  tibialis  anterior; 
T,  tendon  of  anterior  or  long  digital  extensor;    1,  pelvic  sur- 
face of  ilium;  S,  section  of  symphysis  pelvis;  3,  tuber  ischii; 
4.  internal  condyle  of  femur;  6,  ligamentum  patella*;  6,  7,  in- 
face  of  tibia;   S.  tarsus;   S',  fibular  tarsal  bone;  9, 
s       (LUenberger-Baum,  Anat.  d.  Hundes.) 


The  semimembranosus  is  large  and  arises  from  the  ischium  only.  It  divides 
into  two  portions:  the  anterior  portion  ends  on  the  tendon  of  the  pectineus,  on  the 
femur  above  the  internal  contlyle,  and  on  the  inner  (Vesalian)  sesamoid  bone; 
the  posterior  portion  ends  on  the  internal  condyle  of  the  tibia,  the  tendon  passing 
under  the  internal  lateral  ligament  of  the  stifle  joint. 

The  rectus  femoris  has  only  one  tendon  of  origin.  The  single  patellar  ligament 
acts  as  the  tendon  of  insertion  of  the  quadriceps. 


328  THE    MUSCLES    OK   THE    DOG 

The  capsularis  is  usually  present,  but  is  small  and  pale. 

The  sartorius  consists  of  two  portions.  It  arises  from  the  external  angle 
and  border  of  the  ilium.  The  anterior  portion  ends  on  the  patella,  the 
posterior  on  the  internal  surface  of  the  tibia,  its  tendon  blending  with  that 
of  the  gracilis. 

The  graciles  are  not  so  much  fused  at  their  origin  as  in  the  other  annuals. 

The  pectineus  is  long  and  slender.  It  arises  from  the  ilio-pectineal  eminence 
and  enils  on  the  internal  branch  of  the  linea  aspera  above  the  distal  end  of  the 
femur. 

There  are  two  distinct  adductors.  The  small  anterior  one  ends  on  the  jiroximal 
third  of  the  femur,  the  posterior  one  on  the  distal  part  of  the  femur  and  on  the 
inner  face  of  the  stifle  joint. 

The  quadratus  femoris  is  short  and  strong.  The  other  external  rotators  of 
the  thigh  present  no  special  features. 

The  peroneus  tertius  is  represented  by  a  tendinous  band  which  arises  on  the 
internal  surface  of  the  tibia  below  the  crest.  It  passes  downward  on  the  inner 
surface  of  the  tibialis  anterior,  blends  with  the  annular  ligament  above  the  tarsus, 
and  is  attached  to  the  joint  capsule  and  the  proximal  end  of  the  third  metatarsal 
bone. 

Arloing  and  Lesbre  say:  "The  third  peroneus  is  a  proper  extensor  of  the  fifth  digit;  it 
is  a  very  feeble,  fleshy  band,  situated  behind  the  peroneus  brevis,  which  it  partially  covers. 
It  is  attached  to  the  upper  part  of  the  fibula,  and  is  continued  by  a  long,  delicate  tendon  which 
passes  in  the  same  malleolar  groove  with  the  muscle  mentioned;  it  then  crosses  behind  the 
tendon  of  the  peroneus  longus  and  extends  to  the  phalanges  of  the  outer  digit,  where  it  joins 
one  of  the  branches  of  the  common  extensor." 

The  tibialis  anterior  is  large  and  superficial.  It  arises  on  the  external  condyle 
and  crest  of  the  tibia,  and  is  inserted  into  the  first  metatarsal  bone,  or  into  the  fir.st 
tarsal  and  second  metatarsal. 

There  are  foiu'  extensors  of  the  digits. 

1.  The  anterior  or  long  digital  extensor  (M.  extensor  digitalis  longus)  is  fusi- 
form, and  lies  largely  under  the  preceding  muscle.  It  arises  from  the  extensor  fossa 
of  the  femur.  The  tendon  is  bound  down  by  two  annular  ligaments,  and  divides 
below  the  tarsus  into  four  branches,  which  end  on  the  distal  phalanges  of  the  digits 
(second  to  fifth). 

2.  The  lateral  digital  extensor  CSl.  extensor  digitalis  lateralis)  is  feeble  and  semi- 
pennate.  It  arises  on  the  fil)ula  below  the  head.  The  tendon  passes  under  the 
lateral  ligament  of  the  tarsus  and  joins  the  branch  of  the  tendon  of  the  long  extensor 
for  the  fifth  digit. 

3.  The  extensor  hallucis  longus  is  a  very  thin  muscle  which  arises  from  the 
fibula  tmdcr  the  long  extensor.  Its  delicate  tendon  accompanies  that  of  the  tibialis 
anterior  to  the  first  metatarsal  I)one,  or  becomes  lost  in  the  fascia. 

4.  The  extensor  digitalis  brevis  has  three  divisions.  It  arises  on  the  fibular 
tarsal  bone  and  the  adjacent  ligaments.  The  three  tendons  are  inserted  into 
the  second,  third,  and  fourth  digits,  blending  with  the  interossei.  (Sometimes 
there  is  found  a  tendon  to  the  rudimentary  first  tligit,  which  may  represent  the 
extensor  hallucis  brevis.  There  may  Vie  a  fourth  belly  for  the  tendon  to  the  second 
digit.) 

The  peroneus  longus  arises  on  the  external  condyle  of  the  tibia,  the 
head  of  the  fibula,  and  the  lateral  ligament.  The  long  tendon  passes  down 
the  leg  parallel  to  the  fibula,  crosses  the  plantar  (posterior)  surface  of  the 
tarsus  transversely,  and  ends  on  the  first  metatarsal  bone.  A  short  branch  is 
detached  to  the  external  metatarsal  bone. 

The  peroneus  brevis  is  semipennate  and  arises  from  the  distal  half  or  more 
of  the  outer  face  of  the  tibia  and  the  fibula.     Its  tendon  accompanies  that  of 


MI'SCLES    OF    THE    PELVIC    LIMB  329 

the  lateral  extensor  over  the  external  malleolus  of  the  tibia,  and  ends  on  the 
proximal  end  of  the  fifth  metatarsal  bone. 

The  soleus  is  absent.     (It  is  present  and  large  in  the  cat.) 

The  gastrocnemius  arises  on  the  rough  lines  above  the  condyles  of  the  femur. 
The  heads  of  origin  each  contain  a  bone  about  the 
size  of  a  pea — the  sesamoid  of  \'esal — which  articu- 
lates with  the  corresponding  condyle  of  the  femur. 
The  tendon  comports  itself  as  in  the  horse.  ^ 

The  superficial  digital  flexor  has  a  large  round  ^^C 

belly.     It  arises  in  coininon  witli  the  outer  head  of  ^r  fw 

the  gastrocnemius   from  the  external  rough  line  and  m      ai  -i  \» 

Vesalian  sesamoid  bone,  and  from  the  aponeurosis 
of  the  vastus  externus.  The  tendon  winds  around 
that   of   the   gastrocnemius,   passes   over  the  tuber  WBllJ. 

calcis  (where  it  is  arranged  as  in  the  horse),  and 
divides  below  the  tarsus  into  two  branches.  Each 
of  these  divides  into  two  branches  which  end  as  in 
the  fore  limb.  The  outer  and  inner  branches  detach 
slips  to  the  suspensory  ligaments  of  the  large  digital  lu  jt 

pad.  Muscle-fibers  often  occur  in  the  tendon  in  the 
metatarsal  region.  r.      //    /J 

The   deep    digital    flexor    has   two  heads.     The 
large  outer   head,  the  flexor   hallucis  longus,  arises 
from   the    tibia    and    fibula,  filling    the    interosseous          It'  '^/// 
.space.     The  small  inner  head,  flexor  digitalis  pedis 
longus,  also  arises  from  the  tibia  and  fibula,  its  tendon 
joining  that  of  the  large  head  below  the  tarsus.     The           „. 
common  tendon  detaches  a  branch  to  the  large  digital                    m\m\\ 
patl  and  terminates  as  in  the  fore  limb.  / ^^^\ 

The   tibialis   posterior    is   a   small   but   distinct  ">-   -^iW^ 

muscle,   which    arises    on    the   proximal  part   of   the  ^VW' 

fibula.     The   thin   tendon   accompanies  that  of   the  Iw^W 

flexor  longus  and  ends  on  the  internal  lateral  liga-  VVr 

ment  of  the  tarsus.  J»\\ 

The  tendon  of    the   popliteus  contains  a  small 
sesamoid  bone. 

Tlie  adductors  of  the  second  and  fifth  digits,  the 
lumbricales,  antl  the  interossei  are  arranged  as  in  the      ^"=-  237.— Mcscles  of  Leg  and 

,,  .      ,.      ,  Foot    of    Dog,    External 

thoracic  limb.  View. 

The  quadratus  plantae  arises  on  the  outer  surface  a.  Quadriceps  femoris;  b,  gas- 

of  the  distal  end  of  the  fibular  tarsal  bone  and  on  the      trocnemius.  external  bead-,  c,  super- 

1,1,  IT  .  I  ]!•  1  ficial  digital  flexor:    d,  deep  digital 

lateral  tarsal  ligament,  passes  downward  and  inward,  g^^„^.  I  p^„„^„^  i„„g„^.  ^  ,^„. 
and  terminates  on  a  thin  tendon  which  fuses  with  don  of  lateral  extensor;  »,  peroneus 
that  of  the  deep  flexor.  •"■«"*■  *•  '°"8  °""  an'^ior  digital 

rr.1-         1-j       i        J-    -i-  •    i-    •  11  1  extensor;  A',  A".  A'",  tendons  of  pre- 

Ihe  abductor  dlgltl  qUintl    is  a  very  small    muscle        ceding;  i.  tibialis  anterior;  a.  exten- 

which    consists  of    two  parts.       One  of    these   is   a   ten-        sorbrevls;  (.slips  from  interossei  (m); 

dinous  slip  which  extends  from  the  posterior  surface      ^-  ^'''er'.ai  <:ondyieof  femur;  «,pa, 

'   .  '  tella;  3.  tibia:  4.  tuber  calcis;  5.5,  an- 

of  the  proximal  part  of  the  fibular  tarsal  bone  to  the     nuiar ligaments.  (.\fterEiienberger, 

head   of   the   fifth   metatarsal   bone:  the  other  part      in  Leiserings  Atlas.) 

arises  from   the  inner  surface  of   the  fibular  tarsal 

bone  (or  from  the  tendinous  part)  and  ends  on  the  first  phalanx  of  the  fifth  digit. 

In  case  the  skeleton  of  the  first  digit  is  well  developed,  there  are  found  three 
muscles  homologous  with  those  of  the  same  digit  in  the  fore  limb.  These  are  the 
abductor  hallucis,  adductor  hallucis,  and  flexor  hallucis  brevis. 


THE  DIGESTIVE  SYSTEM 

This  system  consists  of  the  organs  directly  concerned  in  the  reception  and 
digestion  of  tlie  food,  its  passage  through  the  liody,  and  the  expulsion  of  the  un- 
absorbed  portion.  These  organs  are  conveniently  grouped  under  two  heads, 
viz.:   (1)  the  alimentary  canal;   (2)  the  accessory  organs. 

The  alimentary  canal  (Tractus  alimentarius)  is  a  tube,  about  100  feet  (ca. 
30  m.)  in  length  in  the  horse,  and  extends  from  the  lips  to  the  anus.  It  has  a  com- 
plete lining  of  mucous  membrane,  external  to  which  is  an  almost  continuous  muscu- 
lar coat.  The  abdominal  portion  of  the  tube  is  largely  covered  with  a  serous 
membrane — the  visceral  jjeritoneum.  The  canal  consists  of  the  following  consecu- 
tive segments: 

1.  Mouth.  4.  Stomach. 

2.  Pharynx.  5.  Small  intestine. 
.3.  (Tvsophagus.  6.   Large  intestine. 

The  accessory  organs  are  the  teeth,  tongue,  salivary  glands,  liver,  and  pancreas. 


DIGESTIVE  SYSTEM  OF  THE  HORSE 
THE  MOUTH 

The  mouth'  (Cavum  oris)  is  the  first  part  of  tlie  alimentary  canal.  In  the 
horse  it  is  a  long  cylindrical  cavity,  and  when  closed,  it  is  almost  entirely  filled  up 
by  the  contained  structures.  The  entrance  to  it  (Rima  oris)  is  closed  by  the  lips. 
Laterally  it  is  bounded  by  the  cheeks;  above,  by  the  hard  palate;  below,  by  the 
body  of  the  mandible  and  the  mjdo-hyoid  muscles;   behind,  by  the  soft  palate. 

The  cavity  of  the  mouth  is  subdivided  into  two  parts  by  the  teeth  and  alveolar 
processes.  The  space  external  to  these  and  inclosed  externally  l)y  the  lips  and 
cheeks  is  termed  the  vestibule  of  the  mouth  (Vestibulum  oris).  In  the  resting 
.state  of  the  parts  the  walls  of  this  cavity  are  in  contact,  anil  the  space  is  practically 
obliterated.  Its  existence  becomes  very  evident  in  facial  jiaralysis,  when  the  food 
tends  to  collect  in  it  laterally,  pouching  out  the  cheeks.  The  space  within  the 
teeth  and  alveolar  processes  is  termed  the  mouth  cavity  proper  (Cavum  oris  pro- 
prium).  When  the  teeth  are  in  contact,  it  communicates  with  the  vestibule  only 
by  the  interdental  spaces  and  the  intervals  behind  the  last  molar  teeth.  Poste- 
riorly it  communicates  with  the  pharynx  through  the  isthmus  of  the  fauces. 

The  mucous  membrane  lining  the  mouth  (Tunica  mucosa  oris)  is  continuous 
at  the  margin  of  the  lips  with  the  common  integument,  and  behind  with  the  mucous 
lining  of  the  pharynx.     During  life  it  is  chiefly  of  a  pink  color. 

The  lips  (Labia  oris)  are  two  musculo-membranous  folds  which  surround  the 
orifice  of  the  mouth.  Their  angles  of  union  (Anguli  oris  s.  commLssurffi  labiorum) 
are  situated  near  the  first  cheek  tooth  and  are  rounded.  Each  lip  presents  two 
surfaces  and  two  borders.  The  outer  surface  is  covered  by  the  skin,  which  ]ire- 
sents  long  tactile  hairs  in  addition  to  the  ordinary  fine  hair.     The  upper  lip  shows 

'  The  term  "mouth"  is  commonly  used  to  sifjnify  either  the  oral  ravity  (Cavum  oris)  or  the 
entrance  to  it  (Rima  oris). 

330 


THE    MOUTH 


331 


a  shallow  median  furrow  (Philtrum),  the  lower  a  rounded  prominence,  the  chin 
(Mentum).     The  inner  or  oral  surface  is  covered  with  mucous  membrane  which  is 


commonly  more  or  less  pigmented.  The  small  papillae  on  this  surface  show 
on  their  summits  the  openings  of  the  ducts  of  the  labial  glands.  Small  folds  of 
mucous  membrane  which  pass  from  the  lip  to  the  gum  represent  the  frsenula  labii 


332  DIGESTIVE    SYSTEM    OF   THE    HORSE 

(supcrioris,  infcrioris).  The  free  border  of  the  lip  is  dense  and  presents  short, 
very  stiff  hairs.  The  attached  border  is  continuous  with  the  surrounding  struc- 
tures, and  is  adherent  to  the  alveolar  borders  of  the  bones  of  the  jaws. 

Structure. — The  lips  are  covered  externally  by  the  skin,  and  are  linetl  liy 
mucous  membrane;  between  these  are  muscular  tissue  and  glands.  The  skin 
lies  directlj'  on  the  muscles,  many  fibers  of  which  are  inserted  into  the  former.  The 
muscles  have  been  described  (page  214).  The  labial  glands  (CdanduliP  labiales) 
form  a  compact  mass  near  the  angles;  they  are  numerous  in  the  upper  lip,  fewer 
in  the  lower.  The  raucous  membrane  is  often  pigmented,  and  is  reflected  upon 
the  bones  of  the  jaws  to  form  the  gums. 

Blood-vessels  and  Nerves. — The  arteries  are  derived  from  the  superior  and 
inferior  lal)ial  and  palato-labial  arteries.  The  sensory  nerves  come  from  the 
trigeminus,  anil  the  motor  from  the  facial  nerve. 

The  cheeks  (Buccte)  form  the  sides  of  the  mouth,  and  are  continuous  in  front 
with  the  lips.  They  are  attached  above  and  below  to  the  alveolar  borders  of  the 
bones  of  the  jaws. 

Structure. — This  comprises:  (1)  The  skin;  (2)  the  muscular  and  glandular 
layer;  (3)  the  mucous  membrane.  The  skin  offers  nothing  in  particular  to  notice. 
The  muscular  tissue  is  formed  mainly  by  the  buccinator,  but  also  by  parts  of  the 
panniculus,  zygomaticus,  dilatator  naris  lateralis,  levator  nasolabialis,  and  depressor 
labii  inferioris.  The  buccal  glands  (Glandulse  buccales)  are  arranged  in  two  rows. 
The  upper  row  (superior  buccal  or  molar  glands)  is  found  on  the  outer  surface  of 
the  buccinator  muscle,  near  its  upper  border.  The  anterior  part  of  the  row  con- 
sists of  scattered  lobules;  the  posterior  part,  which  lies  under  cover  of  the  masseter 
muscle,  is  more  developed  and  compact.  The  lower  row  ( inferior  buccal  or  molar 
glands),  less  voluminous  than  the  upper,  is  situated  in  the  submucous  tissue  at  the 
lower  border  of  the  buccinator  muscle.  The  mucous  membrane  is  reflected  above 
and  below  upon  the  gums,  and  is  continuous  behind  with  that  of  the  soft  palate. 
It  is  reddish  in  color  and  frequently  shows  pigmented  areas.  Opposite  the  third 
upper  cheek  tooth  is  the  opening  of  the  parotid  (Stenson's)  duct,  surrounded  by  a 
circular  fold  of  the  mucous  membrane.  A  linear  series  of  small  papillae  above 
and  below  indicates  the  orifices  of  the  small  ducts  from  the  buccal  glands. 

Blood-vessels  and  Nerves. — The  blood-supiily  is  derived  from  the  facial  and 
buccinator  arteries.  The  sensory  nerves  come  from  the  trigeminus  and  the  motor 
from  the  facial  nerve. 

The  gums  (Gingivae)  are  composed  of  a  dense  fibrous  tissue  intimately  united 
with  the  periosteum  of  the  alveolar  processes,  and  blending  at  the  edges  of  the  alveoli 
with  the  alveolar  periosteum,  which  fixes  the  teeth  in  their  cavities.  They  are 
covered  by  a  smooth  mucous  membrane,  destitute  of  glands,  and  of  a  low  degree 
of  sensibility. 

The  hard  palate  (Palatum  durum)  is  bounded  in  front  and  on  the  sides  by 
the  alveolar  arches;  behind  it  is  continuous  with  the  soft  palate.  Its  osseous  basis 
is  formeil  by  the  premaxilla,  maxilla,  and  palate  bones.  The  mucous  membrane 
is  smooth,  and  is  attached  to  the  bones  by  a  submucosa  which  contains  in  its 
anterior  part  an  exceedingly  rich  venous  plexus,  constituting  an  erectile  tissue. 
A  central  raphe  (Raphe  palati)  divides  the  surface  into  two  equal  portions.  Each 
of  these  presents  about  eighteen  transverse  curved  ridges  (Rugae  palatini)  which 
have  their  concavity  and  their  free  edges  directed  backward.  They  are  further 
apart  and  mor(>  prominent  anteriorly.     There  are  no  glands  in  the  submucosa. 

Vessels  and  Nerves. — The  blood-supply  is  derived  chiefly  from  the  palatine 
arteries  and  the  nerves  from  the  trigeminus. 

The  soft  palate  (Palatum  moUo)  is  a  musculo-membranous  curtain  which 
separates  the  cavity  of  the  mouth  from  that  of  the  pharynx.  It  slo])es  downward 
and  backward  from  its  junction  with  the  hard  palate.     The  oral  surface  faces 


THE    MOUTH 


333 


downward  and  forward,  and  is  covered  with  a  mucous  membrane  continuous  with 
that  of  the  hard  palate.  It  is  corrugated  and  presents  numerous  small  orifices 
(of  gland-ducts)  and  two  sagittal  ridges.  On  each  side  a  short,  thick  fold  passes 
to  join  the  ba.se  of  the  tongue;  this  is  the  anterior  pillar  of  the  soft  palate  (Arcus 
glossopalatinus).  The  pharyngeal  surface  looks  upward  and  backward  and  is 
covered  by  a  mucous  membrane  continuous  with  that  of  the  nasal  cavity.  The 
free  border  (Arcus  palatinus)  is  concave  and  thin;  it  is  in  contact  (except  during 
deglutition)  with  the  epiglottis.  It  is  continuous  with  a  fold  of  the  mucous  mem- 
brane, which  ]5asses  on  each  side  along  the  lateral 
wall  of  the  pharynx  and  unites  with  its  fellow 
over  the  beginning  of  the  a\so])hagus;  this  fold 
is  termed  the  posterior  pillar  of  the  soft  palate 
(Arcus  pharyngopalatinus).  The  space  between 
the  diverging  anterior  and  posterior  pillars  (Sinus 
tonsillaris)  is  occupied  by  the  faucial  tonsil.  In 
the  horse,  however,  there  is  not  a  compact  tonsil, 
as  in  man,  dog,  etc.,  but  a  somewhat  extended 
group  of  mucous  glands  and  masses  of  lymphoid 
tissue.  These  cause  elevations  of  the  surface,  on 
which  are  seen  numerous  depressions  (crypts)  in 
which  the  gland-ducts  open.  The  soft  palate  is 
greatly  developed  in  equidse,  its  length  being  five 
to  six  inches  (12  to  15  cm.).  Its  length  and  con- 
tact with  the  epiglottis  account  for  the  fact  that 
in  these  animals  mouth-breathing  does  not  occur 
under  normal  conditions,  and  that  in  vomiting  the 
ejected  matter  escapes  usualh'  through  the  nasal 
cavity.' 

Structure. — The  soft  palate  consists  of:  (1) 
The  oral  mucous  membrane,  continuous  with  that 
of  the  hard  palate;  (2)  the  palatine  glands  (Glan- 
dulse  palatinie),  which  form  a  layer  al)out  half  an 
inch  in  thickness;  (3)  the  aponeurotic  and  mu.s- 
cular  layer;  (4)  the  pharyngeal  mucous  mem- 
brane, continuous  with  that  of  the  nasal  cavity. 

The  muscles  proper  to  the  soft  palate  are  the 
azygos  uvulte,  the  levator  palati,  and  the  tensor 
palati. 

The  azygos  uvulae  (M.  palatinus)  consists  of 
two  small  muscular  bundles  which  lie  together 
at  the  median  line.  It  is  attached  through  the 
medium  of  the  palatine  aponeurosis  to  the  pala- 
tine arch,  and  terminates  near  the  free  edge  of 
the  soft  palate.  Its  action  is  to  shorten  and 
raise  the  soft  palate. 

The  levator  palati  (M.  levator  veli  palatini)  arises  from  the  muscular  process 
of  the  petrous  temporal  bone  and  from  the  Eustachian  tube,  and  passes  forward 
and  downward  externally  to  the  latter,  to  spread  out  on  the  pharjTigeal  surface 
of  the  soft  palate.  It  raises  the  soft  palate,  thus  closing  the  posterior  nares 
during  deglutition. 

The  tensor  palati  (M.  tensor  veli  palatini)  is  larger  than  the  levator,  and  is 
fusiform  and  flattened.     It  arises  from  the  muscular  process  of  the  petrous  tem- 
poral bone  and  the  Eustachian  tube,  and  passes  forward  external  to  the  levator. 
'  The  epiglottis  may  be  either  in  front  of  or  behind  the  soft  palate;   most  often  it  is  prevelar. 


Flo.  239. — Hard   Palate  and  Part  o; 
Soft  Palate  of  Horse. 
1 ,  Raphe  palati;  S,  ridges  of  palate 
3,  atlterior  end  of  soft  palate,  showing  on 
fices  of  ducts  of  palatine  glands. 


334 


DIGESTIVE    SYSTEM    OF    THE    HORSE 


Its  tendon  is  then  reflected  around  tlie  hamulus  of  the  pterygoid  bone,  being  held 
in  position  by  a  fibrous  band  and  lubricated  by  a  bursa.  It  turns  inward  and  ex- 
pands in  the  aponeurosis  of  the  soft  palate.     It  tenses  the  soft  palate. 

Vessels  and  Nerves. — The  blood-supply  of  the  soft  palate  is  derived  from  the 
internal  and  external  maxillary  arteries.  The  nerves  come  from  the  trigeminus, 
vagus,  and  glosso-pharyna:eal  nerves. 

The  floor  of  the  mouth  in  its  anterior  part  is  free  and  is  formed  by  the  body  of 
the  mandii)h',  covered  by  mucous  membrane.  The  remainder  is  concealed  by  the 
attacheil  portion  of  the  tongue,  with  the  exception  of  a  narrow  space  on  each  side 


Septum  nasi       Superior  meatus 


Naso-hirrimnl  duet 


Infraorbital  nerve 
and  vessels 

Levator  labii  superi- 
oris  proprius 


Superior  buceal 
neri'c 
Facial  artery 

Superior  buccal 
glands 

Parotid  duct 


Lnhial  r 
Inferior  labial  a 

M  ijlo-hijoide 


Digastricus      Suhlmyual  orlenj 

Fig.  240. — Cnoss-SKCTION  of  Head  op  Hobse  jdst  in  Front  or  Facial  Crest. 

/,  Cavity  of  .superior  turbinal;  2,  cavity  of  inferior  turbinal;   3,  cavuni  oris;   4.  4,  Kenio-glossi;  5,  5.  genio-hyoidei; 

G,  hyo-glojisus:    7,  upper,  7',  lower  fourth  cheek  tooth.     Line  to  facial  artery  crosse.s  zygoiiiaticus. 


Superior  turbinal 
Common  vicatus 

Moldle  meatus 

Inferior  turbinal 
Inferior  meatus 

Viixiltari/  sinus 
<!iilirior  eud) 

Palatine  artery 
Facial  artery 

Buccal  jiiucous 
membrane 


Hypoglossal 
nerre 
Lingual  artery 

'erieir  buccal  nerve 
dies  of  lingual  nerve 


of  the  latter,  .\bout  opposite  the  canine  tooth  on  each  side  is  a  papilla,  the 
caruncula  sublingualis,  through  which  the  tluct  of  the  submaxillary  gland  opens. 
Just  Ijehinil  tliese  papillte  is  a  median  fold  of  mucous  memlirane  which  ])asses  to  the 
under  surface  of  the  tongue,  constituting  the  frenum  linguas.  On  either  side  are 
the  sublingual  crests,  which  extend  from  the  fnnuim  to  the  level  of  the  fourth 
cheek  tooth.  The  crest  presents  numerous  small  papilla-,  through  which  open  the 
ducts  from  the  subjacent  sublingual  gland.'     Behind  the  last  tooth  a  vertical  fold 

'  In  the  undisturlipcl  state  of  the  parts  there  is  no  .space  between  the  tongue  and  the  rami 
of  tlie  lower  jaw;   consequently  the  tongue  must  be  drawn  aside  to  see  the  sublingual  crest. 


THE    TONGUE  335 

of  the  mucous  nipmbrane  passes  from  upper  to  lower  jaw.     This  is  termed  the  plica 
ptcrygomandibularis:    it  coutains  a  ligament  of  like  name. 

The  isthmus  faucium  is  the  orifice  of  communication  between  the  mouth  and 
the  pharynx.  It  is  bounded  above  by  the  soft  palate,  below  by  the  root  of  the 
tongue,  and  laterally  by  the  anterior  pillars  of  the  soft  palate.  It  is  long,  relatively 
small,  and  not  very  dilatable  in  the  horse,  and  is  closed  by  the  soft  palate  under 
normal  conditions,  except  dur- 


ing deglutition. 


Tliijruid  gland 


Foliate  papilla 


Vallate  papillos 


Trachea 


Crico-arytenoid- 
eus  posterior 

Arijtenoideus 

Arijtnioid  carti- 
.  lages 

Vocal  cord 


Aditiis  larijngis 
Epiglottis 

Tonsil 

Adenoid  tissue  of 
root  of  tongue 

A  nterior  pillar  of 
soft  palate  (cut) 


Dorsum  linguce 


THE  TONGUE 

The  tongue  (Lingua)  is 
situated  on  the  floor  of  the 
mouth,  between  the  rami  of 
the  mandible,  and  is  sup- 
ported mainly  in  a  sort  of 
sling  formed  by  the  mylo- 
hyoid muscles.  Its  posterior 
portion,  the  root  (Radix 
linguae),  is  attached  to  the 
hyoid  bone,  soft  palate,  and 
pharynx.  Only  the  upper 
surface  of  this  part  is  free, 
and  slopes  downward  and 
backward.  The  middle  por- 
tion, the  body  (Corpus  linguse), 
has  three  free  surfaces.  The 
upper  surface  or  dorsum  (Dor- 
sum linguse)  is  rounded.  The 
lateral  surfaces  are  nearly  flat 
for  the  most  part,  but  an- 
teriorly become  rounded  and 
narrower.  The  lower  surface 
is  attached  to  the  mandible. 
The  apex  or  tip  (Apex  linguse) 
is  free,  spatula-shaped,  and 
presents  superior  and  inferior 
surfaces  and  a  rounded  border. 

Structure. — The  tongue 
consists  of:  (1)  The  mucous 
membrane;  (2)  the  glands; 
(3)  the  muscles. 

The  mucous  membrane 
(Tunica  mucosa  linguae)  ad- 
heres intimately  to  the  sul:)jacent  tissue,  except  on  the  lower  part  of  the 
lateral  surfaces  of  the  body  and  the  under  surface  of  the  tip.  It  varies 
considerably  in  thickness.  On  the  dorsum  it  is  very  thick  and  dense. 
Underneath  this  portion  there  is  a  dense  fibrous  cord,  which  extends  medially 
a  distance  of  five  or  six  inches  forward  from  the  vallate  papillae.  On 
the  sides  and  under  surface  of  the  tongue  the  membrane  is  much  thinner  and 
smooth,  and  can  more  readily  be  dissected  off  the  muscular  tissue.  From 
the  under  surface  of  the  free  part  of  the  tongue  a  fold  of  the  mucous  membrane 
passes  to  the  floor  of  the  mouth,  forming  the  frenum  linguae.  This  contains  the 
anterior  edges  of  the  genio-glossi  muscles.     Posteriorly  a  fold  passes  on  each  side 


Apex  linguce. 


Fig.  241. — Tongue  of  Horse,  Dorsal  .\s 


336 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


from  the  edge  of  the  dorsum  to  join  the  soft  palate,  forming  the  anterior  pihars  of 
the  latter.  A  central  glosso-epiglottic  fold  (Plica  glossoepiglottica)  passes  from 
the  root  to  the  base  of  the  epiglottis.  The  mucous  membrane  presents  numerous 
papillae,  which  are  of  four  kinds— filiform,  fungiform,  vallate,  and  foliate.  The 
filiform  papillffi  (PapilliB  filiformes)  are  fine,  pointed  projections.  They  cover  the 
upi)er  surface  of  the  body  and  tip,  to  which  they  give  a  distinct  pile.  The  fungi- 
form papillae  (Papilhr  fuiigiformes)  are  rountled  at  the  free  end,  which  is  supported 
by  a  neck.  They  occur  principally  on  the  lateral  part  of  the  tongue,  but  are  also 
found  scattered  over  the  dorsum  anti  upper  surface  of  the  free  portion.  The 
vallate  papillae  (Papillae  vallatse)  are  usually  two  or  three  in  number.  The  two 
constant  ones  have  a  diameter  of  about  7  mm.,  and  are  found  on  the  posterior  part 
of  the  dorsum,  one  on  each  side  of  the  median  plane,  about  an  inch  (ca.  3cm.)  apart. 


Thyroid  gland 


Trachea 


He 


Fig.  242. — Muscles  of  Toxgue,  Hyoid  Bone,  Pharynx,  e 
T.  p..  Tensor  palati;   L.  p.,  levator  p.alati;   Pi.  p.,  pterygo-pharyngeus;   P.  p.,  palato-pharynKeus;   S.  p., 
6tylo-i)haryngeu^;   Th.  p.,  thyro-pharyngeus;  C.  p.,  crico-pharyngeus:   Th.  h.,  thyro-hyoideus;  Hyo.  gl.,  hyo-glossus; 
O.  p. .guttural  pouch;  F.  p.,  foliate  papilla;  .4.  y.,  facial  artery  and  vein.     The  concealed  parts  of  the  hyoid  bone  are 
indicated  by  dotted  line. 


The  third,  when  present,  is  behind  these,  is  centrally  situated,  and  is  always  smaller. 
Rarely  a  fourth  may  be  seen.  They  are  rounded,  broader  at  their  exposed  than 
at  their  attached  surfaces,  and  are  situated  in  a  cup-shaped  cavity.  The  foliate 
papillae  (Papillae  foliatte)  are  situated  just  in  front  of  the  anterior  pillars  of  the  soft 
palate,  where  they  form  a  rounded  eminence  about  an  inch  (ca.  2  to  3  cm.)  in  length, 
marked  by  transverse  fissures.  The  last  three  varieties  are  covered  with  micro- 
scopic secondary  papilliE  and  are  furnished  with  taste-buds.  The  mucous  mem- 
brane of  the  root  of  the  tongue  presents  numerous  folds  and  depressions.  Into 
the  latter  open  the  ducts  from  the  lingual  glands  (Glandulie  linguales),  wdiich 
constitute  a  thick  layer  in  the  loose  submucous  tissue.  Mucous  glands  are  found 
also  on  the  tlorsum  and  sides  of  the  tongue.  In  the  submucosa  of  the  root  is 
found  also  a  large  quantity  of  lymjih  follicles  (FoUiculi  tonsillares)  and  diffuse 
lymphoid  tissue. 


THE    TONGUE 


337 


The  muscular  tissue  may  be  divided  into  intrinsic  and  extrinsic  The  in 
tnnsic  musculature  consists,  not  of  distinct  muscles,  but  rather  of  systems  of  fibers 
which  run  longituchnally,  vertically,  antl  transversely,  blending  with  the  extrinsic 
muscles,  which  are  now  to  be  described. 

1.  Stylo-glossus.— This  is  a  long,  thin  muscle,  which  lies  on  the  lateral  part 


in- 


of  the  tongue.  It  arises  by  a  thin  tendon  from  the  outer  surface  of  the  great 
cornu  ot  the  hyoid  bone,  near  the  articulation  with  the  small  cornu.  It  terminates 
near  the  tip  of  the  tongue  by  blending  with  its  fellow  of  the  opposite  side  and  with 
the  intrinsic  musculature.  The  action  is  to  retract  the  tongue.  Unilateral  con- 
traction would  also  draw  the  tongue  toward  the  side  of  the  muscle  acting. 


338  DIGESTIVE    SYSTEM    OF   THE    HORSE 

2.  Hyo-glossus. — This  is  a  wide,  flat  muscle,  somewhat  thicker  than  the  pre- 
ceding. It  lies  on  the  lateral  part  of  the  root  and  body  of  the  tongue,  partly  under 
cover  of  the  preceding  muscle.  Its  deep  face  is  related  to  the  genio-glossus.  It 
arises  from  the  lateral  aspect  of  the  hyoid  bone,  from  the  lingual  process  to  the  oral 
extremity  of  the  great  cornu,  and  from  the  thyroid  cornu.  The  fibers  pass  obliquely 
forward  and  upward,  and  for  the  most  part  turn  toward  the  median  plane  of  the 
dorsum  of  the  tongue.     Its  action  is  to  retract  and  depress  the  tongue. 

(It  is  usually  possible  to  recognize  in  this  muscle  three  portions,  which  would 
correspond  to  the  baseo-,  kerato-,  and  chontlro-glossus  of  human  anatomy.) 

3.  Genio-glossus. — This  is  a  fan-shaped  muscle,  which  lies  parallel  to  the  me- 
dian plane  of  the  tongue.  It  is  separated  from  the  muscle  of  the  opposite  side  by  a 
quantity  of  fat  and  connective  tissue.  It  arises  from  the  inner  surface  of  the  ramus 
of  the  mandible  near  the  symphysis.  From  the  tendon  the  fibers  pass  in  a  radiating 
manner,  some  toward  the  tip,  others  toward  the  dorsum,  and  others  toward  the 
root  of  the  tongue;  some  fibers  pass  from  the  posterior  end  of  the  tendon  to  the 
body  and  small  cornu  of  the  hyoid  bone.  The  muscle  as  a  whole  is  a  depressor  of 
the  tongue,  and  especially  of  its  middle  portion;  when  both  muscles  act,  a  median 
groove  is  formed  on  the  dorsum.  The  posterior  fibers  protrude  the  tongue,  the 
middle  fibers  depress  the  tongue,  and  the  anterior  fibers  retract  the  tip  of  the 
tongue. 

Vessels  and  Nerves. — The  arteries  of  the  tongue  are  the  lingual  and  sub- 
lingual branches  of  the  external  maxillary  artery.  The  sensory  nerves  are  the 
lingual  and  glosso-pharyngeal,  and  the  muscles  are  innervated  by  the  hypoglossal 
nerve. 

THE  TEETH 
The  teeth  are  hard  white  or  yellowish-white  structures,  implanted  in  the  alveoli 
of  the  bones  of  the  jaws — premaxilla,  maxilla,  and  mandible.  Morphologically 
they  are  large  calcified  papillae.  Functionally  they  are  organs  of  prehension 
and  mastication,  and  may  serve  as  weapons  of  offense  and  defense.  They  are 
classified  according  to  form  and  position  as  follows: 

1.  The  incisor  teeth  (Dentes  incisivi)  are  situated  in  front  and  are  implanted 
in  the  ]ircniaxilla  and  mandible. 

2.  The  canine  teeth  (Dentes  canini)  are  situated  a  little  further  back,  at  or 
near  the  premaxillary  suture  in  the  upper  jaw;  in  the  lower  jaw  they  are  nearer 
the  incisors. 

3.  Thecheekteeth  (Dentespremolares  etmolares),theremaining  teeth,  occupy 
the  sides  of  the  dental  arch.  The  space  between  the  incisors  and  cheek  teeth  is 
termed  the  interdental  or  interalveolar  space.  It  is  customary  to  divide  the  check 
teeth  into  an  anterior  series,  termed  premolars,  which  appear  as  temporary, 
deciduous,  or  milk  teeth,  and  are  replaced  Ijy  permanent  successors,  and  a  posterior 
series,  the  molars,  which  appear  only  as  permanent  teeth  without  deciduous  pre- 
decessors. 

As  the  teeth  of  the  two  sides  of  the  jaws  are  alike  in  numlier  and  character 
(in  normal  cases),  the  complete  dentition  may  lie  briefly  indicated  by  a  dental 
formula  such  as  the  following: 


2  (  I  -  C  -  P  -  M  ^  )  =  32. 
V    2      1      2       3/ 


In  this  formula  the  letters  indicate  the  kinds  of  teeth,  and  the  figures  above  and 
below  the  lines  give  the  number  of  teeth  of  one  side  in  the  upper  and  lower  jaw 
respectively  in  man. 

The  inchvidual  t(>eth  of  each  group  are  designated  numerically,  the  starting- 
point  being  the  middle  line;  thus  the  incisor  on  either  side  of  the  middle  line  is  the 


THE   TEETH  339 

first  incisor,  and  may  be  conveniently  indicated  by  the  notation  I'.  The  tem- 
porary or  deciduous  teeth  may  be  designated  in  a  similar  manner,  prefixing  D 
(for  deciduous)  to  the  letter  indicating  the  kind  of  tooth.  In  addition  to  the  above 
systematic  method  of  notation  other  terms  have  received  the  sanction  of  popular 
usage.  Thus  the  first  incisors  are  commonly  called  "pinchers,"  or  "nippers"; 
the  second,  intermediate;  and  the  third,  corner  teeth.  The  canines,  when  highly 
developed,  may  be  termed  tusks  or  fangs.  The  vestigial  and  inconstant  first 
premolar  of  the  horse  is  popularly  termed  the  "wolf  tooth." 

Each  tooth  presents  for  description  a  portion  coated  with  enamel,  termed  tlie 
crown  (Corona  dcntis),  and  a  portion  covered  with  cement,  termed  the  root  (Radix 
dentis).  The  line  of  union  of  these  parts  is  the  neck  (CoUum  dentis).'  In  many 
teeth  the  neck  is  distinct  and  is  embraced  by  the  gum,  e.  g.,  the  teeth  of  the  dog 
and  the  temporary  incisors  of  the  horse.  In  other  teeth  no  constriction  is  seen,  as 
in  the  permanent  incisors  of  the  horse.  Between  these  extremes  may  be  noted 
the  molars  of  the  horse,  in  which  the  neck  is  seen  only  in  atlvanced  age. 

The  surface  of  a  tooth  directed  toward  the  lips  is  termed  labial ;  toward  the 
cheek,  buccal;  and  toward  the  tongue,  lingual  (Facies  labialis,  buccalis,  lingualis). 
The  surface  opposed  to  a  neighboring  tooth  of  the  same  dental  arch  is  termed  the 
contact  surface  (Facies  contactus).  The  grinding  or  masticatory  or  "table" 
surface  (Facies  masticatoria)  is  that  which  comes  in  contact  with  a  tooth  or  teeth 
of  the  opposite  jaw. 

Structure. — Teeth  are  composed  of  four  tissues,  which  are  considered  here 
from  within  outward.  The  pulp  (Pul]ia  dentis)  is  a  soft  gelatinous  tissue,  which 
occupies  a  space  in  the  central  part  of  the  tooth  termed  the  pulp  cavity  (Cavum 
dentis).  The  pulp  is  well  supplied  with  blood-vessels  and  nerves.  It  occupies 
a  relatively  large  space  in  young  growing  teeth,  but  later  the  dentine  deposited 
on  its  surface  gradually  encroaches  on  it  until,  in  advanced  age,  the  cavity  is 
obliterated  or  much  reduced.  The  dentine  (Substantia  eburnea)  forms  the  bulk 
of  most  teeth,  covering  the  surface  of  the  pulp.  It  is  very  hard,  and  is  yellowish- 
white  in  color.  The  enamel  (Substantia  adamantina)  constitutes  a  layer  of  varying 
thickness  covering  the  dentine  of  the  crown  of  the  tooth.  It  is  easily  distinguished 
by  its  clear  bluish-white  appearance  and  its  extreme  density.  The  cement 
(Substantia  ossea)  is  always  the  outermost  tooth  substance.  In  simple  teeth  it 
forms  usually  a  thin  layer  on  the  surface  of  the  dentine  of  the  root  only,  but  in  com- 
plex teeth  it  exists  in  considerable  quantity,  tending  to  fill  in  the  spaces  between  the 
enamel  folds  of  the  crown  also.  Its  structure  is  practically  the  same  as  that  of 
bone  without  Haversian  canals,  and  even  these  occur  where  the  cement  forms  a. 
very  thick  layer.  The  embedded  part  of  the  tooth  is  attached  to  the  alveolus  by 
a  vascular  layer  of  connective  tissue,  the  alveolar  periosteum  (Periosteum  alveolare), 
which  constitutes  the  periosteum  at  once  of  tooth  antl  alveolus. 

The  blood-supply  to  the  pul]i  is  derived  from  the  alveolar  or  dental  branches 
of  the  internal  artery ;   the  nerve-supply  comes  from  branches  of  the  trigeminus. 

•  It  will  be  noted  that  this  definition  of  crown  and  root  does  not  agree  exactly  with  the 
popular  view  that  the  crown  is  the  free  portion  and  the  root  the  embedded  portion.  The  objec- 
tion to  the  latter  statement  lies  in  the  fact  that  it  is  not  capable  of  general  application.  Tims 
the  morphological  crown  of  the  permanent  molars  in  the  horse  is  extremely  long,  and  is,  for  the 
most  part,  embedded  in  the  Ijone  in  the  young  animal.  The  root  proper  begins  to  form  at  four 
or  five  years  of  age,  and  continues  its  growth  for  about  eight  years.  As  the  exposetl  part  of  the 
crown  wears  down,  the  embedded  part  pushes  out  of  the  alveolus,  thus  preventing  deficiency  of 
length.  On  the  old  ba.sis  we  should  have  to  .say  that  successive  portions  of  the  root  become 
crown,  while  in  point  of  fact  it  is  only  in  very  extreme  age  that  the  true  root  comes  into  wear. 


340 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


The  Teeth  of  the  Horse 

The  Permanent  Teeth 
The  formula  of  the  permanent  teeth  of  the  horse  is: 


(3     1     3or4       :i\ 
I  -  C  -  P  M  -   I  = 
3      13  3/ 


40  or  42 


Fig.  24-J. — Upper  Teeth  of  Horse,  About  Fodr  amd  One-hai.f 

Veaks  Old. 

/',  /-,  /',  Incisors;  C,  cauiiie;  1",  P',  pa,  P\  premolars;  M',  M^,  .IP, 

molars. 


Fig.  245. — Lower  Teeth  of  Horse, 
Four  Years  of  Age. 
/',  /'-,  First  and  second  permanent 
incisors;  Di^^  third  deciduous  incisor.  The 
cheelc  teeth  are  numbered  according  to 
popular  usage. 


In  the  mare  the  canines  u.sually  are  very  small  antl  do  not  erupt,  reducing  the  num- 
ber to  36  or  38.' 

'  Ellciihorgcr  found,  as  thp  result  of  extensive  observations  (8000  subjects),  that  about 
2  to  3  per  cent,  of  mares  have  erupted  canines  in  both  jaws;  tliat  6  to  7  per  cent,  have  tliem  in 
the  upper  jaw;   wliile  20  to  30  per  cent,  liave  them  in  the  lower  jaw. 


THE    TEETH    OF    THE    HORSE 


341 


Incisor  Teeth. — These  are  twelve  in  numlter.  The  six  in  each  jaw  are  placed 
close  together,  so  that  their  labial  edges  form  almost  a  semicircle.  They  have  the 
peculiarity  (not  found  in  existing  mammals  other  than  the  equidie)  of  presenting, 
insteatl  of  the  simjile  cap  of  enamel  on  the  crown,  a  deep  invagination,  the  infundi- 
bulum,  which  becomes  partly  filled  up  with  cement.  Hence  as  the  tooth  wears 
the  table  surface  has  a  central  ring  of  enamel  surrounding  this  cavity  in  addition 
to  the  peripheral  enamel.  Tlie  cavity  becomes  darkened  l)y  dejjosits  from  the 
food,  and  is  commonly  termed  the  "cup"  or  "mark."  Each  tooth  is  curved  so 
that  the  labial  surface  is  convex  and  the  roots  converge.  The  average  length  of 
the  incisors  at  five  or  six  years  of  age  is  about  two  and  a  half  to  three  inches  (ca.  7 
cm.).  They  taper  regularly  from  crown  to  root,  without  any  constriction,  and 
in  such  a  manner  that  in  young  horses  the  exposed  crown  is  broad  transversely; 
toward  the  middle,  the  two  diameters  of  a  cross-section  are  about  equal;  near  the 
root  the  antero-posterior  diameter  is  considerably  greater  than  the  transverse. 

This  fact  is  of  value  in  the  determination  of  age  by  the  teeth,  since  the  table 
surface  at  different  ages  represents  a  series  of  such  cross-sections.     As  the  exposed 


Fig.  246. — Lower    Incisor    and  CANr 
Horse,  Five  Years  Old. 


-Upper    Incisor    a> 
Horse,  Five  Yea 


Cani.ne  Teeth  of 


crown  wears  down  the  embedded  part  (reserve  crown)  pushes  up  out  of  the  alveolus, 
so  that  the  tables  of  the  first  and  second  lower  incisors  are  at  first  oval,  with  the 
long  diameter  transverse;  later — at  about  fourteen  years  usually  for  the  first  lower 
incisors — the  tables  are  triangular,  with  the  base  at  the  labial  edge.  At  the  .same 
time  the  infundibulum  or  cup  becomes  smaller,  approaches  the  lingual  border,  and 
finally  disappears;  it  remains  longer  on  the  upper  incisors,  as  it  is  deeper  in  them. 
Another  marked  feature  in  old  age  is  the  progressive  approach  to  a  horizontal  direc- 
tion as  seen  in  profile;  at  the  same  time  the  teeth  become  parallel  and  finally  con- 
vergent. 

Canine  Teeth. — These  are  four  in  number  in  the  male;  in  the  mare  they  are 
usually  absent  or  rudimentary.'  They  interrupt  the  interdental  space,  dividing 
it  into  two  unequal  parts.  The  upper  canine  is  situated  at  the  junction  of  the  pre- 
maxilla  and  the  maxilla;  the  lower  canine  is  placed  nearer  the  corner  incisor. 
The  canines  are  simple  teeth,  smaller  than  the  incisors,  and  are  curved  with  the 
concavity    directed  backward.     The  crown  is  compressed,  convex,  and    smooth 

'  It  is  interesting  to  notice  that  vestigial  canines  are  not  at  all  uncommon  in  mares,  espe- 
cially in  the  lower  jaw.  They  are  very  small,  and  do  not  usually  erupt;  their  presence  is  indi- 
cated in  the  latter  case  by  a  prominence  of  the  gum.  This  is  in  conformity  with  the  fact  that 
they  were  present  in  both  sexes  in  Eocene  and  Miocene  ancestors  of  existing  equidae. 


342 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


externally;  concave  with  a  median  ridge  internally;  its  edges  are  sharp,  and  the 
apex  is  pointed  in  the  unworn  tooth.  The  root  is  round  and  the  pulp  cavity  is 
large,  persisting  to  advanced  age. 

Cheek  Teeth  (Premolars  and  Molars).' — The  constant  number  of  these  is 

twenty-four  -  twelve  in  each  jaw. 


Infundibulum 


Cement 
Peripheral  enamel 
Dentine 

Central  enamel 
( 


Lingua, 


Puljj-caviiy 


Cement 


Labial  surface 


Quite  commonly,  however,  the 
number  is  increased  by  the  pres- 
ence in  the  upper  jaw  of  the  so- 
called  wolf-tooth.  This  tooth  is 
usually  situated  just  in  front  of 
the  first  well-developed  tooth;  it 
is  a  much-reduced  vestige,  not 
often  more  than  one-half  or  three- 
fourths  of  an  inch  (ca.  1  to  2  cm.) 
in  length.  (It  is  interesting  as 
being  the  remnant  of  a  tooth 
which  was  well  developed  in  the 
Eocene  ancestors  of  the  horse.) 
It  may  erupt  during  the  first  six 
months,  and  is  often  shed  about 
the  same  time  as  the  milk-tooth 
behind  it,  but  may  remain  in- 
definitely. The  occurrence  of  a 
similar  tooth  in  the  lower  jaw — 
which  rarely  erupts — increases 
the  dental  formula  to  44,  which 
is  considered  the  tj-jiical  number 
for  mammals.  Thej'  may  be 
regarded  as  liclonging  to  the  permanent  set,  having  no  predecessors.  The  cheek 
teeth  are  very  large,  prismatic  in  form,  and  quadrilateral  in  cross-section,  except 
the  first  and  last  of  the  series,  which  are  triangular.  The  crown  is  remarkably 
long,  most  of  it  being  embedded  in  the  bone  or  situated  in  the  maxillary  sinus  in 


248. — LONGITUDIXAL     SkCTION     OF     PERMANENT     InCISOR 

Tooth  of  Horse,  .\bout  Natural  Size. 


Central 

enamel     Infundibulum 


:-\d~. 


Canine  tooth 


Fin.  249. — IxcisoR  Tooth  of  Horse,  Lingual  Aspect. 
(After  Ellenbcrger-Baum,  .-Vnat.  fiir  Kiinstler.) 


Fig.  250. — Canine  and  Incisor  Teeth  of  Horse. 

The  bone  has  been  removed  to  show  the  embed- 
ded parts  of  the  teeth,  (.\fter  Ellenberger-Baum,  .\nat. 
fiir  Kiinstler.) 


the  young  horse.     As  the  cxposcil  part  wears  down  the  embedded  part  pushes  up 
to  replace  it,  so  that  a  functional  crown  of  about  four-fifths  of  an  inch  (ca.  2  cm.) 

'  It  is  common  in  veterinary  works  to  call  all  the  cheek  teeth  molars,  since,  in  the  horse 
particularly,  the  premolars  are  molariform,  i.  e.,  do  not  differ  materially  from  the  true  molars 
in  size  or  form.     The  term  cheek  teeth  conveniently  includes  the  premolars  and  molars. 


THE    TEETH    OK    THE    HORSE 


343 


is  maintaiopil.  Tlio  root  begins  to  grow  at  four  or  five  years  of  age,  and  is  com- 
plete at  twelve  to  fourteen,  althougli  the  deposition  of  cement  may  continue 
indefinitely. 

The  upper  or  maxillary  teeth  are  embedded  in  the  alveolar  processes  of  the 


maxilla.  The  exposed  parts  of  the  crowns  are  normally  in  close  contact,  forming  a 
continuous  row  which  is  slightly  curved,  with  the  convexity  toward  the  cheek. 
The  embedded  parts  diverge  in  the  manner  shown  in  the  annexed  figures  (Figs. 
251,  2.53).     Thus  the  long  axis  of  the  first  is  directed  upward  and  a  little  forward, 


344 


DIGESTIVE    SYSTEM    OF    THE    HORSE 


that  of  the  second  is  ahnost  vertical,  while  in  the  remainiler  it  is  curved  backward 
in  an  increasing  degree.  The  average  length  at  six  years  of  age  is  about  three  to 
three  and  a  half  inches  (ca.  7  to  9  cm.)-  The  buccal  (or  outer)  surface  presents  a 
central  ridge  running  lengthwise,  and  separating  two  grooves;  the  first  tooth  has,  in 
addition,  a  less  prominent  ridge  in  front  of  the  primary  one.  The  lingual  (or 
inner)  surface  is  marked  by  a  wide,  rounded  ridge,  the  accessory  pillar  or  colunni, 
which  separates  two  very  shallow  grooves.  The  masticatory  or  table  surface 
presents  two  infundibula,  an  anterior  and  a  posterior.  It  slopes  obliciuely  <lown- 
ward  and  outward,  so  that  the  outer  edge  is  prominent  and  sharp.  The  first  and 
last  teeth  have  three  roots,  the  remainder  four  or  three. 

The  position  of  the  embedded  crowns  and  roots  of  the  last  four  varies  at 
different  ages  and  in  different  subjects.  Two  factors  in  this  variation  may  be 
noted.  All  these  teeth  are  developed  in  the  maxillary  sinus  close  to  the  orbital 
fossa.  As  growth  proceeds  the  teeth  move  forward,  so  that  commonly  only  the 
last  three,  but  sometimes  also  the  third,  remain  (except  as  to  their  free  crowns) 
in  the  sinus.  The  second  cause  of  variation  is  the  fact  that  the  anterior  limit  of 
the  maxillary  sinus  may  be  at  the  extremity  of  the  facial  ridge,  or  more  than  an 
inch  beyond  it.     In  the  latter  case  the  third  tooth  projects  into  the  sinus.' 


Buccal  (outer)  surfaces  fac 


Fig.  252. — Cross-sections  of  C 

!  to  left.     .4,  Upper  tooth.  B,  lowe 

almost  filled  up  wi 


infunilibulum.  both 


The  structure  is  quite  complex.  Two  infundibula  run  vertically  through  the 
entire  length  of  the  crown;  these  become  filled  with  cement.  There  are  five  main 
divisions  of  the  pulp-cavity  and  five  enamel  folds,  four  of  which  are  arranged 
symmetrically,  while  the  fifth  is  an  outgrowth  from  the  inner  side  of  the  antero- 
internal  fold.  On  the  exposed  crown  of  the  unworn  tooth  the  enamel  folds  form 
rounded  ridges  covered  with  a  thin  layer  of  cement.  After  the  tooth  comes  into 
wear  the  enamel  on  the  masticatory  surface  stands  out  in  the  form  of  sharp 
prominent  ridges.  Progressive  cementation  of  the  periphery  of  the  tooth  takes 
place,  thus  leveling  up  the  irregularities  of  surface  to  a  considerable  extent. 

The  lower  or  mandibular  cheek  teeth  are  implanted  in  the  rami  of  the  mandi- 
ble, forming  two  straight  rows  which  diverge  behind.  The  space  between  the  rows 
is  considerably  less  than  that  separating  the  upper  teeth,  especially  in  the  middle 
of  the  series.  The  length  of  the  lower  teeth  is  about  the  same  as  that  of  the  upper 
set.  Their  direction  is  also  similar,  but  the  emliedded  portions  diverge  even  more, 
with  the  exception  of  the  first  and  second.  The  long  axis  of  the  first  is  vertical; 
the  remainder  project  downward  and  backward  in  a  gradually  increasing  obliquity. 
The  buccal  (outer)  surface  has  a  longitudinal  furrow;  the  last  molar  has  a  secon- 

'  Tlie  stiulent  is  advised  to  amplify  these  very  general  .<!tatements  by  the  examination  of 
he.ids  of  .stil)j(-ct.s  of  varying  ages.  It  may  also  be  noted  that  the  position  of  the  septum  between 
the  two  divisions  of  the  sinus  varies  much. 


THE   TEETH    OF   THE    HORSE 


345 


dary,  shallower  furrow  in  addition.  The  lingual  (inner)  surface  is  uneven,  but  the 
grooves  are  not  regular:  there  are  usually  three  on  the  first  and  last  tooth.  The 
masticatory  or    table  surface  is  oblique,  sloping    upward  and  inward  in  corre- 


spondence with  the  opposing  tooth;  thus  the  inner  edge  is  prominent.  The  first 
five  have  two  roots,  while  the  sixth  commonly  has  three.  The  width  of  the  lower 
molars  is  a  little  more  than  half  that  of  the  upper.  There  are  two  infundibula, 
which  are  open  along  the  inner  face  of  the  tooth  until  closed  by  cement.     The 


346  DIGESTIVE    SYSTEM    OF   THE    HORSE 

pulp-cavity  has  two  principal  divisions,  and  four  or  three  secondary  diverticula. 
The  enamel  folds  correspond,  forming  a  pattern  even  more  comiilicated  than  on 
the  upper  teeth. 

The  Temporary  Teeth 
The  deciduous,  temporary,  or  "milk"  teeth  (Dentes  decidui)  are  smaller  and 
fewer  than  those  of  the  permanent  set.     The  formula  is: 


(3        0        3\ 
Di  -  Dc  -  Dp  -  )  =  ; 
3         0         3/ 


The  deciduous  incisors  are  much  smaller  than  the  permanent  ones.  They 
have  a  distinct  neck  at  the  junction  of  the  crown  and  root.  The  crown  is  short, 
white  in  color,  and  its  labial  surface  is  smooth.  The  infundibulum  is  shallow. 
The  root  is  flattened;  it  undergoes  absorption  as  the  permanent  tooth  develops 
behind  it. 

The  deciduous  canines  are  quite  vestigial.  They  occur  in  both  sexes  as  slender 
spiculce  about  a  Cjuarter  of  an  inch  in  length,  but  do  not  erupt.  The  lower  one 
develops  close  to  the  corner  incisor.  They  are  not  usually  incluiled  in  the  formula, 
as  they  are  never  functional. 

The  deciduous  cheek  teeth  differ  from  the  permanent  set  chiefly  in  that  they 
have  much  shorter  crowns  than  the  latter.  The  roots  form  earl}-,  so  that  a  distinct 
neck  occurs. 

The  subjoined  table  indicates  the  average  periods  of  the  eruption  of  the  teeth: 

Teeth  Eruption 

A.  Deciduous: 

1st   incisor (Di   1)  Birth  or  first  week. 

2nd      "       (Di   2)  4-6  weeks. 

3rd      "      (Di  3)  6-9  months. 

Canine (Dc    ) 

1st   premolar ^^^VA  Birth  or  first 

2nd  (Dp  3)   I-  .  , 

3rd        "        (Dp  4)  J  *^°  ^^^'"^• 

B.  Permanent: 

1st   incisor (I  1)  2J2  J'ears. 

2nd      "       (I  2)  31^  years. 

3rd       "       (I  3)  Hi  years. 

Canine (C  )  4-5  years. 

1st  premolar  (or  wolf-tooth) (P  1 )  5-6  months. 

2nd        "         (P  2)  2}.;  years. 

3rd         "         (P  3)  3  years. 

4th         "         (P  4)  4  years. 

1st   molar (M  1)  1()-12  months. 

2nd      "     (M  2)  2  years. 

3rd       "     (M  3)  3J2-4  years. 

(The  periods  given  for  P  3  and  4  refer  to  the  upper  teeth;  the  lower  ones  may  erupt  about  si.x 
months  earhcr.) 

THE  SALIVARY  GLANDS 

This  term  is  usually  restricted  to  the  three  pairs  of  large  glands  situated  on  the 
sides  of  the  face  and  the  adjacent  part  of  the  neck — the  parotid,  submaxillary,  and 
sublingual.     Their  ducts  open  into  the  mouth. 

The  parotid  gland  (Glandula  parotis)  (Fig.  172)- — so  named  from  its  proximity 
to  the  ear — is  the  largest  of  the  salivary  glands  in  the  horse.  It  is  situated  chiefly 
in  the  space  between  the  ramus  of  the  mandible  and  the  wing  of  the  atlas.  It  is 
somewhat  triangular  in  shape,  the  apex  partially  embracing  the  base  of  the  external 
ear.  Its  length  is  about  eight  to  ten  inches  (ca.  20  to  25  cm.),  and  its  average  thick- 
ness nearlv  an  inch  (ca.  2  cm.).  Its  average  weight  is  about  seven  ounces  (ca. 
200  to  225  g.). 


THE    SALIVARY    GLANDS  347 

It  presents  for  description  two  surfaces,  two  borders,  a  base,  and  an  apex. 
The  external  (or  superficial)  surface  is  covered  by  the  parotid  fascia,  the  panniculus, 
and  the  parotido-auricularis  muscle.  It  is  crossed  obliquely  by  the  jugular  vein, 
which  is  embedded  in  the  gland  tissue  to  a  varying  e.xtent.  It  is  also  related  to 
the  great  auricular  vein,  the  cervical  branch  of  the  facial  nerve,  and  branches  of  the 
second  cervical  nerve.  The  internal  (or  deep)  surface  is  very  uneven,  and  has  nu- 
merous important  relations.  Some  of  these  are:  the  guttural  pouch,  and  the  great 
cornu  of  the  hyoid  bone;  the  masseter,  stylo-maxillaris,  digastricus,  and  occipito- 
hyoideus  muscles;  the  tendons  of  the  mastoido-humeralis  and  sterno-cephalicus 
(which  separate  the  parotid  from  the  underlying  submaxillary  gland) ;  the  external 
carotid  artery  and  some  of  its  branches;  the  facial  nerve;  the  pharyngeal 
lymph  glands.  The  anterior  (or  facial)  border  is  closely  attached  to  the  ramus  of 
the  mandible  and  the  masseter  muscle;  it  overlaps  the  latter  to  a  varying  extent. 
(In  some  cases  there  is  a  well-marked  triangular  facial  process,  which  covers  the 
temporo-mandibular  joint,  the  facial  nerve,  and  the  transverse  facial  vessels.) 
The  posterior  (or  cervical)  border  is  somewhat  concave,  and  is  loosely  attached  to 
the  underlying  muscles.  The  base  or  ventral  border  is  related  to  the  external 
maxillary  vein.  The  apex  is  attached  to  the  base  of  the  external  ear,  which  it 
partially  embraces. 

The  gland  has  a  yellowish-gray  color  and  is  distinctly  lohulated.  It  is  in- 
closed in  a  capsule  formed  by  the  parotid  fascia.  The  parotid  duct  (Ductus  paro- 
tideus  Stenonis)  is  formed  at  the  lower  part  of  the  gland,  near  the  facial  edge,  by 
the  union  of  three  or  four  radicles.  It  leaves  the  gland  about  an  inch  (ca.  2  to  3 
cm.)  above  the  external  maxillary  vein,  crosses  the  tendon  of  the  sterno-cephalicus, 
and  gains  the  inner  face  of  the  pterygoideus  internus.  It  then  runs  forward  in  the 
submaxillary  space  below  the  external  maxillary  vein  and  winds  around  the  lower 
border  of  the  mandible  behind  the  vein,  passes  upward  between  the  vein  and  the 
masseter  muscle  for  about  two  inches  (ca.  5  cm.),  turns  forward  underneath  the 
facial  vessels,  and  perforates  the  cheek  obliquely  opposite  the  third  upper  cheek 
tooth.  Before  piercing  the  cheek  it  is  somewhat  dilated,  but  its  termination  is 
small,  and  is  surrounded  by  a  circular  mucous  fold  (Papilla  salivalis). 

Blood-supply. — Branches  of  the  carotid  and  maxillary  arteries. 

Nerve-supply. — Trigeminal,  facial,  and  sympathetic  nerves. 

The  submaxillary  gland  (Glandula  submaxillaris)  is  much  smaller  than  the 
parotid.  It  is  long,  narrow,  and  curved,  the  dorsal  edge  being  concave.  It 
extends  from  the  fossa  below  the  wing  of  the  atlas  to  the  body  of  the  hyoid  bone, 
so  that  it  is  covered  partly  by  the  parotid  gland,  partly  by  the  lower  jaw.  Its 
length  is  about  eight  to  ten  inches  (ca.  20  to  25  cm.),  its  width  an  inch  to  an  inch 
and  a  half  (ca.  2.5  to  3  cm.),  and  its  thickness  about  half  an  inch  (ca.  1  cm.).  It 
weighs  about  one  and  a  half  to  two  ounces  (ca.  45  to  60  g.).  It  is  often  divisible 
into  two  parts. 

It  presents  for  description  two  surfaces,  two  borders,  and  two  extremities. 
The  external  surface  is  covered  by  the  parotid  gland,  the  stylo-maxillaris,  digas- 
tricus, and  pterygoideus  internus  muscles.  The  tendon  of  the  sterno-cephalicus 
crosses  this  surface,  and  is  a  useful  guide  in  separating  the  parotid  gland  from  it. 
The  internal  surface  is  related  chiefly  to  the  flexor  muscles  of  the  head;  the  gut- 
tural pouch;  the  larynx;  the  division  of  the  carotid  arterj-;  and  the  tenth,  eleventh, 
and  sj'mpathetic  nerves.  The  superior  border  is  concave  and  thin.  It  is  related 
to  the  guttural  pouch  and  the  duct  of  the  gland.  The  inferior  border  is  convex 
and  thicker.  It  is  related  to  the  thyroid  gland  and  the  external  maxillary  vein. 
The  posterior  extremity  is  loosely  attached  in  the  fossa  atlantis.  The  anterior 
extremity  lies  at  the  side  of  the  root  of  the  tongue,  and  is  crossed  externally  bj' 
the  external  maxillarv  arterv. 


348  DIGESTIVE    SYSTEM    OF    THE    HORSE 

The  submaxillary  duct  (Ductus  subniaxillaris  Whartoni)  is  formed  by  tlic  union 
of  small  radicles  which  emerge  along  the  concave  edge.  It  runs  forward  along  this 
border,  and,  after  leaving  the  anterior  extremity,  crosses  the  intermediate  tendon 
of  the  digastricus,  passes  between  the  hyo-glossus  and  mylo-hyoideus,  and 
gains  the  inner  surface  of  the  sublingual  gland.  Its  terminal  part  lies  on 
the  Ijoily  of  the  mandible,  under  the  mucous  membrane,  which  it  pierces 
opposite  the  canine  tooth.  The  orifice  is  at  the  eiul  of  a  flattened  papilla 
(Caruncula  sublingualis). 

Blood-supply. — Occipital,  external  carotid,  and  external  maxillary  arteries. 

Nerve-supply. — Chorda  tympani  and  sympathetic  nerves. 

The  sublingual  gland  (Glandula  sublingualis)  is  situated  beneath  the  mucous 
membrane  of  the  mouth,  between  the  body  of  the  tongue  and  the  ramus  of  the 
mandible.  It  extends  from  the  symphysis  to  the  third  or  fourth  lower  cheek  tooth. 
Its  length  is  about  five  or  six  inches  (ca.  12  to  15  cm.)  anil  its  weight  about  half  an 
ounce  (ca.  15  to  16  g.). 

It  is  flattened  laterally,  and  has  a  thin  upper  border  which  causes  an  elevation 
of  the  mucous  membrane  of  the  floor  of  the  mouth,  termed  the  sublingual  crest 
(Plica  sulilingualis).  The  external  surface  is  related  to  the  mylo-hyoideus  muscle, 
anil  the  internal  surface  to  the  genio-glossus  and  stylo-glossus,  the  submaxillary 
duct,  and  branches  of  the  lingual  nerve.  The  inferior  border  is  related  to  the  genio- 
hyoid muscle. 

The  sublingual  ducts  (Ductus  sublinguales  minores),  about  thirty  in  number, 
are  small,  short,  and  twisted;   they  open  on  small  papillte  on  the  sublingual  crest. 

Blood-supply. — .Sublingual  artery. 

Nerve-supply. — Trigeminal  and  sympathetic  nerves. 


THE  PHARYNX 

The  ]5harynx  is  a  musculo-membranous  sac  which  belongs  to  the  digestive  and 
respiratory  tracts  in  common.  It  is  funnel-shaped,  the  base  joining  the  mouth 
and  nasal  cavity,  while  the  apex  is  continued  by  the  oesophagus.  Its  long  axis 
is  directed  obliquely  downward  anil  backward,  and  has  a  length  of  about  six  inches 
(ca.  15  cm.). 

The  pharynx  is  attached  by  its  muscles  to  the  palate,  pterygoid,  and  hyoid 
bones,  and  to  the  cricoid  and  thyroid  cartilages  of  the  larynx. 

Its  principal  relations  are:  dorsally,  the  base  of  the  cranium  and  the  guttural 
pouches;  ventrally,  the  larynx;  laterally,  the  internal  pterygoid  muscle,  the  great 
cornu  of  the  hyoid  bone,  the  internal  and  external  maxillary  arteries,  the  glosso- 
pharyngeal, superior  laryngeal,  and  hypoglossal  nerves,  the  submaxillary  salivary 
gland,  and  the  jjharyngeal  lymph  glands. 

It  presents  seven  openings.  The  posterior  nares  (Choance)  communicate 
dorsally  with  the  nasal  chaniljers.  The  ])haryngeal  orifices  (Ostia  pharyngea)  of 
the  two  Eustachian  tubes  are  situated  on  the  lateral  wall  behind  the  nares  and  a  little 
below  the  level  of  the  inferior  nasal  meatus.  They  are  slit-like  openings,  slightly 
oblique  downward  and  backward,  and  are  a  little  more  than  an  inch  (ca.  3  cm.)  in 
length.  They  are  bounded  internally  l^iy  a  valvular  flap  formeil  by  the  expanded 
extremity  of  the  cartilaginous  Eustachian  tul)e.  Th(>  isthmus  faucium  is  situated 
below  and  in  front.  It  is  clo.sed  by  the  soft  palate  exceiit  during  swallowing.  The 
laryngeal  orifice  (Aditus  laryngis)  occu])ies  the  greater  part  of  tlie  ventral  wall  or 
floor  of  the  pharynx.     Behind  this  is  the  oesophageal  opening. 

The  wall  of  the  pharynx  comprises  from  without  inward:  the  muscles,  the 
pharyngeal  aponeurosis,   and  the  mucous  membrane. 

The  muscles  (Figs.  243,  244)  are  covered  by  the  pharyngeal  fascia,  which  is 


THE    PHARYNX 


349 


attached  to  the  base  of  the  skull,  the  great  cornu  of  the  hyoid  bone,  and  the 
thyroid  cartilage  of  the  larynx.     Thej-  are  as  follows: 

1.  The  stylo-pharyngeus  arises  from  the  inner  surface  of  the  dorsal  third  of  the 
great  cornu  of  the  hyoid  bone,  passes  downward  and  inward,  and  enters  the  wall  of 
the  pharynx  bj'  passing  between  the  iiterygo-pharyngeus  and  palato-pharyngeus. 
Its  fibers  radiate,  many  passing  forward,  others  inward  lieneath  the  hj-o-pharj-ngeus. 
It  raises  and  dilates  the  pharynx  to  receive  the  bolus  in  swallowing. 


Fig.  254 — Posterior  Part 


Left  ' 


.  Section  of  Head  of  Horse,  Cut  about  1  cm.  to 
Median  Plane. 

/,  Posterior  nares;  2,  phar\-ngeal  orifice  of  Eustachian  tube;  3,  aditus  Jaryngis;  4>  entrance  to  cesophagus; 
6,  posterior  pillar  of  soft  palate;  o' ,  junction  of  -5  with  its  fellow  over  entrance  to  oesophagus;  6,  einglottis;  7,  body 
of  thyroid  cartilage;  5,  arytenoid  cartilage:  5.  9,  cricoid  cartilage;  10,  true  vocal  cord;  II,  false  vocal  cord;  12, 
lateral  ventricle  of  larynx;  13,  crico-arytenoideus  post.  s.  dorsalis;  14,  ce3ophagU':j;  15.  external  carotid  artery;  10, 
hypoglossal  nerve;  77,  giosso-phar>-ngeal  nerve;  18,  great  cornu  of  hyoid  bone;  19,  Eustachian  tube;  J?0,  body  of 
hyoid  bone;  21,  hyoideus  transversus;  23,  ridges  of  hard  palate;  22',  soft  palate;  23,  septum  between  frontal 
sinuses;  24,  olfactory  mucous  membrane;  25,  sphenoidal  sinus;  26,  basilar  part  of  occipital  bone;  26',  supra- 
occipital;  27,  body  of  sphenoid  bone;  2S,  pituitary  body;  2S,  chiasma  opticum;  30,  corpora  quadrigemina;  31 , 
thalamus;  3^,  arachnoid;  JJ.  oJontoid  ligament;   34,  posterior  auricular  muscles. 


2.  The  palato-pharyngeus  arises  by  means  of  the  aponeurosis  of  the  soft 
palate  from  the  palate  and  pterygoid  hones.  Its  fibers  pass  backward  on  the  lateral 
wall  of  the  pharynx,  and  are  inserted  in  part  into  the  upper  edge  of  the  thyroid 
cartilage,  in  part  turn  inward  to  end  at  the  median  fibrous  raphe.  Its  action  is  to 
shorten  the  phar^'nx,  and  to  draw  the  larynx  and  oesophagus  toward  the  root  of  the 
tongue  in  swallowino;. 

3.  The  pterygo-phar5Tigeus  is  flat  and  triangular.  It  lies  on  the  anterior  part 
of  the  lateral  wall  of  the  pharj-nx.     It  arises  from  the  pterygoid  bone  above  the 


350  DIGESTIVE    SYSTEM    OF    THE    HORSE 

preceding  muscle — from  which  it  is  not  distinctly  separated — crosses  the  levator 
palati,  and  is  inserted  into  the  median  raphe.    Its  action  is  similar  to  the  preceding. 

4.  The  hyo-pharyngeus  may  consist  of  two  portions: 

(n)  The  kerato-pharyngeus  is  a  small  and  inconstant  muscle  which  arises 
from  the  inner  surface  of  the  great  cornu  of  the  hyoid  bone  near  its  lower  end. 
It  passes  upward  and  hackwaril,  turns  inward  toward  the  raphe,  and  spreads  out 
under  the  next  muscle. 

(h)  The  chondro-pharyngeus,  broad  and  fleshy,  arises  from  the  thyroid  cornu 
of  the  hyoid  bone  and  by  a  thin  fasciculus  from  the  wing  of  the  thyroid  cartilage  and 
ends  at  the  median  rajihe. 

5.  The  thyro-pharyngeus  arises  from  the  lateral  surface  of  the  wing  of  the 
thyroid  cartilage.     Its  fil)ers  pass  forward  and  inward  to  the  median  raphe. 

6.  The  crico-pharyngeus  arises  from  the  cricoid  cartilage  and  ends  at  the 
raph6.  The  fibers  are  directed  upward,  forward,  and  inward;  they  blend  behind 
with  the  longitudinal  fil)crs  of  the  oesophagus. 

The  last  three  muscles  are  constrictors  of  the  pharj'nx. 

The  phar3mgeal  aponeurosis  is  attached  to  the  base  of  the  cranium.  It  is 
well  developetl  on  the  inner  face  of  the  palato-pharyngeus  muscle  and  forms  a 
median  raphe  (Raphe  ]ihar.yngis)  dorsally,  which  is  wide  in  its  posterior  part. 

The  mucous  membrane  of  the  pharynx  is  continuous  with  that  of  the  several 
cavities  which  ojicn  into  it.  It  is  thin  and  closely  adherent  to  the  base  of  the  skull 
in  the  vicinity  of  the  posterior  nares,  where  the  muscular  wall  is  absent.  Behind 
the  Eustachian  openings  is  a  median  cul-de-sac,  the  pharyngeal  recess.  The  recess 
is  somewhat  variable,  but  is  usually  about  an  inch  in  depth  and  will  admit  the  end 
of  the  finger.  In  the  ass  and  mule  it  is  much  deeper.  Here  also  the  muscular 
wall  is  absent  and  the  mucous  membrane  lies  against  the  guttin-al  pouches.  From 
the  Eustachian  opening  a  fold  of  the  mucous  membrane  (Plica  salpingo-pharyngea) 
passes  toward  but  docs  not  reach  the  laryngeal  opening.  Below,  a  horizontal  folil, 
the  posterior  pillar  of  the  soft  palate  (Arcus  pharyngo-palatinus),  passes  along  the 
lateral  wall  and  unites  with  its  fellow  over  the  entrance  to  the  oesophagus.  The 
upper  part  of  the  cavity  (the  naso-pharynx)  is  lined  with  a  ciliated  epithelium, 
while  the  lower  part  (oro-pharynx)  has  a  stratified  squamous  epithelium.  The 
communication  between  the  two  is  oval  and  is  lioun<led  l)y  the  free  edge  of  the  soft 
palate  and  its  posterior  pillars ;  it  is  termed  the  pharyngeal  isthmus.  On  either  side 
of  the  laryngeal  opening  is  a  narrow  deep  depression,  the  pyriform  sinus  (Recessus 
piriformis). 

The  submucous  tissue  contains  numerous  mucous  glands  (Glandulse  pharyn- 
geifi).  In  the  young  sul>ject  the  lymph  follicles  are  numerous  and  form  a  collection 
dorsally  and  between  the  Eustachian  openings,  known  as  the  pharyngeal  tonsil. 

Blood-supply. — External  carotid,  external  maxillary,  and  thyro-laryngeal 
arteries. 

Nerve-supply. — Glosso-pharyngeal,  vagus,  and  symj^athetic  nerves. 


THE  (ESOPHAGUS 
The  oesophagus  is  a  musculo-membranous  tube,  about  50  to  60  inches  (ca. 
125  to  150  cm.)  in  length,  which  extends  from  the  pharynx  to  the  stomach.  It 
begins  in  the  median  plane  above  the  cricoid  cartilage  of  the  larynx.  In  its  course 
it  shows  several  changes  of  direction.  At  the  level  of  the  fourth  cervical  vertebra 
it  inclines  to  the  left  sitle  of  the  trachea,  and  continues  this  relation  to  the  level  of 
the  third  thoracic  vertebra.  Here  it  again  gains  the  dorsal  surface  of  the  trachea, 
and  passing  backward,  crosses  the  left  bronchus,  being  here  almost  in  the  median 
plane.  It  continues  in  the  metliastinum  between  the  lungs  backward,  upward, 
and  a  little  to  the  left,  to  reach  the  hiatus  a'sophageus  of  the  diaphragm.     Passing 


THE    (ESOPHAGUS 


351 


through  this  it  terminates  at  once  at  the  cardiac  orifice  of  the  stomach,  at  the  level 
of  the  fourteenth  thoracic  vertebra,  a  little  to  the  left  of  the  median  plane,  and 
about  four  or  five  inches  (ca.  10  to  12  cm.)  ventral  to  the  vertebral  column. 

\'ie\ved  with  reference  to  the  frontal  plane,  its  course  is  downward  and  l:)ack 
ward  till  it  enters  the  thorax  and  passes  upward  to  gain  the  dorsal  faceof  the  trachea. 
For  a  short  distance  {i.  e.,  to  the  root  of  the  lung)  its  direction  is  almost  horizontal; 


Temporal  muscle 


Thyroid  cornu  of 
hyoid  bone 


Parotid  duct 


Lynipli  gland 


Coronoid  process 


Transverse  fa- 
cial vessels 
Transrerse  fa- 
cial nerve 
External  ptery- 
goid muscle 

Internal  max- 
illary vein 
Internal  ptery- 
goid muscle 
Ramus  of 
miiiidilile 
Hyo-pliaryn- 
geus  muscle 
Isthmus  fau- 
ciutn 
Tmsil 
Dii/iislrirus 
{intirmal.  ten- 
don) 

Anterior  end  of 
submaxillary 
gland 

Lingual  vein 

External  max- 
illary vein 


Fig.  255. — Cross-section  of  Head  of  Horse. 
The  section  passes  through  the  temporo-mandibular  articulation,  but  is  slightly  oblique.     1.  Corpus  cal- 
losum;  .?,  lateral  ventricle  of  brain;  .?,  caudate  nucleus;  ^.  internal  capsule;  .5,  lenticular  nucleus;  5.  optic  chiasma; 
7,  middle  cerebral  artery;   8,  sphenoidal  sinuses;   9,  cavernous  sinus;    10,  Eustachian  tube,  inner  lamina;     11,  11, 
guttural  pouches;    12.  soft  palate;    13,  epiglottis;    14,  hyo-epiglottic  muscle;    15,  thyro-hyoid  muscle. 


behind  this  it  passes  somewhat  upward  to  its  termination.  The  cervical  part  of 
the  tube  is  about  four  to  six  inches  (10  to  15  cm.)  longer  than  the  thoracic  part, 
while  the  so-called  abdominal  part  is  about  an  inch  (2  to  3  cm.)  long.' 

•  Careful  observations  (especially  on  frozen  subjects  and  those  in  which  the  organs  have  been 
hardened  in  situ)  show  that  there  is  no  abdominal  part  of  the  oesophagus  in  the  strict  sense  of  the 
term.  The  stomach  here  lies  directly  on  the  diaphragm,  so  that  the  last  inch  or  so  of  the  oesopha- 
gus is  placed  obliquely  in  the  liiatus  a'sophageiis,  and  is  partly  co\'ered  by  the  pleura,  but  not  by 
peritoneum.  In  soft  subjects  the  weight  of  the  stomach,  or  traction  on  it,  draws  part  of  the 
oesophagus  into  the  abdomen,  inclosed  in  a  collar  of  peritoneum. 


352  DIGESTIVE    SYSTEM    OF   THE    HORSE 

The  principal  relations  of  the  oesophagus  at  its  origin  are:  to  the  cricoid 
cartilage  below;  to  the  guttural  pouches  and  the  ventral  straight  muscles  above; 
and  to  the  carotid  arteries  laterally.  In  the  middle  of  the  neck  the  relations  are: 
to  the  left  longus  colli  muscle  above;  to  the  trachea  internally;  to  the  left  carotid 
artery,  vagus,  sympathetic,  and  recurrent  nerves  externally.  At  its  entrance 
into  the  thorax  it  has  the  trachea  on  its  inner  side;  the  first  rib,  the  roots  of  the 
brachial  plexus  of  nerves  and  the  inferior  cervical  ganglion  externally.  After 
gaining  the  upper  surface  of  the  trachea,  it  has  the  aorta  on  its  left  and  the  vena 
azygos  and  right  vagus  nerve  on  its  right  side.  In  its  course  through  the  posterior 
mediastinum  the  oesophageal  trunks  of  the  vagus  nerves  lie  above  and  below  it, 
and  the  o'sojihageal  artery  is  dorsal  to  it. 

Structure. — The  wall  is  composed  of  four  coats:  (1)  A  fibrous  sheath;  (2)  the 
muscular  coat;  (3)  a  submucous  layer;  (4)  the  mucous  membrane.  The  muscular 
coat  is  of  the  striped  variety  as  far  as  the  base  of  the  heart,  where  it  rapidly  changes 
to  the  unstriped  type.  In  addition  to  this  change,  the  muscular  coat  becomes 
much  thicker  and  firmer,  while  the  lumen  is  diminished.'  The  outer  fibers  are 
arranged  longitudinally,  beginning  in  two  bundles  attached  in  the  interval  be- 
tween the  arytenoid  and  cricoid  cartilages.  The  inner  fibers  run  in  two  sjjiral 
strata  to  the  terminal  part  of  the  tulje,  where  the  arrangement  is  an  outer  longi- 
tudinal and  an  inner  circular  layer.-  The  mucous  membrane  is  pale,  and  is  covered 
with  squamous  stratified  epithelium.  It  is  loosely  attached  to  the  muscular  coat 
by  an  abundant  submucosa,  and  lies  in  longitudinal  folds  which  obliterate  the  lumen 
except  during  deglutition. 

Blood-supply. — Carotid,  broncho-oesojihageal,  and  gastric  arteries. 

Nerve-supply. — Vagus,  glosso-pharyngeal,  and  sympathetic  nerves. 


THE  ABDOMINAL  CAVITY 

The  abdominal  cavity  (Cavum  abdominis)  is  the  largest  of  the  body  cavities. 
It  is  separated  from  the  thoracic  cavity  by  the  diaphragm  and  is  continuous  behind 
with  the  pelvic  cavity. 

It  is  ovoid  in  form  but  somewhat  compressed  laterally.  Its  long  axis  extends 
obliquely  from  the  center  of  the  pelvic  inlet  to  the  sternal  part  of  the  diaphragm. 
Its  dorso-ventral  diameter  is  greatest  at  the  first  lumbar  vertebra,  while  its  greatest 
transverse  diameter  is  a  little  nearer  the  pelvis. 

The  dorsal  wall  or  roof  is  formed  by  the  lumbar  vertebrae,  the  lumbar  muscles, 
and  the  lumlmr  part  of  the  diaphragm. 

The  lateral  walls  are  formed  by  the  oblique  and  transverse  abdominal  muscles, 
the  abdominal  tunic,  the  anterior  parts  of  the  ilia,  the  cartilages  of  the  asternal 
ribs,  and  the  parts  of  the  posterior  ribs  which  are  below  the  attachment  of  the  dia- 
phragm. 

The  ventral  wall  or  floor  consists  of  the  two  recti,  the  aponeuroses  of  the  oblique 
and  transverse  muscles,  the  abdominal  tunic,  and  the  xiphoid  cartilage. 

The  anterior  wall  is  formed  by  the  diaphragm,  which  is  very  deeply  concave, 
thus  greatly  increasing  the  size  of  the  abdomen  at  the  expense  of  the  thorax. 

It  should  be  noted  that  the  diaphragm  also  concurs  practically  in  the  formation  of  a  con- 
siderable part  of  the  lateral  walls,  since  its  costal  portion  even  during  ordinary  inspiration  lies 
directly  on  the  ribs  over  a  width  of  four  or  five  inches  (ca.  10  to  12  cm.);  in  expiration  this  area 

'  The  potential  lumen  is  difficult  to  determine  at  all  accurately.  When  distended,  its  diam- 
eter (according  to  RubcH)  \-aries  from  .5.7  cm.  at  its  origin  to  4  cm.  at  its  cardiac  end.  The 
thickness  of  tlic  wall  varies  (inversely  as  the  lumen)  from  4  mm.  to  1.2  cm.  or  more. 

-  At  the  origin  of  the  tube  muscular  bundles  arise  on  the  raphe  pharyngis  and  blend  with  the 
crico-pharyngcus.  Vcntrally  fibers  come  from  the  depression  l)ctween  the  cricoid  and  arytenoid 
cartilages.  Bundles  of  striped  fibers  may  be  continued  in  the  superficial  part  of  the  muscular 
coat  as  far  as  the  cardia. 


THE    PERITONEUM  353 

of  cont;ict  would  be  aliout  twice  as  wide,  including  about  all  of  the  fleshy  rim.  This  fact  is  of 
clinical  importance,  with  reference  to  auscultation  and  percussion,  and  penetrating  wounds. 
The  cupola  of  the  diaphragm  extends  as  far  forward  as  a  plane  through  the  sixth  intercostal 
space  to  the  right  of  the  heart. 

There  is  no  wall  between  the  abdominal  and  pelvic  cavitie.s.  The  line  of  de- 
marcation here  is  the  terminal  line  (Linea  terminalis)  or  brim  of  the  pelvis;  it  is 
formed  by  the  base  of  the  sacnini,  the  ilio-pectineai  lines,  and  the  anterior  borders 
of  the  pnbic  bones. 

The  muscular  walls  are  lined  by  a  layer  of  fascia,  distinguished  in  different 
parts  as:  (1)  the  diaphragmatic  fascia;  (2)  the  transversalis  fascia;  (3)  the  iliac 
fascia;    (4)  the  deep  layer  of  the  lumbo-dorsal  fascia. 

The  subperitoneal  or  extraperitoneal  connective  tissue  (Tela  subserosa)  unites 
the  fascia  and  peritoneum.  It  is  composed  of  areolar  tissue,  more  or  less  loaded 
with  fat  according  to  the  condition  of  the  subject,  except  over  the  diaphragm.  It 
sends  laminse  into  the  various  peritoneal  folds. 

The  peritoneum,  the  serous  membrane  which  lines  the  cavity,  will  lie  tlescribed 
later. 

The  abdominal  walls  are  pierced  in  the  adult  In'  five  apertures.  These  are: 
the  three  openings  in  the  diaphragm  which  transmit  the  aorta,  posterior  vena  cava, 
and  the  oesophagus;  the  inguinal  canals,  which  contain  the  spermatic  cord  or  the 
round  ligament  (in  female  carnivora).  In  the  fa'tus  there  is  the  umbilical  opening 
also. 

The  cavity  contains  the  greater  part  of  the  digestive  and  urinar\^  organs,  part 
of  the  internal  generative  organs,  numerous  nerves,  blood-vessels,  lymph  vessels  and 
glands,  ductless  glands  (spleen  and  adrenal  bodies),  and  certain  foetal  remains. 

For  topographic  purposes  the  abdomen  is  divided  into  nine  regions  by  imagin- 
ary planes.'  Two  of  these  planes  are  sagittal,  and  two  are  transverse.  The 
sagittal  planes  cut  the  middles  of  the  inguinal  (Poupart's)  ligaments;  the  transverse 
planes  pass  through  the  last  thoracic  and  fifth  lumbar  vertebra,  or  the  lower  end 
of  the  fifteenth  ril)  and  the  external  angle  of  the  ilium  respectively.  The  transverse 
planes  divide  the  abdomen  into  three  zones,  one  behind  the  other,  viz.,  epigastric, 
mesogastric,  and  hypogastric:  these  are  subdivided  by  the  sagittal  planes  as  in- 
dicated in  the  subjoined  table. 

Left  parachondriac Xiphoid Right  parachondriac 

Left  lumbar Umbilical Right  lumbar 

Left  iliac Prepubic . .'. Right  iUac. 

Other  useful  regional  terms  are:  sublumbar,  diaphragmatic,  inguinal.  The 
first  two  require  no  explanation.  The  inguinal  regions  (right  and  left)  lie  in  front 
of  the  inguinal  (Poupart's)  ligament.  The  flank  is  that  part  of  the  lateral  wall 
which  is  formed  only  of  soft  structures.  The  depression  on  its  upper  part  is  termed 
the  paralumbar  fossa. 

THE  PERITONEUM = 
The  peritoneum  is  the  thin  serous  membrane  which  lines  the  abdominal  and 
(in  part)  the  pelvic  cavity,  and  covers  to  a  greater  or  less  extent  the  viscera  con- 
tained therein.  In  the  male  it  is  a  completely  closed  sac,  but  in  the  female  there 
are  two  small  openings  in  it;  these  are  the  abdominal  orifices  of  the  Fallopian  tubes, 
which  at  their  other  ends  communicate  with  the  uterus,  and  so  indirectly  with  the 
exterior.     The  peritoneal  cavity  is  only  a  potential  one,  since  its  opposing  walls 

'  This  method  of  di\dsion,  although  long  in  use,  is  of  very  little  value  for  accurate  descrip- 
tion. It  is  mentioned  here  chiefly  because  agreement  on  a  more  useful  topographic  method  has 
not  been  arrived  at. 

-  Only  a  general  account  of  the  arrangement  of  the  peritoneum  is  given  in  this  section,  since 
a,  detailed  tiescription  cannot  be  understood  without  a  knowledge  of  the  viscera  concerned. 
23 


354  DIGESTIVE    SYSTEM    OF   THE    HORSE 

are  normally  separated  only  by  the  thin  film  of  serous  fluid  (secreted  by  the  mem- 
brane) which  acts  as  a  lubricant. 

The  free  surface  of  the  membrane  has  a  glistening  appearance  and  is  very 
smooth.  This  is  due  to  the  fact  that  this  surface  is  formed  by  a  layer  of  flat  en- 
dothelial cells,  and  is  moistened  by  the  peritoneal  fluid.  Friction  is  thus  reduced 
to  a  minimum  during  the  movements  of  the  viscera.  The  outer  surface  of  the  jieri- 
toneum  is  related  to  the  subperitoneal  tissue,  which  attaches  it  to  the  abdominal 
wall  or  the  viscera. 

In  order  to  understand  the  general  disposition  of  the  peritoneum,  w^e  may 
imagine  the  abdominal  cavity  to  be  empty  and  lined  by  a  simple  layer  of  perito- 
neum, termed  the  parietal  layer  (Lamina  parietalis).  We  may  regard  the  organs  as 
beginning  to  develoii  in  the  subperitoneal  tissue,  enlarging,  and  migrating  into  the 
cavity  to  a  varying  extent.  In  doing  so  they  carry  the  peritoneum  before  them, 
producing  introversion  of  the  simple  sac,  and  forming  folds  which  connect  them 
with  the  wall  or  with  each  other.  The  viscera  thus  receive  a  more  or  less  complete 
covering  of  peritoneum,  termed  the  visceral  layer  (Lamina  visceralis).  The  con- 
necting folds  are  termed  omenta,  mesenteries,  ligaments,  etc.  They  contain  a 
varying  quantity  of  connective  tissue,  fat  and  lymph  glands,  and  furnish  a  path  for 
the  vessels  and  nerves  of  the  viscera.  Some  contain  unstriped  muscular  tissue.  An 
omentum  is  a  fold  which  passes  from  the  stomach  to  other  viscera.  There  are  three 
of  these,  namely:  (1)  the  small  or  gastro-hepatic  omentum  (Omentum  minus),  which 
passes  from  the  lesser  curvature  of  the  .stomach  to  the  liver;  (2)  the  gastro-splenic 
omentum  (Ligamentum  gastrolienale),  which  extends  from  the  greater  cur\atia'e 
of  the  stomach  to  the  spleen;  (3)  the  great  omentum  (Omentum  majus),  which 
passes  from  the  greater  curvature  of  the  stomach  and  from  the  spleen  to  the  terminal 
part  of  the  great  colon  and  the  origin  of  the  small  colon.  It  does  not  pass  directly 
from  one  organ  to  the  other,  but  forms  an  cxtcn.sive  loose  sac  (Figs.  278,  279). 
A  mesentery  (Mesenterium)  is  a  fold  which  attaches  the  intestine  to  the  dorsal 
wall  of  the  abdomen.  There  are  two  mesenteries,  namely:  (1)  the  great  mesentery 
which  connects  the  greater  part  of  the  small  intestine  with  the  dorsal  abdominal 
wall;  (2)  the  colic  mesentery,  which  attaches  the  small  colon  to  the  dorsal  abdom- 
inal wall.  Ligaments  are  folds  which  pass  between  viscera  other  than  parts  of  the 
digestive  tube,  or  connect  them  with  the  abdominal  wall.  The  term  is  also  applied 
to  folds  which  attach  parts  of  the  digestive  tract  to  the  abdominal  wall,  but  do  not 
contain  their  blood-vessels  and  nerves.  In  some  cases  (e.  g.,  the  lateral  and  cor- 
onary ligaments  of  the  liver)  they  are  strengthened  by  fibrous  tissue ;  in  other  cases 
(e.  g.,  the  broad  ligaments  of  the  uterus)  they  contain  also  unstriped  muscular  tissue. 


THE  PELVIC  CAVITY 

The  pelvis  is  the  posterior  part  of  the  trunk.  It  incloses  the  pelvic  cavity 
(Cavum  pelvis),  which  communicates  in  front  with  the  abdominal  cavity,  the  line 
of  demarcation  being  the  pelvic  brim  or  terminal  line. 

The  dorsal  wall  or  roof  is  formed  by  the  sacrum  and  first  three  coccygeal 
vertebrfe.  The  lateral  walls  are  formed  by  the  parts  of  the  ilia  behind  the  ilio- 
pectineal  lines  and  the  sacro-sciatic  ligaments.  The  ventral  wall  or  floor  is  formed 
by  the  pubic  and  ischial  bones.  The  boundary  of  the  outlet  is  formed  by  the  third 
coccygeal  vertebra  dorsally,  the  ischial  arch  ventrally,  and  the  posterior  edges  of 
the  sacro-sciatic  ligaments  and  the  semimembranosus  muscles  laterally.  The  out- 
let is  closed  by  the  perineal  fascia;  this  consists  of  superficial  and  deep  layers, 
which  are  attached  around  the  margin  of  the  outlet  and  centrally  to  the  organs  at 
the  outlet — the  anus  and  its  muscles,  the  vulva  (in  the  female),  and  the  root  of  the 
penis  (in  the  male). 

The  cavity  contains  the  rectum,  parts  of  the  internal  generative  and  urinary 


THE    PELVIC    CAVITY 


355 


organs,    some   foetal   remnants,    muscles,   vessel; 
the  fascia  pelvis,  and  in  part  by  the  peri- 
toneum. 

The  pelvic  peritoneum  is  continuous  in 
front  witli  tiiat  of  the  abdomen.  It  lines 
the  cavity  as  far  back  as  the  third  or  fourth 
sacral  vertebra  in  the  horse,  where  it  is  re- 
fleeted  on  to  the  viscera,  and  from  one  organ 
to  another.  We  may  therefore  distinguish 
an  anterior,  peritoneal,  and  a  posterior,  re- 
troperitoneal part  of  the  cavity.  Along  the 
mid-dorsal  line  it  forms  a  continuation  of 
the  colic  mesentery,  the  mesorectum,  which 
attaches  the  first  or  jjeritoneal  part  of  the 
rectum  to  the  roof.  In  animals  in  fair  con- 
dition a  considerable  quantity  of  subperi- 
toneal and  retroperitoneal  fat  is  found  on 
the  walls  and  in  the  various  interstices. 

In  the  male  the  general  disposition  of 
the  peritoneum  here  is  as  follows.  If 
traced  along  the  dorsal  wall,  it  is  re- 
flected at  the  third  or  fourth  sacral  verte- 
bra on  to  the  rectum,  forming  the  visceral 
peritoneum  for  the  first  part  of  that  tube. 
Laterally  it  is  reflected  in  a  similar  fashion. 


s,    and   nerves.      It   is   lined   by 


\M    OF  Sagittal  Section   of 
TO    SHOW   Disposition   of 


a.  Pouch  between  rectum  and  roof  of  cavity, 
continuous  laterally  with  6,  recto-genital  pouch; 
c,  vesico-genital  pouch;  d,  pouch  below  blaiUler 
and  its  lateral  ligaments.  The  lateral  line  of  re- 
flection of  the  peritoneum  is  dotted.  The  area 
of  rectum  covered  by  i)eritoneum  varies  widely. 
When  the  rectum  is  empty,  the  reflection  dorsally 
may  be  at  the  posterior  end  of  the  sacrum;  when 
the  rectum  is  very  full,  the  reflection  may  occur  a 
short  distance  behind  the  promontory. 


If  the  rectum  be  raised,  it  will  be  seen 


Fig.  257 


Ho 


[N  M.ale; 


-Schematic  Cross-sections  to  show  Arrangement  of  Pelvic  Peritone 
B,  IN  Female. 
.1;  a,  b.  Recto-genital  pouch;    c,  c,  vesico-genital  pouch;  d,  d,  pouch  below  bladder  and  its  lateral  ligaments; 
1,  mesorectum;    2,  2,  urogenital  fold;  3,  S.  lateral.  4,  median  ligaments  of  bladder;  r.  d.,  vas  deferens;  u   m.,  uterus 
mascuUnus.     B:    a,  b,  recto-genital  pouch;    c,  c,  vesico-genital  pouch;    d,  d,  pouch  below  bladder  and  its  lateral 
ligaments;    7,  mesorectum;  2,  g,  broad  ligaments  of  uterus;  S,  3,  lateral.  .4,  median  ligaments  of  bladder. 


that  the  peritoneum  passes  from  its  ventral  surface  and  forms  a  transverse  fold 
which  hes  on  the  dorsal  surface  of  the  bladder  (Fig.  272).     This  is  the  urogenital 


356 


DIGESTIVE    SYSTEM    OF   THE    HOHSE 


fold  (Plica  urogenitalis).  Its  concave  free  edge  passes  on  either  side  into  the  in- 
guinal canal.  The  ventral  layer  of  this  fold  is  reflected  on  to  the  dorsal  surface 
of  the  bladder  near  its  neck.  Thus  there  is  formed  a  pouch  between  the  rectum 
and  bladder — the  recto-vesical  pouch  (Excavatio  recto-vesicalis),  which  is  partially 
subdivided  by  the  urogenital  fold  into  recto-genital  and  vesico-genital  cavities. 
The  fold  contains  the  vasa  deferentia,  part  of  the  vesiculse  seminales,  and  the 
uterus  masculinus  (a  fcetal  remnant).  The  space  on  either  side  of  the  rectum  is 
occupied  by  coils  of  the  small  colon  and  the  pelvic  flexure  of  the  great  colon  usually. 
If  the  bladder  is  now  raised,  it  is  seen  that  the  peritoneum  passes  from  its  ventral 
surface  on  to  the  pelvic  floor,  forming  a  median  fold,  the  so-called  middle  ligament 
(Plica  umbilicalis  media).     It  also  forms  on  each  side  a  lateral  fold,  the  lateral 


Saccus  cwciis  {left  cxlrcmily) 


Area  of  attachment  to  dia- 
phragm {non-peritoneal) 


Fig.  25S. — Stomach  of 
Fixerl  in  situ  when  full  liut  not  ilisi 


P.vRiET.\L  Surface, 
The  larger  branches  of  the 
veins  are  shown. 


First  Part  of  Duodenum. 
anterior  gastric  artery  with  two  satellite 


ligament  (Plica  umbilicalis  lateralis),  which  contains  in  its  edge  the  so-called  round 
ligament  ( Ligamentum  teres) — the  partially  occluded  umbilical  artery,  which  is  a 
large  vessel  in  the  foetus. 

In  the  female  the  arrangement  is  motlified  liy  the  i)resence  of  the  uterus; 
the  urogenital  fold  is  very  large,  so  as  to  inclose  the  uterus  and  a  small  jiart  of  the 
vagina.  It  forms  two  extensive  folds,  th(>  broad  ligaments  of  the  uterus  (Liga- 
menta  lata  uteri),  which  attach  that  organ  to  the  sides  of  the  pelvic  cavity  and  the 
lumbar  part  of  the  abdominal  wall  (Fig.  271).  It  thus  divides  the  recto-vesical 
pouch  completely  into  dorsal  and  ventral  compartments — the  recto-genital  pouch 
(Excavatio  recto-uteriiia),  and  the  vesico-genital  jiouch  (Excavatio  vesico-uterina). 

Further  details  will  be  given  in  the  tlescription  of  the  pelvic  viscera. 


THE    STOMACH 


357 


THE  STOMACH 
The  stomach  (Ventriculus)  is  the  hir^e  dilatation  of  the  ahmentary  canal  be- 
tween the  a'sophagus  antl  the  small  intestine.  It  is  a  sharply  curved,  U-shaped 
sac,  the  right  branch  being,  however,  much  shorter  than  the  left  one.  The  con- 
vexity is  directeil  ventrally.  When  moderately  distended,  there  is  often  a  slight 
constriction  which  intlicatcs  the  division  into  right  and  left  sacs.  It  is  relatively 
small,  and  is  situated  in  the  dorsal  part  of  the  abdominal  cavity  behind  the  dia- 
phragm and  liver,  mainly  to  the  left  of  the  median  plane. 


Area  of  attachment  to  dia- 
phragm (non-peritoneal) 


Fig.  259. — Stomach  of  Horse,  Visceral  Surface,  with  First  Part  of  Duodenum. 
I  situ  when  full  but  not  distended.     The  posterior  ga.stric  artery  and  its  larger  branches  with  two  satelUte 
veins  are  shown. 


It  presents  for  description  two  surfaces,  two  curvatures,  and  two  extremities. 
The  parietal  surface  (Fades  parietalis)  is  convex  and  is  directed  forward,  upward, 
and  toward  the  left;  it  lies  against  the  diaphragm  and  liver.  The  visceral  surface 
(Facies  visceralis),  also  convex,  faces  in  the  opposite  direction;  it  is  related  to  the 
terminal  part  of  the  large  colon,  the  pancreas,  the  small  colon,  and  the  small  in- 
testine. The  lesser  curvature  (Curvatura  minor)  is  very  short,  extending  from  the 
termination  of  the  a'sophagus  to  the  junction  with  the  small  intestine.  When 
the  stomach  is  in  situ,  its  walls  are  here  in  contact,  and  the  cardia  and  pylorus 
close  together.  The  greater  curvature  (Curvatura  major)  is  very  extensive.  From 
the  cardia  it  is  first  directed  upward  and  curves  over  the  left  extremity;  it  then 
descends,  passes  to  the  right,  crosses  the  median  plane,  and  curves  upward  to  end 
at  the  pylorus.  Its  left  portion  is  related  to  the  spleen,  while  its  ventral  portion 
rests  on  the  left  divisions  of  the  great  colon.  The  left  extremity  or  saccus  caecus 
is  a  rounded  cul-de-sac  which  lies  under  the  upper  ends  of  the  fourteenth,  fifteenth. 


358 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


and  sixteenth  ribs  and  the  diaphragm.'  It  is  rehited  to  the  pancreas  behinfl  and 
the  base  of  the  spleen  externally.  The  right  or  pyloric  extremity  is  much  smaller 
and  is  continuous  with  the  duodenum,  the  junction  being  indicated  by  a  marked 
constriction.  It  lies  on  the  liver,  a  little  to  the  right  of  the  median  plane,  and  a 
little  lower  than  the  cardiac  opening.  About  two  or  three  inches  (ca.  5  to  8  cm.) 
from  the  pylorus  there  is  a  constriction  which  marks  off  the  antrum  pylori  from  the 
rest  of  the  right  sac.  The  oesophageal  orifice  or  cardia  is  situated  at  the  left  ex- 
tremity of  the  lesser  curvature,  but  aljout  eight  to  ten  inches  (ca.  20  to  25  cm.) 
from  the  left  extremity.  The  oesophagus  joins  the  stomach  very  obliquely.  The 
opening  is  closed  by  the  sphincter  cardiiE  and  numerous  folds  of  mucous  membrane. 
The  pyloric  orifice  communicates  with  the  duodenum.  Its  position  is  indicated 
externally  by  a  distinct  constriction.  Internally  it  presents  a  circular  ridge  pro- 
duced by  a  ring  of  muscular  tissue — 
the  sphincter  pylori. 

The  stomach  is  held  in  position 
mainly  by  the  pressure  of  the  surround- 
ing viscera  and  by  the  oesophagus.  The 
following  peritoneal  folds  connect  it 
with  the  adjacent  parts: 

1.  The  gastro-phrenic  ligament 
(Lig.  gastrophrenicum)  connects  the 
great  curvature,  from  the  cardia  to 
the  left  extremity,  with  the  crura  of 
the  diaphragm.  This  leaves  a  narrow 
area  uncovered  with  peritoneum,  and 
here  the  stomach  is  attached  to  the 
diaphragm  by  loose  connective  tissue. 

2.  The  small  or  gastro-hepatic 
omentum  (Omentum  minus)  connects 
the  lesser  curvature  and  the  first  part 
of  the  duodenum  with  the  liver  below 
the  oesophageal  notch  and  the  portal 
fi.ssure. 

3.  The  gastro-splenic  omentum 
(Lig.  gastro-lienale)  passes  from  the 
left  part  of  the  great  curvature  to  the 
hilus  of  the  spleen. 

4.  The  great  or  gastro-colic  omen- 
tum (Omentum  majus)  connects  the 
ventral    ]iart   of   the   great   curvature 

and  the  first  curve  of  the  duodenum  with  the  terminal  part  of  the  great  colon  and 
the  initial  ])art  of  the  small  colon. 

5.  The  gastro-pancreatic  fold  (Plica  gastro-pancreatica)  extends  from  the  left 
sac  above  the  cardia  to  the  duodenum.  It  is  attached  tlorsally  to  the  liver  and 
vena  cava,  ventrally  to  the  pancreas. 

The  stomach  of  the  equidse  is  relatively  small,  its  cajiacity  varying  from  two 
to  four  gallons  (ca.  8  to  15  liters). 

The  size,  form,  and  po.silion  of  the  .stomach  are  .subject  to  considerable  variation.  When 
the  .stomach  is  nearly  empty  the  saccus  caecus  contains  only  ga.s  and  is  strongly  contracted;  the 
middle  portion  (pliysiolocical  fundus)  contains  the  ingesta  and  preserves  its  rounded  oharacter, 
wliile  the  pylorii'  ijortion  is  contracted.  Wlien  distended  the  middle  portion  settles  down  .some 
fom-  or  five  inches,  pushing  back  coils  of  the  small  colon  and  small  intestine  which  may  lie  between 
the  great  curvature  and  the  large  colon,  and  also  pushing  to  the  left  or  right  the  left  dorsal  part  of 

'  This  is  the  position  in  the  expiratory  phase  a.s  usually  seen  in  the  dead  subject.  In  inspira- 
tion the  saccus  ca;cus  lies  under  the  upper  parts  of  the  sixteenth  and  seventeenth  ribs. 


s\\>?S^ 


Fig.  260. — Everted  Stomach  op  Horse  from  which 
THE  Mucous  Membrane  has  been  Removed. 
O,  Qisophagu.s;  D,  duoflenum;  6,  circular  layer; 
c',  internal  oblique  fibers;  c",  loop  around  cardia;  r"', 
transition  of  internal  to  external  oblique  fibers;  d,  fibers 
connecting  the  two  branches  of  the  cardiac  loop;  p, 
antra!  sphincter;  p' ,  pyloric  sphincter.  (EUenberger- 
liauin,  .\nat.  d.  Haustiere.) 


THE    STOMACH  359 

the  great  colon;  the  .spleen,  small  colon,  and  small  intestines  are  pushed  back  by  the  distention  of 
the  left  sac. 

Structure. — The  wall  is  composed  of  four  coats — serous,  muscular,  submucous, 
and  mucous. 

The  serous  coat  (Timica  serosa)  covers  the  greater  part  of  the  organ  and  is 
closely  adherent  to  the  muscular  coat  except  at  the  curvatures.  It  partiallj^  bridges 
over  the  lesser  curvature,  and  covers  here  elastic  tissue  which  assists  in  retaining 
the  bent  form  of  the  stomach.     The  peritoneal  folds  have  been  described. 

The  muscular  coat  consists  of  three  incomplete  layers,  an  external  of  longitu- 
dinal, a  middle  of  circular,  and  an  internal  of  oblique  fibers.  The  layer  of  longi- 
tudinal fibers  (Stratum  longitudinale)  is  very  thin  and  exists  only  along  the  curva- 
tures and  at  the  antrum.     At  the  lesser  curvature  it  is  continuous  w'ith  the  longi- 


Saccus  cacus 
(left  extremity) 


(Esophageal  region 
(non-glamhilar) 


Fundus 
gland 
region 


Duodenal 
diverticulum 


Pylorus 
Pyloric  gland  region 


261. — Froxtal  Section'  of  Stomach  an-d  First  Part  of  Dcon 
C,  Cardiac  orifice.     Photograph  of  specimen  fixed  in  t,ili 


tudinal  fibers  of  the  oesophagus.  On  the  antrum  pylori  it  forms  a  well  developed 
complete  layer.  The  layer  of  circular  fibers  (Stratum  circulare)  exists  only  on 
the  right  sac.  At  the  pyloric  orifice  it  forms  a  thick  ring — the  pyloric  sphincter. 
Another  ring,  the  antral  sphincter,  is  found  at  the  left  end  of  the  antrum  pylori. 
The  oblique  fibers  (Fibrte  obliquae)  are  arranged  in  two  laj'ers:  the  external  stratum 
covers  the  left  sac  and  is  a  continuation  (in  part)  of  the  longitudinal  fibers  of  the 
cesophagus;  the  internal  stratum  is  found  also  on  the  left  sac,  and  exchanges  fibers 
with  the  circular  and  external  oblique  layers.  It  forms  a  remarkable  loop  around 
the  cardiac  orifice,  constituting  a  powerful  cardiac  sphincter  (Sphincter  cardise). 
The  submucous  coat  is  a  layer  of  loose  connective  tissue  which  connects  the 
muscular  and  mucous  coats;  in  it  the  vessels  and  nerves  ramify  before  entering 
the  mucosa. 


360 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


The  mucous  coat  is  dearly  divided  into  two  parts.  That  which  lines  the  left 
sac  resembles  the  a^sophageal  mucous  membrane,  and  is  termed  oesophageal  or 
cuticular.  It  is  white  in  color,  destitute  of  glands,  and  covered  with  a  thick, 
squamous,  stratified  epithelium.  At  the  cardiac  orifice  it  presents  numerous  folds 
which  occlude  the  opening.'  It  terminates  abruptly  at  an  elevated,  denticulated, 
sinuous  line,  termed  the  cuticular  ridge  (Margo  plicatus).  Below  and  to  the  right 
of  this  line  the  mucous  membrane  has  a  totally  different  character,  being  soft 
and  velvety  to  the  touch,  and  covered  by  a  mucoid  secretion.  It  is  glandular,  and 
three  zones  may  be  recognized,  although  no  sharp  line  of  demarcation  exists.  A 
narrow  zone  next  to  the  cuticular  ridge  has  a  yellowish-gray  color,  and  contains 
short  tubular  cardiac  glands  (Cardiac  gland  region).  Next  to  this  is  a  large  area 
which  has  a  mottled  reildish-brown  color,  and  contains  fundus  glands  (fundus  gland 

region).  This  part  of  the  mucous 
membrane  is  thick  and  very  vascular, 
and  corresponds  to  the  fundus  of 
the  stomach  in  man  and  the  dog. 
The  remainder  of  the  mucous  mem- 
brane has  a  reddish-gray  color  and 
contains  branched,  tubular,  pyloric 
glands  (pyloric  gland  region);  it  cor- 
responds to  the  pyloric  portion  of 
man  and  the  dog. 

The  folding  of  the  stomacli  wall 
at  the  lesser  curvature  produces  a 
prominent  ridge  which  projects  into 
the  cavity  of  the  stomach.  Circular 
ridges  occur  at  the  antral  antl  pyloric 
sphincters. 

Blood-vessels    and    Nerves. — The 
stomach    receives    blood    from    all    the 
branches   of   the    coeliac    artery.     The  gastric  veins  drain  into  the  portal  vein. 
The  nerves  are  deriveil  from  the  vagus  and  sympathetic  nerves. 


-Diagram  of  Zones  of  Mucous  Memb 
OF  Stomach  of  Horse. 


THE  SMALL  INTESTINE 

The  small  intestine  (Intestinum  tenue)  is  the  tube  which  connects  the  stomach 
with  the  large  intestine.  It  begins  at  the  pylorus  and  terminates  at  the  lesser 
curvature  of  the  caecum.  Its  average  length  is  about  seventy  feet  (ca.  22  meters). 
When  distended  Jts  diameter  varies  from  two  to  four  inches  (5  to  10  cm.).  Its 
capacity  is  about  twelve  gallons  (40  to  50  liters). 

It  is  clearly  divisible  into  a  fixed  and  a  mesenteric  or  floating  portion.  The 
fixed  portion  is  termed  the  duodenum,  while  the  mesenteric  portion  (Intestinum 
tenue  mesenteriale)  is  arbitrarily  divided  into  parts  termed  the  jejunum  and  ileum. - 

The  duodenum  is  about  three  to  four  feet  (ca.  1  to  1.25  m.)  long.  Its  shape 
is  somewhat  like  a  horsesiioe,  the  convexity  being  directed  toward  the  right.  The 
first  part  is  directed  to  the  right  and  forms  an  w  -shajied  curve.  The  convexity  of 
the  first  j)art  of  the  curve  is  dorsal,  of  the  second  ventral.  It  lies  on  the  middle 
and  right  lobes  of  the  liver,  and  presents  two  dilatations  (Ampullae)  with  a  constric- 
tion between  them.     The  duodenal  angle  or  head  of  the  pancreas  lies  in  the  con- 

'  This  occlusion  is  usually  so  complete  that  distention  of  the  stomach  by  air  or  fluid  forced 
in  tliiough  the  pylorus  may  be  carried  far  enough  to  rupture  tiie  stomach  without  ligating  the 
ccsopliagus. 

"-  Xo  natural  line  of  demarcation  exists,  but  there  is  a  marked  iiKrcasc  of  (he  thickness  of 
the  wall  toward  the  terminal  part.     Other  differences  will  be  noted  in  thr  furl  her  description. 


THE    SMALL   INTESTINE 


3G1 


cavity  of  the  second  curve,  and  here,  five  to  six  inches  (ca.  12  to  15  cm.)  from  the 
pylorus,  the  pancreatic  duct  and  the  bile  duet  pierce  the  bowel  wall.  The  second 
part  passes  upward  and  backward  on  the  right  lobe  of  the  liver  and,  on  reaching 
the  right  kidney  and  the  base  of  the  caecum,  it  curves  toward  the  median  plane, 
opposite  the  last  rib.  The  third  part  passes  almost  transversely  from  right  to 
left  behind  the  base  of  the  ciEcum,  crosses  the  median  plane  under  the  third  and 
fourth  lumbar  vertebra,  and  turns  forward  to  become  continuous  with  the  jejunum 
under  the  left  kidney.  The  sacculations  of  the  first  part  have  a  diameter  of  three 
to  four  inches  (ca.  7.5  to  10  cm.). 

It  is  attached  by  a  short  peritoneal  fold  termed  the  mesoduodenum.  This 
fixes  the  first  part  of  the  duodenum  closely  to  the  liver  and  the  right  florsal  part 
of  the  colon;   the  remainder  is  somewhat  less  closely  attached  by  it  to  the  ca;cum 


Fig.  26.3. — Topography  of  Viscera  of  Horse,  Left  View. 
I.R.,  First  thoracic  vertebra;  I.L.,  first  lumbar  vertebra;  3.K.,  second  sacral  spine;  S.,  scapula:  '1.. 
humerus;  .S^,  sternum;  i?..  ilium;  O.,  femur;  Z...  lung  in  complete  expiration;  /.,  dotted  line  indicating  contour  of 
lung  in  inspiration:  H ,  pericardium;  Z,  costal  part  of  diaphragm;  Z',  tendinous  center  of  diaphragm;  I.N.,  left 
kidney:  l.v.C,  left  ventral  colon;  v.Q.,  sternal  flexure  of  colon;  d.Q.,  diaphragmatic  flexure  of  colon;  D.,  small 
intestine;  ^f.,  small  colon;  M',  rectum;  a,  coccygeus  muscle;  b,  retractor  ani;  c,  c  ,  sphincter  ani  externus:  d, 
cnnstrictor  vulvce;  e,  sacro-coccygeus  inferior:  /.  anterior  gluteal  artery:  g,  internal  pudic  artery;  h,  abdominal 
wall  in  section.      (After  Ellenberger,  in  Leisering"s  .\tlas.  reduced.) 


and  right  kidney,  the  sublumbar  muscles,  and  (more  closely)  to  the  terminal  part 
of  the  great  colon  and  the  first  part  of  the  small  colon.' 

The  jejunum  and  ileum  together  (Jejuno-ileum)  constitute  the  mesenteric  or 
floating  portion  of  the  small  intestine.  No  distinct  point  exists  at  which  to  make 
the  demarcation.  With  the  exception  of  the  last  two  or  three  feet,  the  mesenteric 
part  of  the  intestine  varies  so  much  in  position  that  only  a  general  statement  can 
be  made.  It  lies  in  numerous  coils  (Ansae)  mingled  with  those  of  the  small  colon, 
chiefly  in  the  dorsal  part  of  the  left  half  of  the  abdomen,  from  the  visceral  surface 
of  the  stomach  to  the  pelvis.  It  may  insinuate  itself  between  the  left  portions  of 
the  colon  and  the  abdominal  wall;  also  between  the  ventral  portions  of  the  colon, 
reaching  the  floor  of  the  abdomen.  The  terminal  part  of  the  intestine  (ileum) 
ascends  almost  vertically,  a  little  to  the  right  of  the  median  plane,  to  open  into  the 

'  It  will  be  noticed  that  the  mesoduodenum  is  not  continuous  with  the  great  mesentery,  but 
ends  by  a  free  edge.  The  mesentery  begins  on  the  opposite  surface  of  the  end  of  the  duodenum, 
so  that  the  bowel  is  attached  by  two  peritoneal  folds  at  this  point. 


362 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


caecum  at  the  lesser  curvature  of  its  base.  The  average  diameter  of  the  jejuiio- 
ileum  is  about  two  and  a  half  to  three  inches  (ca.  6  to  7  cm.).  In  the  cadaver  one 
finds  most  of  the  tube  presenting  irregular  constricted  and  dilated  parts.  The 
last  three  or  four  feet  (ca.  1  meter)  are  usually  tightly  contracted,  resembling  some- 
what the  terminal  part  of  the  oesophagus.     This  part  may  be  termed  the  ileum. 

The  mesenteric  part  is  connected  with  the  dorsal  abdominal  wall  by  the  great 
mesentery.  This  is  a  wide  fan-shaped  fold,  consisting  of  two  layers  of  peritoneum, 
between  which  the  vessels  and  nerves  reach  the  bowel;  it  also  contains  the  mesen- 
teric lymph  glands  and  some  fat.  The  visceral  border  of  the  mesentery  contains 
the  intestine,  while  the  parietal  border  or  root  (Radix  mesenterii)  is  attached  to  a 
small  area  around  the  great  mesenteric  trunk  under  the  first  and  second  lumbar 
vertebrae.  The  root  is  thick,  as  it  contains  a  large  number  of  vessels  and  nerves 
placed  close  together.  The  mesentery  is  short  at  first,  but  soon  reaches  a  length 
of  one  and  a  half  to  two  feet  (ca.  50  cm.) — sufficient  to  allow  coils  of  the  intestine 
to  reach  the  abdominal  floor,  the  pelvic  cavity,  or  even  to  descend  into  the  scrotum 
through  the  inguinal  canal.     Near  its  termination  the  intestine   (ileum)   leaves 

the  border  of  the  mesentery,  so  that 


Pancreatic 


Diverliculurn 
duodeni 

Fig.  264. — Diagram  of  Section  of  Diverticulum  Duo- 
deni OF  Horse. 
.Solid  line  indicates  mucous  membrane. 


the  latter  has  a  free  edge  which  passes 
to  the  caecum. 

Structure. — The  wall  consists  of 
four  coats — serous,  muscular,  sub- 
mucous, and  mucous,  enumerated 
from  without  inward. 

The  serous  coat  is  complete  ex- 
cept at  the  mesenteric  edge,  where 
the  vessels  and  nerves  reach  the 
bowel. 

The  muscular  coat  consists  of 
an  outer  longitudinal  and  an  inner 
circular  layer,  the  latter  being  the 
thicker.  In  the  last  few  feet  of  the 
intestine  the  muscular  coat  is  very 
thick,  and  being  usually  firmly  con- 
tracted in  the  dead  subject,  gives  the  impression  that  this  part  of  the  bowel  is  of 
smaller  caliber;  such,  however,  is  not  the  case  during  life. 

The  submucous  coat  is  a  layer  of  areolar  tissue  in  which  the  vessels  and  nerves 
ramify.  It  contains  also  the  duodenal  glands  and  the  bases  of  the  solitary  glands 
and  Peyer's  patches. 

The  mucous  membrane  is  soft  and  velvety.  It  has  a  grayish  or  yellowish-red 
color  and  is  very  vascular.  About  five  or  six  inches  from  the  p^dorus  it  forms  a 
pouch,  the  diverticulum  duodeni,  in  which  the  pancreatic  and  hepatic  ducts  open. 
On  a  small  papilla  opposite  this  is  the  termination  of  the  accessory  pancreatic  duct. 
.\t  the  ileo-ctecal  opening  the  mucous  membrane  projects  slightly  into  the  cavity 
of  the  ctEcum,  forming  the  ileo-caecal  valve.  The  free  surface  is  thickly  beset  with 
villi,  small  projections  of  the  mucous  membrane  which  can  be  seen  well  by  placing 
a  piece  of  the  membrane  in  water.  They  are  relatively  short  and  thick  and  have  a 
distinct  neck  in  the  horse.  Each  contains  a  central  lymph-vessel  (lacteal),  and 
around  this  a  plexus  of  capillaries,  lymphoid  tissue,  and  unstriped  muscle-fibers. 
They  are  important  agents  in  absorption  from  the  contents  of  the  intestine.  The 
epithelium  is  columnar,  with  many  goblet  cells.  Underneath  the  liasement  mem- 
brane is  a  layer  of  unstriped  muscle-fibers,  the  muscularis  mucosae. 
The  glands  of  the  small  intestine  are  of  three  kinds: 

1.  The  intestinal  glands  (Glandulse  intestinales  Lieberkuehni)  are  found 
throughout.     They  are  simple  tubular  glands  which  open  between  the  villi. 


THE    LARGE    INTESTINE THE    CAECUM 


363 


2.  The  duodenal  glands  (Glandulse  duodenales  Brunneri)  arc  found  in  the 
first  twenty  feet  (ca.  6  meters)  of  the  bowel.  They  are  racemose  glands,  and  are 
situated  in  the  submucosa,  so  that  their  ducts  perforate  the  muscularis  mucosa  and 
the  mucous  membrane. 

3.  The  lymph  follicles  (Xoiluli  lymphatici)  are  found  either  .scattered  or  in 
groups.  In  the  former  case  they  are  termed  solitary  glands  (Noduli  lymphatici 
solitarii),  in  the  latter  Peyer's  patches  (Xoduli  lymphatici  aggregati).  The 
solitary  glands  are  about  the  size  of  a  millet-seed  or  a  small  sago  grain.  Peyer's 
patches  are  situated  chiefly  along  the  surface  opposite  to  the  mesenteric  attachment 
and  begin  about  three  or  four  feet  from  the  pylorus.  They  number  one  to  two 
hundred,  anil  are  usually'  one  to  two  inches  (2  to  5  cm.)  long  and  a  quarter  of  an 
inch  to  one-half  inch  (ca.  2  to  14  mm.)  wide.  Larger  ones  occur  in  the  terminal 
part,  where  one  patch  may  have  a  length  of  seven  to  fifteen  inches  (ca.  17  to  38 
cm.)  and  a  width  of  half  an  inch  to  one  inch  (ca.  5  to  25  mm.)  in  young  horses 
(Ellenberger).     They  undergo  atrophy  in  old  subjects. 


Vessels  and  Nerves. — The  arteries  of  the  small  intestine  come  from  the 
coeliac  and  anterior  mesenteric  arteries.  The  veins  go  to  the  portal  vein.  The 
lymph-vessels  are  numerous  and  go  to  the  mesenteric  lymph  glands.  The  nerves 
are  derived  from  the  vagus  and  sympathetic  through  the  solar  plexus. 


THE  LARGE  INTESTINE 
The  large  intestine  (Intestinum  crassum)  extends  from  the  termination  of  the 
ileum  to  the  anus.  It  is  about  twenty-five  feet  (ca.  7.5  to  8  m.)  in  length.  It 
differs  from  the  small  intestine  in  its  greater  size,  in  being  sacculated,  for  the  most 
part,  possessing  longitudinal  bands,  and  ha\nng  a  more  fixed  position.  It  is  divided 
into  caecum,  great  colon,  small  colon,  and  rectum. 

The  Caecum 
The  caecum  (Intestinum  csecum)  is  a  great  cul-de-sac  intercalated  between  the 
small  intestine  and  the  colon.     It  has  a  remarkable  size,  shape,  and  position  in  the 
horse.     Its  length  is  three  to  four  feet  (ca.  1  to  1.25  m.),  and  its  capacity  about 


364 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


seven  to  eight  gallons  (ca.  25  to  30  liters).  Tt  is  conical  in  form,  and  is  curved 
somewhat  like  a  reversed  comma.  It  is  situated  almost  entirely  to  the  right  of 
the  median  plane,  extending  from  the  right  iliac  and  sublumbar  regions  to  the  ab- 
dominal floor  behind  the  xiphoid  cartilage.  Both  extremities  are  blind,  and  the 
two  orifices  are  placed  close  together  on  the  concave  curvature.  It  presents  for 
description  a  base,  a  bodj',  and  an  apex. 

The  base  (Saccus  ctecus)  extends  from  about  the  thirteenth  intercostal  space 
l)ackward  almost  to  the  pelvic  inlet.  Its  greater  curvature  is  dorsal,  its  lesser 
ventral;  connected  with  the  latter  are  the  termination  of  the  ileum  and  the  origin 
of  the  colon.  The  body  (Corpus  ciEci)  extends  downward  and  forward  from  the 
base  and  rests  largely  on  the  ventral  wall  of  the  abdomen.  Its  lesser  curvature  is 
about  parallel  with  the  costal  arch  and  aliout  five  to  six  inches  (10  to  15  cm.)  below 
it.  The  apex  (Apex  caeci)  lies  usually  on  the  abdominal  floor  about  a  hand's 
length  behind  the  xiphoid  cartilage. 

The  base  is  attached  dorsally  by  connective  tissue  and  peritoneum  on  the 
ventral  surface  of  the  pancreas  and  right  kidney,  the  psoas  muscles,  and  the  iliac 
fascia;   internally,  it  is  attached  to  the  terminal  part  of  the  great  colon,  and  ven- 


Origin  of  small  colon 


Sternal 
flexure 


AM  OF  Cecum  and  Large  Colon  of  Horse. 


trally  to  the  origin  of  the  great  colon.  The  body  is  attached  dorsally  to  the  first 
part  of  the  colon  by  the  cseco-colic  fold.  The  apex  is  free,  and  consequently  may 
vary  in  position. 

The  ciEcum  has  four  longitudinal  bands  (Ttenise),  situated  on  the  dorsal, 
ventral,  right,  and  left  surfaces;  these  cause  four  rows  of  sacculations  (Haustra). 
The  ventral  band  is  entirely  exposed  or  free  (Taenia  libera) ;  the  dorsal  band  is 
free  on  the  apex.  The  csecal  arteries  are  placed  on  the  other  two.  The  right  or 
parietal  surface  of  the  caecum  is  related  chiefly  to  the  right  abdominal  wall,  the 
diaphragm,  duodenum,  and  liver.  The  left  or  visceral  surface  lies  against  the  left 
divisions  of  the  colon,  the  root  of  the  great  mesentery,  and  the  small  intestine. 

The  ileo-caecal  orifice  (Ostium  ileocaecale)  is  situated  in  the  lesser  curvature 
of  the  base,  about  four  or  five  inches  (ca.  10  to  12  cm.)  to  the  right  of  the  median 
plane  and  about  o])posite  the  lower  end  of  the  last  rib.  The  end  of  the  ileum  is 
partially  telescoped  into  the  caecum,  so  that  the  orifice  is  surrounded  by  a  fold  of 
mucous  membrane,  forming  the  ileo-caecal  valve  (Valvula  ileocaecalis).  The 
peritoneum  and  limgitudinal  muscle-fibers  do  not  take  part  in  its  formation. 

The  caeco-colic  orifice  (Ostium  caecocolicum)  is  placed  above  and  external  to 


THE    GREAT   COLON 


365 


the  preceding  one;  the  interval  between  tliem  is  only  about  two  inches  (ca.  5  cm.), 
and  they  are  separated  by  a  distinct  ridge  which  projects  into  the  interior  of  the 
caecum.  The  orifice  is  slit-like  and  is  small  in  relation  to  the  size  of  the  cjecum 
and  colon.     It  has  a  valvular  fold  (\'alvula  caecocolica)  at  its  lower  margin  and  a 


Fig.  267. — Topography  of  Viscera  of  Horse,  Right  View. 
i/?..  First  thoracic  vertebra;  iL.,  first  lumbar  vertelara;  ;^iv'.,  second  sacral  spine;  5.,  scapula;  -l .,  humerus; 
5(.,  sternum;  5..  ilium;  O.,  femur;  /..,  right  iung;  //..  pericardium;  Z.,  diaphragm  (pars  costalis);  r.v.C,  right 
ventral  colon;  i\Q.,  sternal  flexure  of  colon;  rf.Q.,  diaphragmatic  flexure  of  colon;  C,  body  of  ca-cum;  C,  base  of 
csecum:  C".,  apex  of  c^cum;  D.,  small  intestine:  F.,  pelvic  flexure  of  colon;  M.,  rectum;  a.,  abdominal  wall  in 
section;  6,  duodenum:  c,  coccygeus  muscle:  rf,  retractor  ani;  e.  e' ,  sphincter  ani  externus;  /,  anterior  gluteal  ar- 
tery; g.  internal  pudic  artery;   h,  xiphoid  cartilage,     (.\fter  Eilenberger,  in  Leisering's  Atlas.) 


muscular  ring  (Sphincter  cseci).  Large  crescentic  or  semilunar  folds  (Plicae  cieci) 
project  into  the  cavity  of  the  bowel,  and  between  these  are  large  pouches  (Cellulse 
caeci). 

Vessels  and  Nerves. — The  csecal  arteries  come  from  the  great  mesenteric 
artery.     The   veins   go  to  the  portal   vein. 
The    nerves    are   derived    from    the    great  ? 

mesenteric  plexus  of  the  sympathetic. 


The  Great  Colon 
The  great  colon  (Colon  crassum)  begins 
at  the  cseco-colic  orifice,  and  terminates  by 
joining  the  small  colon  behind  the  saccus 
csecus  of  the  stomach.  It  is  ten  to  twelve 
feet  (ca.  3  to  3.7  m.)  long,  and  its  average 
diameter  (exclusive  of  its  narrowest  part)  is 
about  eight  to  ten  inches  (ca.  20  to  25 
cm.).      Its    capacity    is    more    than    double 

that  of  the  caecum.  When  removed  from  the  abdomen,  it  consists  of  two  jjarallcl 
portions,  which  are  connected  by  peritoneum  and  partially  by  areolar  tissue  also. 
In  situ,  it  is  folded  so  that  it  consists  of  four  parts,  which  are  designated  according 
to  their  position  or  numerically.     The  three  bent   connecting  parts  are  termed 


Fig.  268. — Ileo-cecal  Orifice  of  Horse. 
a,  Mucous  membrane  of  CKCum;  b,  ileum; 
c,  ileo-ciecal  orifice;  d,  fold  of  mucous  membrane. 
(.\fter  P.  .Schumann.) 


366 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


the  flexures.  The  first,  right  ventral  part  (Colon  ventrale  dextrum),  begins  at 
the  cseco-colic  orifice  about  opposite  the  middle  of  the  last  rib,  passes  downward 
and  forward  along  the  right  costal  arch,  and  reaches  the  floor  of  the  abdomen. 
Over  the  xijihoid  cartilage  it  bends  sharply  to  the  left  and  backward,  forming  the 
sternal  flexure  (Flcxura  diaphragmatica  ventralis).  The  second,  left  ventral 
part  (Colon  ventrale  sini.strum),  passes  backward  on  the  left  part  of  the  abdomi- 


FiG.  269. — Abdo-minal  Viscera  of  Horse,  Ventral  View. 
The  ventral  wall  and  part  of  the  lateral  walls  of  the  abdomen  are  removed.  C,  Csecum;  r.v.C,  right  ventral 
part  of  colon;  v.Q.,  sternal  flexure  of  colon;  l.v  C,  left  ventral  pari  of  colon;  d.Q.,  diaphragmatic  flexure  of  colon; 
D,  small  intestine;  M,  small  colon;  a,  ventral  free  band  of  ciccum;  b,  inner  band  of  CEecum;  c,  lateral  band  of 
ventral  part  of  colon;  rf,  ventral  band  of  ventral  part  of  colon;  c.  point  of  elbow;  /,  anterior  end  of  sternal  region; 
0,  xiphoid  cartilage;   h,  teats,     (.\fter  EUenberger-Baum,  Top.  .\nat.  d.  Pferdes.) 


nal  floor,  and,  on  reaching  the  pelvic  inlet,  bends  sharply  dorsally  and  forward, 
forming  the  pelvic  flexure  (Flexura  pelvina).  This  is  continued  by  the  third,  left 
dorsal  part  (Colon  dorsalc  sinistrum),  which  passes  forward  above  the  left  ventral 
portion.  On  reaching  the  stomach,  diaphragm,  ami  left  lolje  of  the  liver,  it  turns 
to  the  right,  forming  the  diaphragmatic  or  gastro-hepatic  flexure  (Flexura  dia- 
phragmatica dorsalis).  The  fourth  or  right  dorsal  part  (Colon  tlorsale  dextrum) 
passes  backward  above  the  first  portion,  and  on  reaching  the  inner  or  left  surface 


THE    GREAT   COLON 


367 


of  the  base  of  the  cfficum  it  turns  upward  and  to  the  left  behind  the  left  sac  of 
the  stomach;  here  it  becomes  constricted,  and  joins  the  small  colon  below  the  left 
kidney. 

The  caliber  of  the  great  colon  varies  greatly  at  different  points.  At  its  origin 
it  is  only  about  two  to  three  inches  (ca.  5  to  7.5  cm.)  in  diameter.  This  soon 
increases  to  about  eight  to  ten  inches  (ca.  20  to  25  cm.)  for  the  ventral  portions. 
Beyond  the  pelvic  flexure  the  diameter  is  reduced  to  about  three  or  four  inches 
(ca.  8  to  9  cm.).  Near  the  diaphragmatic  flexure  the  caliber  rapidly  increases, 
and  reaches  its  maximum  in  the  last  division,  where  it  may  be  about  twenty  inches 
(.50  cm.)  in  its  widest  part.  This  is  succeeded  by  a  somewhat  funnel-shaped 
terminal  contraction. 


Fig.  270. — Topography  of  Viscera  of  Horse,  Right  Side,  Deeper  View. 
i.iZ.,  First  thoracic  vertebra;  i.L., first  lumbar  vertebra;  ;?.A'.,  second  sacral  spine;  5,  scapula;  A, humerus; 
B,  ilium;  O.,  femur;  Sch.,  pubis;  Si.,  ischium;  St.,  sternum;  L.,  right  lobe  of  liver;  r.N.,  right  kidney;  C, 
body,  C,  base,  C".,  apex  of  caecum:  r.v.C,  right  ventral  colon;  i-.Q.,  sternal  flexure  of  colon;  d.Q.,  diaphragmatic 
fJexure  of  colon;  r.rf.C,  right  dorsal  colon;  F.,  pelvic  flexure  of  colon;  D.,  small  intestine;  //.,  urinary  bladder; 
M.,  rectum;  a,  left  ventricle;  a' ,  right  ventricle:  b,  b' ,  right  coronary  artery;  c,  left  atrium;  c  ,  right  atrium;  rf. 
small  (left)  coronary  vein;  c,  vena  azygos;  /,  anterior  vena  cava;  17,  posterior  vena  cava;  h,  sinus  venosus;  i, 
right  phrenic  nerve:  k,  right  vagus,  with  its  dorsal  ik')  and  ventral  {k")  divisions;  I,  aorta;  m,  oesophagus:  n. 
trachea;  0,  diaphragm  {median  section);  p,  right  lateral  ligament  of  liver;  q,  duodenum;  r,  dotted  line  indi- 
cating position  in  median  section  of  diaphragm  in  inspiratory  phase;  s,  recto-coccygeus;  t,  suspensory  ligament 
of  rectum;  u,  sphincter  ani;  v,  vesicula  seminalis;  w,  prostate;  x,  bulbo-urethral  (Cowper's)  gland;  y,  urethra; 
2,  abdominal  wall;   z*,  xiphoid  cartilage.     (After  EUenberger,  in  Leisering's  .\tlas,  reduced.) 


The  first  part  of  the  great  colon  is  attached  to  the  lesser  curvature  of  the  cfecum 
by  two  layers  of  peritoneum  which  form  the  caeco-colic  fold.  The  ventral  parts  of 
the  colon  are  similarly  connected  to  the  dorsal  parts  of  the  same  side  by  the  meso- 
colon. The  right  portions  are  united  also  by  areolar  tissue  and  muscular  fibers, 
the  surface  of  contact  being  about  four  or  five  inches  (ca.  10  to  12  cm.)  wide;  the 
left  portions  are  attached  to  each  other  by  a  peritoneal  fold  wide  enough  to  allow 
them  to  be  drawn  apart  five  or  six  inches  (ca.  12  to  15  cm.)  near  the  pelvic  flexure. 
The  terminal  part  of  the  colon  is  attached  by  peritoneum  and  areolar  tissue  to 
the  ventral  surface  of  the  pancreas  dorsally  and  to  the  base  of  the  caecum  exter- 
nally. It  is  connected  indirectly  with  the  diaphragm  and  liver  by  means  of  a  fold 
derived  from  the  right  lateral  ligament  of  the  liver. 


368 


DIGESTIVE    SYSTEM    OF    THE    HORSE 


The  relations  are  coinijlex,  liut  the  more  important  facts  are  as  follows :  The 
ventral  portions  (first  and  second)  have  extensive  contact  with  the  abdominal  wail 
ventrally  and  laterally.  On  the  right  side  the  colon  is  almost  entirely  excluded  from 
contact  with  the  flank  by  the  caecum;  on  the  left  side  it  has  no  contact  with  tlie 
upper  part  of  tlie  flank,  being  excluded  here  by  coils  of  the  small  colon  and  small 
intestine.  Dorsally  the  chief  relations  are  to  the  stomach,  duodenum,  liver, 
pancreas,  small  colon,  small  intestine,  aorta,  vena  cava,  and  portal  vein.  Since 
there  are  no  transverse  attachments  of  the  right  and  left  portions,  and  the  latter 
have  no  attachment  to  the  wall,  they  are  subject  to  considerable  displacement.' 


Fig.  271. — Topography  of  Viscera  of  Horse,  Left  Deep  View. 
//?.,  First  thoracic  vertebra;  /L.,  hrst  lumbar  vertebra:  ;gA'.,  second  sacral  spine;  tS'.,  scapula:  .1.,  humerus; 
/i., ilium:  /''..femur;  ScA.,  pubis;  Si.,  ischium;  Z,..  liver  (left  lobe);  il/o.,  stomach,  the  posterior  contour  of  which 
is  indicated  by  dotted  line  x:  Mi,  spleen;  I.  N.,  left  kidney,  concealed  part  indicated  by  dotted  Une  ;  M .,  small 
colon;  D.,  small  intestine,  parts  of  which  have  been  removed;  I.  d.  C,  left  dorsal  colon;  l.v.C,  left  ventral  colon; 
V.Q.,  sternal  flexure;  d.Q.,  diaphragmatic  flexure;  O.,  left  ovary;  U.,  cornu  uteri;  L.l,  broad  ligament 
M' .,  rectum;  V .,  vagina:  H.,  bladder;  a,  left  ventricle;  a',  right  ventricle:  6,  left  coronary  artery  with  descending 
(I)')  and  circumflex  (h")  branches;  c,  left  auricle;  rf,  pulmonary  artery  (cut);  e,  aorta;  /,  ligamentum  arteriosum; 
ff.  brachiocephalic  trunk  (anterior  aorta);  A,  trachea;  (',  cesophagus;  A*,  left  phrenic  nerve;  /,  diaphragm  in  median 
section;  m.  Fallopian  tube;  n,  bursa  ovarica;  o,  urethra;  p,  cut  edge  of  broad  ligament;  q,  line  of  reflection  of 
pelvic  peritoneum;  r,  recto-coccygeus;  s,  so-called  suspensory  ligament  of  rectum;  /,  sphincter  ani  internus;  n, 
sacro-coccygeus  inferior;  v,  abdominal  wall  in  section;  w,  xiphoid  cartilage.  (After  EUenberger,  in  Leisering's 
Atlas.) 


The  pelvic  flexure  is  variable  in  position,  but  usually  it  is  directed  to  the  right 
across  the  pelvic  inlet. 

The  ventral  portions  of  the  colon  have  four  longitudinal  muscular  bands 
(Tffiniffi)  which  produce  four  rows  of  sacculations  (Haustra).  On  the  first  ])art 
the  external  and  internal  bands  are  free;  the  dorsal  band  is  covered  by  the  adhesion 
to  the  overlying  dorsal  division,  while  the  ventral  band  is  largely  covered  by  the 
adhesion  to  the  ccecum.  On  the  left  ventral  part  the  external  and  ventral  bands 
are  free;  of  the  two  dorsal  bands,  the  inner  one  is  concealed  by  the  mesocolon,  the 
outer  one  is  chiefly  free.  The  pelvic  flexure  has  a  band  on  its  lesser  curvature, 
which  is  continued  on  to  the  third  part,  concealed  by  the  peritoneal  attachment; 
these  parts  are  practically  non-sacculated.     Near  the  diaphragmatic  flexure  two 

'  Abnormal  displacement,  e.  g.,  torsion  of  the  left  parts,  is  not  rare,  and  is  liable  to  produce 
death  if  not  promptly  reduced. 


THE    SMALL    COLON 


369 


other  bands  ajipear,  so  that  the  flexure  has  three  bands;  two  of  these  are  dorsal 
and  free,  the  tliird  is  ventral  and  concealed.  The  last  part  has  three  bands,  of 
which  the  inner  and  outer  ones  are  free,  the  ventral  one  covered. 

The  Small  Colon 
The  small  colon  (Colon  tenue)  begins  at  the  termination  of  the  great  colon, 
behind  the  saccus  ciecus  of  the  stomach  and  lielow  the  left  kidney,  and  is  continued 
by  the  rectum  at  the  pelvic  inlet.     Its  length  is  about  ten  to  twelve  feet  (ca.  3.5  m.), 
and  its  diameter  about  three  to  four  inches  (ca.  7.5  to  10  cm.). 


Fig.  272. — Pelvic  Ixlf.t  and  Posterior  Part  of  Abdominal  Wall  of  Horse,  Viewed  from  the  Front. 
The  left  inguinal  canal  is  partially  opened.  The  peritoneum  is  retained  except  over  a  part  of  the  left  ore- 
master  muscle.  The  subluiubar  region  is  greatl.v  foreshortened  in  this  view,  a,  a'.  Kidneys;  a",  adrenal;  b., 
ureter;  c,  renal  artery;  rf,  aorta;  e,  coeliac  artery  (cut);  /,  anterior  mesenteric  artery  (cut);  (7,  posterior  mesenteric 
artery;  h,  circumflex  iliac  artery;  i,  external  iliac  artery;  k,  internal  iliac  artery;  /,  spermatic  artery  in  peritoneal 
fold  (plica  vasculosa),  m;  n,  vas  deferens,  inclosed  in  urogenital  fold,  o;  p,  urinary  bladder;  q,  round  ligament  of 
bladder;  r,  middle  ligament  of  bladder;  s.  rectum;  t,  margin  of  vaginal  ring;  u,  posterior  abdominal  artery;  r, 
external  pudic  arter\-;  w,  rectus  abdominis  muscle;  J,  transversus  and  obliquus  internus  abdominis:  y,  ij' ,  cre- 
master  externas;    z,  posterior  vena  cava  (cut),      (.\fter  EUenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


Its  coils  lie  in  the  space  between  the  stomach  and  the  pelvic  inlet,  dorsal  to 
the  left ;  portions  of  the  great  colon.  They  are  mingled  with  those  of  the 
small  intestine,  from  which  they  are  easily  distinguished  by  the  tsenise  and 
sacculation. 

It  is  attached  to  the  sublumbar  region  by  the  colic  mesentery,  and  to  the 
termination  of  the  duodenum  by  a  .short  peritoneal  fold  (Lig.  duodeno-colicum). 
The  great  omentum  is  also  attached  to  the  origin  of  the  bowel.  The  colic  mesen- 
tery is  narrow  at  its  origin,  but  soon  reaches  a  width  of  about  three  feet  (ca. 
24 


370  DIGESTIVE    SYSTEM    OF    THE    HORSE 

80  to  !)0  cm.).  Its  parietal  Ijorder  is  attached  along  a  line  extending  from  the 
ventral  surface  of  the  left  kidney  to  the  sacral  promontory;  it  is  continuous  in 
front  with  the  I'oot  of  th(^  great  mesentery,  and  behind  with  the  mesorectum. 

There  are  two  taeniae  and  two  rows  of  sacculations.  Of  the  taenia?,  one  is  free, 
the  other  concealed  by  the  mesentery.  When  the  bowel  is  hardened  in  situ  its 
lumen  between  the  pouches  is  reduced  to  a  narrow  slit. 

The  Rectum 

The  rectmn  (Intestinum  rectum)  is  the  terminal  part  of  the  bowel;  it  extends 
from  the  pelvic  inlet  to  the  anus.'  Its  length  is  about  one  foot  (ca.  30  cm.).  Its 
direction  may  be  straight  or  oblique.  The  first  or  peritoneal  part  of  the  rectum  is 
like  the  small  colon,  and  is  attached  by  a  continuation  of  the  colic  mesentery  termed 
the  mesorectum.  The  second  or  retroperitoneal  part  forms  a  fiask-shaped  dilata- 
tion tennetl  the  ampulla  recti ;  it  is  attached  to  the  surrounding  structures  by  con- 
nective tissue  and  muscular  bands. 

The  first  part  of  the  rectum  is  related  to  the  small  colon  and  the  pelvic  flexure 
of  the  great  colon.  It  is  frequently  deflected  to  the  left  by  the  latter.  The  second 
part  of  the  rectum  is  related  dorsally  and  laterallj'  to  the  pelvic  wall,  ^'entrally 
the  relations  differ  in  the  two  sexes.  In  the  male  they  are  the  bladder,  the  ter- 
minal parts  of  the  vasa  deferentia,  the  vesiculjE  seminales,  the  prostate,  the  bulbo- 
urethral (Cowper's)  glands,  and  the  urethra.  In  the  female  they  are  the  uterus, 
vagina,  and  vulva." 

Structure  of  the  Large  Intestine. — The  serous  coat  covers  the  different  parts 
in  varying  degrees.  It  does  not  cover  (a)  the  opposed  surfaces  of  the  caecum 
and  colon  which  are  between  the  layers  of  the  cseco-colic  fold  and  mesocolon; 
(b)  the  areas  of  attachment  of  the  CiEcum  and  colon  to  the  pancreas,  right  kidney, 
and  sublumbar  region;    (c)  the  second  part  of  the  rectum. 

The  muscular  coat  consists  of  longitudinal  and  circular  fibers.  The  bulk  of 
the  former  is  in  the  bands  already  described.  Some  of  the  circular  fibers  pass 
from  one  part  of  the  colon  to  another,  where  they  are  attached  to  each  other, 
forming  the  fibrse  transversiE  coli.  The  nmscular  coat  of  the  second  part  of  the 
rectum  presents  special  features.  The  longitudinal  layer  of  fibers  is  very  thick 
and  consists  of  large  bundles,  loosely  united.  A  large  band,  the  recto-coccygeus, 
is  detached  from  it  on  either  side,  and  passes  upward  and  backward  to  be  inserted 
into  the  fourth  and  fifth  coccygeal  vertebrae. 

The  submucous  tissue  is  abundant  in  the  wall  of  the  rectum,  so  that  the  mucous 
membrane  is  loosely  attached  to  the  muscular  coat,  and  forms  numerous  folds 
when  the  bowel  is  empty. 

The  mucous  membrane  of  the  large  intestine  is  thicker  and  darker  in  color 
than  that  of  the  small  intestine.  It  forms  large  crescentic  or  semilunar  folds  cor- 
responding to  the  ext(Tnal  constrictions.  It  has  no  villi,  Brunner's  glands,  or 
Peyer's  patches.  The  intestinal  glands  (of  Lieberkiihn)  are  large  antl  numerous. 
Solitary  glands  are  also  numerous,  especially  at  the  apex  of  the  cajcum  ami  in  the 
left  dorsal  j^art  of  the  colon. 

Blood-supply. — Greater  and  lesser  mesenteric  and  internal  pudic  arteries. 
The  veins  go  to  the  portal  vein. 

Nerve-supply. — Mesenteric  plexus  of  the  sympathetic  nerves. 

'  There  is  no  natural  line  of  demarcation  between  tlip  stnall  colon  and  rectum:  the  plane 
of  the  pelvic  inlet  is  selected  for  convenience  of  description. 

-  The  .anterior  part  of  the  rectum  is  very  variable  in  position  and  relations.  It  is  not  often 
median,  but  may  bo  dodccted  either  to  right  or  left.  Most  often  it  is  pushed  to  the  left  by  the 
pelvic  flexiire  of  the  colon.  In  other  cases — especially  when  empty — it  may  lie  against  the  right 
wall,  and  the  space  to  the  left  is  occupied  by  the  small  colon.  The  amount  coveretl  by  peritoneum 
dorsally  and  laterally  is  very  variable,  and  appears  to  be  in  inverse  proportion  to  the  fullness  of 
the  bowel. 


THE    PANCREAS  371 

The  anus  is  the  terminal  orifice  of  the  ahmentary  canal.  It  is  situated  Ijelow 
the  root  of  the  tail,  where  it  forms  a  round  projection,  with  a  central  depression 
when  contracted.  It  is  covered  externally  by  an  integument  which  is  thin,  liairlcss, 
and  provided  with  numerous  sebaceous  and  sweat  glands.  The  mucous  lining  is 
pale,  glandless,  and  covered  with  a  thick,  squamous,  stratified  epithelium. 

There  are  three  muscles  of  the  anus. 

1.  The  sphincter  ani  intemus  is  merely  a  terminal  thickening  of  the  circular 
coat  of  the  bowel. 

2.  The  sphincter  ani  extemus  is  a  broad  liand  of  striped  muscle-fibers  outside 
the  internal  sphincter.  Some  fil:)ers  are  attached  to  the  coccygeal  fascia  above, 
others  to  the  perineal  fascia  lielow.     Its  action  is  to  close  the  anus. 

3.  The  retractor  ani  (M.  levator  ani)  is  a  flat  muscle  which  lies  between  the 
rectum  and  the  sacro-sciatic  ligament.  It  arises  from  the  superior  ischiatic  spine 
and  the  sacro-sciatic  ligament,  and  ends  under  the  external  sphincter.  Its  action 
is  to  reduce  the  partial  prolapse  which  the  anus  undergoes  during  defecation. 

The  suspensory  ligament  of  the  anus  is  a  band  of  unstriped  muscle  which  arises 
from  the  first  cocc^'geal  vertebra,  passes  downward  over  the  retractor,  and  unites 
with  its  fellow  below  the  anus.  In  the  male  it  is  largely  continued  ijy  the  retractor 
penis  muscle;  in  the  female  it  blends  with  the  constrictor  vulvje.  It  may  act  as 
an  accessory  sphincter  of  the  anus. 

Blood-supply. — Internal  pudic  artery. 

Nerve-supply. — Hiemorrhoidal  and  perineal  nerves  (for  the  sphincter  ani  exter- 
nus  and  retractor  ani). 

THE  PANCREAS 

The  pancreas  is  situated  transversely  on  the  dorsal  wall  of  the  abdomen,  the 
greater  part  being  to  the  right  of  the  mechan  plane.  Its  central  part  lies  under  the 
sixteenth  and  seventeenth  thoracic  vertebrae. 

When  fresh  it  has  a  reddish  cream  color,  but  if  left  in  the  unpreserved  cadaver 
it  rapidly  decomposes  and  becomes  dark.  It  resembles  the  salivary  glands  in 
appearance,  but  is  softer,  and  its  lobules  are  more  loosely  united.  Its  average 
weight  is  about  twelve  ounces  (ca.  350  g.). 

When  hardened  in  situ  its  shape  is  very  irregular.  It  is  triangular  in  outline, 
and  presents  for  description  two  surfaces,  three  borders,  and  three  angles.' 

The  dorsal  surface  faces  upward  and  forward.  It  is  partially'  covered  by 
peritoneum.  It  is  related  chiefly  to  the  ventral  surface  of  the  right  kidne\-  and 
adrenal,  the  posterior  vena  cava,  the  portal  vein,  the  coeliac  artery  and  its 
divisions,  the  gastro-phrenic  ligament  and  the  saccus  caecus  of  the  stomach, 
the  right  and  caudate  lobes  of  tlie  liver,  and  the  gastro-pancreatic  fold.  There 
are  grooves  for  the  divisions  of  the  ca?liac  artery,  and  a  large  one  for  the  splenic 
vein. 

The  ventral  surface  looks  do^\-nward  and  liackward ;  it  is  in  general  conca\-e. 
It  presents  two  impressions,  separated  b\'  an  oljlique  ridge.  The  smaller  of 
these  (Impressio  caecalis)  lies  to  the  right,  and  is  caused  bj'  the  pressure  of  the 
base  of  the  caecum;  the  larger  one  (Impressio  colica)  indicates  the  area  of  con- 
tact with  the  terminal  part  of  the  great  colon  and  its  junction  with  the  small  colon. 
It  has  usually  no  peritoneal  covering  except  over  a  small  area  at  the  anterior  angle. 

The  right  border  is  nearly  straight;  it  is  related  to  the  second  part  of  the  duo- 
denum and  the  caudate  lobe  of  the  liver. 

The  left  border  is  slightly  concave,  and  is  related  to  the  first  part  of  the  duode- 
num, the  left  sac  of  the  stomach,  and  the  splenic  vessels. 

'  A  descriptive  method  based  on  that  in  use  in  human  anatomy  cannot  be  applied  with 
clearness  to  the  organ  in  the  horse. 


372 


DIGESTIVE    SYSTEM    OF    THE    HORSE 


The  posterior  border  presents  a  deep  notch  to  the  right  of  the  median  plane 
for  the  portal  vein,  which  passes  through  the  gland  very  obliquely.  There  is  a 
thin  bridge  of  gland  tissue  dorsal  to  the  vein,  thus  forming  the  portal  ring  (Amiulus 
portarum).  The  root  of  the  great  mesentery  is  in  contact  with  the  border  just  to 
the  left  of  the  median  jjlaiie. 

The  anterior  or  duodenal  angle  (Caput  pancreatis)  is  attached  to  the  concavity 
of  the  second  curve  of  the  duodenum,  anil  the  adjacent  part  of  the  right  lobe  of  the 
liver.     The  ducts  leave  at  this  extremity. 

The  left  or  splenic  angle  (Cauda  pancreatis)  corresponds  to  the  tail  of  the  pan- 
creas in  man.  It  is  in  contact  with  the  base  of  the  spleen,  the  left  kidney  and 
adrenal  body,  and  the  saccus  ciECUS  of  the  stomach. 


Right 
kr'c/ney 


Stomach 


Fig.  273. — Pancreas  or  Horse  with  I  in 
duct  and  its  two  chief  radicles  are  indicated  by 
gland. 


ubstance  of  the 


The  right  angle  is  rounded,  and  lies  on  the  ventral  surface  of  the  right  kidney 
and  adrenal  body. 

The  pancreas  is  attached  dorsally  by  connective  tis.sue  to  the  kidneys  and 
adrenal  bodies,  the  gastro-phrenic  ligament  and  the  suspensory  ligament  of  the 
spleen,  the  posterior  vena  cava,  the  portal  fissure,  and  the  gastro-pancreatic  fold. 
The  ventral  surface  is  mainly  attached  by  areolar  tissue  to  the  base  of  the  cijecum 
and  the  terminal  part  of  the  great  colon. 

There  are  almost  invariably  two  ducts.  The  large  one  is  termed  the  pan- 
creatic duct  (Ductus  pancreaticus  [Wirsungi]).  It  is  formed  by  the  union  of  two 
radicles  which  come  from  the  right  and  left  extremities,  and  passes  through  the  duo- 
denal angle  to  end  at  the  duodenal  diverticulum  alongside  of  the  bile-duct.     The 


THE    LIVER  373 

duct  is  noarly  half  an  inch  (ca.  1  cm.)  wide,  and  is  very  thin-walled.  It  is  situated 
in  the  .substance  of  the  g.liuu\  near  its  dorsal  surface;  none  of  it  is  free.  The  acces- 
sory pancreatic  duct  (Ductus  pancreaticus  accessorius  [Santorini])  arises  either 
from  the  chief  duct  or  its  left  radicle,  and  ends  on  a  papilla  in  the  duodenum  oppo- 
site the  chief  duct. 

Structure. — The  j^ancreas  belongs  to  the  class  of  tubulo-alveolar  glands,  the 
alveoli  being  long,  like  those  of  the  duodenal  glands;  in  other  respects  it  resembles 
the  serous  salivary  glands  very  closely.  It  has  no  proper  capsule  and  the  lobules 
are  rather  loosely  united. 

Vessels  and  Nerves. — The  arteries  of  the  pancreas  come  from  the  branches  of 
the  cipliac  and  anterior  mesenteric  arteries.  The  nerves  are  derived  from  the 
coeliac  and  mesenteric  plexuses  of  the  sympathetic. 


THE  LIVER 

The  liver  (Hepar)  is  the  largest  gland  in  the  body.  It  is  situated  obliquely 
on  the  abdominal  surface  of  the  diaphragm.  Its  highest  point  is  at  the  level  of 
the  right  kidney,  its  lowest  on  the  left  side,  usually  about  three  or  four  inches 
(ca.  8  to  10  cm.)  from  the  abdominal  floor,  opposite  the  lower  end  of  the  seventh 
or  eighth  rib.     The  greater  part  of  it  lies  to  the  right  of  the  median  plane. 

It  is  red-brown  in  color  and  is  rather  friable.  Its  average  weight  is  about  ten 
to  twelve  pounds  (ca.  5  kg.).  AVhen  in  the  body,  or  if  hardened  in  situ,  it  is 
strongly  curved  and  accurately  adapted  to  the  abdominal  surface  of  the  diaphragm. 
When  removed  in  the  soft  state,  it  flattens  out  into  a  cake-like  form  quite  different 
from  its  natural  configuration.  It  presents  for  description  two  surfaces  and  a 
circumference,  which  may  be  divided  into  four  borders. 

The  parietal  surface  (Facies  diaphragmatica)  is  stronglj*  convex,  and  lies 
against  the  diaphragm.  It  faces  chiefly  upward  and  forward.  It  presents,  just 
to  the  right  of  the  mecUan  plane,  a  sagittal  groove  for  the  posterior  vena  cava  (Fossa 
vense  cavse).  The  vein  is  partially  embedded  in  the  substance  of  the  gland,  and 
receives  the  hepatic  veins. 

The  visceral  surface  (Facies  visceralis)  faces  in  general  downward  and  back- 
ward; it  is  concave  and  irregular,  being  moulded  on  the  organs  which  lie  against  it. 
It  presents,  a  little  to  the  right  of  the  median  plane,  the  portal  fissure  (Porta 
hepatis).  Through  this  the  portal  vein,  hepatic  artery,  and  hepatic  plexus  of 
nerves  enter,  and  the  hepatic  duct  and  lymph  vessels  leave  the  liver.  The  portal 
or  hepatic  lymph  glands  are  also  found  here.  The  pancreas  is  attached  at  and  to 
the  right  of  the  fissure,  and  the  gastro-hepatic  omentum  to  the  left  of  it.  Above 
the  fissure  is  a  ridge  which  represents  the  caudate  lobe  (Lobus  caudatus  Spigelii), 
and  is  continued  to  the  right  by  the  pointed  caudate  process  (Processus  caudatus). 
Further  to  the  left  there  is  a  large  depression  (Impressio  gastrica)  for  the  stomach. 
To  the  right  of  this  may  be  seen  a  groove  passing  to  the  right  and  dorsally;  this  is 
the  duodenal  impression  (Impressio  duodenalis).  Ventral  to  these  is  a  large  de- 
pression for  the  great  colon  (Impressio  colica).  Dorsal  to  this  is  a  smaller  depres- 
sion for  the  blind  end  of  the  base  of  the  caecum.'  Coils  of  the  small  intestine  may 
also  lie  on  this  surface,  and  the  apex  of  the  spleen  may  reach  to  it  when  the  stomach 
is  empty. 

The  dorsal  border  (Margo  obtusus)  is  thick  for  the  most  part.  It  presents 
from  right  to  left:  (1)  a  depression  for  the  right  kidney  (Impressio  renalis);  (2)  a 
notch,  which  is  the  dorsal  end  of  the  fossa  vense  cavse;   (3)  a  deep  notch  (Impressio 

'  These  impressions  are  not  evident  on  the  soft  organ.  In  hanlened  material  they  are 
clearly  mapperl  out,  although  of  course  variable  in  size,  in  conformity  with  the  degree  of  fullness 
of  the  various  hollow  \'iscera.  The  caecal  impression  may  not  be  evident  if,  as  often  happens  in 
old  horses,  the  right  lobe  of  the  liver  is  much  atrophied. 


374 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


ocsoi^hagea)  wliicli  is  mainly  occupied  by  the  thick  margin  of  the  ajsophajical  open- 
ing of  the  (Haphrafiin. 

The  ventral  border  is  thin,  and  is  marked  by  two  deep  interlobar  fissures  or 
incisuies  (Incisura>  intcrloliares),  which  partially  divide  the  organ  into  three  prin- 
cipal lobes — right,  middle,  and  left.  The  right  lobe  is  the  largest,  except  in  old 
subjects,  in  which  it  is  frequently  much  atrophied.  The  middle  lobe  is  the  smallest. 
It  is  marked  by  several  small  fissures,  and  by  the  umbilical  fissure  (Incisura  um- 
bilicalis);  the  latter  contains  the  umbilical  vein  in  the  fu>tus,  which  is  transformed 
into  the  round  ligament  after  birth. 

The  right  border  is  thin  and  long.  It  is  nearly  vertical,  and  extends  backward 
to  about  th(>  middle  of  the  sixteenth  rib. 

The  left  border  is  thin  and  short.     It  extends  backward  to  a  point  opposite 


Right  lateral  ligament 
\ 


Fight 

lobe 


Posterior  vena  cava 


(Esophageal 

notch  ^'^f^  lateral  ligament 


lobe 


Falciform  ligament 


Flo.  274.— Liv 


Round 
ligament 

E,  H.\RDENED  in  sUu,  Parietai.  Surface. 


the  lower  part  of  the  ninth  or  tenth  rib.     The  ventral  and  lateral  borders  together 
constitute  the  margo  acutus. 

The  liver  is  held  in  position  largely  by  the  pressure  of  the  other  viscera  and 
by  its  close  application  to  the  diaphragm.     It  has  six  ligaments. 

1.  The  coronary  ligament  (Lig.  coronarium  hepatis)  attaches  it  closely  to 
the  diaphragm.  It  consists  of  two  laminEe.  The  right  one  is  attached  to  the 
right  of  the  fossa  vense  cavse;  the  left  one  begins  to  the  left  of  the  vena  cava  and 
passes  upward  and  outward,  becoming  continuous  with  the  left  lateral  ligament  at 
the  left  margin  of  the  a-sophageal  notch;  it  detaches  a  middle  fold  which  extends 
to  the  notch  and  is  continuous  with  the  small  omentum.  The  two  laminae  unite 
below  the  vena  cava  to  form  the  next  ligament. 

2.  The  falciform  ligament  (Lig.  falciforme  hepatis)  is  a  crescentic  fold  which 
attaches  the  middle  lobe  to  the  sternal  part  of  the  diaphragm  and  to  the  abdominal 
floor  for  a  varial)le  tlistance.     In  its  concave  free  eilge  is  found 


THE    LIVER 


375 


3.  The  round  ligament  (Lig.  teres  hepatis),  a  fibrous  cord  which  extends 
from  the  uinliiUcal  fissure  t6  the  unibihcus;  it  is  the  vestige  of  the  umbiHcal 
vein,  which  hi  tiie  fcetus  carries  the  blood  from  the  placenta  to  the  liver. 

4.  The  right  lateral  ligament  (Lig.  triangulare  dextrum)  is  a  wide  fold  which 
attaches  the  dorsal  border  of  the  right  IoIm'  to  the  costal  part  of  the  diaphragm. 


Poskriur  vena  cava 


Renal  iinprexmon 


AUackment  of  (/astro-piincreatic  fold 


Portal  fissure   _ 
Hepatic  artery  ; 


Attachment  of  lesser  omentum 
Hepatic  duct 
(Esophageal  notch 


Left  lateral 
ligament 


Umbilical  fissure 


Fig.  275. — Liver  of  IIonsR,  Visceral  Surf.\ce. 
.Specimen  from  middle-aged  subject,  hardened  in  situ. 


5.  The  left  lateral  ligament  (Lig.  triangulare  sinistrum)  attaches  the  dorsal 
edge  of  the  left  lol)e  to  the  tenilinous  center  of  the  diaphragm. 

6.  The  hepato-renal  or  caudate  ligament  (Lig.  hepatorenale)  attaches  the 
caudate  process  to  the  right  kidney  and  the  Imse  of  the  caecum.  The  gastro-hepatic 
omentum  and  the  mesoduodenum  have  been  described. 

As  stated  above,  the  liver  is  divided  by  fissures  into  three  principal  lobes — 
right,  middle,  and  left.      The  right  lobe  is  the  largest  in  the  young  subject  and  is 


376  DIGESTIVE    SYSTEM    OF   THE    HORSE 

irregularly  quadrilateral  in  form.  On  its  dorsal  part  is  the  caudate  lobe,  which 
ends  in  a  pointed  process  directed  outward,  and  assists  in  forming  the  cavity  for 
the  right  kidney.  The  middle  lobe  is  normally  much  the  smallest.  The  left  lobe 
is  oval  in  outline  and  thickest  centrally.  In  old  or  middle-aged  subjects  it  often 
exceeds  the  right  one  in  size.  In  some  cases  the  atrophy  of  the  right  lobe  is  so 
extreme  that  tlie  midiUe  lobe  may  exceed  it  in  size.' 

The  hepatic  duct  (Ductus  hepaticus)  is  formed  at  the  ventral  part  of  the  portal 
fissure  by  the  union  of  right  and  left  chief  lobar  ducts.  It  is  two  or  three  inches 
(ca.  5  to  8  cm.)  long  and  about  half  an  inch  (ca.  1  to  1.5  cm.)  wide.  It  passes  be- 
tween the  two  la.ycrs  of  the  lesser  omentum,  and  pierces  the  wall  of  the  duodenum 
about  five  or  six  inches  (ca.  12  to  15  cm.)  from  the  pylorus,  alongside  of  the  pan- 


Renal  impression 


Posterior  rena  cara 

Portal  vein 
Hepatic  artery 
Hepatic  duct 
(Esop/iagcal  notch 


Middle  lobe 


L'mbilcca!  rein 

Fig    276. — Liver  of  New-born  Foal,  Hardened  in  situ.   Visceral  Surface. 
The  differences,  when  compared  with  the  organ  in  the  adult,  are  very  striking. 

creatic  duct.  The  ducts  pass  obliquely  through  the  wall  of  the  duodenum  for  about 
half  an  inch  (ca.  1  cm.)  before  opening  into  the  diverticulum  duodeni.  The 
arrangement  forms  an  effective  valve,  which  jirevents  regurgitation  from  the 
intestine.     There  is  no  gall-bladder. 

Structure. — The  liver  is  covered  by  an  outer  .serous,  and  an  inner  fibrous  coat. 
The  serous  coat  covers  the  gland  excejjt  at  the  attachment  of  the  pancreas  and  at 
the  portal  fossa;  it  is  reflected  from  it  to  form  the  ligaments  and  the  lesser  omentum. 
The  fibrous  capsule  is  in  general  thin;  it  sends  laminae  into  the  ligaments,  and  also 

'  Flower  and  Rugo  describe  the  mammalian  liver  as  being  primarily  divided  by  the  umbilical 
fissure  into  two  parts,  the  right  and  left  lobes.  Secondary  fissures  on  either  side  may  subdivide 
each  of  these  primary  lobes.  On  this  basis  we  may  recognize  in  the  liver  of  the  horse  right  lateral, 
right  central,  left  central,  and  left  lateral  lobes.  In  the  young  foal  these  four  lobes  are  distinctly 
recognizable.  The  two  central  lolies  would  correspond'to  the  middle  lobe  of  the  foregoing  de- 
scription, and  the  right  ccntial  lobe  would  be  the  equivalent  of  the  quadrate  lobe  of  man. 


THE    SPLEEN  377 

delicate  strands  into  the  gland  substance.  At  the  portal  fissure  it  is  abuntlant  and 
surrounds  the  vessels  and  ducts,  which  it  accompanies  in  the  portal  canals  of  the 
gland  substance. 

The  gland  substance  is  composed  of  the  parenchyma  and  the  interstitial 
tissue.  The  parenchyma  is  made  up  of  lobules,  1  to  2  mm.  in  diameter,  which  are 
held  together  by  a  small  amount  of  interlobular  connective  tissue.  On  account  of 
the  very  small  amount  of  the  latter,  the  lobulation  of  the  horse's  liver  is  not  usually 
at  all  distinct  to  the  naked  eye;  for  the  same  reason  the  organ  is  also  quite 
friable.' 

Vessels  and  Nerves. — The  portal  vein  enters  at  the  portal  fissure.  It  conveys 
blootl  from  tlie  digestive  tract  and  the  spleen,  which  contains  various  products  of 
digestion  and  numerous  white  blood-cells.  The  hepatic  artery  also  enters  at  the 
portal  fissure;  it  may  be  termed  tlie  nutrient  vessel.  All  the  l)lood  is  returnetl  from 
the  liver  to  the  posterior  vena  cava  by  the  hepatic  veins.  The  portal  vein  and  the 
hepatic  artery  both  divide  into  interlobular  l)ranches,  which  run  together  in  the 
portal  canals  of  the  interlobular  tissue.  The  branches  of  the  portal  vein  (Vense 
intcrlobulares)  give  off  intralobular  branches  which  form  plexuses  of  capillaries  in 
the  lobules  and  give  rise  to  a  central  vein  (Vena  centralis).  The  branches  of  the 
hepatic  artery  (Rami  arteriosi  intcrlobulares)  are  of  relatively  small  size.  They 
supply  mainly  (if  not  exclusively)  the  interlobular  tissue,  the  capsule,  and  the  walls 
of  the  vessels  and  ducts.  The  hepatic  veins  -  (Vense  hepaticie)  empty  into  the  vena 
cava  as  it  lies  in  the  fossa  of  the  gland.  Their  ultimate  radicles  are  the  central 
lobular  veins,  which  emerge  from  the  bases  of  the  lol:)ules  and  join  the  sublobular 
veins  (Vente  sublobulares) ;  the  latter  unite  to  form  the  hepatic  veins.  The  largest 
hepatic  veins,  three  or  four  in  number,  join  the  posterior  vena  cava  just  before  it 
leaves  the  liver  to  pass  through  the  diai^hragm. 

The  nerve-supply  comes  from  the  hepatic  plexus,  composed  of  branches  from 
the  vagus  and  sympathetic  nerves. 


THE  SPLEEN 

The  spleen  (Lien)  is  the  largest  of  the  ductless  glands.'  It  is  situated  chiefly 
in  the  left  parachondrium,  in  close  relation  to  the  left  part  of  the  great  curvature 
of  the  stomach,  to  which  its  long  axis  corresponds.  Its  size  and  weight  vary  greatly 
in  different  subjects,  and  also  in  the  same  subject  under  different  conditions,  de- 
pending chiefly  on  the  great  variability  of  the  amount  of  blood  contained  in  it. 
The  average  weight  is  about  35  ounces  (ca.  1  kg.),  its  length  about  20  inches  (ca. 
50  cm.),  and  its  greatest  width  about  8  to  10  inches  (ca.  20  to  25  cm.).  It  is  usually 
bluish-red  or  somewhat  purple  in  color.  In  the  natural  state  it  is  soft  and  yielding, 
but  not  friable. 

The  weight  appears  to  vary  ordinarily  from  about  one  to  eight  pounds,  ahhough  in  large 
horses  the  latter  figure  even  may"  be  exceeded  without  any  apparent  evidence  of  disease.  There 
does  not  seem  to  be  any  constant  relation  to  the  body-weight.  For  example,  the  spleen  of  a 
colt  about  ten  months  old  weighed  three  and  a  half  pounds,  while  it  often  weighs  less  than  two 

'  In  the  young  foal  the  interlobular  tis.sue  is  more  abundant  and  the  loljulation  correspond- 
ingly distinct. 

-  The  hepatic  veins  may  be  recognized  on  section  from  the  fact  that  they  remain  open, 
being  connected  closely  with  the  parenchyma. 

^  The  ductless  glands  are  organs  which  elaborate  substances  which  pass  directly  into  the 
veins  or  lymphatics,  instead  of  being  conveyed  away  by  ducts.  This  process  is  termed  internal 
secretion.  The  ductless  glands  include  the"  lymph  glands,  which  are  described  with  the  organs 
of  circulation;  the  thvroid  and  thymus  bodies,  described  usually  with  the  respiratory  organs; 
the  adrenal  or  suprarenal  bodies,  described  •with  the  urinary  organs;  the  pineal  and  pituitary 
bodies,  described  with  the  brain;  and  the  spleen,  described  with  the  digestive  system  as  a  matter 
of  convenience.  The  spleen  is  not,  strictly  speaking,  a  gland  at  all:  it  is  not  epithelial  in  origin 
or  structure,  but  is  mesenchymatous. 


378 


DIGKSTIVE    SYSTEM    OF    THE    HORSE 


pounds  in  lior.scs  weighing  1000  to  1200  pounds.     The  chief  variation  in  outhne  consists  of  increase 
of  width,  especially  of  the  dorsal  part. 

It  extends  obliquely  in  a  curved  direction  from  the  left  crus  of  the  diaphragm 
and  the  saccus  esecus  of  the  stomach  to  the  ventral  third  of  the  ninth  or  tenth  rib. 
It  presents  for  description  two  surfaces,  two  borders,  and  two  extremities. 

The  parietal  or  external  surface  (Facies  jjarietalis)  is  convex,  and  lies  chiefly 
against  the  dia])hragin,  but  is  in  direct  contact  with  the  upper  parts  of  the  last 
two  ril)s  and  to  a  small  extent  with  the  flank  at  the  lumbo-costal  angle. 

The  visceral  or  internal  surface  (Facies  visceralis)  is  in  general  concave.  It 
is  divided  into  two  uneciual  portions  by  a  longitudinal  ridge;  on  this  is  a  groove, 
the  hilus,  in  which  the  vessels  and  nerves  are  situated.  The  area  in  front  of  the 
ridge  (Facies  gastrica)  is  moulded  on  the  great  curvature  of  the  stomach;  it  is  about 
two  inches  (ca.  5  cm.)  wide.     The  area  liehind  the  ridge  (Facies  intestinalis)  is 


Posterior  basiil  angle 


Attachment  of  xiis/x^nsonj  \ 
ligament      ) 


Tmt 

impression        / 


.1  nterior  basal  ang 
Splenic  artery 
Splenic  vein 

Anterior  border 


^7 — Spleen  of  Horse 

arketl  intestinal  impression  is  related  t 


much  more  extiMisive;  it  is  related  chiefly  to  the  small  colon,  the  small  intestine, 
and  the  grctit  omcntiiin.     It  may  be  marked  by  one  or  two  fissures. 

The  anterior  border  (Margo  anterior)  is  concave  and  thin. 

The  posterior  border  (\Iargo  posterior)  is  convex  and  thin. 

Tlie  base  or  dorsal  extremity  is  beveled,  and  fits  into  the  interval  between 
the  left  kidney  and  the  left  crus  of  the  diaphragm  and  the  psoas  major.  When 
hardened  iti  silii,  it  shows  an  impression  (Facies  renalis)  where  it  lies  against  the 
kidney.  The  left  extremity  of  the  pancreas  touches  it  also.  The  anterior  basal 
angle  fits  in  between  the  saccus  caucus  of  the  stomach  and  the  left  kidney;  the 
jiosterior  basal  angle  usually  lies  against  the  flank  just  behind  the  last  rib. 

The  apex  or  ventral  extremity  is  small;  it  lies — when  the  stomach  is  not  full — 
between  the  left  lobe  of  the  liver  and  the  left  dorsal  portion  of  the  colon;  when 


THE    PERITONEUM  379 

the  stomach  is  full,  the  spleen  is  pushed  further  back  and  loses  contact  with 
the  liver. 

The  spleen  is  attached  by  two  peritoneal  folds,  the  suspensory  ligament  and 
the  gastro-splenic  omentum.  The  suspensory  ligament  (Lig.  suspensorium  licnis) 
attaches  the  base  to  the  left  crus  of  the  diaphragm  and  the  left  kidney;  it  contains 
a  quantity  of  elastic  tissue.  The  part  which  passes  to  the  diaphragm  is  the  liga- 
raentum  phrenico-lienale,  and  blends  with  the  gastro-phrenic  ligament;  the  part 
which  goes  to  the  kidney  is  termed  the  ligamentum  renolienale.  The  gastro- 
splenic  omentum  (Lig.  gastrolienale)  passes  from  the  hilus  to  the  left  part  of  the 
great  curvature  of  the  stomach.  It  is  narrow  above,  where  it  joins  the  suspensory 
ligament;  below  it  becomes  much  wider  and  is  continuous  with  the  great  omentum. 

Small  globular  or  lenticular  ma.-ises  of  splenic  tissue  may  be  found  in  the  gastro-splenic 
omentum.     They  are  termed  accessory  spleens  (Lienes  accessoria;). 

Structure. — The  spleen  has  an  almost  complete  serous  coat.  Subjacent  to 
this  antl  intimately  united  with  it  is  a  capsule  of  fibrous  tissue  (Tunica  albuginea), 
which  contains  many  elastic  fibers  and  some  unstriped  muscular  tissue.  Numerous 
trabeculae  (Trabeculae  lienis)  are  given  off  from  the  deep  face  of  the  capsule  and 
ramify  in  the  substance  of  the  organ  to  form  a  supijorting  network.  In  the  inter- 
stices of  this  framework  is  the  spleen  pulp  (Pul]ia  lienis),  a  dark  red,  soft,  grumous 
material.  This  is  supported  by  a  delicate  adenoid  reticulum,  and  contains  numer- 
ous leukocytes,  the  large  splenic  cells,  red  blood-corpuscles,  and  pigment.  The 
pulp  is  richly  supplied  with  blood.  The  branches  of  the  splenic  artery  enter  at 
the  hilus  and  pass  along  the  trabeculae.  The  arteries  which  enter  the  pulp  have  a 
sheath  of  lymphoid  tissue,  which  collects  on  the  vessel  wall  at  certain  points,  form- 
ing small  lymph  nodules,  the  so-called  Malpighian  corpuscles  (Noduli  lymphatici 
lienales).  These  are  visible  to  the  naked  eye  as  white  spots,  about  as  large  as  the 
head  of  a  jDin.  The  blood  passes  into  cavernous  sj^aces  lined  bj'  endothelium 
w'hich  is  continuous  with  the  cells  of  the  reticulum  of  the  pulp.  From  these  the 
veins  arise.  The  splenic  vein  runs  in  the  hilus  in  company  with  the  artery  and 
nerves,  and  joins  the  posterior  gastric  vein  to  form  a  large  radicle  of  the  portal  vein. 

Blood-supply. — Splenic  artery. 

Nerve-supply. — Splenic  plexus. 


THE  PERITONEUM 

The  general  disposition  of  the  peritoneum  has  been  described,  and  other  facts 
in  regard  to  it  were  mentioned  in  the  description  of  the  viscera.  It  is  now  desirable 
to  study  it  as  a  continuous  whole.'     (Figs.  256,  257,  278,  279.) 

We  may  consider  the  peritoneum  as  consisting  of  tw-o  sacs — a  greater  and  a 
lesser.  The  greater  sac  lines  the  greater  part  of  the  abdominal  cavitj^  and  covers 
most  of  the  viscera  which  have  a  peritoneal  investment.  The  lesser  sac  is  an 
introversion  or  recess  of  the  greater  sac,  formed  during  the  development  of  the  vis- 
cera. The  two  sacs  communicate  by  a  relatively  narrow  passage,  termed  the 
epiploic  foramen  of  Winslow  (Foramen  ei^iploicum) .  This  opening  is  situated  on  the 
visceral  surface  of  the  liver  above  the  jjortal  fissure.  It  can  be  entered  by  passing 
the  finger  along  the  caudate  lobe  of  the  liver  toward  its  root.  Its  dorsal  (or  an- 
terior) wall  is  formed  by  the  caudate  lobe  and  the  posterior  vena  cava.  Its  ventral 
(or  posterior)  wall  consists  of  the  pancreas,  the  gastro-pancreatic  fold,  and  the  portal 
vein.  The  walls  are  normally  in  contact,  and  the  passage  merely  a  potential  one. 
It  is  usually  about  four  inches  (ca.  10  cm.)  in  length.     It  is  narrowest  at  the  right 

'  The  student  is  strongly  recommended  to  study  the  peritoneum  of  a  foal  or  other  small 
subject  when  the  opportunity  occurs,  a.s  in  these  the  viscera  are  easily  handled,  and  the  course 
of  the  peritoneum  can  be  followed  without  difficulty. 


380 


DIGESTIVE    SYSTEM    OF   THE    HORSE 


extremity,  where  it  is  about  an  inch  (ca.  2.5  to  3  cm.)  wide.'  If  the  finger  is  passed 
into  the  foramen  from  right  to  left,  it  enters  the  cavity  of  the  lesser  sac.  If  now 
an  opening  is  made  in  the  great  omentum  and  the  other  hand  introduced  through 
it,  the  fingers  of  the  two  hands  touch  each  other  over  the  lesser  curvature  of  the 
stomach.  The  formation  and  boundaries  of  the  lesser  sac  should  now  be  examined 
by  spreading  out  the  great  omentum.  It  will  be  found  that  the  latter  now  incloses 
a  considerable  cavity  behind  the  stomach;  this  is  termed  the  omental  cavity 
(Bursa  omentalis).  Passing  forward  over  the  lesser  curvature  of  the  stomach, 
we  enter  another  space,  the  vestibule  of  the  omental  cavity  (Vestibulum  Ijurste 
omentalis).  This  space  is  closed  on  the  left  by  the  gastro-phrenic  ligament,  below 
and  on  the  right  by  the  lesser  omentum,  and  dorsally  by  the  gastro-pancreatic 
fold,  which  is  attached  to  the  dorsal  border  of  the  liver  and  to  the  posterior  vena 
cava.  Above  the  oesophageal  notch  the  fingers  can  be  passed  around  the  border 
of  the  liver  and  the  vena  cava  till  the  coronary  ligament  is  encountered.  Thus 
the  vestiinile  is  closed  except  (1)  on  the  right,  where  it  communicates  with  the  cavity 


Fig.  278. — Diagram  of  General  Arrangement  of  Peritoneum  ( 

a.  Pouch  between  rectum  and  roof  of  pelvis,  continuous  witli  b,  recto-genital  pouch; 
d,  pouch  below  blaihier  and  its  lateral  Ugaments;  /,  lesser  omentum;  Int.,  small  intest 
to  the  epiploic  foramen  (of  Winslow). 


Sagittal  Tracing. 
c,  vesico-genital  ijouch; 
The  arrow  points 


of  the  greater  .sac  by  the  epiploic  foramen;   and  (2)  l)ehind,  where  it  communicates 
with  the  cavity  of  the  omentum. 

The  general  arrangement  of  the  great  omentum  has  already  been  indicated. 
We  may  now  trace  its  line  of  attachment,  which  would  correspond  to  the  mouth  of 
the  sac.  Beginning  at  the  ventral  part  of  the  great  curvature  of  the  stomach,  the 
line  passes  to  the  ventral  face  of  the  pylorus,  then  crosses  obliquely  the  first  part  of 
the  duodenum  to  the  point  where  the  pancreas  is  adherent  to  it.  Here  it  passes 
to  the  anterior  face  of  the  terminal  transverse  part  of  the  great  colon,  runs  along 
this  transversely  (from  right  to  left),  and  continues  for  some  ten  or  twelve  inches 
(ca.  25  to  30  cm.)  on  the  small  colon.  It  then  forms  an  acute  angle,  passes  inward 
and  forward  along  the  small  colon  to  the  dorsal  part  of  the  hilus  of  the  spleen, 
where  it  b!ends  with  the  suspensory  ligament  of  the  latter,  and  forms  a  recess 
(Recessus  lienalis)  behind  the  saccus  CiECus  of  the  stomach.  It  now  passes  along 
the  hilus  of  the  spleen,  and  is  continued  to  the  great  curvature  of  the  stomach  l)y  the 
gastro-splenic  omentum.     It  is  convenient  to  regard  the  spleen  as  being  intercal- 

'  The  passage  is  subject  to  a  good  deal  of  variation  in  caliber  and  is  sometimes  completely 
occluded. 


THE    PERITONEUM 


381 


ated  in  the  left  part  of  tlie  great  omentum;  on  this  basis  the  gastro-splenic  omentum 
woukl  he  that  part  of  the  great  omentum  which  connects  the  hilus  of  the  spleen 
with  the  great  curvature  of  the  stomach.  The  great  omentum  is  relativelj^  small 
in  the  horse,  and  is  usually  not  visible  when  the  abdomen  is  opened.  It  is  gc-nerally 
folded  up  in  the  space  between  the  visceral  surface  of  the  stomach  and  the  intestine.^ 

The  lesser  sac  furnishes  tlie  peritoneal  covering  for:  (1)  the  visceral  surface  of  tlie  stomach 
and  a  small  area  of  the  first  curve  of  the  duodenum;  (2)  a  large  part  of  the  dorsal  surface  of  the 
pancreas  and  portal  vein ;  (8)  a  small  part  of  the  visceral  surface  of  the  Uver  above  the  attachment 
of  the  lesser  omentum  anil  llic  poiial  fossa;  (4)  the  posterior  vena  cava,  from  the  level  of  the  epi- 
ploic foramen  [of  Winsldul  iiiiN  ]i;issage  through  the  diaphragm  (in  so  far  as  it  is  not  embedded); 
(n)  the  part  of  the  parietal  surface  of  the  liver  between  the  right  and  middle  di\isions  of  the  cor- 
onary ligament;  (6)  the  corresponding  part  of  the  diaphragm,  and  the  right  part  of  the  right  crus 
of  the  same;  (7)  part  of  the  anterior  surface 
of  the  terminal  part  of  the  great  colon,  and  , 

the  origin  of  the  small  colon;  (<S)  the  left  ex- 
tremity of  the  pancreas  (inconstant);  (9)  the 
spleen. 

We  may  now  trace  the  peritoneum 
in  a  longitudinal  direction,  beginning 
in  front.  It  is  reflected  from  the  ven- 
tral abdominal  wall  and  the  diaphragm 
upon  the  liver,  forming  the  ligaments 
and  serous  coat  of  the  gland.  It  leaves 
the  visceral  surface  of  the  liver  as  lesser 
omentum,  and  the  crura  of  the  dia- 
phragm as  the  gastrophrenic  ligament, 
reaches  the  saccus  cibcus  and  lesser 
curvature  of  the  stomach  and  the  first 
curve  of  the  duodeiaum,  covers  these 
organs,  and  is  continued  by  the  great 
omentum. 

On  the  left  it  passes  from  the  left 
crus  of  the  diaphragm  and  the  left 
kidney  to  form  the  suspensory  liga- 
ment of  the  spleen,  clothes  that  organ, 
and  leaves  it  to  be  continued  by  the 
great  omentum. 

On  the  right  it  passes  from  the 
right  crus  of  the  diaphragm  and  the 
dorsal  border  of  the  liver  to  the 
concave  border  of  the  duodenum, 
forming  the  gastro-pancreatic  fokl 
(second  part  of  the  mesoduodenum), 
and  covering  part  of  the  dorsal  sur- 
face of  the  pancreas.  From  the  margin  of  the  pancreas,  the  right  kidney,  and  a 
small  area  of  the  sublumbar  region  behind  the  latter,  it  pa.sses  on  to  the  base  of 
the  caecum  and  the  terminal  part  of  the  great  colon.  From  these  it  passes  on  the 
right  to  the  duodemmi,  forming  the  third  part  of  the  mesoduodenum.  On  the 
left  it  clothes  part  of  the  ventral  surface  and  the  outer  border  of  the  left  kidney,  from 
which  it  passes  to  the  l^ase  of  the  spleen,  forming  the  ventral  layer  of  the  suspen- 
sory ligament  of  the  latter.  Behind  the  terminal  part  of  the  great  colon  it  is  reflected 
around  the  great  mesenteric  artery  to  form  the  great  mesentery.  Behind  this  it 
is  reflected  almost  transversely  from  the  roof  of  the  cavity  and  from  the  origin  of 
the  small  colon  on  to  the  duodenum,  forming  the  terminal  part  of  the  mesoduo- 

'  In  dissecting-room  subjects  (which  are  usually  aged)  the  omentum  often  exhibits  patho- 
logical changes,  such  as  adhesions,  rents,  tumors,  formation  of  twisted  strands,  etc. 


Flo.  279. — Di.iGRAM  OF  Abdomi.nal  Peritoneum  in 
Frontal  (Horizontal)  Tracing. 
D,  Duodenum.  The  arrow  indicates  the  epiploic 
foramen  (of  Winslow).  By  an  oversight  the  leader  Hne 
to  the  great  omentum  is  omitted,  and  the  coronary  Hga- 
meot  of  the  Uver  is  erroneously  marked  lesser  omentum; 
the  latter  e.xtends  from  liver  to  stoniach,  but  is  not 
marked. 


382  DIGESTIVE    SYSTEM    OF   THE    OX 

denuiii.  The  line  of  origin  of  the  colic  nicsontcry  begins  on  the  inner  part  of  the 
ventral  surface  of  the  left  kithiey,  and  extends  to  the  sacral  promontory,  where 
the  mesorectuni  begins.  At  the  termination  of  the  latter  the  peritoneum  is  re- 
flected from  the  rectum  on  the  dorsal  and  lateral  walls  of  the  pelvic  cavity.  Below 
the  rectum  it  forms  the  urogenital  fold,  antl  passes  on  to  the  dorsal  surface  of  the 
bladder,  covers  its  anterior  part,  and  is  reflected  on  to  the  body-wall  laterally  and 
ventrally,  forming  the  lateral  and  middle  ligaments  of  the  bladder.  In  the  female 
the  broacl  ligaments  of  the  uterus  replace  the  urogenital  fold,  with  which  they  are 
homologous. 

In  the  new-born  foal  certain  folds  arc  specially  large.  The  falciform  ligament 
of  the  liver  extends  to  the  umbilical  opening,  and  contains  in  its  free  edge  the  large 
uml:)ilical  vein.  The  bladder — at  this  time  an  abdominal  organ — has  a  ventral 
median  fold,  which  connects  it  and  the  urachus  with  the  abdominal  floor.  This  is 
flanked  on  either  side  by  a  fold  which  also  extends  to  the  umbilicus,  and  contains 
the  large  umbilical  artery. 


DIGESTIVE  SYSTEM  OF  THE  OX 
THE  MOUTH 
The  cavity  of  the  mouth  is  shorter  and  wider  than  that  of  the  horse,  and  the 
vestibule  is  more  capacious. 

The  lips  are  thick,  wide,  and  comparatively  immobile.  The  middle  jjart  of 
the  upper  lip  and  the  surface  between  the  nostrils  is  bare,  and  is  termed  the  muzzle 
(Planum  nasolabiale).     It  is  smooth,  and  (in  health)  is  kept  cool  and  moist  by  a 


Conical  jKipiUw  yT 

\ 
Floor  of  moulh 


„.    ,  .     .        ,     ,,     _A-^-^?^      A   'f''^?»'/ ia^^BT  Angle  of  mouth 

First  mcisoT  luolh Xj  •  S^s-i__I*rS^- **iii^^Br\ 

''Conical  papilla; 

''Lower  lip 

Fic.  280. — Anterior  Part  of  Lower  Jaw  of  Ox. 
00,  Tip  of  tongue.      (After  EUenberger-Baum,  Anat.  fiir  Kiinstler.) 

clear  fluid  secreted  by  a  layer  of  subcutaneous  glands  (Glandulse  nasolabiales) 
about  half  an  inch  (ca.  1.5  cm.)  thick.  It  shows  irregular  lines,  mapping  out  small 
polygonal  areas  on  which  the  orifices  of  the  gland  ducts  are  visible.  A  narrow 
bare  strij)  also  exists  along  the  edge  of  the  lower  lip.  The  remainder  of  the  integu- 
ment is  provided  with  ordinary  and  tactile  hairs.  The  free  edge  and  the  lining 
membrane  present  verrucose,  horny  papillie.  The  labial  glands  form  compact 
masses  near  the  angles  of  the  mouth. 

The  cheeks  are  more  capacious  than  in  the  horse.  The  mucous  meml)ranc 
presents  large  conical  pointed  papillae,  which  are  directed  toward  the  fauces  and 
are  covered  with  a  horny  epithelium.     The  largest  of  tliese  have  a  length  of  about 


THE    MOUTH 


383 


half  an  inch  (ca.  1  to  1.5  cm.)  and  are  situated  around  the  angle  of  the  mouth  and 
parallel  with  the  cheek  teeth.  The  orifice  of  the  parotid  duct  is  opposite  the  fifth 
upper  cheek  tooth.  (In  the  sheep  and  goat  it  is  opposite  the  fourth  tooth.)  The 
buccal  or  molar  glands  are  very  well  developed,  and  are  arranged  in  three  parts. 
The  dorsal  row  extends  from  the  maxillary  tuberosity  to  the  angle  of  the  mouth. 
Its  lobules  are  of  a  light  yellow  color.     The  ventral  part  consists  of  a  compact 


Cavity  of  great  ethmolurhinal 


Cavily  of  superior  turbinal 


Cavities  of  inferior  turhina 


M  ylo-hyoideU: 
muscle 


Fig.  281. — Sagittal  Sectio>j  of  Head  of  Cow,  Cn  a  little  to  the  Right  of  the  Median-  Plane. 
i.  Cerebral  hemisphere;  5.  corpus  striatum;  3,  hippocampus;  .{,  olfactory  bulb;  o,  corpora  quailrigemina; 
e,  optic  nerve;  7,  pons;  S,  medulla  oblongata;  9.  spinal  corJ;  /O.  pituitary  body;  //,  .sphenoid  sinus;  /5,  lateral 
mass  of  ethmoid;  13,  ventral  straight  muscles;  H,  pharyngeal  (retropharyngeal)  lymph  gland;  IS,  longus  colli; 
16,  soft  palate;  17.  vallate  papilla;;  IS,  tonsillar  sinus;  19,  conical  papilte  of  cheek;  20,  hyo-epiglotticus  mus- 
cle; «i,  epiglottis;  ^3,  hyo-glossus  muscle;   C1,C3,  atlas,  axis.     Subject  was  hardened  with  mouth  open. 


bro-miish  mass  which  reaches  from  the  angle  of  the  mouth  a  short  distance  under' 
the  masseter  muscle.     The  mifldle  part  consists  of  loosely  arranged  yellow  lobules. 

A  linear  series  of  large  papilla  exists  on  the  floor  of  the  mouth  on  each  side  of 
the  frenum  lingua;.  Near  these  are  found  the  openings  of  the  small  ducts  of  the 
sublingual  gland.  The  papilla  on  which  the  submaxillary  duct  opens  is  wide,  hard, 
and  has  a  serrated  edge. 

The  hard  palate  is  wide,  and  is  usually  more  or  less  pigmented.  The  body  of 
the  premaxilla  is  covered  with  a  thick  layer  of  dense  connective  tissue,  which  has  a 


384 


DIGESTIVE    SYSTEM    OF   THE    OX 


thick,  horny  epitheUal  covering — forming  the  so-called  dental  plate  or  patl.  The 
palatine  ridges  extend  from  this  backward  about  two-thirds  of  the  length  of  the 
hard  palate.  They  are  nearlj'  straight,  and,  for  the  most  part,  are  serrated  on  the 
free  edge.  A  median  furrow  extends  between  the  ridges.  The  posterior  thirtl  of 
the  palate  is  smooth.  Between  the  dental  plate  and  the  first  ridge  is  the  triangular 
papilla  incisiva;  on  either  side  of  this  is  a  deep  furrow,  in  which  is  the  oral  opening 


Cai'Uy 
Superior    Superior     Septum     of  superior 
turbinal        meatus        nasi        turbinal 


Frontal 


Middle  meatus 
Inferior  turbinal 

Inferior  meatus 
Maxillary  sinus 
Palatine  sinus 

Palatine  artery. 


Inferior  labial 


Hypoglossal  nerve 


Naso-laerimal  duct 


Infraorbiial  nerve 
Masselcr 


Sujjerior  buc- 
cal yla/ids 

Facial  artery 
Facial  vein 


Inferior  buccal 
ylands 


Subiiiigual  (/land 
Digastrieus 


Sulmiaxil-         Lingual 
lary  duet  nerve 

Vic.  2S2. — Cross-section  of  Head  of  Ox. 
The  .section  passes  through  the  internal  canthi.     L.n.,  Lincual  arteries.     The  arrow  indicates  the  communicatii 


lietv 


llary  and  palatine  sinu 


of  the  naso-palatine  canal.  This  canal  is  two  inches  or  more  (ca.  5  to  6  cm.)  in 
lengtli  ami  ojicns  on  the  floor  of  the  nasal  cavity;  it  also  communicates  by  a  slit- 
like opening  with  the  organ  of  Jacobson. 

The  soft  palate  is  somewhat  shorter  than  that  of  the  horse,  but  is  long 
enough  to  close  the  isthmus  of  the  fauces.  The  posterior  pillars  do  not 
extend  to  the  entrance  of  the  oesophagus.     The  azygos  muscle  is  much  better 


THE    TONGUE 


385 


developed   than   in   the    horse.     The   fibrous   ajioneurosis   is   for   the   most   part 
replaced  by  muscular  tissue. 

The  isthmus  faucium  is  wide  and  dilatable.  On  either  side,  b(>hind  the  an- 
terior pillar  of  the  soft  palate,  is  a  deep  depression,  the  sinus  tonsillaris ;  external 
to  this  is  the  compact  bean-shaped  tonsil,  which  is  about  one  to  one  and  a  half 
inches  (ca.  3  to  4  cm.)  in  length.  The  tonsil  does  not  project  into  the  fauces,  but 
outward  instead:  hence  it  does  not  occupy  the  tonsillar  sinus,  and  is  not  visible 
internally,  as  is  the  case  in  most  animals. 


(Esophagus- 
Apices  of  aryljnni't. 
Aditus  laryngis 

Epiylutl 


Thyroid  gland 

Wall  of  pharynx  reflected 


Posterior  pillar  of  soft 
palate 


Soft  palate  cut  and 
reflected 


Vallate  papiUce 


TonsiiL:r  sinus 


Eminence  of  dorsum 


Fungiform  papilla 


Tic.  283. — Tongue  of  Ox,  Dohs.\i.  Aspect. 
Pharynx,  soft  palate,  and  origin  of  oesophagus  are  cut  dorsally 


THE  TONGUE 
The  tongue  of  the  ox  is  often  variably  pigmented.  The  root  and  body  are 
wider  than  that  of  the  horse,  but  the  free  part  is  more  pointed.  The  posterior  part 
of  the  dorsum  forms  a  remarkable  elliptical  prominence,  which  is  sharply  defined 
in  front.  The  filiform  papillae  in  front  of  this  prominence  are  large  and  horny,  with 
sharp  points  directed  backward.  They  impart  to  the  tongue  its  rasp-like  roughness. 
The  papillae  on  the  prominence  are  large,  broad  and  horny;  some  have  a  blunt 
conical  form,  others  are  rounded  or  flattened.  Behind  the  prominence,  the  papilte 
are  long  and  soft,  ;'.  e.,  not  horny.  The  fungiform  pajjillse  are  numerous  and  dis- 
tinct; they  are  scattered  more  generally  over  the  dorsum  and  edges  of  the  free 
25 


386 


DIGESTIVE    SYSTEM    OF    THE    OX 


part.  The  vallate  papillse  are  about  twenty  or  thirty  in  number;  they  are  smaller 
than  those  of  the  horse,  and  are  irregularly  distributed  on  either  side  of  the  posterior 
part  of  the  prominonee  of  the  dorsum.  The  foliate  papillae  and  the  lingual  fibrous 
cortl  are  absent.  The  muscles  are  well  developed;  the  hyo-glo.ssus  arises  by 
additional  portions  from  the  great  and  middle  cornua  of  the  hyoid  bone.  The 
tongue  is  highly  protractile  and  is  the  chief  organ  of  prehension. 


THE  TEETH 
The  dental  formula  of  the  ox  is: 


/  0     0     3      3\ 
2  I  I-C'-P-M-  I  =  32 
V    4     0     3      3/ 


The  incisors  are  absent  from  the  upper  jaw.  There  are  eight  incisors  in  the 
lower  jaw,  arranged  in  a  somewhat  fan-like  manner.  They  are  simple  teeth,  without 
infundibulum.     The    crown    is    white,   short,   and    shovel-shaped.     The   root    is 


Fig.  285. — Incisoh  Tooth  of  Ox. 

2A' ,  Lingual  surface  of  crown;  2It'\  masti- 
cators' surface.  The  crown  is  clearly  marked  off 
from  the  rounded  root  by  a  neck,  (.\fter  Ellen- 
berger-Baum,  .\nat,  fiir  Kimstler.) 


rounded,  and  is  embeddeil  in  the  jaw  in  such  a  manner  as  to  allow  a  considerable 
degree  of  movement.  There  is  a  distinct  neck.  In  addition  to  the  simjjle  numeri- 
cal designation,  the  following  terms  are  commonly  applied  to  the  indiviilual  teeth: 
pinchers  or  central,  first  intermediate,  second  intermediate,  and  corner  incisors. 
It  is  probaljle  that  the  latter  are  much  modified  canines.  The  incisors  of  the 
ox  do  not  advance  out  of  the  alveoli,  as  is  the  case  in  the  horse;  in  old  age,  how- 
ever, the  gum  retracts  so  that  the  roots  are  partly  exposed  and  may  come 
into  wear.' 

The  deciduous  incisors  differ  from  the  permanent  set  chiefly  in  being  much 
smaller.     The  crowns  are  narrower  anil  diverge  more. 

The  canines  are  absent  (unless  the  fourth  incisors  be  considered  to  rejiresent 
them). 

The  cheek  teeth  (Fig.  286)  resemble  those  of  the  horse  in  number  and  general 
arrangement.       They  are,  however,  smaller,  and  also  differ  in  the  fact  that  they 

'  The  student  will  note  here  the  difference  between  the  structure  and  behavior  of  the 
brachydont  (short-crowned)  incisors  of  the  ox  and  the  hypsodont  (long-crowned)  type  of  the  horse. 


THE    TEETH 


387 


388  DIGESTIVE    SYSTEM    OK    THE    OX 

progressively  increase  in  size  from  before  liackward.  This  feature  is  so  marked 
that  the  first  tooth  is  quite  small,  and  the  space  occupied  by  the  first  three  {i.  e., 
the  premolars)  is  only  about  one-half  of  that  required  for  the  posterior  three 
(i.  e.,  the  true  molars).  The  enamel  folds  stand  out  even  more  prominently  in 
relief  on  the  masticatory  surface  than  in  the  horse.  The  occurrence  of  wolf-teeth 
is  rare. 

The  formula  of  the  decitluous  teeth  is: 


(0       0       3\ 
Di-  De  -  Dp-  I  =  20 
4       0        3/ 


T.VBLE  OF  AVERAGE  PERIODS  OF  ERUPTION  OF  THE  TEETH  IX  THE  OX 

Teeth  Eruption 

A.  Temporary: 

First  incisor  (Di  1) 

Second  incisor  (Di  2) I  n-  ii   »    -y        i 

Third  incisor  (Di  3). |  ^''^^  '°  ^  weeks. 

Fourth  incisor  (Di  4) J 

First  cheek  tootli  (Dp  1) Birth  to  3  weeks. 

Second  cheek  tooth  ( Dp  2) 1  „.  ,,   ,    , 

Third  cheek  tooth  (Dp  3) /  ^'^th  to  few  days. 

B.  Permanent: 

First  incisor  (II) 1 J^  to  2  years. 

Second  incisor  (12) 2  to  2J4  years. 

Third  inci.sor  (13) 3  years. 

Fourth  incisor  (14) 33>^  to  4  years. 

First  cheek  tooth  (PI) 2  to  2}^  years. 

Second  cheek  tooth  (P  2) 1 '  2  to  2}^  years. 

Third  cheek  tooth  (P  3) 2}^  to  3  years. 

Fourtli  cheek  tooth  (Ml) 5  to  6  months. 

Fifth  cheek  tooth  (M2) 1  to  1}^  years. 

Sixth  cheek  tooth  (M3) 2  to  2^  years. 

The  eruption  of  the  permanent  teeth  is  subject  to  great  variation.  The  above 
figures  are  the  average  of  observations  of  improved  breeds  under  favorable  condi- 
tions. 

THE  SALIVARY  GLANDS 

The  parotid  gland  is  smaller  than  that  of  the  horse,  and  is  light  red-brown  in 
color.  It  has  somewhat  the  form  of  a  very  narrow  long  triangle,  and  lies  chiefly 
on  the  posterior  part  of  the  masseter  muscle.  The  thick  wide  upper  end  partly 
covers  a  large  subparotid  lymph  gland.  The  small  lower  end  is  bent  forward  and 
fits  into  the  angle  of  union  of  the  jugular  and  external  maxillary  veins;  it  lies  on 
the  submaxillary  gland.  The  parotid  duct  leaves  the  lower  part  of  the  deep  face; 
in  its  course  it  resembles  that  of  the  horse,  but  it  pierces  the  cheek  opposite  the 
fifth  upper  cheek  tooth. 

The  submaxillary  gland  is  very  large,  and  is  pale  j^ellow  in  color.  It  is  covered 
to  a  small  extent  \>y  the  parotid.  Its  general  form  resembles  that  of  the  horse, 
but  its  lower  (or  anterior)  end  is  large  and  rounded,  and  is  separated  by  a  small 
interval  only  from  the  gland  of  the  other  side.  This  part  can  be  distinctly  felt  in 
the  living  animal,  and  is  related  externally  to  a  large  submaxillary  lymph  gland. 
The  duct  leaves  the  middle  of  the  superficial  face  of  the  gland,  crosses  the  stylo- 
hyoideus  and  the  intermediate  tendon  of  the  digastricus,  and  is  then  disposed  as 
in  the  hcrse. 

The  sublingual  gland  consists  of  two  parts.  The  dorsal  part  (Glandula  sub- 
lingualis parvicanalaris)  is  long,  thin,  and  pale  yellow  in  color.  It  extends  from  the 
anterior  pillar  of  the  soft  palate  about  to  the  symphysis  of  the  jaw.  It  has  numer- 
ous small  tortuous  ducts  (Ductus  sublinguales  minores),  which  open  between  the 
jjapillae  under  the  side  of  the  tongue.     The  ventral  part  is  shorter  and  thicker,  and 


THE    PHARYNX — THE    CESOPHAGUS 


389 


is  salmon  pink  in  color.     It  has  a  single  duct  (Ductus  sublingualis  major),  which 
either  opens  alongside  of  or  joins  the  submaxillary  duct. 


THE  PHARYNX 

The  pharjTix  is  short  and  wide.     The  vault  (Fornix  pharyngis)  is  divided  into 

two  cul-de-sacs  by  a  median  fold  of  mucous  membrane  (Septum  nasi  membrana- 

ceum),  which  is  a  continuation  of  that  of  the  .septum  nasi;    on  the  outer  wall  of 

each  is  the  relatively  small  opening  of  the  Eustachian  tube,  which  is  covered  by  a 


Fir..  2S7.— Salivary  Glands  of  Ox. 
a.  Parotid  gland;    b,  submaxillary  gland;    c,  inferior,  d,  midtlle,  and  e,  superior  buccal  glanils;    /,  labial 
glands;  ff,  buccinator  nerve;   ft,  buccinator  vein;    /,  masseter  (cut);  2,  ramus  of  mandible;   5,  zygomaticus  muscle; 
4,  conical  papili*  of  lip:   5,  buccinator  muscle.     (After  Ellenberger,  in  Leisering's  .\tla3.) 


The  posterior  nares  are  small.     The  entrance 


simjile  fold  of  mucous  membrane, 
to  the  oesophagus  is  large. 

On  the  dorsal  wall  of  the  pharynx  are  two  large  pharyngeal  lymph  glands,  which,  when 
enlarged,  cause  difficulty  in  swallowing  and  breathing  (Fig.  281). 


THE  CESOPHAGUS 
This  is  much  shorter,  wider,  and  more  dilatable  than  that  of  the  horse.  Its 
average  diameter  (when  moderately  inflated)  is  about  two  inches  (ca.  5  cm.),  and 
its  length  in  a  large  animal  is  about  three  to  three  and  a  half  feet  (ca.  90  to  100  cm.). 
The  wall  is  relatively  thin,  and  the  muscular  tissue  is  striped  throughout.  The 
latter  consists  of  two  strata  of  spiral  fibers,  except  near  the  stomach,  where  they 
are  longitudinal  and  circular.     Fibers  are  continued  into  the  wall  of  the  stomach 


390  DIGESTIVE    SYSTEM    OF    THE    OX 

for  some  distance.     There  are  submucous  glands  in  the  first  part  of  the  tube.     There 
is  no  terminal  dilatation,  and  no  part  in  the  abdominal  cavity. 

A  very  large  mediastinal  lymph  gland  lies  above  the  posterior  part  of  the  ccsophagus  and 
may,  if  enlarged,  obstruct  it  (Fig.  289). 

THE  ABDOMINAL  CAVITY 
The  abdominal  cavity  of  the  ox  is  very  capacious,  both  absolutely  and  rela- 
tively, as  compared  with  that  of  the  horse.  This  is  due  to  several  factors.  The 
lumbar  portion  of  the  spine  is  about  one-fourth  longer  than  that  of  the  horse.  The 
transverse  diameter  l)et\veen  the  last  ribs  is  greater.  The  costal  attachment  of  the 
diaphragm  is  almost  vertical  in  direction  from  the  lower  part  of  the  ninth  rib  to 
the  extreme  upper  i)art  of  the  thirteenth;  in  fact,  the  attachment  to  the  last  rib 
is  not  constant.  Thus  the  abdomen  is  increased  at  the  expense  of  the  thorax,  and 
the  last  three  or  four  ribs  enter  more  largeh'  into  the  formation  of  the  abdominal 
wall  than  in  the  horse.  The  flank  is  also  much  more  extensive.  The  ilia,  on  the 
other  hand,  do  not  extend  forward  beyond  a  transverse  plane  through  the  middle 
of  the  last  lumbar  vertebra.  The  epigastric  and  mesogastric  regions  would  he 
separated  by  a  plane  through  the  lower  end  of  the  tenth  pair  of  ribs,  or  through  the 
last  thoracic  vertebra.  Tlie  chief  differential  features  in  the  arrangement  of  the 
peritoneum  will  be  described  with  the  viscera. 


THE  PELVIC  CAVITY 
The  pelvic  cavity  is  relatively  long  and  narrow.  The  inlet  is  more  olilique 
than  that  of  the  horse;  it  is  elliptical  in  outline,  and  the  transverse  diameter  is 
smaller  than  that  of  the  horse.  The  anterior  (pubic)  part  of  the  floor  is  about 
horizontal,  but  the  posterior  (ischial)  part  slopes  upward  and  backward  to  a  marked 
degree;  this  part  is  also  deeply  concave  transversely.  The  roof  is  concave  in 
both  directions.  The  peritoneum  extends  backward  as  far  as  the  first  coccygeal 
vertebra,  so  that  the  retroperitoneal  part  of  the  cavity  is  short. 


THE  STOMACH 

General  Arrangement. — The  stomach  of  the  ox  is  very  large,  and  occupies 
nearly  three-fourths  of  the  abdominal  cavity.  It  fills  all  of  the  left  half  of  the  cavity 
(with  the  exception  of  the  small  space  occupied  by  the  s])leenj  and  extends  con- 
siderably over  the  median  plane  into  the  right  half. 

It  is  compound,  lieing  composed  of  four  divisions,  viz.,  rumen,  reticulum, 
omasum,  and  abomasum.'  The  division  is  clearly  indicated  externall>'  by  furrows 
or  constrictions.  The  first  three  divisions  may  be  regarded  as  provcntriculi  or 
a-sophageal  sacculations,  the  fourth  being  the  stomach  proper  (in  the  narrower 
sense  of  the  term).  The  oesophagus  opens  into  the  stomach  on  a  sort  of  dome 
formed  by  the  rumen  and  reticulum,  and  is  continued  through  the  latter  by  the 
ccsophageai  groove.  From  the  ventral  end  of  the  latter  a  groove  traverses  the 
ventral  wall  of  the  omasum,  thus  giving  a  direct  path  to  the  abomasum  for  finely 
diviiled  or  fluid  food.     The  abomasum  joins  the  small  intestine. 

Capacity. — Th(>  capacity  of  the  stomach  varies  greatly,  depending  on  the  age 
and  size  of  the  animal.  In  cattle  of  medium  size  it  holds  30  to  40  gallons,  in  large 
animals  40  to  60,  in  small  25  to  35.  The  relative  sizes  of  the  four  parts  vary  with 
age.     In  the  new-born  calf  the  rumen  and  reticulum  together  arc  about  half  as 

'  In  popular  language  these  are  conveniently  regarded  as  so  many  stomachs,  and  termed 
arcordingly  "first,"  "second,"  etc.  Otlier  names  are  in  common  use,  e.  g.,  paimch,  honeycomb, 
manifold  or  manyijfies,  antl  rennet  or  true  stomacli. 


THE    STOMACH 


391 


Iarp;e  as  the  aliomasum;  in  ten  or  twelve  weeks  this  ratio  is  reversed.  During 
tiiis  ])erioci  the  omasum  a])])ears  to  he  contracted  and  functionless.  At  four  months 
the  rumen  and  reticuhun  together  are  about  four  times  as  large  as  the  omasum 
antl  abomasum  together.  At  about  one  and  one-half  years  the  omasum  equals 
(or  nearly  so)  the  abomasum  in  capacity.  The  four  divisions  have  now  reached 
their  definitive  relative  capacities,  the  rumen  constituting  about  80  per  cent.,  the 
reticulum  5  per  cent.,  the  omasum  7  or  8  per  cent.,  anrl  the  abomasum  8  or  7  per 
cent,  of  the  total  amount. 

Exterior  and  Relations 
The  rumen  occupies  almost  all  of  the  left  half  of  the  abdominal  cavity,  and 
extends  considerably  over  the  median  plane  ventrally  and  in  its  middle.  It  is  some- 
what compressed  laterally,  and  may  be  described  as  having  two  surfaces,  two  curva- 
tures or  borders,  and  two  extremities.  The  parietal  (or  left)  surface  (Facies 
parietalis)  is  convex  and  is  related  to  the  diaphragm,  spleen,  and  the  left  wall  of 
the  abdomen.     It  extends  from  the  lower  part  of  the  seventh  intercostal  space 


Fig.  288. — Projection  of  Viscera  of  Cow  on  Body-wall,  Left  .Side. 
Oes..  Oesophagus:  Ret.,  reticulum;    b.s.,  anterior  blind  sac;    b.s.',  b.s"..  posterior  blind  sacs  of   rumen;    0, 
ovary.     The  left  kidney,  concealed  by  the  dorsal  sac  of  the  rumen,  is  indicated  by  dotted  line.     The  median 
line  of  the  diaphragm  is  dotted. 


almost  to  the  pelvis.  The  visceral  (or  right)  surface  (Facies  visceralis)  is  somewhat 
irregular,  and  is  related  chiefly  to  the  omasum  and  abomasum,  the  intestine,  the 
liver,  pancreas,  kidneys,  the  uterus  in  the  female,  and  the  posterior  aorta  and  vena 
cava.  The  dorsal  curvature  (Curvatura  dorsalis)  is  convex,  following  the  curve 
formed  by  the  diaphragm  and  sublumbar  muscles.  It  is  firnilj'  attached  to  the 
left  portion  of  the  crura  of  the  diaphragm  and  the  sublumbar  muscles  by  peri- 
toneum and  connective  tissue.  The  ventral  curvature  is  also  com-ex  and  lies  on 
the  floor  of  the  abdomen.  The  surfaces  arc  marked  by  the  right  and  left  longitudi- 
nal furrows  (Sulci  longitudinales),  which  indicate  externally  the  division  of  the 
rumen  into  dorsal  and  ventral  sacs.'  The  reticular  (or  anterior)  extremity  (Ex- 
tremitas  reticularis)  is  divided  ventrally  by  a  transverse  groove  (Sulcus  ruminis 
cranialis)  into  two  sacs.  The  dorsal  sac  is  the  longer  of  the  two,  and  curves  ven- 
trally over  the  round,  blind  end  of  the  ventral  sac.     The  former  only  is  continuous 

'  It  has  been  customary  to  term  the  sacs  left  and  right  respectively,  but  these  do  not  repre- 
sent the  relations  as  they  exist  in  situ  and  as  they  are  presented  on  frozen  sections. 


392  DIGESTIVE    SYSTEM    OF   THE    OX 

with  the  reticulum,  a  ventral  groove  (Sulcus  runiino-reticularis)  being  the  only 
external  line  of  demarcation.  Dorsally  no  natural  separation  exists,  the  rumen 
and  reticulum  together  forming  a  dome-like  vestibule  (Atrium  ventriculi)  on  which 
the  cesophagus  terminates.  The  pelvic  (or  i)osterior)  extremity  (Extremitas 
pelvina)  extends  nearly  to  the  pubis,  and  is  related  to  the  intestine  and  bladder, 
and  the  uterus  in  the  cow.  It  is  divided  into  dorsal  and  ventral  blind  sacs  (Saccus 
csecus  caudalis  dorsalis,  ventralis)  by  a  deep  transverse  groove  (Sulcus  ruminis 
caudalis)  in  which  the  longitudinal  furrows  terminate.  The  blind  sacs  are  marked 
off  from  the  remainder  of  the  rumen  by  the  dorsal  and  ventral  coronary  grooves 
(Sulcus  coronarius  dorsalis,  ventralis). 

The  left  longitudinal  groove  (Sulcus  longitudinalis  sinister)  begins  at  the  anterior  transverse 
groove,  passes  somewhat  dorsally  and  backward  and  divides  into  two  grooves.  The  ventral 
one  is  the  chief  groove  and  passes  backward  to  terminate  in  the  angle  of  union  of  the  posterior 
blind  sacs.  The  dorsal  (accessory)  groove  curves  dorsally  and  then  backward  to  terminate  in 
the  dorsal  coronary  sulcus.  On  the  right  surface  there  are  two  longitudinal  grooves.  The  dorsal  one 
is  the  chief  sulcus" (Sulcus  longitudinalis  dexter).  It  extends  in  a  curved  direction  (the  convexity 
being  dorsal)  and  is  continuous  with  the  left  longitudinal  groo\c  by  means  of  the  grooves  between 
the  dorsal  and  ventral  blind  sacs  at  each  enrl.  The  ventral  groove  (Sulcus  accessorius)  curves 
somewhat  vent  rally  and  backward  to  rejoin  the  chief  sulcus  between  the  posterior  blind  sacs. 

The  reticulum  is  the  smallest  of  the  four  divisions  in  the  ox.  It  is  also  the 
most  anterior,  and  Hes  on  the  concave  surface  of  the  diaphragm,  so  that  the  median 
plane  divides  it  into  two  nearly  equal  portions.  It  is  somewhat  pyriform, 
but  much  compressed  from  before  backward.  The  parietal  or  phrenic  surface 
(Facies  diaphragmatica)  is  convex  and  lies  against  the  diaphragm  and  liver.' 
The  ruminal  (or  posterior)  surface  (Facies  ruminalis)  is  flattened  by  the  pressure 
of  the  other  three  compartments;  it  ends  dorsally  by  joining  the  wall  of  the  rumen, 
the  concave  line  of  junction  forming,  in  the  interior  of  the  stomach,  the  lower  margin 
of  the  large  rumino-reticular  orifice.  The  omasal  (or  right)  surface  is  narrow  and 
concave,  and  is  connected  with  the  omasum.  The  dorsal  curvature  by  its  left 
portion  joins  the  rumen  to  form  the  atrium,  and  by  its  right  portion  touches  the 
liver.  The  ventral  curvature  lies  on  the  sternal  portion  of  the  diaphragm ,  opposite 
the  sixth  and  seventh  ribs.  The  right  extremity  forms  a  rounded  cul-de-sac, 
which  is  in  contact  with  the  liver,  omasum,  and  abomasum. 

The  omasum  (Fig.  294)  is  ellipsoidal  in  form  and  somewhat  compressed  laterally. 
It  is  very  clearly  marked  off  from  the  other  divisions.  It  is  situated  ahuost  entirely 
to  the  right  of  tlic  median  plane,  opposite  the  seventh  to  the  eleventh  ribs.  The 
parietal  (right)  surface  (Facies  dextra)  lies  against  the  diaphragm,  liver,  and  lateral 
wall  of  the  abdomen.  The  contact  with  the  latter  extends  over  a  small  area  only 
(ventral  part  of  seventh  to  ninth  intercostal  spaces).  The  visceral  (left)  surface 
(Facies  sinistra)  is  in  contact  with  the  rumen  and  reticulum.  The  dorsal  (greater) 
curvature  is  convex,  and  is  related  to  the  diaphragm,  liver,  and  vena  cava.  The 
ventral  (lesser)  curvature  is  concave,  and  rests  on  the  abomasum  chiefly,  the  junc- 
tion with  the  latter  appearing  as  a  constriction  near  the  middle  of  the  curvature; 
at  its  anterior  part  there  is  a  neck  (Collum  omasi)  which  is  the  connection  with  the 
reticulum. 

The  abomasum  (Fig.  294)  is  an  elongated  pyriform  or  flask-shaped  sac,  which 
lies  for  the  most  part  on  the  abdominal  floor,  to  the  right  of  the  ventral  sac  of  the 
nnnen.  Its  narrow  posterior  part  is  strongly  curved,  the  concavity  being  dorsal. 
The  parietal  (right)  surface  lies  against  the  abdominal  wall  from  the  seventh  to  the 
twelfth  intercostal  space.  The  visceral  (left )  surface  is  related  chiefly  to  the  ventral 
sac  of  the  rumen.  The  dorsal  (lesser)  curvature  is  concave,  and  is  in  contact  with  the 
omasum;  the  junction  of  the  two  sacs  is  indicated  by  a  constriction  about  four  or 

'  It  is  important  to  notice  that  the  reticulum  is  separated  from  the  pericardium  by  an 
interval  of  about  1  to  P-2  inches  (ca.  2  to  4  cm.)  only,  since  foreign  bodies  which  are  often  .swal- 
lowed by  cattle  lodge  in  the  reticulum,  and  not  rarely  (if  sharp)  perforate  the  reticulum  and 
diaphragm. 


THE    STOMACH  393 

five  inches  (ca.  10  to  12  cm.)  from  the  anterior  extremity  of  the  abomasum.  The 
ventral  (greater)  curvature  is  convex,  and  rests  on  the  abdominal  wall  from  the 
xiphoid  cartilage  to  the  ventral  part  of  the  last  (right)  intercostal  space.  The 
anterior  extremity  forms  a  rounded  blind  sac  which  lies  against  the  reticulum. 
The  posterior  i  or  ]jvloric)  extremity  is  much  smaller  and  bends  upward  and  forward 
to  join  the  duodenum.  About  six  to  eight  inches  (ca.  15  to  20  cm.)  from 
the  pylorus  is  a  constriction  which  marks  off  the  pyloric  portion  from  the  fundus. 

The  rumen  is  attached  by  peritoneum  and  connective  tissue  to  the  crura  of 
the  diaphragm  and  left  psoas  muscles,  from  the  hiatus  cesophageus  backward  to 
about  the  third  or  fourth  lumbar  vertebra. 

The  lesser  omentum  attaches  the  right  face  of  the  oma.sum  and  tlie  pyloric 
liortion  of  the  abomasum  to  the  visceral  surface  of  the  liver. 

A  small  area  of  the  anterior  part  of  the  right  face  of  the  rumen  is  adherent  to 
the  adjacent  surface  of  the  abomasum.  The  greater  part  of  the  ventral  curvature 
of  the  omasum  is  attached  by  connective  tissue  to  the  dorsal  face  of  the  abomasum. 

(Adhesion  of  the  reticulum  to  the  diaphragm  is  frequently  present,  but  is 
pathological;   the  same  is  true  in  regard  to  adhesion  to  the  liver.) 

Interior 

The  cavity  of  the  rumen  is  partially  divided  into  dorsal  and  ventral  sacs  by 
the  pillars ;  these  are  folds  of  the  wall,  strengthened  by  additional  muscular  fibers, 
and  correspond  with  the  grooves  on  the  outside.  The  two  most  extensive  ones 
project  like  shelves  into  the  anterior  and  posterior  ends  of  the  cavity  forming  the 
Ijjind  sacs  at  either  extremity;  they  are  termed  the  chief  piUars.  The  anterior 
chief  pUlar  (Pila  cranialis)  projects  obliquely  backward  and  upward  from  the  ventral 
wall,  and  has  a  thick  concave  free  edge  which  is  opposite  to  the  tenth  and  eleventh 
ribs.  Its  width  from  the  middle  of  the  free  edge  to  its  anterior  border  is  about 
eight  to  ten  inches  (ca.  20  to  2.5  cm.).  It  is  continued  on  either  side  b}'  the  rela- 
tively narrow  longitudinal  pUlars,  which  connect  it  with  the  posterior  pillar.  The 
posterior  pillar  (Pila  caudahs)  is  more  nearly  horizontal  than  the  anterior  one,  and 
separates  the  large  dorsal  and  ventral  posterior  blind  sacs.  Its  concave  free  border 
is  about  a  hand's  breadth  in  front  of  a  transverse  plane  through  the  external  angles 
of  the  ilia.  From  it  are  detached  three  accessory  pillars  on  either  side;  of  these, 
two  pass  around  the  blind  sacs  to  meet  the  corresponding  pillars  of  the  opposite 
side.  They  thus  mark  off  the  posterior  blind  sacs  from  the  general  cavity,  and  are 
termed  the  coronary  pillars.  It  will  be  noticed  that  the  ventral  coronary  pillar  is 
complete,  while  the  dorsal  one  is  not.  The  other  accessory  pillars  join  the  right 
and  left  longitudinal  pillars.  The  right  longitudinal  pillar  is  in  part  double; 
its  ventral  cU\asion  fades  out  about  the  middle  of  the  surface,  while  the  dorsal  one 
joins  the  posterior  chief  pillar.  The  distance  between  the  middles  of  the  anterior 
and  posterior  pillars  is  only  alx)ut  sixteen  to  eighteen  inches  (ca.  40  to  45  cm.)  in 
a  cow  of  medium  size.  In  this  space  the  dorsal  and  ventral  sacs  communicate 
freely. 

The  anterior  dorsal  blind  sac  of  the  rumen  is  separated  from  the  reticulum 
by  an  almo.st  vertical  fold  formed  l\v  the  apposition  of  the  walls  of  the  two  compart- 
ments. This  rumino-reticular  fold  (Pila  rumino-reticularis)  is  opposite  to  the 
seventh  rib  and  intercostal  space.  Its  free  upper  edge  is  concave  and  forms  the 
lower  and  outer  margin  of  the  large,  oval  rumino-reticular  orifice  (Ostium  rumino- 
reticulare).  The  inner  margin  of  the  fold  if  continued  would  end  about  at  the 
cardia,  but  there  is  in  this  region  no  demarcation  between  rumen  and  reticulum; 
hence  it  is  termed  the  atrium  ventrical!  or  vestibule. 

If  the  rumino-reticular  fold  and  an  imaginary  completion  of  it  be  taken  as  the  boundary 
between  the  rumen  and  reticulum,  it  will  be  seen  that  the  cardia  belongs  to  the  latter.  The 
outer  border  of  the  rumino-reticular  fold  ends  above  and  behind  the  cardia,  the  inner  one  just 


394 


DIGESTIVE    SYSTEM    OF   THE    OX 


beliiiiil  the  cpsophagoal  groove  and  about  four  to  five  inches  lower  down.  Undoubtedly  food 
or  water  swallowed  with  a  moderate  ilegree  of  force  passes  first  into  the  rumen.  Foreign  bodies 
(which  arc  commonly   swallowed  by  cattle)  are,  however,  found  in  the  reticulum 

The  cardiac  orifice  is  opposite  the  seventh  rib,  a  little  to  the  left  of  the  median 
plane  ami  al«iut  four  inches  (ca.  10  cm.)  below  the  spine;   it  is  not  funnel-shaped. 

The  mucous  membrane  of  the  rumen  is  brown  in  color,  except  on  the  margins 
of  the  pillars,  where  it  is  pale.  It  is  for  the  most  part  thickly  studded  with  large 
papilhe,  many  of  which  are  nearly  half  an  inch  (ca.  1  cm.)  long.  The  edges  of  the 
chief  pillars  and  a  large  part  of  the  wall  of  the  middle  of  the  dorsal  sac  are,  however, 
not  papillated.  The  papillary  arrangement  is  most  marked  in  the  blind  sacs. 
The  papilliB  vary  much  in  size  and  form;  the  largest  are  foliate,  many  are  narrow 
or  filiform,  and  others  are  conical  or  club-shaped.  The  mucous  membrane  on  the 
inner  wail  of  the  atrium  is  finely  wrinkled  and  non-])apillated,  while  above  and 


Fig.  2S9. — Thoracic  and  Anterior  Abdominal  Viscera  of  Ox,  Deep  Dissection. 
Most  of  the  rumen  has  been  removed  and  the  left  wall  of  the  reticulum  cut  away.     .4.,  Left  pulmonary 
artery:    B.,  left  bronchus;    V .  V.  V.,  pulmonary  veins;    b.  b.,  bronchial  lymph  glands;   L,g.,  posterior  mediastinal 
lymph-gland;    D.,  termination  of  duodenum;    F,  ruraino-reticular  foM. 


externally  it  is  papillated.  The  papillary  arrangement  also  extends  over  the  edge 
of  the  rumiiKj-reticular  fold  an  inch  or  two  (ca.  2  to  5  cm.). 

The  oesophageal  groove  (Sulcus  oesophageus)  is  a  semicanal  which  iiegins  at 
the  cardia  and  passes  downward  (ventrally)  on  the  right  wall  of  the  reticulum  to 
end  at  the  reticulo-omasal  orifice.  It  is  about  six  or  seven  inches  (ca.  15  to  18 
cm.)  in  length.  Its  axial  direction  is  practically  vertical,  but  it  is  twisted  in  a  spiral 
fashion;  thus  its  thickened  edges  or  lips  project  first  backward,  then  to  the  left, 
and  finall.v  forward.  The  twist  involves  chiefly  the  left  lip,  and  the  relative  irosi- 
tions  of  the  lips  is  reversed  at  the  ventral  end. 

The  mucous  membrane  on  the  lips  of  the  trsophageal  groove  is  brown  and 
wrinkled,  like  that  of  the  atrium;  in  the  bottom  of  the  groove  it  is  pale,  like  that 
of  the  (I'sophagus,  marked  by  longitudinal  folds,  and  presents  pointed  horny  iiajiilla* 
on  the  lower  i)art. 

The  reticulo-omasal  orifice  (Ostium  reticulo-omasicura)  is  situated  in  the  right 


THE    STOMACH 


395 


wall  of  the  reticulum  aliout  five  or  six  inehes  above  the  bottom  of  the  latter.  It 
is  rounded,  antl  is  limited  below  and  laterally  by  the  junction  of  the  lijis  of  the 
oesophageal  groove. 

In  the  reticulum  the  mucous  membrane  is  raised  into  folds  about  half  an  inch 
high,  which  inclose  four-,  five-,  or  six-sided  spaces  (Celluloe  reticuli) ;  this  peculiar 
arrangement  suggested  the  scientific  name,  and  also  the  popular  term  "honey- 
comb." These  cells  are  subdivided  by  smaller  folds,  and  the  bottoms  are  studded 
with  pointed  horny  papilla?.  The  cells  grow  smaller  and  gradually  disappear  near 
the  oesophageal  groove  and  the  edge  of  the  rumino-reticular  fold;  an  inch  or  two 
from  the  latter  the  mucous  membrane  has  the  papillary  arrangement  of  the  rumen. 


M 


Fig.  290. — Reticulum  of  f)x,  from  Photoghaph. 
The  specimen  was  cut  along  the  greater  curvature  and  laid  open  by  reflecting  the  anterior  wall.     C,  is  the 
cardia.     The  arrow  points  to  the  reticulo-omasal  oritice.     The  spiral  twist  of  the    cesophageal   groove  was  of 
necessity  partly  undone  by  reflecting  the  wall;   its  lips  are  drawn  apart,  showing  some  of  the  peculiar  birdclaw-like 
papillse  in  the  lower  part. 


At  the  reticulo-omasal  orifice  there  are  peculiar  horny  papilla?,  which  are  curved 
antl- resemble  the  claws  of  a  small  bird. 

The  cavity  of  the  omasum  is  occupied  to  a  considerable  extent  by  about  a 
hundred  longitudinal  folds,  the  laminae  (Laminse  omasi),  which  spring  from  the 
dorsal  and  lateral  walls.  The  largest  of  these — a  dozen  or  more  in  number — have 
a  convex  attached  edge,  and  a  ventral,  free,  slightly  concave  edge  which  reaches 
to  within  a  short  distance  of  the  ventral  wall  of  the  sac.  If  these  are  drawTi  apart 
or  a  cross-section  is  made,  it  will  be  seen  that  there  is  a  second  order  of  shorter 
laminse,  and  a  third  order  still  shorter;  finally,  there  is  a  series  of  very  low  folds 
or  lines.  The  food  is  pressed  into  thin  layers  in  the  narrow  spaces  between  the 
laminje  (Recessus  interlaminares),  and  reduced  to  a  fine  state  of  division  by  being 
ground  down  by  the  numerous  rounded  horny  papillse  which  stud  the  surfaces  of 
the  folds.     The  ventral  wall  of  the  omasum  forms  a  groove  (Sulcus  omasi),  which 


396 


DIGESTIVE    SYSTEM    OF   THE    OX 


connects  the  reticulo-omasal  opening:  with  the  omaso-abomasal  opening;  it  is 
about  three  or  four  inches  (ca.  8  to  10  cm.)  long,  and  is  directed  backward  and  a 
Httle  downwartl  and  to  the  right.  It  is  free  from  leaves,  but  marked  usually  by 
slight  folds  and  small  papillae;  it  forms  a  direct  path  from  the  reticulum  to  the 
abomasum  for  fluid  and  finely  divided  food.  In  the  neck  of  the  omasum  there  are 
thick  folds,  and  a  number  of  the  peculiar  papilhe  already  mentioned  as  occurring 
in  the  lower  part  of  the  oesophageal  groove.  The  omaso-abomasal  orifice  (Ostium 
omaso-aljomasicum)  is  oval,  and  is  about  four  inches  (ca.  10  cm.)  long.  It  is 
bounded  in  front  by  a  thick  muscular  pillar  which  fades  out 
above  on  the  lateral  walls  of  the  omasum.  Laterally  there 
are  two  folds  (Valvulae  terminales),  which  probably  prevent 
regurgitation  of  the  contents  of  the  aliomasum. 

The  cavity  of  the  abomasum  is  divided  by  a  constric- 
tion into  two  areas.  The  first  of  these  (fundus  gland  region) 
is  lined  with  a  soft  glandular  mucous  membrane,  which  forms 
about  a  dozen  large,  slightly  spiral  folds  (Plicae  spirales). 
The  second  part  (pyloric  region)  is  much  narrower  and  re- 
sembles in  appearance  the  corresponding  region  of  the  horse's 
stomach.  A  small  cardiac  gland  zone  surrounds  the  omaso- 
abomasal  orifice.     The  pyloric  orifice  is  small  and  round. 

Structure. — The  serous  coat  invests  all  of  the  free  sur- 
face of  the  stomach.  The  surface  of  the  rumen  which  is 
attached  to  the  dorsal  abdominal  wall  is  of  course  uncoveretl, 
as  well  as  the  adjacent  area  to  which  the  spleen  is  attached. 
The  furrows  are  bridged  over  by  the  peritoneum  and  super- 
ficial muscle-fibers,  and  contain  fat  and  (in  most  cases) 
branches  of  the  gastric  arteries.  The  lesser  omentum  passes 
from  the  visceral  surface  of  the  liver  to  tlic  right  (parietal) 
face  of  the  omasum  and  the  pyloric  portion  of  the  abomasum. 
There  is  a  fold  between  the  ventral  curvature  of  the  omasum 
and  the  dorsal  curvature  of  the  abomasum.  The  great  omen- 
tum is  foimed  by  the  peritoneum  leaving  the  stomach  along 
the  left  longitudinal  and  ]iosterior  transverse  furrows  and  the 
right  surface  of  the  rumen  below  the  longitudinal  furrow,  also 
the  ventral  curvature  of  the  al)omasum.  Its  superficial  (ven- 
tral) part  is  attached  on  the  right  to  the  duodenum,  while  the 
tleep  (dorsal)  part  blends  with  the  mesentery.  It  conceals 
the  greater  part  of  the  intestine  on  the  right  side,  with  the 
exception  of  the  duodenum,  and  covers  the  ventral  sac  of  the 
rumen  almost  entirely.  It  is  not  lace-like,  as  in  the  horse, 
and  contains  a  large  amount  of  fat  in  animals  in  good  condi- 
tion. The  epiploic  foramen  (of  Winslow)  is  almost  sagittal 
in  direction. 

The  muscular  coat  of  the  rumen  consists  of  an  external 

longitudinal,   and  a    thicker  internal    circular    layer.     The 

latter  forms  the  bulk  of  the  chief  pillars,  where  it  is  aljout  one-half  to  one  inch 

(ca.   1  to  2  cm.)  thick.     Scattered  bundles  of  striped  muscle-fibers  radiate  from 

the  cardia  m  the  wall  of  the  atrium. 

The  muscular  coat  of  the  reticulum  consists  of  two  chief  layers  which  begin 
and  end  at  the  (csojihageal  groove;  they  pass  in  a  circular  or  oblique  fashion 
around  the  sac,  the  fibers  of  the  two  laj'ers  crossing  each  other  at  an  acute  angle. 
The  walls  of  the  cells  contain  a  central  muscular  layer.  The  lips  of  the  a:'sophageal 
groove  contain  a  thick  layer  of  longitudinal  fibers,  which  are  largely  continuous  at 
or  cross  each  other  below  the  reticulo-omasal  orifice.     The  bottom  of  the  groove 


Fkj.    291. — Mrscni.ATi-nE 

OF  GisOPHAGEAL 

Groove  and  .-Vd- 
jACENT  Part  of 
Stomach     of    Ox, 

si:  FN'  from  with- 
in AFTER  Removal 
OF  MuCOl'S  MtM- 
URANK. 

a,  U-^sophaKUs;  b,  in- 
ner muscular  la.\-er  of  atri- 
um; f/,  reticulo-omasal  ori- 
fice; c,  e',  muscle  of  lips  of 
groove;  ft,  lower  end  of 
umscle  of  larger  lip,  wliich 
curves  arountl  the  reticulo- 
omasal  orifice  in  part  ami 
spreads  out  in  the  inner 
muscular  layer  of  the  reti- 
culum in  part;  A.  lower  end 
of  muscle  of  smaller  lip 
which  in  part  curves 
around  the  reticulo-omasal 
orifice  and  is  in  part  con- 
tinuous with  theinner  mus- 
cular layer  of  the  oinasal 
groove  and  the  omasum; 
(*,  inner  muscular  layer  of 
reticulutn.  (Ellenberger- 
Baum,  Anat.  d.  Haustiere.) 


THE    INTESTINE 


397 


has  two  layers  of  oblique,  unstriped  muscle-fibers,  with  a  variable  outer  layer  of 
striped  muscle  contiuiious  with  that  of  the  cesophagus. 

The  muscular  coat  of  the  omasum  consists  of  a  thin  external  longitudinal  laj'er 
and  a  thick  internal  circular  layer.  At  the  omasal  groove  there  is  an  additional 
inner  layer  of  longitudinal  fibers.  The  lamina  contain  three  muscular  strata — a 
central  layer  of  vertical  fibers,  flanked  on  either  side  by  a  layer  of  longitudinal 
fibers,  which  are  continuous  at  the  attached  border  with  the  muscularis  mucosa-. 

The  muscular  coat  of  the  abomasum  consists  of  longitudinal  and  circular 
layers;   the  latter  forms  a  well-developed  pyloric  sphincter. 

The  mucous  membrane  of  the  first  three  divisions  is  destitute  of  glands,  and 
is  covered  with  a  thick,  stratified,  squamous  epithelium;  the  superficial  part  of 
the  latter  is  horny,  and  is  shed  in  large  patches  in  the  rumen  and  omasum.     The 


-7^      Oesophagus 


blind  Sacs  /  -  ,       ,      \  ^ 


Fig.  292. — Stom 


corium  (Tunica  propria)  is  papillated.  The  mucous  membrane  of  the  abomasum 
is  glandular,  and  corresponds  to  that  of  the  right  sac  of  the  stomach  of  the  horse. 
The  short  fundus  glands  occur  in  that  part  which  presents  the  large  folds,  while 
the  long  pyloric  glands  are  found  in  the  remainder,  except  about  the  omaso- 
abomasal  orifice,  where  cardiac  glands  occur.  The  mucosa  of  the  fundus  gland 
region  is  very  thin  as  compared  with  that  of  the  horse.  There  is  a  round  prominence 
on  the  pyloric  valve. 


THE  INTESTINE 
The  intestine  of  the  ox  lies  almost  entirely  to  the  right  of  the  median  plane, 
chiefly  in  contact  with  the  right  face  of  the  rumen.     It  is  attached  to  the  sublumbar 
region  by  a  common  mesentery. 


398 


DIGESTIVE    SYSTEM    OF    THE    OX 


The  small  intestine  has  an  average  length  of  about  130  feet  (ea.  40  m.)  and 
a  tlianieter  ui  alxjut  two  inches  (ca.  5  to  6  cm.). 

Tlie  duodenum  is  about  three  or  four  feet  (ca.  1  m.)  in  length.  It  passes  for- 
ward to  the  visceral  surface  of  the  hver;  here  it  forms,  ventral  to  the  right  kidney,  an 
S-shaped  curve.  Thence  it  runs  backward  ahnost  to  the  external  angle  of  the  ilium, 
where  it  turns  on  itself,  passes  forward  alongside  of  the  terminal  part  of  the  colon, 
and  joins  the  mesenteric  part  (jejunum)  under  the  right  kidney.  It  is  attached  to 
the  liver  by  the  lesser  omentum,  to  the  abomasum  by  the  great  omentum,  and  to 

the  terminal  part  of  the  colon.  The  bile  duct 
opens  in  the  ventral  part  of  the  S-shaped  curve, 
about  two  feet  (oa.  60  cm.)  from  the  pylorus. 
Tlio  pancreatic  duct  opens  ai)out  a  foot  (ca.  30 
cm.)  further  back. 

The  remainder  of  the  small  intestine  is  ar- 
ranged in  numerous  very  close  coils,  in  contact 
chiefly  with  the  right  face  of  the  ventral  sac  of 
the  rumen,  forming  a  sort  of  festoon  at  the  edge 
of  the  mesentery.  It  is  not  subject  to  much 
variation  in  position,  but  a  few  coils  may  find 
their  way  behind  the  blintl  sacs  of  the  rumen 
to  the  left  side. 

The  orifices  of  the  pancreatic  duct  and  the 

bile  duct  are  on  papillae,  no  diverticulum  being 

present.     There  are  permanent  transverse  folds 

of    the    mucous   membrane    (Plicse   circulares). 

,  Duodenal  glands  (of  Brunner)  occur  in  the  first 

fe;        i  c"'  ■■■  fifteen  feet  or  more  (4  to  5  m.),  intestinal  glands 

\>'   •'     '  iHi  tliroughout.      Peyer's   patches   are   larger   and 

more   distinct    than    in    the    horse,    and    vary 

greatly  in  size   and  number;    in  adult   cattle 

there  are  eighteen  to  forty;   in  calves,  twenty 

to  fifty-eight.     They  usually  have  the  form  of 

narrow   bands.     Close   to   the   ileo-esecal  valve 

there    is    always    a   patch,   and  in   most   cases 

there   is   also    a    patcli    on    the    csecal   side    of 

the  valve. 

The  large  intestine  is  much  smaller  in 
caliber  than  that  of  the  horse,  has  no  bands, 
and  is  not  sacculated.  Most  of  it  is  situated 
between  the  layers  of  the  common  mesentery. 

The  caecum  is  about  20  to  30  inches  (ca.  50 

to  60  cm.)  long,  4  to  5  inches  (ca.  10  to  12  cm.) 

Fig. 293— Pkyebs  rAT.nis,,!  sm m i  In-     wide,  and  has  a  capacity  of  about  2J^  gallons 

TKSTiNKoi-ox  (aboiii  ;  „Miu,;,i  M^e-).  (g^.    9   to    10   Htcrs) .     It   begins   opposite  the 

lower  part   of   the   eleventh    rili,    and    extentls 

upward  and   backward   against  the  right   flank;  its  rounded   blind  end   is  free, 

and  lies  near  or  in  the  pelvic  inlet. 

The  colon  is  about  35  feet  (ca.  10  m.)  long;  its  diameter  is  at  first  about  the 
same  as  that  of  the  caecum,  but  diminishes  to  about  two  inches  (ca.  5  cm.).  Its 
capacity  is  about  6  to  8  gallons  (ca.  25  to  30  liters).  With  the  exception  of  its 
first  and  terminal  parts,  it  is  arranged  in  double  elliptical  coils  between  the  layers 
of  the  mesentery;  the  adjacent  parts  are  therefore  alternately  centripetal  and 
centrifugal  (Gyri  centripetalcs  et  centrifugales).  The  first  part  (Ansa  proximalis)  is 
market!  off  from  the  caecum  only  by  the  ileo-ctccal  opening;  it  forms  an  S-shaped 


THE    LIVER 


399 


Fig.  294. — Projection  of  Viscer.\  of  Bull  ox  Body-wall,  Right  Side. 
P.,    Pylorus;   G.b.,  gall-bladder;    R.K.,  right  kidney;    L.K.,  left  kidney;    P.,  (above  duodenum)  pancreas; 
i?/.,  urinary  bladder;    F.  s.,  ve.sicula  seminalis;    if.  {/.,  buJbo-urethral  (Cowper's;    gland.     Costal  attachment  and 
median  line  of  diaphragm  are  indicated  by  dotted  lines. 


Gall-bladder 


Falciform  ligament  (cui 


Coronanj  ligament  (cut) 

Poslcriar  nna  cava 

Hepatic  veins 
(E.foj)liage(d  notch 


Fig.  295 — Liver  of  Ox,  Pvrif.tal  .Surface;    Hard 


400 


DIGESTIVE    SYSTEM    OF    THE    OX 


curve  and  is  continueil  by  the  spiral  part  (Ansa  spiralis).  The  coils  of  this  are 
attached  to  each  other  by  connective  tissue,  and  are  best  seen  from  the  inner  side. 
The  bowel  grailually  diminishes  in  cahber,  and  the  terminal  part  (Ansa  distalis) 
leaves  the  spiral  mass,  passes  forward  to  the  great  mesenteric  artery  and  turns 
backward  between  the  duodenum  and  the  initial  sigmoid  part.  From  the  ventral 
surface  of  the  right  kidney  it  passes  backward,  forms  an  S-shaped  curve  near  the 
pelvic  inlet,  and  joins  the  rectum;  this  part  is  attached  to  the  sublumbar  muscles 
by  a  short  mesentery,  and  is  also  attached  to  the  dorsal  part  of  the  duodenum. 

The  rectum  is  somewhat  shorter  than  that  of  the  horse,  and  is  usuall.v  covered 
with  peritoneum  as  far  back  as  the  first  coccygeal  vertebra.  The  retroperitoneal 
part  is  surrounded  by  a  quantity  of  fat.     The  anus  is  not  prominent. 


Caudate  lobe 


Area  of  attachment  to  dia- 
phragm {nonperitoncal) 


Renal  im prea^tion 


(irij  lir/nment 


ncT  vena  cava 


hayec.t  notch 


^ 


Fig    296.— Liv 


Hardf.ned   m  situ. 


The  serous  coat  is  of  course  absent  on  the  adherent  surfaces  of  the  spiral  i)art 
of  the  colon.  There  is  a  large  amount  of  fat  in  the  mesentery.  The  longitudinal 
muscular  coat  is  evenly  distrilnited,  consequently  there  is  no  sacculation  of  the 
bowel.  There  is  a  valvular  mucous  fold  at  the  ileo-ca^cal  orifice.  A  Peyer's  patch 
occurs  in  the  beginning  of  the  cajcum  and  one  in  the  first  jiart  of  the  colon. 


THE  LIVER 
The  liver  lies  almost  entirely  to  the  right  of  tlie  median  plane.  Its  long  axis 
is  directed  obliquely  downward  anil  forward,  about  parallel  with  the  median  plane, 
and  corresponds  to  the  curvature  of  the  right  portion  of  the  diaphragm.  It  is  less 
extensive,  but  thicker  than  that  of  the  horse.  Its  average  weight  is  about  10  to 
12  pounds  (ca.  4.5  to  5.5  kg.). 


THE    LIVEK 


401 


In  .small  subjects  the  weight  (aoconiing  to  Schmaltz)  varies  from  (j'2  to  10  pounds  (ra. 
3  to  4.0  kg.),  in  large  subjects  from  11  to  13  pounds  (ca.  5  to  (1  kg.).  According  to  Schneider, 
the  average  weight  is  alxnit  13  pounds  (ca.  6  kg.) — a  little  over  1  per  cent,  of  the  live  weight  ami 
about  2  per  cent,  of  the  ilrcssed  carcass. 

When  hardened  in  situ,  its  configuration  adapts  it  accurately  to  tlie  structures 
with  which  it  is  in  contact. 

The  parietal  surface  is  convex  and  is  for  the  most  part  applied  to  the  right 
]iart  of  the  diaphragm,  hut  a  small  part  of  it  is  in  direct  contact  with  the  last  two 
ribs  and  with  the  tlaiik  at  the  lumho-costal  angle.  It  faces  ujiward,  forwartl,  and 
to  the  right. 

The  curvature  of  the  parietal  surface  is  not  regular.  It  is  marked,  except  in  its  \entral 
liart,  by  a  blunt  oblique  ridge  wliich  corresponds  to  the  basal  border  of  the  right  lung.  This 
prominence  divides  the  sui'face  into  two  areas.     Of  these,  the  external  one  is  directed  outward, 


Renal  impression 


Hepatic  aricry 
Portal  vein  — 
Bile-duct 


Lesser  omentum  (cut) 
(Esophageal  notch 


I' ml, ilical  fissure 


Fig.  297. — Liver  of  Young  Ox,  Visceral  Surface;    Hardened  j'n  fj'tu. 

is  only  slightly  convex,  and  often  shows  impressions  of  the  last  three  ribs.  The  inner  area  pre- 
sents a  depression  produced  by  the  right  crus  of  the  diaphragm,  and  otherwise  is  regularly  convex 
and  adapted  to  the  tendinous  center  and  sternal  portion  of  the  diaphragm.  The  falciform 
ligament  is  attached  to  the  surface  from  the  resophageal  notch  to  the  umbilical  fissure. 

The  visceral  surface  is  concave  and  very  irregular;  it  presents  impressions  of 
the  chief  organs  which  are  in  contact  with  it — the  omasum  and  reticulum.  It  is 
also  related  to  the  pancreas  and  duodenum. 

The  following  markings  are  quite  distinct  on  the  visceral  surface  of  well-hardened  speci- 
mens: (1)  The  omasal  impression  ilmpressio  omasica)  is  a  deep  central  cavity  l>clow  the  portal 
fissui'c.  (2)  The  reticular  impression  Ilmpressio  reticularis)  is  a  smaller  marginal  depression  below 
the  oesophageal  notch  and  the  inner  part  of  the  preceding,  from  which  it  is  separated  l)y  a  rounded 
ridge.  (3)  The  abomasal  impression  (Impressio  abom.a.sica ) ,  present  only  in  the  calf,  is  produced 
by  the  anterior  part  of  the  abomasum.  It  lies  along  the  ventral  part  of  the  surface,  and  is  sep- 
arated bv  ridges  from  the  preceding  impressions.  It  disappears  as  the  omasum  and  reticulum 
'26 


402 


DIGESTIVE    SYSTEM    OF    THE    OX 


increase  in  size  and  displace  tlie  abomasum  from  contact  with  the  liver.  (4)  Shallow  grooves  for 
the  S-shapod  portion  of  (he  duodenum  (Irapressio  duodenalis)  may  be  found  above  and  external 
to  the  portal  fissure.  (5)  The  fossa  of  the  gall-bladder  (Fossa  vesica;  fellece)  is  distinct  when 
that  organ  is  full.  In  the  calf  the  omasal  impression  is  small,  and  the  abomasal  one  large  in 
correspondence  with  the  relative  sizes  of  these  two  sacs. 

The  portal  fissure  is  a  well-defined  rounded  depression,  situated  dorsal  to  the 
omasal  impression.  It  contains,  besides  the  vessels  and  duet,  several  large  hepatic 
lymph  glands.     Above  and  external  to  it  a  part  of  the  pancreas  is  attached. 

The  dorsal  border  is  short  and  thick;    it  extentls  backward  a  short  distance 


:e  Drawixu  of  Liver  of  Ox,  Visceral  SrRF 
L.<i.,  Hepatic  lymph-glands  at  portal  fissu 


Soft  Specimen. 


beyond  the  upper  part  of  the  last  rib.  It  presents  the  large,  thick,  quach-ilatcral 
caudate  lobe,  and  a  deep  depression  for  the  right  kidney  and  adrenal. 

The  ventral  border  is  short  and  thin  and  has  no  interloliar  incisures. 

The  right  (or  external)  border  is  marked  by  a  small  umbiHcal  fissure,  in  which 
the  ligamentum  teres  is  attached  in  the  young  subject. 

The  left  border  presents  the  oesophageal  notch  below  its  middle.  Above  this 
it  is  practically  median  in  position,  and  lodges  the  posterior  vena  cava,  which  is 
partially  embedded  in  tlie  gland.  Below  the  notch  the  border  extends  an  inch  or 
two  (ca.  2.5  to  5  cm.)  to  the  left  of  the  median  jjlane  opposite  the  ventral  thircl  of 
the  sixth  ril). 

There  is  no  left  lateral  ligament.     The  falciform  ligament  is  usually  present, 


THE    LIVER 


403 


hut  the  ligamentum  teres  is  found  only  in  young  subjects.  The  lesser  omentum 
leaves  the  liver  along  a  line  extending  from  the  oesophageal  notch  to  the  portal 
fissure.  The  only  distinct  lobe  in  the  adult  is  the  caudate  (Processus  caudatus). 
A  gall-bladder  (Vesica  fellea)  is  present.  This  is  a  pear-shaped  sac,  four  to 
six  inches  (ca.  10  to  15  cm.)  long,  which  lies  partly  on  the  visceral  surface  of  the 
liver  (to  which  it  is  attached),  but  largely  on  the  abdominal  wall  at  the  lower  part 
of  the  eleventh  or  twelfth  intercostal  space.  It  may  be  regarded  as  a  diverticulum 
of  the  bile-duct,  enlarged  to  form  a  reservoir  for  the  bile.  Its  neck  is  continued  by 
the  cystic  duct  (Ductus  cysticus),  which  joins  the  hepatic  duct  at  an  acute  angle 


Caudate  lobe  of  liver 


Pancrialic  duct 


Fig.  299. — Pancre.\s  of  Ox,  Gastro-intestin-al  Surface,  with  Related  Orgaxs. 

The  position  of  .^ome  of  the  larger  lymph  glands  (/.ff.)  is  indicated  by  dotted  hne;  also  the  intraglandular  course  of 

the  pancreatic  duct.     Probe  is  passed  through  epiploic  foramen  (of  Winslow). 


just  outside  of  the  portal  fissure,  to  form  with  it  the  Ijile-duct  (Ductus  choledochus). 
The  latter  is  short  and  enters  the  second  bend  of  the  S-shaped  curve  of  the  duo- 
denum, i.  e.,  about  two  feet  (ca.  60  cm.)  from  the  pylorus.  Several  small  ducts 
(Ductus  hepato-cystici)  open  directly  into  the  gall-bladder. 

In  the  new-born  calf  the  liver  is  relatively  much  larger  than  in  the  adult.  The  visceral 
surface  presents,  below  the  portal  fissure,  a  large  rounded  eminence,  which  is  caused  by  the 
presence  in  the  underlying  gland  substance  of  a  large  \-enous  sinus  into  which  the  umbilical  and 
portal  veins  empty.  A  large  vessel,  the  ductus  venosus,  leads  from  this  sinus  directly  to  the 
posterior  vena  cava.  Just  external  to  this  elevation  is  a  small  but  distinct  lobe  about  two 
inches  long  (Proce.s.sus  papillaris?).  The  umbilical  fissure  is  deep  and  partially  divides  the  gland 
into  two  chief  lobes. 


404-  DIGESTIVE    SYSTEM    OF    THE    OX 

THE  PANCREAS 
The  pancreas  of  the  ox  is  irregularly  quadrilateral  in  form,  and  lies  almost 
entirely  to  the  right  of  the  median  plane.  Its  weight  is  about  the  same  as  that  of 
the  horse.  Its  dorsal  surface  is  related  to  the  crura  of  the  diaphragm,  the  celiac 
and  anterior  mesenteric  arteries,  and  the  liver.  It  is  attached  to  the  liver  at  and 
external  to  the  portal  fissure,  and  to  the  crura  of  the  diaphragm.  Between  these 
adhesions  it  is  free  and  forms  the  ventral  wall  of  the  epiploic  foramen  (of  Winslow). 
On  the  right  side  it  extends  backward  beyond  the  caudate  lobe  of  the  liver  between 
the  layers  of  the  mesoduodenum ;  here  it  is  in  contact  with  the  upper  part  of 
the  flank  at  the  lumbo-costal  angle,  and  is  related  above  to  the  right  kidney  and 
by  its  ventro-lateral  border  to  the  ventral  part  of  the  duodenum.     The  gastro- 


DoTsal  extremily 


Area  of  nllachmenl  iorumen- 
{non-periloneal) 


Posterior  border   — 

I 

Line  of  peritoneal  reflection  — j 


Ventral  extremity 
Fig.  300 — Splken  of  Ox;    Visckhal  Sx'rface. 

intestinal  or  ventral  surface  is  in  contact  with  the  dorsal  curvature  of  the  rumen 
and  the  intestine.  The  jiortal  vein  passes  through  the  gland.  The  left  extremity 
is  small;  the  right  or  posterior  is  wide  and  thin  and  is  often  divided  into  two 
branches.  The  duct  leaves  the  posterior  part  of  the  ventro-lateral  (or  right) 
border  and  enters  the  duodenum  about  twelve  inches  (ca.  30  cm.)  further  back 
than  the  bile-duct. 

THE  SPLEEN 

The  spleen  has  an  elongated,  elliptical  outline,  both  extremities  being  thin, 
rounded,  and  similar  in  size. 

Its  average  weight  is  about  30  ounces  (ca.  800  to  900  gm.),  or  about  |  per 
cent,  of  the  boily-weight.     Its  length  is  about  Ifito  20  inches  (ca.  40  to  50  cm.). 


DIGESTIVE    SYSTEM    OF   THE    SHEEP  405 

its  width  about  5  to  6  inches  (ca.  12  to  15  cm.),  and  in  the  middle  its  thickness  is 
about  ail  inch  (en.  2  to  3  cm.)- 

The  dorsal  extremity  lies  under  the  upper  ends  of  the  last  two  ribs ;  the  ventral 
extremity  is  usually  opposite  the  seventh  or  eighth  rib,  about  a  handbreadth  above 
its  junction  with  the  cartilage.  The  parietal  surface  is  convex,  and  is  related  to 
the  diaphragm.  The  visceral  surface  is  concave,  and  is  related  chiefly  to  the  left 
face  of  the  rumen,  but  also  usually  to  a  narrow  adjacent  area  of  the  reticulum. 
The  dorsal  part  is  attached  to  the  left  crus  of  the  diaphragm  and  the  left  surface 
of  the  rumen  by  peritoneum  and  connective  tissue;  the  ventral  part  is  free.  The 
hilus  is  situated  on  the  dorsal  third  of  the  visceral  surface,  near  the  anterior  border. 

About  one-half  of  the  visceral  surface  of  the  .spleen  is  attached  directly  to  the  rumen  and  is 
not  covered  by  peritoneum;  the  line  of  reflection  of  the  latter  crosses  the  surface  obliquely,  from 
the  upper  part  of  the  posterior  border  to  the  anterior  border  a  Uttle  below  the  middle.  Similarly 
there  is  a  narrow  vmcovered  area  on  the  upper  part  of  the  parietal  surface  along  the  anterior 
border.  The  hilus  is  not  a  groove,  but  a  simple  depression.  When  hardened  in  situ,  the  organ 
is  seen  to  be  somewhat  twisted,  so  that  the  upper  part  of  the  parietal  surface  faces  upward  and 
forward,  while  below  it  is  directed  outward. 


DIGESTIVE  SYSTEM  OF  THE  SHEEP 

The  lips  are  thin  and  mobile;  the  upper  one  is  marked  by  a  very  distinct 
philtrum,  and  otherwise  is  not  bare. 

The  anterior  part  of  the  hard  palate  is  prominent  and  smooth;  on  the  pos- 
terior part  of  this  area  there  are  two  narrow  depressions  in  the  form  of  a  V,  at  the 
deep  anterior  ends  of  which  the  naso-palatine  ducts  open.  The  ridges  of  the  palate 
are  irregular  and  their  edges  are  smooth.  The  posterior  third  or  rather  more  of 
the  palate  is  not  ridged  and  presents  numerous  orifices  of  ducts  of  the  palatine 
glands.     The  mucous  membrane  is  often  more  or  less  pigmented. 

The  mucous  membrane  of  the  cheeks  is  covered  with  large  papillse,  many  of 
which  are  long  and  sharp-pointed,  while  others  are  short  and  blunt.  There  is  also  a 
series  of  conical  papillae  on  the  floor  of  the  mouth  under  the  lateral  part  of  the  tongue. 

The  tongue  resembles  that  of  the  ox  in  form,  but  the  tip  is  comparatively 
smooth;  the  papillae  here  are  very  numerous,  but  short  and  blunt.  This  difference 
is  in  conformity  with  the  dissimilarity  in  the  mode  of  prehension.  The  prominence 
of  the  dorsum  is  commonly  not  so  pronounced  nor  so  sharply  marked  off  in  front 
as  in  the  ox.  The  root  is  smooth.  The  mucous  membrane  of  the  dorsum  is  often 
pigmented  in  spots. 

The  dental  formula  is  the  same  as  that  of  the  ox.  The  incisor  teeth  form  a 
narrow  and  strongly  curved  arch.  The  crowns  are  long  and  narrow;  their  labial 
surfaces  are  strongly  convex  and  end  at  a  sharp  edge  which  is  used  in  cropping  the 
grass.     The  roots  are  more  firmly  embedded  than  in  the  ox. 

The  cheek  teeth  resemble  those  of  the  ox.  There  is  a  thinner  layer  of  cement, 
which  is  usually  black. 

The  average  periods  of  eruption  of  the  teeth  are  indicated  in  the  subjoined  table. 


Teetb  Temporary  Permanent 

I, At  birth  or  first  week 1  to  IH  years 

Ij P'irst  or  second  week 1  }^  to  2  years 

I3 Second  or  third  week 2J'2  to  .3  years 

I4 Third  or  fourth  week 3J4  to  4  years 

P2  ^    2  to  6  weeks 1  J'2  to  2  years 

M, 3  months  (lower),  5  months  (upper) 

M2 9  to  12  months 

M3 1  J'2  to  2  years 


Dorsal  curvature  uf  rumen 


\ 


>ci/^ac  ofFi^"'"^ 


Fig.  301.— Stomach  of  Sufkp,  Left  View. 

From  photograph  of  specimen  hardened  ?>i  si(«.     The  reticulum  is  somewhat  contracted.     Arrow  points  to  posle 

rior  furrow  between  blind  sac8. 


Pylorus 


Fig,  302 — SToMArn  or  Shfep,  Rh:ht  \'ikw 
From  photoRraph  of  specimen  h.lrdeued  in  siUi.     Dotted  line  in*licates  position  of  sple 

406 


DIGESTIVE    SYSTEM    OF   THE    SHEEP  407 

The  salivary  glands  resemble  those  of  the  ox  in  general,  but  the  parotid  cluet 
crosses  the  surface  of  the  masseter  muscle,  and  opens  opposite  the  third  or  fourth 
cheek  tooth. 

The  tonsil  is  bean-shaped  and  about  half  an  inch  (ca.  12  mm.)  in  length.  It 
does  not  project  into  the  fauces.  The  mucous  membrane  of  the  latter  presents  two 
deep  and  verj-  narrow  tonsillar  sinuses  on  either  side. 


Fig.  303. — Cross-sectiojj  of  Sheep,  throt-c-h  Ninth  Thoracic  Vertebra,  Anterior  View. 
i.  Cardiac  orifice;   5.  crsophageal  groove;  3,  rumiuo-relicular  orifice;   4,  rumino-reticuiar  foid;   5,  dorsal  sar 
6,  body  of  ninth    thoracic  vertebra;    7,  vena   hemiazygos;    S,  aorta;    9,  posterior  mediastinal  Ij-inph 
gland;    70,  /O.  crura  of  diaphragm;    i/.  posterior  vena  cava;    / 2.  portal  vein;    fl./..  right  lung;    L.(..  left  lung;   S, 
spleen  (cut  very  obliquely);   L,  liver;   R,  reticulum  (posterior  wall).     Arrow  points  to  reticulo-omasal  orifice. 

f 

The  fornix  of  the  pharynx  presents  a  median  plicated  fold  which  is  a  continua- 
tion of  the  septum  nasi.  The  pharyngeal  orifice  of  the  Eustachian  tube  has  the 
form  of  a  crescentic  slit,  placed  about  on  a  level  with  the  inferior  nasal  meatus. 
There  are  two  large  Ijmph  glands  and  a  number  of  hfemolymph  glands  above  the 
pharynx. 

The  oesophagus  has  a  lumen  of  about  an  inch  when  moderately  distended; 
otherwise  it  resembles  that  of  the  ox. 


408 


DIGESTIVE    SYSTEM    OF    THE    SHEEP 


The  stomach  is  like  that  of  the  ox  in  its  general  arrangement.  Its  average 
capacity  is  about  four  gallons  (ca.  15  liters).  The  cardiac  opening  is  opposite  the 
middle  of  the  eighth  intercostal  space;  it  is  just  to  the  left  of  the  median  plane  and 
about  two  to  three  inches  (ca.  5  to  7  cm.)  below  the  vertebral  column.  The  ventral 
sac  of  the  rumen  is  relatively  larger  and  e.\tends  further  to  the  right  of  the  median 
plane  than  in  the  ox.  There  are  no  coronary  pillars  in  the  dorsal  sac,  but  its  upper 
part  is  papillated.  The  papilla;  of  the  rumen  are  relatively  large  and  somewhat 
tongue-like;  the  largest  are  about  a  fourth  of  an  inch  (ca.  6  mm.)  in  length.  The 
reticulum  is  relatively  larger  than  in  the  ox.  Its  ventral  part  curves  more  back- 
ward and  less  to  the  right  than  in  the  ox.     The  parietal  surface  extends  forward  as 


Fig.  .304— Ann 


far  as  the  sixth  rib  or  intercostal  space,  and  is  related  to  the  diaphragm  anil  liver. 
The  fundus  lies  on  the  sternal  part  of  the  diaphragm  and  in  contact  with  the  abo- 
masum.  The  oesophageal  groove  is  disposed  much  like  that  of  the  ox,  and  is  about 
four  to  five  inches  (ca.  8  to  10  cm.)  long.  The  omasum  is  much  smaller  than  the 
reticulum,  its  capacity  being  only  about  one  ])int.  It  is  oval  and  compre.s.sed 
laterally.  It  is  situated  almost  entirely  to  the  right  of  the  median  plane,  opposite 
to  the  ninth  and  tenth  ril)s,  higher  than  in  the  ox,  and  has  no  contact  with  the 
abdominal  wall.  It  is  related  on  the  right  to  the  liver  and  gall-bladder,  on  the  left 
to  the  rumen,  and  lielow  to  the  abomasum.  The  lamina^  are  less  numerous  than 
in  the  ox;   in  the  neck  which  connects  the  omasum  with  the  reticulum  they  have 


DIGESTIVE    SYSTEM    OF   THE    SHEEP 


409 


the  form  of  low  thick  ridges,  and  bear  long,  pointed,  horny  papillae.  The  abomasum 
is  relatively  larger  and  longer  than  in  the  ox.  Its  capacity  is  about  twice  that  of 
the  reticulum  and  averages  about  two  quarts  (ca.  1.75  to  2  liters).  The  blind 
anterior  end  lies  almost  centrally  in  the  xiphoid  region,  in  relation  to  the  liver  and 
reticulum.  Its  body  extends  backward  a  little  below  and  almost  parallel  with  the 
right  costal  arch.  The  pylorus  is  opposite  the  ventral  end  of  the  eleventh  or 
twelfth  intercostal  space.  The  cells  of  the  reticulum  are  much  shallower  than  in 
the  ox.  At  the  reticulo-omasal  opening  and  on  the  adjacent  part  of  the  laminae 
of  the  omasum  are  large,  pointed,  horny  papillae.  The  number  of  laminae  is  less 
than  in  the  ox. 

The  general  arrangement  of  the  intestine  is  like  that  of  the  ox.     The  small 


Posterior  rena 
cava 


Portal  vein 


Hepatic  artery 


Omasal  impres- 
sion 


Lesser  omentum 


Reticular  impres- 
sion 


Abomasal 
ivipression 


Fig.  305. — Liver  of  Sh 


intestine  is  about  80  feet  (ca.  24  to  25  m.)  long;  its  average  diameter  is  about  an 
inch  (ca.  2  to  3  cm.),  the  caliber  increasing  in  its  terminal  part,  where  a  very 
e.xtensive  Peyer's  patch  is  found.  The  caecum  is  about  10  to  12  inches  (ca.  25 
to  30  cm.)  long,  2  inches  (ca.  5  cm.)  wide,  and  has  a  capacity  of  about  a  quart 
(ca.  1  liter).  The  colon  is  about  15  feet  (ca.  4  to  5  m.)  long.  Its  caliber  is  at 
first  about  the  same  as  that  of  the  caecum,  but  diminishes  to  about  the  width  of 
the  small  intestine. 

The  Uver  weighs  about  20  to  25  ounces  (ca.  550  to  700  gm.).  It  lies  entirely 
to  the  right  of  the  median  plane.  The  parietal  surface  is  related  almost  exclusively 
to  the  right  part  of  the  diaphragm.  The  visceral  surface  presents  extensive 
reticular  and  abomasal  impressions,  and  a  small  omasal  impression  internal  to  the 
portal  fissure.     The  umbilical  fissure  is  deep  and  partially  divides  the  gland  into 


410 


DIGESTIVE    SYSTEM    OF    THE    PIG 


two  chief  lobes.  The  caudate  lobe  is  prismatic  and  l)lunt-])oiiited.  The  neck  of 
the  gall-bladder  is  long.  The  bile-duct  joins  the  pancreatic  duct  to  form  a  common 
duct  (Ductus  choletlochus  communis)  which  opens  into  the  duodenum  about  one 
foot  (ca.  30  cm.)  from  the  pylorus. 

The  pancreas  is  arranged  as  in  the  ox.     Its  duct  unites  with  the  bile-duct. 

The  spleen  (Fig.  301)  is  somewhat  triangular,  with  the  angles  rounded  off.  It 
weighs  about  three  or  four  ounces  (ca.  100  grams).  Its  length  is  about  five  inches 
(ca.  12  to  13  cm.)  and  its  greatest  width  about  four  inches  (ca.  10  cm.).  The  parietal 
surface  is  convex  and  is  related  to  the  diaphragm,  to  which  rather  more  than  the 
anterior  third  is  adherent.  The  visceral  surface  is  concave  and  its  anterior  half  is 
attached  to  the  dorsal  curvature  of  the  rumen.     The  tlorsal  end  or  base  is  attached 


Umbilical  fissure 


Posterior  pena 


to  the  left  crus  of  the  diaphragm  under  the  last  two  or  three  ribs.  The  hilus  is  at 
the  ijosterior  basal  angle.  The  ventral  end  is  narrower  and  thinner  than  the  base; 
it  is  situated  opposite  the  ninth  and  tenth  ribs  above  their  middles. 


DIGESTIVE  SYSTEM  OF  THE  PIG 
THE  MOUTH 
The  rima  oris  is  extensive,  the  angles  of  the  mouth  being  situated  far  liack. 
The    upper  lip  is  thick  and   short,   and   is   blended   with   the   snout:   the  lower 
lip  is  small  and  pointed.     The  labial  glands  are  few  and  small. 

Tlie  mucous  membrane  of  the  cheeks  is  smooth.     The  buccal  glands  are 


THE    MOUTH  411 

compaftly  arranged  in  two  rows  opposite  the  cheek  teeth.  The  parotid  duct 
opens  opposite  the  fourth  or  fifth  clieek  tooth. 

The  hard  palate  is  long  ami  narrow;  it  is  marked  by  a  median  furrow,  on  eacli 
side  of  which  are  twenty  or  more  ridges.  On  its  anterior  part  there  is  a  triangular 
incisive  ]5a]iilla,  at  which  the  naso-palatine  ducts  open. 

The  soft  palate  is  very  thick.  Its  direction  almost  continues  that  of  the  hard 
palate,  i.  e.,  it  is  nearly  horizontal.  It  extends  to  the  middle  of  the  oral  surface 
of  the  epiglottis.'  It  has  a  median  prolongation  termed  the  uvula.  The  oral 
surface  presents  a  median  furrow,  on  either  side  of  which  is  an  oval  raised  area, 


Fig.  307,— Tovr.nE  of  Pig. 
J,  Apex;  g,  dorsum;  S,  root;  a,  orifices  of  ducts  of  lingual  glands;   b,  papillae  of  root;  c,  vallate  papilla  (not 
really  so  distinct   as  in  figure);  d.  foliate  papilla;  p,  fungiform    papilto;    /.  epiglottis  (pulled  back);  g,  median 
glosso-epiglottic  fold.     (EUenberger-Baum,  .\nat.  d.  Haustiere.) 

marked  by  numerous  crypts;  these  elevations  are  the  tonsils.  Tonsillar  ti.ssue 
also  occurs  in  the  lateral  walls  of  the  fauces. 

The  tongue  is  long  and  narrow  and  the  apex  is  thin.  Two  or  three  vallate 
papillae  are  present.  The  fungiform  papillce  are  small  and  are  most  numerous 
laterally.  The  filiform  papillte  are  soft  and  very  small.  On  the  root  there  are 
soft,  long,  pointed  papilUe,  directed  backward.     Foliate  papillae  are  also  present. 

There  is  a  well-marked  median  glosso-epiglottic  fold,  on  either  side  of  which  is 
a  depression  (^'allecula  epiglottica).     The  frenum  linguae  is  double. 


The  dental  formula  of  the  pig  is: 

(.314      3\ 
I  -  C  -  P  -  M  -  ) 
3     14      3/ 


'  The  epiglottis  in  the  pig  seems  to  be  constantly  retrovelar.  Tlie  pig  frequently  breathes 
through  the  mouth,  and  this  is  no  doubt  possible  only  when  the  soft  palate  is  raised;  it  seems 
probable  that  it  is  also  shortened. 


412 


DIGESTIVE    SYSTEM    OF    THE    PIG 


The  formula  for  the  temporary  teeth  is: 

/     3       1         4\ 
2  I  Di  -  Dc  -  Dp  -  I  =32 
V     3       1  4/ 

The  upper  incisors  are  small ;  they  are  separated  from  each  other  by  spaces, 
and  from  the  eaiiines  l)y  a  larger  interval.  The  first  incisors  are  the  largest,  are 
convergent,  and  have  no  distinct  neck.  The  second  are  narrower  and  somewhat 
smaller.  The  third  (corner)  incisors  are  much  smaller,  arc  flattened  laterally, 
and  have  three  small  eminences  on  the  crown. 

The  lower  incisors  are  almost  horizontal  and  are  convergent  and  close  to- 
gether.    The  first  and  secontl  are  about  equal  in  size,  prismatic,  and  deeply  im- 


FlG.  308.— Sk 


Half  Old,  SccLprrRED  to 
THE  Teeth. 
es;    Pl-4,  premolars;    Ml-S, 


l)lanted  in  the  jaw.  The  labial  surface  is  slightly  convex,  the  lingual  concave  and 
marked  near  its  extremity  lay  a  ridge.  The  third  incisor  is  much  smaller  and 
has  a  short  narrow  crown  and  a  distinct  neck. 

The  canine  teeth  or  tusks  of  the  male  are  greatly  developed  and  project  out 
of  the  mouth.  The  upper  canine  of  the  boar  may  be  about  three  or  four  inches 
(ca.  8  to  10  cm.)  long.  The  crown  is  conical  and  is  curved  somewhat  backward 
and  outward;  the  embedded  part  is  curved  and  has  a  large  pulp  cavity.' 
The  lower  canine  may  reach  a  length  of  eight  inches  or  more  (ca.  20  cm.) ;  the  crown 
is  prismatic  and  is  curved  backward  and  outward  in  front  of  the  upper  one,  so  that 
the  friction  between  the  two  keeps  a  sharp  edge  on  the  lower  tooth.  In  the  sow 
they  are  much  smaller. 

The  cheek  teeth  increase  in  size  from  before  backward.     They  have  (with 


'  The  canines  of  the  pig  are  "permanent  pulp"  tooth  and  thcrcfoio 
growth,  and  are  without  roots  in  the  strict  sense. 


ipable  of  continued 


THE    MOUTH 


413 


certain  exceptions  noted  below)  complex  tuberculate  crowns;  the  term  hunodont 
is  applied  to  this  condition,  as  distinguished  from  the  selenodont  structure  in 
horses  and  cattle,  in  which  there  are  prominent  ridges  of  enamel.  Thej-  are 
short-cro^\Tied  teeth  with  a  distinct  neck  and  root.  The  first  tooth  in  each 
jaw  is  small,  simple,  and  appears  only  once;  in  the  lower  jaw  it  is  near  the 
canine,  in  the  upper  near  the  second  cheek  tooth.  The  next  two  teeth  are  larger, 
laterally  compressed,  and  sectorial.  The  fourth  tooth  below  is  larger,  but  otherwise 
like  the  jireceding  ones,  while  the  upper  one  is  much  wider  and  is  tuberculate. 


Fig.  309. — Superfici.\l  Glands  of  Head  of  Pig. 
a.  Parotid  gland;    a',  a",  cenical  and  submaxillary  angles  of  a;    b,  c,  ventral  and  dorsal  buccal  glands; 
d,  labial  glands;   e,  masseter  muscle;  /./'.Ij-mph  glands;    g,  dotted  line  indicating  outline  of  submaxillary  gland, 
which  is  concealed.      (Eiienberger-Baum,  .\nat.  d.  Haustiere.) 


The  average  periods  of  eruption  of  the  teeth  are  given  in  the  subjoined  table. 


Tooth 
I,.. 
I,.. 

Iv 
C  .  . 
Pi.. 
P,.. 
P.,.. 


m;. 


Eruptiox  Ch.axge 

2  to  4  weeks 12  months 

/  upper  2  to  3  months 

\  lower  1 } .;  to  2  months 16  to  20  months 

Before  birth S  to  10  months 

Before  birth 9  to  10  months 

.5  mont  hs 

5  to  7  weeks 

/  upper  4  to  8  days. .  .  

\  lower  2  to  4  weeks .  . 

/  upper  4  to  S  days .  . 

\  lower  2  to  4  weeks 

4  to  6  months 

8  to  12  months 

18  to  20  months 


1 
I 
}■  12  to  15  months 

I 


414 


DIGESTIVE    SYSTEM    OF    THE    PIG 


The  parotid  gland  is  large  and  trirailiate.  It  extends  very  little  on  to  the  mas- 
seter  muscle  and  its  upper  angle  does  not  quite  reach  the  base  of  the  ear.  It  is 
pale  in  color,  and  is  embedded  in  fat  in  animals  in  good  condition.  On  its  deep 
face  are  several  large  subparotid  lymph  glands,  some  of  which  are  onlj'  partially 


Fig.  310. — Dissection  of  Mouth  and  Pharyngeal  Region 


Pio 


/,  Ilaril  piilate;  2,  tongue  showing  distinctly  fungiform  papilla;;  5,  foliate  papilla;  ^,  lymph  nodulea  of  soft 
palate;  5,  stylo-gio.ssus  muscle,  out  of  which  a  portion  has  been  cut;  G,  hyo-glossus;  7,  genio-glossus;  8,  genio- 
hyoi<ieus:  9,  mylo-hyoiiieus  (reflected);  10,  stylo-hyoideus;  11,  great  cornu  of  hyoid  bone;  IS,  tensor  palati; 
lii,  levator  palati;  ;4.  pterygo-  et  palato-pharyngeus;  15,  gtylo-phar,\-ngeus;  16,  chondro-pharyngeus;  17, 
sterno-  et  omo-hyoideus;  IS,  retropharj-ngeal  lymph  glands;  a,  bulla  o.ssea;  b,  parama,stc>id  process.  (Elleti- 
berger-Baum,  .\nat.  d.  Haustiere.) 


covered  by  the  parotid.  The  duct  arises  on  the  deep  face,  has  a  course  similar 
to  that  of  the  ox,  and  perforates  the  cheek  opposite  the  fourth  or  fifth  upper  cheek 
tooth.  Small  accessory  glands  (Glandulte  parotideaj  accessorise)  may  be  found 
along  the  course  of  the  duct. 


THE   MOUTH 


415 


The  submaxillary  gland  is  small,  reddish  in  color,  and  oval  in  outline;  it  is 
covered  by  the  parotid.  Its  superficial  face  is  convex,  and  is  marked  by  rounded 
prominences.     From  its  deep  face  a  narrow  process  extends  forward  about  two  or 


Fig.  311. — Sagitt.\l  Section  of  Ph.\ryngeal  Region  of  Pig,  Partly  Schematic. 
;,  Palate  bone;  2.  sphenoid  bone;  3' ,  sphenoidal  sinus;  2" ,  occipital  bone;  S,  epiglottis;  J,,  arytenoid  carti- 
lage; o,  thyroid  cartilage;  6,  root  of  tongue;  7,  mouth  cavity;  8,  isthmus  faucium;  9,  hard  palate;  10,  septum  nasi; 
ii,  ventral  muscles  of  head;  a,  soft  palate;  a',  free  edge  of  a;  b,  dorsal  wall  of  pharynx;  c,  forni.x  of  pharynx;  d, 
cavity  of  laryn.x;  c,  y,  naso-phary nx ;  /,  oro-pharyn.x;  h,  posterior  pillar  of  soft  palate;  i,  dotted  line  indicating 
lateral  boundary  between  nasal  cavity  and  pharynx;  k,  aditus  laryngis;  /,  entrance  to  oesophagus;  7«,  Eustachian 
orifice;  n,  pharyngeal  recess;  o,  posterior  naris.      (-\fter  Ellenberger,  in  Leisering's  Atlas.) 

three  inches  (ca.  5  to  7.5  cm.)  beneath  the  mylo-hj'oideus  muscle  along  with  the 
duct.     The  latter  opens  near  the  frenum  linguae,  but  there  is  no  papilla. 

The  sublingual  gland  has  an  arrangement  similar  to  that  of  the  ox.     The  pos- 


Pylurus 


Fig.  312. — Stomach  of  Pig,  Parietal  Surface. 

The  organ  contained  a  rather  small  amount  of  ingesta 

and  hence  is  somewhat  contracted. 


CEsvphcigus 


Diiode 
nuin 


Pylorus 


Fig.  313. — Stomach  of  Pig,  Visceral  Scrface. 
Organ  was  fixed  in  situ  and  is  somewhat  contracted. 


terior  part  (Glandula  sublingualis  grandicanalaris)  is  reddish-yellow  in  color,  and 
is  about  two  inches  (ca.  5  cm.)  long,  and  half  an  inch  wide;  its  posterior  end  is  in 
relation  to   the   submaxillary  gland   and   its  duct.     The  anterior  part  is  much 


416 


DIGESTIVE    SYSTEM    OK    THE    PIG 


larg:er,  licing  two  or  three  inches  (ca.  5  to  7  cm.)  long  and  about  twice  the  wicUh 
and  thickness  of  the  posterior  part.     All  or  most  of  the  ducts  from  the  posterior 


part  unite  to  form  the  ductus  sublingualis  major,  A\hich  opens  near  the  ductus 
suljmaxillaris.  Eight  or  ten  ductus  sublinguales  minores  convey  the  secretion 
from  the  anterior  part  through  the  floor  of  the  mouth. 


Fig.  ai5. — Visceral  Surface  of  Stomach  of  Pig, 


StJF 


COA 


Kkmovkd. 

O,  Gisophagus;  D,  diiotlenum;  Di,  diverticuluii 
external  oblique  libers;  r',  internal  obliiiue  fibers;  c",  ( 
loop;  /,  fold  at  entrance  to  diverticulum;  p,  pyloric  spbii 
d.  Haustiere.) 


Fig.  316. — Everted  Stomach  of  Pig,  from  which  the 
Mucous  Membrane  has   been  Removed. 

a,  a',  a",  a'",  longitutlinal  fibers;  b,  circular  fibers;  c. 
rdiac  loop;  d,  fibers  which  connect  branches  of  cardiac 
ter;   p' ,  pyloric  prominence.      (Ellenberger-Bauni,  .\nat. 


THE  PHARYNX 

The  pharynx  presents  in  its  posterior  part  a  median  cul-de-sac  about  an  inch 

and  a  half  (ca.  3  to  4  cm.)  long,  which  is  situated  between  the  ventral  straight 

muscles  of  the  head  and  the  origin  of  the  opsophagus.     Its  lower  margin  is  formed 

by  the  junction  of  the  posterior  pillars  of  the  soft  palate,  which  contain  muscu- 


THE    (ESOPHAGUS — THE    STOMACH  417 

lar  tissue  derived  from  the  ])alatinus  and  iialato-pharyngeus.  The  vault  of  the 
jiharynx  (Fornix  pharyngis)  is  divided  by  a  median  fold  of  mucous  membrane 
which  is  a  direct  continuation  of  the  septum  nasi.  On  either  side  of  this  is  an  in- 
funilihvilum  in  which  the  Eustacliian  tube  opens. 


THE  (ESOPHAGUS 
The  oesophagus  is  short  and  nearly  straiglit.  It  has  (according  to  Rubeli)  a 
potential  caliber  of  nearly  3  inches  (ca.  7  cm.)  at  either  end,  and  about  1^  inches 
(ca.  4.2  cm.)  in  its  middle  part.'  The  miuscular  coat,  except  near  the  cardia,  is 
striated.  There  are  mucous  glands  in  the  submucosa  to  about  the  middle  of  the 
tube. 


317. — Abdominal  Viscera  of  Young  Piu,  Ventral  ,\spect. 
The  stomach  was  very  large  in  this  subject. 


THE  STOMACH 
The  stomach  is  large  and  pjTiform.     Its  average  capacity  is  about  1^^  to  2 
gallons  (ca.  5.7  to  8  liters).     When  full  it  extends  backward  to  the  last  left  inter- 

'  It  is  usually  stated  that  the  cardiac  end  is  funnel-.sliaped,  but  it  is  not  so  in  formalin 
hardened  cadavers  nor  in  frozen  sections.  The  hiatus  oesophagus  is  a  long  slit  in  the  right  crus  of 
the  diaphragm,  and  the  terminal  part  of  the  oesophagus,  which  lies  in  it,  is  flattened  transversely. 


418 


DKJESTIVE    SYSTEM    OF    THE    PIG 


costal  space  laterally  and  the  uiubilicu.s  veiitrally.  The  left  portion  is  large  and 
rounded,  while  the  right  portion  (Pars  pylorica)  is  small,  and  bends  sharjily  upward 
to  join  the  small  intestine.     The  parietal  surface  is  related  to  the  liver,  gall-bladder, 


centrifugal 


Fig.  318. — Dlvgram  of  Cecum  and  Colox  of  Pig. 
C^oils  of  colon  have  been  pulled  apart  somewhat. 


and  diaphragm.  The  visceral  surface  is  related  to  the  intestine,  the  mesentery, 
and  the  pancreas.  The  great  curvature  is  related  to  the  diaphragm,  spleen,  and 
abdominal  floor.     The  pyloric  end  lies  on  the  right  lateral  lobe  of  the  liver.     The 


V 


■  310. — Solitary  Nodplks  from  Large  Intestine 
V  1*1G.     (Elleuberger-Baum,  Auat.  d.  Haustiere.) 


Fig.  320. — Ileo-c.*:cal  Openinc  and  Adjacent  Part 

OF    C-ECUM    AND    CoLON    OF    PlG. 

a,  Mucous  membrane  of  colon;  6,  mucous  mem- 
brane of  fipcum;  f,  Peyer's  patch;  rf,  ileo-ca'cal  oi>en- 
ing;  e,  end  of  ileum;  /,  folds  (frenula)  of  ileum.  (After 
P.  Schumann.) 


left  extremity  presents  a  flattened  conical  l)lin(l  pouch,  the  diverticulum  ventriculi, 
the  apex  of  which  projects  backward.  Tlie  oesophagus  joins  the  stomach  very 
obliquely,  almost  in  the  median  plane,  and  about  three  or  four  inches  (ca.  8  to  10 


THE    INTESTINE 


410 


cm.)  below  the  twelfth  thoraeie  vertel)ra.  The  cardiac  opening  is  plit-Hke  and  is 
bounded  al)ove  and  to  the  left  by  a  fold  which  contains  a  thickening  of  the  internal 
oblique  layer  of  the  muscular  coat.  The  opening  into  the  diverticulum  is  situated 
above  and  a  little  to  the  left  of  the  cartha;  it  is  transversely  oval,  and  i.s  bounded 
(except  externally)  l)y  a  thick  fold  which  contains  spirally  arranged  muscular 
fibers.  The  mucous  membrane  may  be  divided  into  four  regions.  Over  a  quadri- 
lateral area  around  the  cardia  (about  one  inch  on  the  right  and  two  or  three  inches 
on  the  left  siile  of  the  orifice)  it  is  oesophageal  in  character,  and  presents  a  number  of 
folds.  A  sharp  line  of  demarcation  separates  this  from  the  rest  of  the  mucous 
membrane,  which  is  soft  and  glandular.  The  second  or  cardiac  gland  region  is 
pale  gray  in  color  and  thin  (ca.  0.5  to  1  mm.);  it  extends  about  to  the  middle  of 
the  stomach.  The  third  or  fundus  gland  region  is  readily  distinguished  by  its 
thickness  (ca.  3  mm.)  and  its  brownish-red  mottled  appearance.'  The  fourth  or 
pj'loric  region  is  pale,  thinner  than  the  preceding,  and  presents  a  number  of  irregular 
folds.  At  the  ]5ylorus  there  is  a  remarkable  ridge  which  projects  from  the  wall  of 
the  lesser  curvature  and  diminishes  considerably  the  size  of  the  orifice.  It  is  about 
an  inch  and  a  half  (ea.  3  to  4  cm.)  long  and  nearly  half  an  inch  (ca.  1  cm.)  high. 
Sometimes  it  is  grooveil;  in  other  cases  it  has  the  form  of  a  rounded  eminence 
attached  by  a  pedicle  to  the  wall.  Fibers  from  the  circular  muscular  coat  exteinl 
into  it. 


THE  INTESTINE 
The  small  intestine  is  50  to  65  feet  (ea.  15  to  20  m.)  long.  The  mesen- 
tery of  about  the  first  two  feet  (ca.  60  cm.)  is  two  to  two  and  a  half  inches 
(ca.  5  to  6  cm.)  long;  this  part  may  be  termed  duodenum.  The  remainder  (Jejuno- 
ileum)  has  a  mesentery  about  six  to  eight  inches  (ca.  15  to  20  cm.)  long,  which  is 
thick  and  contains  a  quantity  of  fat,  and  numerous  large  lymph  glands  at  its  root; 
the  root  is  attached  in  the  sublumbar  region  behind  the  stomach  and  blends  here 
with  the  mesentery  of  the  large  intestine.  The  small  intestine  is  arranged  in  close 
coils  and  lies  mainly  on  the  left  side  and  floor  of  the  abdomen,  from  the  stomach 
to  the  pelvis;  some  coils,  however,  lie  against  the  right  flank.  The  opening  of  tiie 
bile  duct  is  about  one  or  two  inches  (ca.  2.5  to  5  cm.)  from  the  pylorus,  and  that 
of  the  pancreatic  duct  about  four  or  five  inches  (ca.  10  to  15  cm.)  beyond  it.    Peyer's 

'  It  will  be  noted  that  the  fundus  gland  region  does  not  extend  up  to  the  lesser  curvature; 
here  the  cardiac  mucosa  joins  the  pyloric. 


420 


DIGESTIVE    SYSTEM    OF    THE    PIG 


patches  and  solitary  glands  aro  numerous  and  very  distinct ;  the  patches  are  usually 
l)and-Hke  and  prominent;  the  solitary  glands  form  projecting  nodules  marked  l)y 
crypts. 

The  large  intestine  is  about  15  feet  (ca.  4  to  5  meters)  in  length,  and  is  for  the 
most  part  much  wider  than  the  small  intestine;  it  is  connectetl  by  a  mesentery 
with  the  dorsal  alxlominal  wall  between  the  kidneys.  The  caecum  is  cylindrical, 
aI)out  8  to  12  inches  (ca.  20  to  30  cm.)  long,  and  3  to  4  inches  (ca.  8  to  10  cm.)  wide. 
It  lies  against  the  upper  part  of  the  right  flank,  its  Islind  end  reaching  to  within 
about  two  inches  (ca.  5  cm.)  of  the  pelvic  inlet.  The  ileum  joins  the  caecum 
obliquely  and  projects  somewhat  into  its  lumen.     The  colon  has  at  first  about  the 


Hepiilic  arlcry 

He/Milic  duel 
(Esophageal  notch 


••.  322. — Liver  of  Pio,  Visceral  Sui 
Photograph  of  specimen  hardened  in  si 


same  caliber  as  the  CiBcum,  but  becomes  gradually  smaller.  Most  of  it  is  arranged 
in  three  close,  double  .spiral  coils  in  the  mesentery,  in  relation  chiefly  to  the  right 
flank  externally,  and  to  the  small  intestine  behind  and  to  the  left.  On  emerging 
from  this  si)iral  labyrinth,  it  passes  forward  to  the  stomach  and  pancreas  antl  then 
turns  backward;  this  terminal  part  is  narrow,  median  in  position,  and  closely 
attached  by  a  short  mesentery  to  the  sublumbar  region.  The  rectum  is  usually 
surrounded  by  a  ciuantity  of  fat.  The  caecum  has  three  longitudinal  muscular 
bands  and  three  rowjs  of  sacculations,  which  are  continued  a  short  distance  on  the 
colon.  The  sjiiral  colon  has  two  bands  and  two  series  of  sacculations,  which, 
however,  gradually  disappear  in  the  centrifugal  part. 


THK    LIVER 


421 


THE  LIVER 
The  liver  is  relatively  large,  its  average  weight  being  about  4  to  i}4  pounds 
(ca.  2  kg.).  It  is  thick  and  very  strongly  curved.'  It  i.s  tlividcd  l)y  three  deep 
interlobar  incisures  into  four  principal  lobes  —  right  lateral,  right  central,  left 
central,  left  lateral;  the  la.st  of  these  is  usually  considerably  the  largest.  On  the 
upper  part  of  the  right  lateral  lobe  is  the  caudate  lobe  and  its  process.  That 
part  of  the  right  central  lobe  which  lies  below  the  portal  fissure  and  to  the  left  of 
the  gall-bladder  and  cystic  duct  is  homologous  \\'ith  the  quadrate  lobe  of  man. 
The  parietal  surface  is  extremely  convex,  its  most  anterior  part  reaching  to  a 
plane  through   the   lower    part  of  the   sixth  or  seventh  intercostal  space.     The 


Umbilical  Jiss  ure 


•phageal  iiuich 


Hejiatic  reins 


Fig.  323.— Livkr  ok  Pk..   Parietal  SntrACE. 
Photograph  of  specimen  hardened  in  situ. 


visceral  surface  is  deeplj-  concave;  most  of  it  is  related  to  the  stomach,  for  which 
there  is  a  correspondingly  large  and  deep  gastric  impression.  There  is  a  duodenal 
impression  on  the  upper  part  of  the  right  lateral  lobe,  but  no  renal  impression,  as 
the  right  kidney  does  not  touch  the  liver.  The  fossa  for  the  gall-bladder  is 
mainly  on  the  right  central  lobe,  but  also  in  part  on  the  adjacent  surface  of  the 
left  central  lobe.  The  posterior  vena  cava  enters  the  dorsal  border  of  the 
caudate  lobe  and  soon  becomes  entirely  embedded  in  the  gland-substance,  emerg- 
ing only  at  its  passage  through  the  diaphragm.  The  CESophageal  notch  is  large 
and   is   occupied   mainly   by  the  large  right  eras  of  the  diaphragm.     The  right 

'  The  description  here  given  is  based  mainly  on  the  appearance  of  the  organ  as  hardened 
in  silii,  which  differs  radically  from  that  of  the  soft  organ,  as  is  seen  on  comparison  of  the  annexed 
figure  (Fig.  321). 


422 


DIGESTIVE    SYSTEM    OF    THE    PTG 


lateral  l^ordcr  pxtonds  backward  to  the  upper  part  of  the  twelfth  intercostal  space 
or  thirteenth  rib.  The  k>ft  lateral  l)order  is  opposite  the  eighth  rib  and  intercostal 
space.     The  ventral  border  extends  backward  about  as  far  as  the  umbihcus. 

There  are  no  lateral  ligaments  and  the  falciform  ligament  disappears  early. 

The  gall-bladder  is  attached  in  the  fossa  vesicae  felleae  on  the  right  central  lobe, 
at  a  considerable  distance  from  the  ventral  border.  The  cystic  duct  joins  the  hepa- 
tic duct  at  an  acute  angle  immediately  after  the  emergence  of  the  latter  from  the 
l)ortaI  fissure.  The  bile  duct  (Ductus  choledochus)  opens  at  the  papilla  duodeni 
about  one  or  two  inches  (ca.  2.5  to  5  cm.)  from  the  pylorus. 

Owing  to  the  large  amount  of  interlobular  tissue,  the  lobules  are  map]3ed  out 
sharply;  they  are  polyhedral  in  form  and  are  1  to  2. .5  mm.  in  diameter.  For  the 
same  reason  the  gland  ti.ssue  is  much  less  friable  than  that  of  the  other  animals, 
from  which  it  is  easily  di.stinguished. 


Fig.  324. — Projection  of  Viscera  of  Pig  on  Body-wall,  Left  Side. 
D,  Costal  line  of  diaphragm;   t/,  ureter;   V.  S.,  vesicula  seminalis;   B.  c,  bulbourethral  gland;  P,  penia 


Fig.  325. — Projection  op  V'ihcera  or  Pig  on  Bon 
£*,  Costal  attachment  of  iliaphragin;  O, 


DIGESTIVE    SYSTEM    OF    THE    DOG — THE   MOUTH 


423 


THE  PANCREAS 
The  pancreas  is  elongated,  and  is  situated  transversely  on  the  dorsal  abdominal 
■nail,  A^-ith  its  right  extremity  on  the  ventral  surface  of  the  right  kidney,  and  the  left 
end  touching  the  dorsal  end  of  the  spleen  and  the  left  kidney.  The  right  portion 
has  two  lolies;  the  posterior  lobe  bends  around  the  great  mesenteric  artery  and 
the  portal  vein;  the  anterior  one  is  pointed,  extends  dowTiward  and  forward  about 
in  the  median  plane,  and  is  attached  to  the  portal  fissure  and  the  duodenum.  The 
left  portion  is  prismatic  and  rests  mainly  on  the  left  sac  of  the  stomach,  its  left 
fxtremity  being  included  between  the  left  kidney  and  the  dorsal  end  of  the  spleen. 
The  pancreatic  duct  passes  from  the  anterior  lobe 
directly  through  the  duodenal  wall,  opening  about  five 
or  six  inches  (ca.  12.5  to  15  cm.)  from  the  pylorus.  The 
interlobular  tissue  usually  contains  a  good  deal  of  fat. 


THE  SPLEEN 
The  spleen  is  long  and  narrow.  Its  long  axis  is 
nearly  dorso-ventral  in  direction,  and  is  slightly  curved 
to  conform  to  the  left  part  of  the  greater  curvature  of 
the  stomach.  The  dorsal  end  lies  under  the  vertebral 
ends  of  the  last  three  ribs.  The  ventral  end  is  smaller, 
reaches  to  the  ventral  abdominal  wall,  and  lies  against 
the  left  lobe  of  the  liver.  The  visceral  surface  has  a 
longitudinal  ridge  on  which  the  hilus  is  situated;  this 
divides  the  surface  into  nearly  equal  gastric  and  in- 
testinal areas.  The  spleen  is  attached  so  loosely  to 
the  stomach  that  it  may  be  regarded  as  being  inter- 
calated in  the  great  omentum.  In  large  subjects  it  may 
reach  a  length  of  15  to  18  inches  (ca.  38  to  45  cm.)  and 
a  width  of  3  to  4  inches  (ca.  8  to  10  cm.). 


DIGESTIVE  SYSTEM  OF  THE  DOG 


Fig.  326. — Tongue  of  Dog. 
a,  Tonsil;  b,  vallate  papil- 
Ise;  c,  foliate  papilla;  d.  fungiform 
papilla":  *'.  median  groove  of  dor- 
sum; /.  epiglottis;  g,  soft  papilUe 
of  root;  k,  middle  glosso-epi- 
glottic  fold;  7,  tip:  B,  root.  (Ellen- 
berger-Baum.  Anat.d.  Haustiere.) 


THE  MOUTH 

The  size  and  form  of  the  mouth  vary  greatly  in 
different  breeds,  the  cavity  being  in  some  long  and 
narrow,  in  others  short  and  wide.  The  rima  oris  is 
very  extensive,  so  that  the  labial  commissure  is  oppo- 
site the  third  or  fourth  cheek  tooth.  The  lips  are  thin 
and  mobile,  and  present  numerous  tactile  hairs.     The 

upper  lip  has  a  small,  central,  bare  area  which  forms  part  of  the  muzzle,  and  is 
marked  by  a  central  groove,  the  philtrum,  or  (as  in  the  bull-dog)  a  fissure,  giving 
the  appearance  of  harelip.  The  lateral  borders  of  the  lower  lip  are  flaccid  and 
denticulated.  The  mucous  membrane  is  usually  pigmented  and  forms  distinct 
frena  labiorum.     The  labial  glands  are  small  and  scanty. 

The  cheeks  are  loose  and  capacious,  and  their  mucous  lining  is  smooth  antl 
more  or  less  pigmented.  The  parotid  duct  opens  usually  opposite  the  third  upper 
cheek  tooth.  Near  the  last  tooth  are  the  openings  of  the  four  or  five  ducts  from 
the  orbital  gland. 

The  hard  palate  is  widest  between  the  fourth  pair  of  cheek  teeth.      It  has 


424 


DIGESTIVE    SYSTEM    OF   THE    DOG 


eight  to  ten  curved  ridges  on  either  side  of  the  raphe.  Behind  the  first  pair  of 
ineisor  t(H>th  is  the  triangular  incisiv^e  pai)illa,  at  wliieh  the  naso-palatine  (hiets 
open.     The  mucous  membrane  i.s  usually  pigmented. 

The  soft  palate  is  thick  except  at  its  margins.  In  the  resting  state  of  the  parts 
it  comes  in  contact  with  the  oral  surface  of  the  epiglottis.  Between  its  anterior 
and  posterior  pillars  on  either  side  is  a  marked  tonsillar  sinus,  in  which  an  elongated 
tonsil  is  situated;  this  is  reddish  in  color,  about  an  inch  long,  and  projects  somewhat 
into  the  fauces  between  two  folds  of  mucous  membrane. 

The  tongue  is  wide,  thin,  and  very  mobile.  It  is  not  ]:)igmented,  but  has  a 
bright  red  color.  The  upper  surface  is  marked  by  a  median  groove  (Sulcus  metli- 
anus  linguie),  and  is  thickly  beset  with  short,  pointed,  filiform  papillae,  the  free  ends 
of  which  are  directed  backward.  On  the  root  the  jjapillte  are  long  and  .scift: 
similar  jiapillae  occur  on  the  lateral  walls  of  the  isthmus  faucium.  The  fungiform 
papilkc  are  small,  and  are  scattered  over  the  dorsum  and  sides  of  the  tongue,  but 
are  absent  on  the  root.  There  are  usually  two  or  three  vallate  papilhr  on  either 
side.  Small  foliate  pa])illae  are  also  present.  In  the  inferior  part  of  the  tip  of  the 
tongue  is  the  lyssa,  a  fusiform  cortl,  composed  of  fibrous  tissue,  muscular  tissue, 
and  fat.     In  large  dogs  it  is  about  two  inches  (ca.  4  to  5  cm.)  long. 


'. —  Skull  of  .Viu-lt  St.  Bkrnard  Dog,  Sculptured  to  Snow  the  EMiiKDnr. 
Il-S^  Inciaors;   C,  caQines;   Pl-4,  premolars;    Ml-S,  molara. 


THE  TEETH 

The  formula  for  the  permanent  teeth  is: 


/  :5     1     4      2\ 

I  I-C'-P-  M  -   I 
V   :5      1      4       3/ 


THE    TEETH 


425 


All  of  tho  teeth  have  short  crowns  and  distinct  necks;  they  erupt  rapiilly. 
The  crowns  are  white,  being  destitute  of  cement. 

The  incisors  are  placed  almost  vertically  and  close  together  in  the  jaw-bones. 
They  do  not  correspond  to  an  opposing  tooth,  but  rather  to  parts  of  two  teeth  of 
the  other  jaw.  The  crowns  are  trituberculatc,  the  central  projection  Ijeing  the 
largest.  They  increase  in  size  from  the  first  to  the  third.  The  labial  surface  is 
convex,  the  lingual  slightly  concave,  and  marked  off  from  the  neck  by  a  V-shaped 
ridge,  the  cingulum.  The  roots  are  flattened  transversely.  The  lower  incisors 
are  smaller  than  the  upper  ones.     One  or  two  supernumerary  teeth  may  be  present. 


32S.— Bask  of  I 
,  premolar.s;     MIS, 

account  of  the  shortn 


anfl  ijremolars  on 


The  canine  teeth  are  large,  conical,  and  curved.  The  upper  canine  is  separated 
from  the  corner  incisor  by  an  interval  into  which  the  lower  canine  is  received  when 
the  jaws  are  closed.'  The  lower  canine  is  close  to  the  corner  incisor.  The  root  is 
about  an  inch  (ca.  2  to  3  cm.)  long  and  is  flattened  laterally. 

The  cheek  teeth  arc  typically  j,  but  in  brachycephalic  breeds  they  are  com- 
monly reduced  to  i,  and  in  extreme  cases  even  to  *.     The  reduction  occurs  at  either 

'  In  the  bull-dog,  which  is  very  prognathic  ("undershot"),  the  lower  canines  are  opposite 
to  or  sUghtly  in  front  of  the  plane  of  the  upper  incisors,  and  the  upper  canines  are  about  opposite 
to  the  first  lower  cheek  teeth.  In  the  epignathic  ("overshot")  dachshund  the  lower  canines  are 
under  or  slightly  behind  the  upper  ones. 


426 


DIGESTIVE    SYSTEM    OF    THE    DOG 


end  or  at  both  ends  of  the  series.'  The  first  tooth  appears  only  onoc.  The  fourth 
tooth  of  the  upper  row  and  the  fifth  of  the  lower  row  are  much  larger  than  the  rest, 
and  termed  sectorial  or  camassial  teeth.  From  these  the  teeth  diminish  in  size 
Ijoth  forwarfl  and  backward.  The  upper  and  lower  teeth  do  not  correspond,  but 
rather  dovetail.  The  teeth  behind  the  sectorial  ones  are  tuberculate,  -i.  e.,  have 
rounded  eminences  on  the  masticatory  surface.  The  others  are  all  sectorial  in 
character,  /.  <>.,  have  sharp-edged,  pointed  projections,  the  middle  one  being  the 
most  prominent.  The  premolars  are  laterally  compressed,  and  are  separated  by 
intervals  from  the  canines  and  from  each  other,  except  in  the  brachycephalic 
breeds.  The  upper  molars  have  w-ide,  somewhat  quadrangular  crowns,  and  three 
roots.  The  crown  of  the  upper  fourth  premolar  (Dens  sectorius)  is  divided  into 
two  pointed  lobes  and  has  an  antero-internal  tubercle;   it  has  three  roots.     The 


Fig.  .329. — Dissection  or  Head  of  Dog,  Showing  Salivary  Glands,  etc. 
".  Ocular  muscles;  6,  pterygoideus  internus  (cut);  c,  stylo-glossus;  rf,  digfLstricus  (cut);  e,  genio-glossus; 
/,  getiiu-hyoideus;  g,  hyo-glossus;  h,  thyro-pharyngeus;  ;',  crico-pharyngeus;  k,  thyro-h.voideus;  /,  zygomatic 
process  of  temporal  (.sawn  off);  1,  parotid  gland;  3,  submaxillary  gland;  3,  posterior  part  of  sublingual  gland; 
3',  anterior  part  of  same;  4,  submaxillary  duct;  5,  ductus  sublingualis  major;  6,  palatine  glands:  7,  orbital  or 
zygomatic  gland:   .¥,  ducts  of  7;  5,  lacrimal  gland.     (Ducts  colorefl  red.)      (.\fter  EUenberger,  in  Leisering's  Atlas.) 


crown  of  the  first  lower  molar  (Dens  sectorius)  is  compressed  laterally  and  has  two 
pointed,  sharp-edged  lobes,  behind  which  are  one  or  two  tubercles;  it  has  two  roots. 
The  average  periods  of  eruption  are  given  below. 

Tooth  Eruption  Chance 

I, 4  to  5  weeks ] 

Ij 4  to  5  weeks )•  4  to  .^  months 

I3 4  weeks J 

C 3  to  4  weeks 4  to  .'i  months 

Pi 4  to  5  months 1 

Pj 4  to  5  weeks .  ,     ,.  .1 

P' 3  to  4  weeks -^  '°  ''  "'°"'*'^ 

P, 3  to  4  weeks J 

M, 4  months 

»j  /  upper  5  to  6  months 

' \  lower  4J^  to  5  months 

Mj 6  to  7  months 

'  Increase  in  number  also  occurs,  the  supernumerary  teeth  being  at  either  end  of  the  series. 


THE    SALIVARY    (ILANDS — THE    PHARYNX  427 

THE  SALIVARY  GLANDS 

The  parotid  gland  is  small.  Its  uj^iier  part  is  wide  and  is  divided  into  twc 
lobes  by  a  deep  noteh  into  whii'h  the  base  of  the  ear  is  received.  The  lower  end 
is  small  and  overlaps  the  submaxillary  gland.  The  duct  leaves  the  gland  at  its 
anterior  border,  crosses  the  masseter  muscle,  and  opens  into  the  mouth  opposite 
the  third  upper  cheek  tooth.  Small  accessory  glands  ((ilandulo"  parotidae  acces- 
sorise) are  .sometimes  found  along  the  cour.se  of  the  duct. 

The  submaxillary  gland  is  usually  larger  than  the  parotid.  In  large  dogs  it 
is  about  two  inches  (ca.  5  cm.)  long  and  an  inch  or  more  (ca.  3  cm.)  wide.  It  is 
rounded  in  outline  and  of  a  pale  yellow  color.  Its  upper  part  is  covered  by  the 
parotid,  but  it  is  otherwise  superficial,  and  is  palpable  in  the  angle  of  junction  of 
the  jugular  and  external  maxillary  veins.  The  duct  leaves  the  deep  face  of  the 
gland,  passes  along  the  surface  of  the  digastricus  and  stylo-glossus,  and  opens  into 
the  mouth  near  the  frenum  linguie  on  a  very  indistinct  papilla. 

The  sublingual  gland  is  divided  into  two  parts.  The  posterior  part  (Glandula 
sublingualis  grandicanalaris)  lies  on  the  digastricus  muscle  in  intimate  relation  with 


Fig.  330. — Sagittal  Section-  of  Pharyngeal  and  Laryngeal  Regions  of  Dog. 
1,  OSsophagus;  2.  larynx;  3,  mouth  cavity,  4,  epiglottis;  5,  arytenoid  cartilage;  6,  soft  palate;  6",  position 
of  soft  palate  when  raised;  7,  vomer;  8,  base  of  cranium;  9,  root  of  tongue;  a,  a',  a",  pharynx;  b,  fornix  of 
pharynx;  c,  posterior  wall  of  pharynx;  d.  floor  of  pharynx;  e,  pharyngeal  surface  of  soft  palate;  /.  origin  of 
cEsophagus;  g,  vestibule  of  larynx;  A,  isthmus  faucium;  i,  Eustachian  opening;  k,  posterior  naris.  (.\fter  EUen- 
berger,  in  Leisering's  .\tlas.) 

the  submaxillary  gland,  but  clearly  separable  from  it  after  removal  of  the  common 
fibrous  capsule.  It  has  a  pointed  anterior  process.  The  duct  (Ductus  sublingualis 
major)  accompanies  the  submaxillary  duct,  and  usually  opens  beside  it,  but  in 
some  cases  joins  it.  The  anterior  part  (Glandula  sublingualis  parvicanalaris)  is 
long  and  narrow;  it  lies  on  the  stylo-glossus  muscle.  It  has  a  number  (8  to  12) 
of  small  ducts  (Ductus  sublinguales  minores),  some  of  which  open  directly  into  the 
mouth,  while  others  join  the  large  duct. 

The  orbital  or  zygomatic  gland  (Glandula  zygomatica)  represents  the  superior 
molar  glands  of  herbivora.  It  is  prismatic  and  is  situated  in  the  orbital  region, 
between  the  zygomatic  arch  and  the  internal  pterygoid  muscle,  in  contact  with  the 
periorbita.  It  has  four  or  five  ducts  (Ductus  zygomatici)  which  open  near  the 
last  upper  cheek  tooth;  one  of  them  (canal  of  Nuck)  is  almost  as  large  as  the 
parotid  duct;  the  others  are  small. 

THE  PHARYNX 
The  fornix  is  narrow.     The  orifices  of  the  Eustachian  tubes  are  .small  and  slit- 
like;   the  end  of  the  tube  causes  a  rounded  projection  of  the  mucous  membrane 


428  DIGESTIVE    SYSTEM    OF    THE    DOG 

(T(irus  tuharius).  The  esophageal  opening  is  rehitively  small  and  is  encircled  l)y  a 
fold  of  the  mucous  membrane.  The  hyo-pharyngeus  muscle  is  clearly  ilivided 
into  a  kerato-pharyngeus  and  a  chondro-pharyngeus. 

THE  (ESOPHAGUS 
The  oesophagus  is  relatively  wide  and  dilatable  except  at  its  origin.  The 
constriction  at  its  origin  is  termed  the  isthmus  oesophagi.  The  cardiac  end  is 
slightly  dilated;  it  joins  the  stomach  under  the  tenth  or  eleventh  thoracic  vertebra, 
slightly  to  the  left  of  the  median  plane.  The  muscular  tissue  is  striated  and  con- 
sists mainly  of  two  layers  of  spiral  fibers  which  cross  each  other;  near  the  cardia, 
however,  the  fillers  are  longitudinal  and  circular.  There  are  mucous  glands  ami 
lymph  glands  in  the  submucosa  throughout. 


(Esophagus 


Lesser  curvature 
Bile-duct 


Pylorus 


Fig.  331. — Stomach  of  Dog,  Pariictat.  .Surface. 
Organ  fixed  in  situ  wlien  well  filled. 

THE  STOMACH 

The  stomach  is  relatively  large.     Its  capacity  in  a  dog  weighing  about  40 

pounds  is  about  six  to  seven  pints. 

Colin  estimates  the  average  capacity  at  al)out  3  liters  (ca.  ()!2  pints),  with  a  range  between 
0.6  and  8  liters  (ca.  Ik  to  17  J  2  pints).  Neumayer  gives  the  capacity  as  100  to  250  c.c.per  kilogram 
of  Ijody-weight  (ca.  2.7  ounces  per  pound).  The  average  capacity  of  the  human  stomacli  is  esti- 
mated at  3.5  to  40  ounces — only  al)Out  one-half  of  that  of  a  dog  of  medium  size. 

When  full  it  is  irregularly  pyriform.  The  left  or  cardiac  part  (Corpus 
ventriculi)  is  large  and  rounded,  while  the  right  or  pyloric  part  (Pars  pylorica)  is 
small  and  cylindrical.  When  empty,  or  nearly  so,  the  left  sac  is  strongly  contracted; 
the  pyloric  part  is  not  materially  affected  by  variations  in  the  amount  of  ingesta. 

The  parietal  surface  of  the  full  stomach  is  very  extensive,  strongly  convex, 
and  faces  partly  forward,  but  largely  to  the  left.  It  is  related  to  the  liver,  the  left 
part  of  the  diaphragm,  and  the  left  and  ventral  abdominal  wall  as  far  back  as  a 
transverse  section  through  the  second  or  third  lumbar  vertebra. 

The  visceral  surface  is  much  less  extensive  and  is  considerably  flattened;  it 
faces  chieHy  to  the  right,  and  is  related  to  the  intestine,  pancreas,  and  left  kidney. 

The  upper  part  of  the  lesser  curvature  is  nearly  straight  and  vertical,  but  the 
lower  part  forms  a  deep,  narrow  angle,  due  to  the  fact  that  the  pjdoric  part  is 
directed  sharply  forward  and  upward. 


THE    STOMACH 


429 


The  greater  curvature  is  nearly  four  times  as  long  as  the  lesser  curvature. 
In  the  full  stomach  it  extends  considerably  behind  the  left  costal  arch  (having 
carried  the  spleen  backward);  ventrally,  it  lies  on  the  abdominal  wall,  almost 
midway  from  the  xiphoiel  cartilage  to  the  pubis. 


(Esophngus 

Lesser  curvature 
Pylorus 


Bile-duct 


Fig.  332. — Stomach 

Organ  fixed  i 


Dog,  Visceral  Surface. 
u  when  well  filled. 


The  left  extremity  or  fundus  is  large  and  rounded;  it  is  the  most  dorsal  part 
of  the  organ,  and  lies  under  the  dorsal  ends  of  the  eleventh  and  twelfth  ribs. 

The  pyloric  extremity  is  small  and  is  directed  forward  and  somewhat  upward; 
it  lies  usually  about  an  inch  or  two  (ca.  3.5  to  5  cm.)  below  the  cardia,  a  little  to 


Fig.  333. — Everted  Stomach  of  Dog  from  which 
THE  Mucous  Membrane  is  Removed. 
O,  CEsophagus;  D,  duodenum;  b,  circular  fibers; 
</,  internal  oblique  fibers;  r",  cardiac  loop;  c'",  transition 
of  internal  to  external  oblique  fibers;  d,  fibers  uniting 
branches  of  cardiac  loop;  p,  pyloric  sphincter;  p',  antral 
sphincter.     (EUenberger-Baum,  Anat.  d.  Haustiere.) 


,\M  of  Zones  of  Mucous  Membra 
Stomach  of  Dog. 


the  right  of  the  median  plane.  It  is  re- 
lated to  the  portal  fissure  of  the  liver 
and  to  the  pancreas. 

The  cardia  is  situated  about  two  to 
three  inches  (ca.  5  to  7  cm.)  from  the  left  extremity,  and  is  oval;  it  lies  a  little  to 
the  left  of  the  median  plane,  below  the  tenth  or  eleventh  thoracic  vertebra. 

When  empty,  or  nearly  so,  the  stomach  is  separated  from  the  ventral  abdomi- 
nal wall  by  the  liver  and  small  intestine,  and  the  greater  curvature  extends  back  to 


430 


DIGKSTIVE    SYSTEM    OF   THE    DOG 


the  eleventh  or  twelfth  rib.  In  this  state  there  is  not  rarely  a  marked  constriction 
between  the  right  and  left  portions. 

The  longitudinal  muscular  fibers  are  found  on  the  curvatures  and  on  the  pyloric 
]iart.  The  oblique  fibers  are  arranged  in  two  layers:  the  external  layer  is  a  con- 
tinuation of  the  longitudinal  fibers  of  the  oesophagus  onto  the  body  and  fundus. 
The  circular  layer  covers  the  whole  stomach  except  the  fundus,  and  forms  a  pyloric 
sphincter  and  an  antral  sphincter.  The  internal  ol)Iique  layer  is  arranged  as  in 
the  horse,  and  forms  a  similar  loop-like,  cardiac  sphincter. 

Three  regions  of  the  mucous  membrane  exist.  Cardiac  glands  are  found  in  a 
very  narrow  pale  zone  around  the  cardiac  opening,  and  also  scattered  along  the  les- 
ser curvature.     The  fundus  gland  region  has  a  thick,  reddish-brown  mucous  mem- 


Superfifiiil  ventral 


Fiu.  335. — Abdominal  Viscera  op  Dog. 
val  of  the  great  omentum.     From  photograph  of  formalin-hardened  subject 


brane,  whicii  lines  aliout  two-thirds  of  the  organ.     The  pyloric  mucous  membrane 
is  thinner  and  pale;   in  the  dead  subject  it  is  often  stained  by  regurgitated  bile. 


THE  INTESTINE 

The  intestine  is  short — about  five  or  six  times  the  length  of  the  body. 

The  small  intestine  has  an  average  length  of  aliout  thirteen  feet  (ca.  4  meters). 
It  occupies  most  of  the  abdominal  cavity  behind  the  liver  and  stomach.  The  duod- 
enum begins  at  the  ])ortal  fissure  and  passes  backward  and  upward,  at  first  on  the 
visceral  surface  of  the  liver,  then  in  contact  with  the  right  flank.  Near  the  pelvis 
it  turns  inward  and  sharply  forward,  passes  along  the  inner  border  of  the  left 
kidney,  and  joins  the  jejunum  to  the  left  of  the  root  of  the  mesentery.  The 
mesoduodcnum  is  given  off  from  the  common  mesentery;  it  is  a  relatively  wide 


THE    INTESTINE 


431 


fold,  except  at  the  terminal  piut.  Here  there  are  two  short  folds,  one  of  which 
joins  the  mesocolon;  the  other  passes  onto  the  terminal  part  of  the  colon.  The 
first  part  of  the  mesoduoilenuin  contains  the  right  l^ranch  of  the  pancreas.  Its 
root  is  blended  with  the  mesocolon  to  form  a  common  mesentery.  The  remainder 
of  the  small  intestine  forms  numerous  coils,  and  is  attached  by  a  wide  mesentery 
to  the  sublumbar  region.  The  pancreatic  and  bile  ducts  open  into  the  duodenum 
about  two  or  three  inches  (ca.  5  to  8  cm.)  from  the  pylorus;  the  accessory  pancreatic 
duct  opens  an  inch  or  two  (ca.  2.5  to  o  cm.)  further  back.  The  mucous  membrane  has 
very  long  villi.  The  duodenal  (Brunner's)  glands  occur  only  near  the  pylorus.  Peyer's 
patches  are  numerous  (about  twenty  in  young  subjects),  and  begin  in  the  duodenum. 
They  are  usually  ellii)tical  in  outline,  but  the  last  one  is  baud-like,  reaches  to  the  end 


Fig.  3.36. — Deep  Dis.sectiun  of  Abdominal  Viscera  of  Dog  (Female). 

B/.,  Bladder;  B.body;  C,  C,  cornua  of  uterus;  O,  O',  ovaries;   L.  K.,  left  kidney.     Tlie  concealed  part  of  the  coIo 

is  indicated  by  dotted  lines.     (From  photograph  of  formalin-hardened  subject  J 


of  the  ileum  and  is  four  to  sixteen  inches  (ca.  10  to  40  cm.)  long  in  young  dogs  (Ellen- 
berger).     There  is  an  ileo-csecal  valve.'     The  muscular  coat  is  relatively  thick. 

The  large  intestine  is  two  to  two  and  a  half  feet  (ca.  60  to  75  cm.)  long. 
Its  caliber  is  about  the  same  as  that  of  the  small  intestine,  and  it  has  neither  longi- 
tudinal bands  nor  sacculations. 

The  caecum  is  about  three  or  four  inches  (ca.  8  to  10  cm.;  long,  and  is  twisted 
in  a  spiral  fashion.     The  twist  is  maintained  by  the  peritoneum,  which  attaches  it 

'  The  valve  does  not  seem  to  be  efficient,  since  experience  shows  that  rectal  injections  can 
be  made  to  pass  beyond  it.  This  may  be  partly  due  also  to  the  fact  that  the  terminal  part  of  the 
ileum  runs  horizontally  forward,  and  the  ileo-CEecal  orifice  faces  into  the  beginning  of  the  colon. 


432 


DKiESTIVE    SYSTEM    OF    THE    DOG 


to  the  ileum.     It  is  situated  usually  against  the  iniildle  of  the  upper  part  of  the  right 
flank,  below  the  duodenum  and  the  right  branch  of  the  pancreas/ 

The  colon  is  attaclied  to  the  sublumbar  region  bj'  a  mesentery,  the  mesocolon. 
It  presents  three  parts,  which  corr(>spond  to  the  ascending,  transverse,  and  descend- 
ing colon  of  man.  The  first  or  right  part  (Colon  ascendens)  is  very  short.  It 
begins  at  the  junction  of  the  ileum  and  csecum,  and  passes  forward  along  the  inner 
surface  of  the  duodenum  and  the  right  branch  of  the  pancreas  till  it  reaches  the 
pyloric  part  of  the  stomach;  here  it  turns  inward  and  crosses  the  median  plane, 
forming  the  transverse  part  (Colon  transversum).  The  third  or  left  part  (Colon 
descendens)  passes  backward  in  the  sublumbar  region  along  the  inner  border  or 
ventral  surface  of  the  left  kidney;  then  inclines  toward  the  median  plane  and  joins 

the  rectum.-  The  caliber  of  the  colon 
is  about  the  same  throughout.  It  has 
no  bands  nor  sacculations. 

The  mucous  membrane  of  the 
caecum  contains  numerous  solitary 
glands;  they  are  found  also  in  the  first 
part  of  the  colon. 

The  rectum  is  almost  completely 
covered  with  peritoneum,  the  line  of  peri- 


(From  Leisering's  Atlas.) 


Fig.  33S.— Termination  or  Ilevm  op  Dog. 
0,  Colon;  6,  ca'cum;  c,  ileum;  d,  ileo-ctpcal  open- 
ing: r.  circular  depression  around  end  of  ileum,     {.\fter 
P.  Schu 


toneal  reflection  being  under  the  second  or  third  coccygeal  vertebra.  At  the  junc- 
tion of  the  rectum  antl  anus  the  mucous  memltrane  has  a  stratified,  squamous 
epithelium,  and  contains  the  anal  glands.  A  small  opening  on  either  side  leads  into 
two  lateral  anal  sacs  (Sinus  paranales) ;  these  are  usually  about  the  size  of  a  hazel- 
nut, and  contain  a  dirt}'  gray,  fatty  substance,  which  has  a  jieculiar  and  very 
unpleasant  odor.  The  skin  which  lines  these  pouches  contains  coil-glaiuls.  Fur- 
ther back  the  skin  contains  large  sebaceous  glands  and  peculiar  circumanal  glands. 
The  retractor  ani  muscle  is  extensive.  It  arises  from  the  shaft  of  the  ilium,  the 
pubis,  and  the  symphysis  pelvis,  and  passes  upward  and  backward  to  end  on  the 
first  coccygeal  vertebrte  and  the  sphincter  ani  externus.  The  retractors,  together 
with  the  coccygei,  form  a  sort  of  pelvic  diaphragm,  analogous  to  that  of  man. 


THE  LIVER 

The  liver  is  relatively  large,  weighing  usually  about  5  per  cent,  of  the  body- 
weight.  It  is  divided  into  six  or  seven  lobes  by  fissures  which  converge  at  the  portal 
fissure.  When  the  gland  is  examined  in  the  soft  condition,  all  the  lobes  are  visible 
on  the  visceral  surface,  but  usually  only  four  on  the  parietal  surface. 

The  left  lateral  lobe  is  the  largest,  and  is  oval  in  outline.     The  left  central  lobe 

'  Rll(!iil)orKor  and  Baiiin  state  that  the  ca>cum  may  reach  a  length  of  20  cm.  in  very  large  dogs. 

-  When  the  stomach  is  very  full,  it  pushes  the  left  portion  of  the  colon  over  to  the  right, 
l)roducing  an  acute  angle  in  place  of  a  transverse  branch.  The  terminal  p.art  of  the  colon  is  thus 
oblifiue  in  direction. 


THE    LIVER 


433 


is  much  smaller  and  is  prismatic.  The  right  central  lobe  is  second  in  size,  and  i)re- 
sents  a  somewhat  tongue-shaped  quadrate  lohc,  markeil  off  by  the  deep  fissure  in 
which  the  gall-bladder  lies.  The  right  lateral  lobe  is  third  in  size,  and  is  oval  in 
outline.     On  its  visceral  surface  is  the  large  caudate  lobe  ;  this  consists  of  two  parts 


poit.  i/eiuz  cai/a 


LeduLct 


/Jmiilical  fissure 


Fig.  339. — Liver  of  Doo. 
Soft  specimen  sketched  with  lobes  drawn  apart. 


Hepatic 
(Esophageal  notch         artery 


Posterior  tcna  cava 


Left  lateral 
ligament 


Right  lateral 
lobe 


Gnll-bladder 
{not  visible) 


Right  central  lobe 

Fig.  340. — Liver  of  Dog.  Visceral  Sdrf.\ce;    H.\rdf.n-ed  m  situ. 
Left  central  lobe,  gall-bladder,  and  great  part  of  right  central  lobe  not  visible. 

— on  the  right,  the  caudate  process;  on  the  left,  the  papillary  process  or  lobe,  both 
often  being  subdivided  by  fissures. 

When  hardened  in  situ  (with  the  stomach  full),  the  gland  presents  the  following 
characters : 

The  visceral  surface  is  marked  by  a  somewhat  oblique  ridge  (corresponding  to 
28 


434 


DIGESTIVE    SYSTEM    OF   THE    DOG 


the  lesser  curvature  of  the  stomach),  which  separates  two  deep  cavities.  The 
depression  to  the  left  of  the  ridge  is  occupied  bj'  the  body  and  fundus  of  the  stomach. 
The  depression  on  the  right  is  smaller,  and  is  occupied  by  the  pyloric  part  of  the 
stomach,  the  origin  of  the  duotlenum,  and  the  right  branch  of  the  pancreas.  The 
gall-bladder  is  not  visible. 

When  the  stomach  is  empty  and  contracted,  the  visceral  surface  of  the  hver  is  strikingly 
different.  There  is  then  a  shallow  impression  for  the  left  part  of  the  stomach  on  the  left  lobe, 
and  a  large  convex  area,  related  to  the  small  intestine  and  a  mass  of  omentum.  The  pyloric 
and  duodenal  impressions  are  not  much  changed.     The  gall-bladder  is  visible. 

The  portal  fissure  is  very  deep  and  might  well  be  termed  a  fossa.    It  is  bountled 

on  the  right  (externally)  by  the  caudate  process,  on  the  left  (internally)  by  the 

papillary  process  or  lobe,  which  is  directed  ventrally.     The  hepatic  artery  enters 

at  the  dorsal  end  and  the  portal  vein  centrally,  while  the  bile  duct  leaves  at  the 

ventral  part.     The  left  central  lobe  is  not  visible,  and  the  right 

^"  central  one  is  largely  concealed. 

The  parietal  surface  is  extremely  convex,  being  adapted  to 
the  diaphragm  and  the  adjacent  part  of  the  ventral  wall  of  the 
abdomen.  On  it  all  the  lobes  except  the  papillary  are  com- 
pletely or  partially  visible.  The  gall-bladder  is  visible  in  the 
fissure  between  the  quadrate  and  chief  portions  of  the  right 
central  lobe. 

The  dorsal  border  presents  a  renal  impression  on  its  right 
portion.  The  posterior  vena  cava  passes  downward  and  forward 
at  first  in  a  deep  groove  on  the  caudate  lobe,  then  largely  embed- 
ded in  the  parietal  surface  of  the  right  lateral  lobe;  it  receives 
two  large  hepatic  veins  just  before  piercing  the  diaphragm. 

The  oesophageal  notch  is  large,  and  is  occupied  on  the  right 
by  the  thick  margin  of  the  hiatus  ocsophageus.  The  left  liorder 
is  opposite  to  the  ninth  and  tenth  ribs;  it  is  thin  and  is  marked 
by  numerous  indentations.  The  caudate  process  extends  usually 
a  little  beyond  the  last  right  rib,  between  the  right  kidnej-  and 
the  right  branch  of  the  pancreas.  The  ventral  border  lies  on 
the  ventral  abdominal  wall  a  variable  distance  behind  the 
xiphoid  cartilage. 

The  gall-bladder  lies  in  the  fossa  vesics  fellea?,  between  the 
two  parts  of  tlio  riglit  central  lobe;  it  does  not  reach  to  the  ven- 
tral border  of  the  liver.  The  cystic  duct  joins  the  hepatic  duct 
at  the  lower  part  of  the  portal  fissure,  forming  with  it  the  bile 
duct  (Ductus  choledochus) ;  the  latter  passes  to  the  right  and 
opens  into  the  duodenum,  about  two  or  three  inches  (ca.  5  to 
8  cm.)  from  the  pylorus. 
Of  the  ligaments,  the  coronary  and  right  lateral  are  well  developed,  but  the 
left  lateral  and  falciform  are  small. 


Fig.  341.— Splk 
Doo 

.SlRFACE. 

a,  a.  Ridge;  6, 
ventral  end:  c,  dorsal 
end.  (.\fter  Ellen- 
berger,  in  Leisering's 
Atlas.) 


THE  PANCREAS 

The  pancreas  is  V-shaped,  consisting  of  two  long  narrow  branches,  which 
meet  at  an  acute  angle  above  the  pylorus.  The  right  branch  extemis  backward 
above  the  first  part  of  the  duodenum,  below  the  caudate  lobe  of  the  liver  and  the 
right  kidney,  and  ends  usually  a  short  distance  behiiul  the  latter.  The  left  branch 
passes  inward  and  backward  on  the  visceral  surface  of  the  stomach,  and  ends 
under  the  left  kidney.  There  are  two  ducts:  the  larger  one  unites  with  the  liile 
duct,  while  the  smaller  one  enters  the  duodenum  an  inch  or  two  (ca.  3  to  5  cm.) 
further  back. 


THE    SPLEEN 


435 


THE  SPLEEN 

The  spleen  is  bright  red  in  color  in  the  fresh  state.     It  is  somewhat  falciform, 

long,  and  narrow;   the  ventral  part  is  the  widest.     Its  position  varies  in  accordance 

with  tlie  fullness  of  the  stomach.     When  that  organ  is  moderately  full  the  long 

axis  of  the  spleen  corresponds  to  the  direction  of  the  last  rib.     Its  parietal  surface 


Fig.  342. — Projectiox  of  ViscEn.i  of  Dog  (Male)  ox  Body  Wall,  Left  Side. 
A,  C,  D,  Apical,  cardiac,  aud  diaphragmatic  lobes  of  lung:   P,  pericardium;   Pr,  prostate.     Costal  attachment 
metiiaa  line  of  diaphragm  are  dotted. 


Fig.  34.3.— ProjeC] 

A,  C,  D,  .\pical,   cardiac. 

Pan.,  right  branch  of  pancreas;  ( 

are  dotted;  also  posterior  contou 


IN  of  Viscera  of  Dor,  (Female)  on  Body  Wall,  Right  Side. 
nd  diaphragmatic  lobes  of  right  lung:    P.,  pericardium:    L.  K.,   right  kidney; 
ovary;  U,  cornu  of  uterus.    Costal  attachment  and  median  line  of  diaphragm 


is  convex  and  lies  largely  against  the  left  flank.  The  visceral  surface  is  concave  in 
its  length,  and  is  marked  by  a  longitudinal  ridge,  on  which  the  vessels  and  nerves 
are  situated.  The  dorsal  end  lies  against  the  left  kidney  and  left  crus  of  the  dia- 
phragm. The  ventral  end  is  a  little  further  back,  and  reaches  to  the  ventral  wall 
of  the  abdomen.  It  is  so  loosely  attached  by  the  great  omentum  as  to  be  regarded 
as  an  appendage  of  the  latter. 


THE  RESPIRATORY  SYSTEM 

The  organs  of  respiration  (Apparatus  respiratorius)  comprise  the  nasal  cavity,' 
the  pharynx,  tlie  larynx,  the  trachea,  the  bronchi,  and  the  lungs.  The  kings  are  the 
central  organs  in  whieh  tlie  exchange  of  gases  between  the  blood  and  the  air  takes 
place;  the  other  parts  of  the  system  are  passages  by  which  the  air  passes  to  and 
from  the  lungs.  The  nasal  cavity  opens  externally  at  the  nostrils,  and  communi- 
cates behind  with  the  jjharynx  through  the  posterior  nares  (C'hoanse) ;  it  contains 
the  peripheral  part  of  the  olfactory  apparatus,  which  mediates  the  sense  of  smell. 
The  pharynx  is  a  common  passage  for  the  air  and  food — a  remnant  of  the  primitive 
embryonic  arrangement;  it  has  been  described  as  a  part  of  the  digestive  tube. 
The  larj'nx  is  a  complex  valvular  apparatus  which  regulates  the  volume  of  air  pass- 
ing through  the  tract;  it  is  also  the  chief  organ  of  voice.  The  trachea,  and  the 
bronchi  formed  by  its  bifurcation,  are  permanently  open  conducting  tubes.  The 
thorax,  the  pleural  sacs  which  it  contains,  and  the  muscles  which  increase  or 
diminish  the  size  of  the  cavity  are  also  parts  of  the  system.  The  bones,  joints, 
and  muscles  of  the  thorax  have  already  been  described. 

For  topographic  reasons  two  ductless  glands,  the  thjToid  and  the  thymus,  are 
usually  described  in  this  section,  although  they  are  in  no  sense  a  part  of  the  respira- 
tory system. 


RESPIRATORY  SYSTEM  OF  THE  HORSE 
THE  NASAL  CAVITY 

The  nasal  cavity  (Cavum  nasi),  the  first  segment  of  the  respiratory  tract,  is  a 
long,  somewhat  cylindrical  passage,  inclosed  by  all  the  facial  bones  except  the 
mandible  and  hyoid.  It  is  separated  from  the  mouth  ventrally  by  the  palate. 
It  opens  externally  at  the  nostrils,  and  communicates  posteriorly  with  the  pharynx 
through  the  posterior  nares. 

The  nostrils  or  anterior  nares  (Nares)  are  somewhat  oval  in  outline,  and  are 
placetl  obliquely,  so  that  they  are  closer  together  below  than  above.  They  are 
bounded  by  two  alae  or  wings  (AIje  nasi),  which  meet  above  and  below,  forming  the 
commissures.  The  outer  ala  is  concave;  the  inner  one  is  convex  above,  concave 
below.  The  upper  commissure  is  narrow,  the  lower  one  wide  and  rounded.  If 
the  finger  is  passed  into  the  nostril  at  the  upper  commissure,  it  enters  the  so-called 
false  nostril,  w  Inch  leads  backward  to  a  blind  cutaneous  pouch.  This  cul-de-sac, 
the  diverticulum  nasi,  extends  backward  to  the  angle  of  junction  of  the  nasal  l)one 
and  the  nasal  process  of  the  premaxilla.  The  posterior  part  of  the  diverticulum 
is  blind,  but  the  false  nostril  communicates  below  and  internally  with  the  vestibule 
of  the  nasal  cavity.  The  external  opening  of  the  naso-lacrimal  duct  is  seen  when 
the  nostril  is  dilated;  it  is  situated  on  the  floor  of  the  vestibule,  perforating  the 
skin  close  to  its  junction  with  the  mucous  membrane,  about  two  inches  (ca.  5  cm.) 
from  the  lower  commissure.  (It  is  not  rare  to  find  one  or  two  accessory  orifices 
further  back.) 

Structure. — The  skin  around  the  nostrils  presents  long  tactile  hairs  as  well  as 
the  ordinary  ones.     It  is  continued  around  the  alae  and  lines  the  vestibule.     In  the 

'  An  external  nose  (Nasus  cxternus),  such  .is  exists  in  man,  forming  a  projection  distinctly 
marked  ofT  from  the  rest  of  the  face,  does  not  exist  in  the  domesticated  animals. 


THE    NASAL    CAVITY 


437 


posterior  part  of  the  diverticuluin  the  skin  is  thin  and  usually  l)Iack,  and  is  covered 
with  exceedingly  fine  hairs;  it  is  iirovided  with  numerous  sebaceous  glands.  The 
inner  wing  is  supported  by  the  alar  cartilage  (Cartilago  alaris),  which  is  shaped 
somewhat  like  a  connna,  the  convex  margin  being  direct  medially.  The  cartilages 
are  attached  by  filirous  tissue  to  the  extremity  of  the  septal  cartilage.  Each  consists 
of  an  upper,  ciuadrilateral  curved  plate,  the  lamina,  and  a  narrow  comu  which 
curves  downwartl  and  outward,  supporting  the  inner  wing  and  the  lower  com- 
missure, but  not  entering  into  the  formation  of  the  outer  wing.  The  lamina  causes 
the  projection  of  the  upper  jiart  of  the  internal  wing,  from  which  the  thick  alar  fold 
(Plica  alaris)  passes  backward  along  the  external  wall  of  the  nasal  cavity  to  cover 
the  cartilaginous  prolongation  of  the  inferior  turbinal  bone.  This  fold  separates  the 
true  from  the  false  nostril.     The  extremity  of  the  cornu  usually  causes  a  slight 


Fig.  344. — Nostrils  of  Horse. 
a,  Diverticulum  nasi  (shown  as  if  distended):  b. 
philtrura;  c.  false  nostril;  d,  true  nostril;  e',  prominence 
caused  by  lamina  of  alar  cartilage;  e",  prominence  over  cornu 
of  same:  /,  external  wing  of  nostril;  g.  internal  wing;  h. 
lower  commissure;  /.  orifice  of  naso-lacrimal  duct.  {EUen- 
berger-Baum,  .\nat.  d.  Haustiere.) 


Fig.  345. — Cross-section  of  N.\ri.\l  Region  of 
Horse. 
1,  Nasal  bone;  2,  tendon  of  levator  labii  su- 
perioris  proprius;  3,  external  nasal  nerve;  4.  nasal 
diverticulum;  5,  outer  wall  of  4'  ^i  dilatator  naris 
inferior;  7,  levator  nasolabialis  •+■  dilatator  naris 
lateralis;  S,  maxilla  and  premaxiUa;  9,  naso-lacrimal 
duct;  10,  II ,  chief  branches  of  superior  labial  ner\'e, 
with  superior  labial  artery  at  their  inner  side;  13, 
nasal  cavity;  13,  superior  turbinal  fold;  i.^,  inferior 
turbinal  fold,  inclosing  cartilaginous  prolongation  of 
inferior  turbinal  bone:  15,  venous  plexus;  16,  sep- 
tum nasi:  16',  parietal  cartilage:  17,  vomero-nasal 
organ  (of  Jacobson):  IS,  venous  plexus  of  palate; 
19,  buccinator;  SO.  skin;  S3,  anterior  nasal  nerve; 
24,  palatine  process  of  premaxilla.  (After  Ellen- 
berger-Baum.  Top.  .\nat.  d.  Pferdes.) 


projection   of   the    skin   a   short   distance 
behind  and  below  the  lower  commissure. 

The  muscles  of  the  nostrils  have  been 
described. 

Blood-supply. — Palato-labial,  superior 
labial,  and  lateral  nasal  arteries. 

Nerve-supply. — Trigeminal  and  facial 
nerves. 

The  nasal  cavity  is  divided  into  two  symmetrical  halves  by  the  median  septum 
nasi.  The  osseous  part  of  the  septum  (Septum  osseum)  is  formed  behind  by  the 
perpendicular  plate  of  the  ethmoid  and  below  by  the  vomer.  A  few  ridges  on 
the  former  correspond  to  the  ethmoidal  meatuses.  The  major  part  of  it,  how- 
ever, is  formed  by  the  septal  cartilage  (Cartilago  septi  nasi).  The  surfaces  of  the 
cartilage  are  marked  l)y  faint  grooves  for  the  vessels  and  nerves  which  course 
over  it.  The  dorsal  border  is  attached  along  the  frontal  and  nasal  sutures,  and 
extends  beyond  the  apices  of  the  nasal  bones  about  two  inches  (ca.  5  cm.). 
From  this  border  a  thin,  narrow  plate,  the  parietal  cartilage  (Cartilago  parietalis) 
curves  outward  for  a  short  distance  on  either  side.  Near  the  no.strils  these  plates 
are  somewhat  wider,  partially  making  good  the  defect  in  the  bony  roof  of  the  cavity 


438 


RESPIRATORY    SYSTEM    OF    THE    HORSE 


in  this  situation 
groove  of  the  v 


Fio.  34r,.— Nasai 

Dorsal  ViKW. 
liauni,  Anat.  fi 

tend  back  so  far 


Tlie  ventral  border  is  thick  and  rounded;  it  Hes  chiefly  in  the 
omer,  but  anteriorly  it  occupies  the  sjjace  lietween  the  premax- 
illary  bones.  The  posterior  border  is  continuous 
with  the  perpendicular  p\aW  of  the  ethnioiti  bone.' 
The  alar  cartilages  are  attached  to  the  anterior 
extremity  l>y  fibrous  tissue  in  such  a  manner  as  to 
allow  very  free  movement — in  fact,  an  actual  joint 
may  be  found.  The  ventral  part  of  the  cartilage 
is  about  half  an  inch  (ca.  1  cm.),  the  middle  part 
aliout  one-tenth  of  an  inch  (ca.  2.5  mm.),  and  the 
dorsal  part  about  a  quarter  to  a  third  of  an  inch 
(ca.  6  to  8  mm.)  in  thickness. 

The  two  turbinal  bones  (C'onclise  nasales) 
project  from  the  lateral  wall,  and  divide  the  outer 
part  of  the  cavity  into  three  meatuses — superior, 
midille,  and  inferior. 

The  superior  meatus  (Meatus  nasi  dorsalis) 
is  a  narrow  passage,  bounded  dorsally  by  the  roof 
of  the  cavity,  and  ventrally  by  the  superior 
turbinal  bone;  its  posterior  end  is  closed  by  the 
junction  of  the  inner  plate  of  the  frontal  bone 
with  the  cribriform  plate  and  lateral  mass  of  the 
ethmoid.  It  transmits  air  to  the  upper  part  of 
the  olfactory  region. 

The  middle  meatus  (Meatus  nasi  medius)  is 
rKiinsiier.)  bctwcen  tlic  two  turbiual  bones.     It  is  somewhat 

larger  than  the  superior  meatus,  and  does  not  ex- 
;  it  ends  near  the  great  ethmoturbinal  and  the  ethmoidal  meatuses. 


iES  OF  Horse 
(After  Ellenberger- 


InJerioT 
meatus 


Superior 

I'lferwr  turbinal  „         .         Ethmo-    Septum  between 

turbinal         Middle  /superior    lurbmals  fronlal  sinuses 
meatus         ^  ^,.^nt„^ 


Fici.  .'MT.— Nasal  Cavity  of  Hohsf,,  Sa. 
/,  Superior  turliinal  fold;    3,  alar  fold,  containing  cartilaginoi 
pointing  to  na-so-inaxillary  fissure;   4.  cranial  cavity;    5,  sphenoidal 
olfactory  mucous  membrane  is  shaded.       Dotted  lines  indicate  antei 
which  inclose  parts  of  frontal  and  maxillar,\'  siruises. 


Sf-ction  with  Septum  Removed. 

prolongation  of  inferior  turbinal;  S,  arrow 
nus;  6.  hamulus  of  pterygoiii  bone.  The 
r  limit  of  uncoiled  parts  of  turbinal  bones. 


In  its  posterior  part  is  found  the  extremely  narrow,  slit-like  interval  by  which  the 

'  Tlie  septal  oartilage  is  to  be  regarded  as  an  unossified  part  of  the  mesethmoid.  It  will  be 
noteil  that  the  line  of  doinarculion  between  the  bone  and  the  cartilage  is  irregular  and  varies 
\yith  age;  extensive  ossilieat ion  (or  ealcifiealionlof  the  cartilage  is  commonly  found  in  old  animals. 
'I'he  process  often  results  in  the  formation  of  calcareous  islands  in  the  cartilage. 


THE    NASAL    CAVITY 


439 


maxillary  f^imis  conmiunicates  with  the  nasal  cavity — the  naso-maxillary  fissure 
(Aditus  naso-maxillaris).  The  fissure  is  not  visible  from  the  nasal  side,  being  con- 
cealed by  the  overhanging  superior  turbinal.  A  fine  flexible  probe,  passed  outward 
and  somewhat  backward  between  the  turbinal  bones,  enters  the  maxillary  sinus;  if  in- 
troduceil  a  little  further  in  the  same  direction,  it  usually  passes  through  the  orifice 
of  communication  between  th(>  maxillary  and  the  frontal  sinus  and  enters  the  latter. 


Superior  in 


Hcptuni  nasi 


Lacrimal  sac 


Transverse 
facial  resscls 

Palatine  artery 

Vena  reflexa 
Palatine  vein 
Biirrinator  and 

Dr/i.  liibii  inf. 
Btin-inator 

vessels  and 

nerve 


Lingual  nerve 
Lingual  artery 
Lingual  vein 

Submaxillary 
duct 

Hypoglossal 
nerve 


Digastricus  {ant.  belly) 


Fig.  348. — Cross-sectiom  of  Head  of  Horse.     The  Section  P.tssES  Thhocgh  the  Internal  Canthi. 

7,  Mylo-hyoideus;   2,  stylo-glossus;   3,  hyo-glossus;    4.  geoio-glossus;    5,  lingual  process  of  hyoid  bone.     An  arrow 

points  to  the  naso-raaxillary  fissure. 


A  small  part  of  the  fissure  usually  brings  the  anterior  division  of  the  maxillary 
sinus  into  communication  with  the  nasal  cavity.  The  spaces  inclosed  by  the  coiled 
portions  of  the  turbinals  also  open  into  the  middle  meatus.  This  passage  may 
be  characterized  as  the  sinu.s-meatus,  but  it  also  conducts  air  to  the  olfactory 
region. 

The  inferior  meatus  (^leatus  nasi  ventralis)  is  situated  between  the  inferior 


440  RESPIRATORY    SYSTEM    OF   THE    HORSE 

turbinal  and  the  floor  of  the  cavity.  It  is  much  larger  than  the  other  two,  anil  is 
the  direct  passage  between  the  nostrils  and  the  pharynx. 

The  common  meatus  (Meatus  nasi  communis)  is  situated  between  the  septum 
and  the  turbinals,  and  is  continuous  externally  with  the  other  meatuses.  It  is 
very  narrow  dorsally,  but  widens  ventrally. 

The  lateral  masses  of  the  ethmoid  bone  project  forward  into  the  posterior 
part  (fundus)  of  the  nasal  cavity  (Fig.  347).  Between  the  ethmoturbinals  of 
which  each  mass  is  composed  there  are  three  principal  and  numerous  small  passages, 
the  ethmoidal  meatuses  (Meatus  ethmoidales). 

The  posterior  nares  (Choanie)  are  two  elliptical  orifices  by  which  the  nasal 
cavity  and  pharynx  communicate.  They  are  in  the  same  plane  as  the  floor  of  the 
nasal  cavity,  and  are  separated  from  each  other  by  the  vomer.  They  are,  taken 
together,  about  two  inches  (ca.  .5  cm.)  wide  and  three  to  four  inches  (ca.  8  to 
10  cm.)  long. 

The  nasal  mucous  membrane  (Membrana  mucosa  nasi)  is  thick,  highly  vas- 
cular, and  is,  in  general,  firmly  attacheil  to  the  underlying  periosteum  and  peri- 
chondrium. It  is  continuous  in  front  with  the  skin  which  lines  the  nostrils, 
and  behind  with  the  mucous  membrane  of  the  pharynx.  It  is  also  continuous 
at  the  naso-maxillary  fissure  with  the  very  thin  and  only  slightly  vascular  mucous 
membrane  which  lines  the  sinuses.  In  the  anterior  part  of  the  cavity  it  forms 
prominent  thick  folds  on  the  lateral  wall,  which  extend  from  the  turbinal 
bones  to  the  nostril.  There  are  usually  two  superior  turbinal  folds  which  unite 
anteriorly.  The  upper  one  incloses  a  thin  plate  of  cartilage  which  is  continuous 
with  the  superior  turbinal  bone.  The  inferior  turbinal  fold  is  curved,  and  incloses 
an  y^,^  shaped  cartilaginous  plate  which  prolongs  the  inferior  turbinal  bone;  this 
fold  is  continuous  with  the  alar  fold  of  the  nostril,  and  forms  with  it  the  upper 
margin  of  the  entrance  from  the  true  nostril  to  the  nasal  cavity.  Below  this  there 
is  a  rounded  ridge  produced  by  the  nasal  process  of  the  premaxilla.  The  mucous 
membrane  of  the  greater  part  of  the  cavity  (Regio  respiratoria)  is  red  in  color, 
and  is  covered  with  a  stratified  ciliated  epithelium.  It  contains  numerous  acinous 
nasal  glands  (Glandulae  nasales).  The  submucosa  contains  rich  venous  plexuses 
which  form  in  certain  situations  a  sort  of  cavernous  tissue  (Plexus  cavernosus), 
composed  of  several  strata  of  freely  anastomosing  veins,  between  which  there  are 
unstriped  muscle-fibers.  This  arrangement  is  most  marked  in  the  turbinal  folds, 
on  the  lower  part  of  the  inferior  turbinal  bone,  and  the  lower  part  of  the  septum. 
On  the  posterior  part  of  the  lateral  masses  of  the  ethmoid  and  the  adjacent  part 
of  the  superior  turbinal  and  the  septum  (Regio  olfactoria)  the  mucous  membrane 
is  brownish-yellow  in  color  and  thicker;  it  contains  the  olfactory  nerve-endings 
in  a  special  non-ciliated  e])ithelium.  In  it  are  numerous  olfactory  glands  (Glandulae 
olfactorite) ;  these  are  long,  tubular,  and  often  branched. 

The  vomero-nasal  organ  of  Jacobson  (Organon  vomeronasale)  is  situated  on 
the  floor  of  the  nasal  cavity,  on  either  side  of  the  ventral  border  of  the  septum  (Fig. 
345.)  It  consists  of  a  tubular  cartilage  lined  with  mucous  membrane,  to  which 
fibers  of  the  olfactory  nerve  may  be  traced.  Its  anterior  part  communicates 
with  the  nasal  cavity  by  a  slit-like  orifice. 

The  paranasal  sinuses  are  described  in  the  Osteology. 


THE  LARYNX 

The  larynx  is  a  short  tube  which  connects  the  j^harynx  and  trachea.  It  is  a 
complex  valvular  apparatus,  which  regulates  the  volume  of  air  in  respiration, 
prevents  aspiration  of  foreign  bodies,  ami  is  the  chief  organ  of  voice. 

It  is  situatetl  partly  between  the  internal  ];)terygoid  muscles,  partly  in  the  neck 


CARTILAGES    OF   THE    LARYNX  441 

between  the  parotid  glands.'  Its  long  axis  is  practically  horizontal  when  the  head 
and  neck  are  extended  (Fig.  254). 

It  is  related  dorsally  to  the  pharynx  and  the  origin  of  the  oesophagus.  Ven- 
trally  it  is  covered  by  the  skin,  fascia,  antl  sterno-hyoid  anil  omo-hyoid  muscles. 
Laterally  it  is  related  to  the  parotid  and  submaxillary  glands  and  to  the  internal 
pterygoid,  stylo-maxillaris,  digastricus,  stylo-hyoid,  and  pharyngeal  constrictor 
muscles. 

It  is  attached  to  the  body  and  thyroitl  cornua  of  the  hyoid  bone,  and  thus  in- 
directly to  the  base  of  the  cranium. 

Its  cavity  communicates  anteriorly  with  the  pharynx  and  (potentially)  with 
the  mouth;   posteriorly,  with  the  trachea. 

The  wall  of  the  larynx  consists  of  a  framework  of  cartilages,  connected  by 
joints  and  ligaments  or  membranes,  and  moved  by  extrinsic  and  intrinsic  muscles. 
The  cavity  is  lined  with  mucous  membrane. 

Cartilages  of  the  Larynx 
There  are  three  single  cartilages  and  one  pair;    the  single  cartilages  are  the 
cricoid,  thyroid,  and  epiglottis;  the  arytenoid  cartilages  are  paired. 


■■ 

m 

^^H^^H[^^^^H 

■■■■ 

^V! 

ll^%JWf  ^ 

^^^^H^^l 

^^ 

^^ 

^^^B|^v 

^^^^^B 

P^^% 

ll^ 

'■    -.-c: 

>f°.'s'^    i=tfeo^3!^S 

i^^ 
s. 

V 

L   ^       ^  -- 

^^' 

"cVico- 

raehzai\     Obiiqut 

Crico'-rth^roid 

Fig.  349. — Larynueal  Cartilages  oe  Horse,  Right  View. 

The  cricoid  cartilage  (Cartilago  cricoidea)  is  shaped  like  a  signet  ring.  The 
dorsal  part  is  a  broatl,  thick,  quadrilateral  plate  termed  the  lamina ;  the  outer 
(dorsal)  surface  of  this  is  marked  by  a  median  ridge  separating  two  shallow  cavities, 
which  give  attachment  to  the  posterior  crico-arytenoid  muscles.  On  either  side 
of  these  depressions  are  two  articular  facets.  The  anterior  facets  (Facies  articu- 
lares  arytsenoidese)  are  placed  at  the  anterior  border,  are  oval  and  convex,  and 
articulate  ^vith  the  arytenoid  cartilages.  The  posterior  facets  (Facies  articulares 
thyreoideffi)  are  situated  on  the  front  of  a  ridge,  a  short  distance  from  the  posterior 
border;  they  are  concave,  and  articulate  with  the  posterior  cornua  of  the  thyroid 
cartilage.  The  ventral  and  lateral  parts  of  the  ring  are  formed  by  a  curved 
band,  called  the  arch  (Arcus),  which  is  narrowest  below.  The  lateral  surfaces 
of  the  arch  are  grooved  for  the  crico-thyroid  muscle.     The  anterior  border  of  the 

'  In  the  ordinar)'  position  of  the  head  and  neck,  and  while  the  parts  are  at  rest,  about  half 
of  the  larynx  lies  between  the  branches  of  the  mandible:  when  the  head  and  neck  are  extended, 
proportionately  more  of  the  larynx  lies  licliiiid  a  plane  through  the  posterior  borders  of  the  rami. 
It  is  here  described  in  the  position  it  occupies  when  the  head  and  neck  are  extended. 


442 


RESPIRATORY    SYSTEM    OF    THE    HORSE 


Posterior 

border 

Arch 


Fig.  350. — Cricoid   C.\rti 


OF  Horse.   Left  L.\teb.\l 


lamina  is  thick  and  slislitly  concave;  the  posterior  border  is  thin  and  irregularly 
notched.  The  anterior  border  of  the  arch  is  concave  ventrally  and  gives 
attachment   to   the   crico-thyroid   membrane;  laterally  it   is  thicker  and  gives 

attachment    to    the    crico-aryten- 
Median  ridge       Lamina  oideus   lateralis  muscle.     The  pos- 

terior border  is  attached  to  the 
first  ring  of  the  trachea  by  an 
elastic  membrane.  The  inner  sur- 
face is  smooth  and  is  covered  with 
mucous  membrane. 

The  thyroid  cartilage  (Cartilago 
thyreoidea)  consists  of  a  median 
thickened  portion,  termed  the 
body,  and  two  lateral  laminae  or 
wings.  The  body  forms  ventrally 
a  slight  prominence  (Prominentia 
laryngea),  which  can  be  felt,  but 
is  not  visible  in  the  living  sub- 
ject; it  supports  the  base  of  the 
epiglottis,  which  is  attached  to  it 
by  an  elastic  ligament.  The  wings 
or  laminae  spring  from  the  body 
on  either  side  and  form  a  large 
part  of  the  lateral  wall  of  the  larynx.  Each  is  a  rhomboid  plate,  presenting  a 
slightly  convex  outer  surface,  which  is  divided  into  two  areas  by  an  oblique  line 
(Linea  obliqua),  on  which  the  thyro-hyoid  and  thyro-pharyngeus  muscles  meet. 
The  superior  (dorsal)  border  is  nearly 
straight;    it  gives  attachment  to  the  Body 

pharyngeal  fascia  and  the  palato- 
pharyngeus  muscle,  and  bears  a  cornu 
at  each  end.  The  anterior  comu 
(Cornu  orale)  is  attached  to  the 
thyroid  cornu  of  the  hyoid  bone; 
below  it  is  a  notch,  which  is  con- 
verted into  a  foramen  (Foramen  thy- 
reoideum)  by  a  fibrous  band,  and 
transmits  the  superior  laryngeal  nerve 
to  the  interior  of  the  larynx.  The 
posterior  comu  (Cornu  caudale)  articu- 
lates with  the  cricoid  cartilage.  The 
inferior  (ventral)  border  is  fused  with 
the  body  in  front;  behind,  it  diverges 
from  its  fellow  to  inclose  a  triangular 
space  (Incisura  thyreoidea  caudalis), 
which  is  occupied  liy  the  crico-thyroid 
membrane.  The  anterior  border  is 
slightly  convex,  and  is  attached  to  the 
hyoid  bone  by  the  thyro-hyoid  mem- 
brane. The  posterior  border  overlaps  p,,.  351.— thyroid  c.^RTiLAni..  of  Horse.  Ven-th.^l 
the  arch  of  the  cricoid  cartilage,  and  view 

gives  attachment  to  the  crico-thyroid 

muscle.  The  inner  surface  is  concave,  and  is  covered  by  mucous  memlirane  to  a 
small  extent. 

The  epiglottis  (Cartilago  epiglottica)  is  situated  above  the  body  of  the  t  hyroid 


Thyroid  notch 

Wiiifj 
Anterior  cornu 


ofiterior  cornu 
surface  for  articu- 
lation with  cricoid 


CARTILAGES    OF    THE    LARYNX 


443 


cartilage  and  curves  toward  the  root  of  the  tongue.  It  is  shaped  somewhat  like  a 
pointed  ovate  leaf,  and  presi'uts  two  surfaces,  two  borders,  a  base,  and  an  apex. 
The  oral  lor  anterior)  surface  is  concave  in  its  length,  convex  transverseh- ;  the 
pharyngeal  (or  jiosterior)  surface  has  the  reverse  configuration.  The  borders 
are  thin,  ilenticulatetl,  and  somewhat  everted.  The  base  is  thick,  and  is  attached 
to  the  dorsal  surface  of  the  body  of  the  thjToid  cartilage  by  elastic  tissue.  From 
each  side  of  it  a  cartilaginous  bar 

projects  backward;  these  processes  Pharyngeal  surface 

correspond  to  the  cuneiform  car- 
tilages of  man.  The  apex  is 
pointed  and  curved  ventrally. 
Nearly  all  of  the  epiglottis  is 
covered  mth  mucous  membrane. 
It  lies  sometimes  in  front  of, 
sometimes  behind,  the  soft  palate. 
The  arytenoid  cartilages  (Car- 
tilagines  arytenoide;p)  are  situated 
on  either  side,  in  front  of  the  cri- 
coid, and  partly  betw-een  the  alse 
of  the  thyroid  cartilage.  They 
are  somewhat  pjTamidal  in  form, 
and  may  be  described  as  ha\ang 
two  surfaces,  two  borders,  a  base, 

and  an  apex.  The  internal  surface  is  concavo-convex,  smooth,  and  covered  by 
mucous  membrane.  The  external  surface  is  di\'ided  by  a  ridge  into  two  areas: 
the  lower  flat  area  faces  outward,  and  is  covered  I:)y  the  th>To-arytenoid  and 
lateral  crico-ar}i:enoid  muscles;  the  upper  concave  area  faces  chiefly  forward, 
and  is  covered  by  the  traasverse  arji;enoid  muscle.  The  anterior  border  is  convex, 
and  at  the  base  of  the  cartilage  forms  a  projection  termed  the  vocal  process  ( Proces- 
sus vocalis) ;  it  is  so  named  because 


Cuneiform  process 
352. — Epiglottis  of  Horse 


Right  Lateral  Vie 


Muscular  process 


Apex 


it  gives  attachment  to  the  vocal 
or  thjTO-arj-tenoid  ligament,  which 
forms  the  basis  of  the  true  vocal 
cord.  The  posterior  border  is 
straight,  and  exlends  from  the 
vocal  process  to  the  facet  on  the 
base.  The  dorsal  border  forms  a 
deep  notch  with  the  ajjex.  The 
base  is  concave  and  faces  chiefly 
backward;  it  presents  an  oval, 
concave  facet  for  articulation  with 
the  anterior  border  of  the  lamina  of 
the  cricoid  cartilage.  The  external 
angle  of  the  base  forms  a  strong 
eminence  termed  the  muscular  pro- 
cess (Processus  muscularis),  which 
gives  attachment  to  the  crico- 
arj-tenoid  muscles.  The  internal  angle  is  attached  to  its  fellow  by  the  transverse 
arj-tenoid  ligament.  The  apex  (Cartilago  corniculata)  curves  upward  and  back- 
ward, forming  vrtth  its  fellow  the  pitcher-shaped  lip,  from  which  the  cartilages 
derive  their  name. 

The  cricoid  and  thyroid  cartilages,  and  the  greater  part  of  the  arytenoid 
cartilages,  consist  of  hyaline  cartilage.  The  apices  and  vocal  processes  of  the 
arjienoid  cartilages  and  the  epiglottis  (^including  the  cuneiform  processes)  consist 


Fig.  353. — Left  .-Vrttenc 


Vocal  process 

Cartilage  of  Horse,  Inner 


444  RESriRATORY    SYSTEM    OF   THE    HORSE 

of  elastic  cartilage;  they  show  no  tendency  toward  ossification  at  any  age.  The 
thyroid  and  cricoid  cartilages  regularly  undergo  considerable  ossification:  the 
process  begins  in  the  bodj-  of  the  thyroid,  and  often  involves  the  greater  part  uf 
the  cartilage. 

Joints,  Ligaments,  and  Membranes  of  the  Lar'nyx 

The  crico-thyroid  joints  (Articulationes  crico-thyreoidese)  are  diarthroses 
formed  by  the  apposition  of  the  convex  facets  on  the  ends  of  the  posterior  cornua 
of  the  thyroid  cartilage  with  corresponding  facets  on  the  sides  of  the  cricoid  car- 
tilage. The  capsule  is  thin,  but  is  strengthened  by  accessory  bands  dorsally, 
externally,  and  internally.  The  movements  arc  chiefly  rotation  around  a  trans- 
verse axis  passing  through  the  centers  of  the  two  joints. 

The  crico-arytenoid  joints  (Articulationes  crico-arytsenoidea)  are  also  diar- 
throdial.  They  are  formed  by  the  apposition  of  the  convex  facets  on  the  anterior 
border  of  the  cricoid  cartilages  with  the  concave  facets  on  the  bases  of  the  arytenoid 
cartilages.  Each  has  a  very  thin,  loose  capsule,  strengthened  by  accessory  bundles 
dorsally  and  internally.  The  movements  are  gliding  and  rotation.  In  the  former 
the  arytenoid  cartilage  glides  inward  or  outward;  in  the  latter  it  rotates  around  a 
longitudinal  axis,  so  that  the  vocal  process  swings  outward  or  inward. 

The  thyro-hyoid  joints  (Articulationes  hyo-thyreoidese)  are  formed  by  the 
anterior  coruua  of  tiie  thyroid  cartilage  and  the  extremities  of  the  thjToid  coi'nua 
of  the  hyoitl  bone.  They  permit  rotation  around  a  transverse  axis  passing  through 
the  two  joints. 

The  crico-thjToid  membrane  (Ligamentum  crico-thyreoideum)  occupies  the 
thyroid  notch  and  extends  backward  to  the  arch  of  the  cricoid  cartilage.  It  is 
triangular  in  form,  and  is  attached  by  its  base  to  the  anterior  border  of  the  arch  of 
the  cricoid  cartilage,  while  its  borders  are  attached  to  the  margins  of  the  thyroid 
notch.  It  is  strong,  tightly  stretched,  and  composed  largelj-  of  elastic  tissue.  It 
is  reinforced  ventrally  by  longitudinal  fibers,  dorsally  bj'  fibers  which  stretch  across 
the  thyroid  notch. 

The  th5rro-hyoid  membrane  (Membrana  hjo-thyreoidea)  connects  the  an- 
terior border  of  the  thyroid  cartilage  with  the  body  and  thyroid  cornua  of  the  hyoid 
bone. 

The  hyo-epiglottic  ligament  (Ligamentum  hyo-epiglotticum)  attaches  the 
lower  part  of  the  oral  surface  of  the  epiglottis  to  the  body  of  the  hyoid  bone.  It 
forms  an  elastic  sheath  for  the  hyo-epiglottic  muscle.  Ventrally  it  Ijlends  with 
the  thyro-hyoid  membrane,  and  dorsally  it  is  not  well  defined. 

The  th5no-epiglottic  ligament  (Ligamentum  thyreo-epiglotticum)  is  strong 
and  thick;  it  is  composed  chiefly  of  elastic  tissue.  It  connects  the  base  of  the 
epiglottis  with  the  body  and  the  adjacent  inner  surface  of  the  laminae  of  the  thyroid 
cartilage.  Other  fibers  attach  the  cuneiform  processes  somewhat  loosely  to  the 
thyroid  laminae. 

The  transverse  arytenoid  ligament  (Ligamentum  aryta^noideum  transversum) 
is  a  slender  Ijand  which  connects  the  inner  angles  of  the  liases  of  the  arytenoid 
cartilages. 

The  vocal  (or  inferior  thyro-arytenoid)  ligament  ( Ligamentum  vocale)  forms  the 
basis  of  the  true  vocal  cord  (Fig.  254).  It  is  elastic  and  is  attached  ventrally  to  the 
body  of  the  thyroid  cartilage  and  the  crico-thyroid  membrane  close  to  its  fellow 
of  the  opposite  side,  and  ends  dorsally  on  the  processus  vocalis  of  the  arytenoid 
cartilage. 

The  ventricular  (or  superior  thyro-arytenoid)  ligament  (Ligamentum  ventri- 
culare)  is  included  in  the  false  vocal  cord.  It  consists  of  loosely  arranged  bundles 
which  arise  chiefly  from  the  cuneiform  process  and  end  on  the  outer  surface  of  the 
processus  vocalis  and  adjacent  part  of  the  arytenoid  cartilage. 


MUSCLES    OF    THE    LARYNX  445 

The  crico-tracheal  membrane  (Ligamentum  crico-trachealc)  comiects  the 
cricoid  cartih^ge  witli  the  first  ring  of  the  trachea. 

Muscles  of  the  Larynx 
A.    Extrinsic  Muscles 

The  stemo-thyro-hyoideus  is  tlescribed  on  p.  226. 

The  thyro-hyoideus  ( AI.  hyo-thjTeoideus)  is  a  fiat,  quadrilateral  muscle,  which 
lies  on  the  outer  surface  of  the  thyroid  lamina  and  the  lateral  jjart  of  the  thj-ro- 
hyoid  membrane.  It  arises  from  the  thyroid  cornu  of  the  hyoid  bone,  and  ends  on 
the  oblique  line  on  the  lamina  of  the  thyroid  cartilage.  Its  action  is  to  draw  the 
laryiLY  toward  the  root  of  the  tongue. 

The  hyo-epiglotticus  (M.  hyo-epiglotticus)  is  a  feeble  muscle  which  occupies  a 
median  position  al)ove  the  central  ])art  of  the  thyro-hyoid  membrane,  inclosed  by 
an  elastic  sheath,  the  hyo-epiglottic  ligament.     It  arises  from  the  l)ody  of  the  hyoid 


Fig.  354. — Larynge.\l  Muscles  of  Horse,  Seen  from  Left  Side  After  Remov.^l  of  M.^jor  P.\rt  of  L.^min-\ 
OF  Thyroid  Cartilage. 
a,  Kerato-hyoideus;  b,  thyro-hyoideus;  c,  crico-thyroideus;  d,  sterno-thyroideus;  f,  ventricularis;  /, 
vocalis;  g,  crico-arytenoideus  lateralis;  h,  crico-arytenoideus  post.  s.  dorsahs;  (,  arytenoideus  transversus;  1, 
lingual  process;  2,  small  cornu;  S,  thyroid  cornu,  of  hyoid  bone;  4.  thyroid  cartilage;  S,  cricoid  cartilage;  6.  epi- 
glottis; 7.  apex  of  arytenoi<l  cartilage:  S.  trachea;  9,  muscular  process  of  arytenoid;  lU,  lateral  lobe  of  thyroid 
gland;    10',  isthmus  of  thyroid  gland;    i  ;.  laryngeal  saccule.      (Ellenberger-Baum, -\nat.  d.  Haustiere.) 

bone  by  two  branches  which  unite  and  are  inserted  into  the  front  of  the  base  of 
the  epiglottis.     Its  action  is  to  draw  the  epiglottis  toward  the  root  of  the  tongue. 

B.  Intrinsic  Muscles 

The  crico-thyroideus  CM.  crico-thyreoideus)  is  a  short  muscle  which  fills  the 
groove  on  the  lateral  surface  of  the  cricoid  cartilage;  its  fibers  are  directed  dorsally 
and  somewhat  forward.  It  arises  on  the  lower  half  of  the  lateral  surface  and 
posterior  edge  of  the  cricoid  cartilage,  and  is  inserted  into  the  posterior  border  and 
adjacent  part  of  the  surfaces  of  the  lamina  of  the  thyroid  cartilage.  Its  action  is 
to  draw  the  thyroid  cartilage  and  the  ventral  part  of  the  cricoid  cartilage  together. 
In  this  action  the  cricoid  cartilage  is  probably  rotated,  carrying  the  bases  of  the 
arjienoid  cartilages  with  it  and  thus  tensing  the  vocal  cords. 

The  crico-arytenoideus  dorsalis  s.  posterior  (M.  crico-arytaenoideus  dorsalis) 
is  a  strong,  somewhat  fan-sha])ed  muscle,  which,  with  its  fellow,  covers  the  dorsal 
surface  of  the  lamina  of  the  cricoid  cartilage.  It  is  partially  divisible  into  two  layers. 
It  has  a  broad  origin  on  half  of  the  lamina  of  the  cricoid  cartilage,  and  its  fibers 
converge  to  be  inserted  into  the  processus  muscularis  of  the  arytenoid  cartilage. 


M6 


RESPIRATORY    SYSTEM    OF    THE    HORSE 


Its  action  is  to  dilate  the  rima  glottidis  by  rotating  the  arj^tenoid  cartilage  so  as  to 
carry  the  vocal  process  and  cord  outward. 

The  crico-arytenoideus  lateralis  (M.  crico-arytcenoideus  lateralis)  lies  on  the 
inner  face  of  the  thyroid  lamina.  It  arises  from  the  anterior  border  of  the  lateral 
part  of  the  arch  of  the  cricoitl  cartilage.  The  fibers  pass  in  a  dorsal  direction  and 
converge  on  the  processus  muscularis  of  the  arytenoid  cartilage.  It  closes  the 
rima  glottidis  by  rotating  the  arytenoid  cartilage  inward. 

The  arytenoideus  transvereus  (M.  arytaenoideus  transversus)  is  an  unpaired 
muscle  which  stretches  across  the  concave  dorsal  surface  of  the  arytenoid  cartilages. 
Its  fibers  are  attached  on  either  side  to  the  processus  muscularis  and  the  ridge  which 
extends  forwartl  from  it.     The  right  and  left  parts  of  the  muscle  meet  at  a  fibrous 


Salpingo- phnri/iigcal 
fold 

Epiglottis 

Aryteno-epiglvUic 
fold 


Root  of  tongue 
Soft  palate  {cut) 


'all  of  pharynx 
■ytcnoid  cartilage  {apex) 

pillar  of  soft  palate 

{origin) 


Fir..  355. — Aditus  Larvnois  of  Horse,  Expo.si.,i.  h\  uiKM.st;  Pharynx  ant 
Median  Dorsal  Line. 
J,  False  vocal  conl;    2.  lateral  ventricle:    S,  true  vocal  cords 


KfHNNING  OF  Qi^SOPHAGUS  AlONG 

rima  glottidis. 


raphe  which  is  connected  with  the  transverse  arytenoid  ligament.  Filters  of  the 
thyro-arytenoideus  muscle  overlaj)  its  anterior  jiart.  It  narrows  tlie  rima  by 
drawing  the  arytenoid  cartilages  together. 

The  thyro-arytenoideus  (Mm.  ventricularis  et  vocalis)  is  situatetl  in  the  lateral 
wall  of  the  larynx,  covered  tiy  the  lamina  of  the  thyroid  cartilage.  It  consists  of 
two  parts,  between  which  the  nmcous  memlirane  of  the  lateral  ventricle  pouches  to 
form  the  saccule.  The  anterior  part  (M.  ventricularis)  arises  from  the  anterior  part 
of  the  cricothyroid  memi)rane  and  the  ventral  border  of  tlie  thyroid  lamina.  Its 
fibers  pass  upward  and  backward  to  end  partly  on  the  processus  muscularis,  partly 
on  the  arytenoideus  transversus,  meeting  its  fellow.  The  posterior  part  (M.  vocalis) 
has  a  more  extensive  origin  on  the  crico-thyroid  membrane.     Its  direction  corre- 


CAVITY    OF    THE    LARYNX  447 

sponds  with  that  of  the  true  vocal  cord.  It  is  inserted  into  the  outer  surface  of 
the  arytenoiil  cartihige  below  the  processus  muscularis.  The  muscle  closes  the 
rima  and  slackens  the  vocal  cords.  With  the  arytenoideus  transversu.s  and  crico- 
arytenoidcus  lateralis  it  forms  a  sphincter  which  closes  the  entrance  to  the  larynx. 

Cavity  of  the  Larynx 

The  cavity  of  the  larynx  (Cavum  laryngis)  is  smaller  than  one  would  expect 
from  its  external  appearance.  On  looking  into  it  through  the  pharyngeal  end  two 
folds  are  seen  projecting  from  its  lateral  walls.  These  are  termed  the  vocal  cords, 
ami  they  divide  the  cavity  into  two  portions. 

The  aditus  laryngis,  or  pharyngeal  aperture,  is  a  large,  oblique,  oval  opening, 
which  faces  forward  ami  upward  into  the  ventral  part  of  the  pharynx.  It  is 
bouuiled   in   front   by   the  epiglottis,    behiml    by   the    arytenoid    cartilages,   and 


Body  of  thyroid  cartilage 


Wing  of  thyroid  cartilage   — fg  I /^B^  I  TlA^   Cuneiform  process 

Ventricular  muscle 
Lateral  rentriclc 

Laryngeal  saccule 


Crico-arytcnoidcus  posterior 
m  usele 

Fig.  356. — Section  op  Larynx  of  Horse. 
The  plane  of  the  section  is  parallel  with  the  vocal  cords. 

laterally  by  the  aryteno-epiglottic  folds  of  mucous  membrane  (Plicie  aryepi- 
glotticse),  which  stretch  between  the  edges  of  the  epiglottis  and  the  arytenoid 
cartilages. 

The  vestibule  of  the  larynx  (Vestibulum  laryngis)  is  that  part  of  the  cavity 
which  extends  from  the  aditus  to  the  vocal  cords.  On  its  lateral  walls  are  the  false 
vocal  cords  (Plicie  ventriculares),  each  of  which  consists  of  a  fold  of  mucous  mem- 
brane covering  the  anterior  part  of  the  thyro-arytenoid  ligament  and  the  cuneiform 
process.  Betw^een  the  false  and  true  vocal  cord  there  is  a  pocket-like  depression 
termed  the  lateral  ventricle  of  the  larynx  (Ventriculus  lateralis  laryngis).  This  is 
the  entrance  to  tlic  laryngeal  saccule  (Appendix  ventriculi  laryngis),  a  cul-de-sac  of 
the  mucous  membrane  which  is  about  one  inch  (ca.  2  to  3  cm.)  long  and  extends 
ujiward  and  backward  on  the  inner  surface  of  the  thyroid  lamina.  There  is  a 
small  middle  ventricle  (\'entriculus  laryngis  medianus)  at  the  base  of  the 
epiglottis. 

The  middle,  narrow  part  of  the  cavity  is  termed  the  glottis  or  rima  glottidis.' 

'  The  term  glottis  is  commonly  used  to  designate  the  interval  between  the  vocal  bands  and 
arytenoid  cartilages  or  the  structures  that  inclose  that  space. 


448  RESPIRATORY    SYSTEM    OF    THE    HORSE 

It  is  bounded  on  either  side  by  the  true  vocal  cord  and  the  inner  surface  of  the  ary- 
tenoid cartilage.  The  true  vocal  cords  (Labia  vocales)  are  situated  behind  the 
false  cords  and  the  lateral  ventricles.  They  extend  from  the  angle  between  the 
body  and  lamince  of  the  thyroid  cartilage  to  the  vocal  processes  of  the  arytenoid 
cartilages.  They  are  prismatic  in  cross-section,  and  their  free  edges  look  forward 
and  somewhat  upward.  The  mucous  membrane  of  the  cord  (Plica  vocalis)  is  very 
thin  and  smooth,  and  is  intimately  attached  to  the  underlying  ligament.  In 
ordinary  breathing  the  rima  is  somewhat  lanceolate  in  form;  when  dilated,  it  is 
diamond-shaped,  the  widest  part  being  between  the  vocal  processes.  The  narrow 
part  of  the  glottis  between  the  vocal  cords  is  termed  the  glottis  vocalis  (Pars 
intermembranacea),  while  the  wider  part  between  the  arytenoid  cartilages  is  the 
glottis  rcspiratoria  (Pars  intcrcartilaginea). 

The  posterior  compartment  of  the  laryngeal  cavity  is  directly  continuous  with 
the  trachea.  It  is  inclosed  by  the  cricoid  cartilage  and  the  crico-thyroid  membrane. 
It  is  oval  in  form,  the  transverse  diameter  being  an  inch  and  a  half  to  two  inches 
(ca.  4  to  5  cm.),  and  the  dorso-ventral  chameter  two  to  two  and  a  half  inches  (ca. 
5  to  6  cm.). 

The  mucous  membrane  which  lines  the  larynx  (Tunica  mucosa  laryngis)  is 
reflected  around  the  margin  of  the  aditus  to  become  continuous  with  that  of  the 
pharynx,  and  behind  it  is  continuous  with  that  which  lines  the  trachea.  It  is 
closely  attached  to  the  pharyngeal  surface  of  the  epiglottis,  but  elsewhere  in  the 
aditus  and  vestibule  it  is  loosely  attached  by  submucous  tissue  which  contains 
many  elastic  fibers.'  It  is  thin  and  very  closely  adherent  o\-er  the  vocal  cords 
and  the  inner  surfaces  of  the  arytenoid  cartilages.  The  epithelium  is  of  the  strati- 
fied squamous  type  from  the  aditus  to  the  glottis,  Ijcyond  which  it  is  columnar 
ciliated  in  character.  There  are  numerous  mucous  glands  (Glandulse  larynge£e), 
except  over  the  glottis  and  the  pharyngeal  surface  of  the  epiglottis,  in  which  situa- 
tions they  are  scanty. 

Blood-supply. — Thyro-larj'ngeal  artery. 

Nerve-supply. — Superior  laryngeal  and  recurrent  laryngeal  nerves  (from  the 
vagus). 

THE  TRACHEA 

The  trachea  extenfls  from  the  larynx  to  the  roots  of  the  lungs, where  it  divides 
into  the  right  and  left  lironchi.  It  is  kept  permanently  open  by  a  series  of  about 
fifty  to  fifty-five  incomplete  cartilaginous  rings  embedded  in  its  wall.  It  occupies 
a  median  position,  except  near  its  termination,  where  it  is  pushed  a  little  to  the 
right  by  the  arch  of  the  aorta.  It  is  approximately  cylindrical,  but  its  cervical 
portion  is  for  the  most  part  depressed  dorso-ventrally  by  contact  with  the  longus 
colli  muscle,  so  that  the  dorsal  surface  is  flattened.  The  average  caliber  is  about 
two  to  two  and  one-half  inches  (ca.  5  to  6  cm.),  but  in  the  greater  part  of  the  neck 
the  transverse  diameter  is  greater  and  the  dorso-ventral  smaller.  It  is  inclosed 
by  a  fascia  propria. 

In  its  cervical  part  the  trachea  is  related  dorsally  to  the  oesophagus  for  a  short 
distance,  but  chiefly  to  the  longus  colli  muscle.  Laterally  it  is  related  to  the 
thyroid  gland,  the  carotid  artery,  the  jugular  vein,  the  vagus,  sympathetic,  and 
recurrent  laryngeal  nerves,  and  the  tracheal  lymph  ducts  and  cervical  lymph  glands. 
The  cesophagus  lies  on  its  left  face  from  the  thirtl  cervical  vertebra  backward. 
The  sterno-cephalicus  muscles  cross  it  very  obliquely,  passing  from  the  ventral 
surface  forward  over  its  sides,  and  diverging  to  reach  the  angles  of  the  jaw.  The 
omo-hyoidei  also  cross  it  very  obliquely,  jiassing  over  the  lateral  surfaces  of  the 
tube,  and  converging  ventrally  to  the  body  of  the  hyoid  bone.     The  sterno-thyro- 

'  In  so-called  ocdoma  glottidis  this  loose  .submucous  tissue  becomes  infiltrated  with  fluid, 
in  some  cases  causing  occlusion  of  the  vestibule. 


THE    TRACHEA 


449 


hyoideus  lies  on  the  ventral  surface.'     The  scaleni  lie  on  either  side  near  the  en- 
trance to  the  thorax. 

The  thoracic  part  of  the  trachea  passes  backward  hetwcen  the  pleural  sacs  and 
divides  into  the  two  bronchi  over  the  left  atrium  of  the  heart.  It  is  related  dorsallj' 
to  the  longus  colli  for  a  short  distance,  and  l)eyond  this  to  the  oesophagus.  Its 
left  face  is  crossed  by  the  aortic  arch,  the  left  brachial  artery,  and  the  thoracic 
duct.  Its  right  face  is  crossed  by  the  vena  azygos,  the  dorso-cervical  and  vertebral 
vessels,  and  the  right  vagus  nerve.     Ventrally   it  is  related  to  the  anterior  vena 


Omo-hyoideus 


Sterno- 
cephalicus 


Slerno-thyroidetis       Sterno-hyoiikus 
Fig.  357. — Cross-sectiox  of  Ventral  P.\rt  of  Neck  of  Horse. 
The  section  is  cut  at  right  angles  to  the  long  axis  of  the  neck,  passing  through  the  junction  of  the  second 
and  third  cenical  vertebrae.     5.C.,  Spinal  cord;    S.v.,  spinal  vein;    V.v.,  V.a.,  vertebral  vein  and  artery;    T.p., 
transver.=e  process  (tip);    F,  intervertebral  fibro-cartilage;    T,    atlantal  tendon  common  to  mastoido-humeralis, 
splenius,  and  lower  part  of  tracheto-mastoideus;    .1/,  digitation  of  mastoido-huraeralis  inserted  by  T. 


cava,  the  brachiocephalic  and  common  carotid  trunks,  ami  the  left  recurrent 
nerve. 

The  bifurcation  of  the  trachea  (Bifurcatio  tracheae)  is  situated  opposite  to  the 
fifth  interco.stal  space,  and  about  five  or  six  inches  (ca.  12  to  15  cm.)  below  the 
seventh  and  eighth  thoracic  vertebree. 

The  trachea  is  composed  of — (1)  A  fibro-elastic  membrane  in  which  are 
embedded  (2)  the  cartilaginous  rings;  (3)  a  muscular  layer;  (4)  the  mucous 
membrane.     The  elastic  membrane  is  intimately  attached  to  the  perichondrium 

'  The  arrangement  of  the  muscles  should  be  noted,  since  the  space  inclosed  by  the  divergence 
of  the  sterno-cephalici  and  the  convergence  of  the  omo-hyoidei  is  the  area  of  election  for  the 
operation  of  tracheotomy. 
29 


450  RESPIRATORY    SYSTEM    OF   THE    HORSE 

of  the  rings.  In  the  intervals  lietween  the  latter  it  constitutes  the  annular  liga- 
ments (Ligamenta  annularia).  The  rings  of  the  trachea  (Cartilagines  tracheales) 
are  composed  of  hyaline  cartilage.  The.y  are  incomplete  dorsally,  and  when  their 
free  ends  are  drawn  ai)art.  resemble  somewhat  the  letter  C.  In  the  cervical  part 
the  thin  wide  free  ends  overlap,  while  in  the  thoracic  part  they  do  not  meet;  here 
the  deficiency  is  made  uji  by  thin  [)lates  of  variable  size  and  form,  embedded  in  a 
membrana  transversa.  Ventrally  the  rings  are  about  one-half  inch  (ca.  1  to  1.2  cm.) 
wide  and  much  thicker  than  dorsally.  The  first  ring  is  attached  to  the  cricoid 
cartilage  liy  the  crico-tracheal  membrane,  and  is  usually  fused  dorsally  with  the 
second  ring.  Various  irregularities,  such  as  partial  bifurcation  or  partial  or  com- 
plete fusion  with  an  adjacent  ring,  are  eonuuon.  The  arrangement  in  the  terminal 
part  is  very  irregular.  The  muscular  layer  (Musculus  trachealis)  consists  of  un- 
striped  fillers  which  stretch  across  the  dorsal  part  of  the  tube.  It  is  separated  from 
the  ends  of  the  rings  and  the  meml)rana  transversa  by  a  quantity  of  areolar  tissue. 
When  it  contracts  the  caliber  of  the  tube  is  diminished.  The  mucous  membrane 
is  pale,  normally,  and  presents  numerous  fine  longitudinal  folds,  in  which  are 
bundles  of  elastic  fibers.  The  epithelium  is  stratified  columnar  ciliated.  Numer- 
ous tubular  mucous  glands  (Glandvilffl  tracheales)  are  present. 

Blood-supply.- -( 'onunon  carotid  arteries. 

Nerve-supply. — Vagus  and  symiiathetic  nerves. 

THE  BRONCHI 
The  two  bronchi,  right  and  left  (Bronchus  dexter,  sinister),  are  formed  by  the 
bifurcation  of  the  trachea.  Each  passes  backward  and  outward  to  the  hilus  of 
the  corresponding  lung.  The  right  bronchus  is  a  little  wider  and  less  oblique  in 
direction  than  the  left.  They  are  related  ventrally  to  the  divisions  of  the  pulmon- 
ary artery,  and  dorsally  to  the  branches  of  the  bronchial  artery  and  the  bronchial 
lymiili  glands.     Their  structure  is  similar  to  that  of  the  trachea. 


THE  THORACIC  CAVITY 

The  thoracic  cavity  (Cavum  thoracis)  is  the  second  in  point  of  size  of  the  body 
cavities.  In  form  it  is  somewhat  like  a  truncated  cone,  much  compressed  laterally 
in  its  anterior  part,  and  with  the  base  cut  off  very  obliquely. 

The  dorsal  wall  or  roof  is  formed  by  the  thoracic  vertel)rae  and  the  ligaments 
and  muscles  connected  with  them. 

The  lateral  walls  are  formed  Ijy  the  ribs  and  the  intercostal  muscles. 

The  ventral  wall  or  floor  is  formed  by  the  sternum,  the  cartilages  of  the  sternal 
ribs,  and  the  muscles  in  connection  therewith.  It  is  about  one-half  as  long  as  the 
dorsal  wall. 

The  posterior  wall,  formed  by  the  diaphragm,  is  very  obliciue  and  is  strongly 
convex. 

Tlie  anterior  aperture  or  inlet  (Apertura  thoracis  cranialis)  is  relatively  small, 
and  of  narrow,  oval  form.  It  is  bounded  dorsally  by  the  fir.st  thoracic  vertebra 
and  laterally  l)y  the  first  pair  of  ribs.  It  is  occupied  by  the  longus  colli  nmscles, 
the  trachea,  fpsophagus,  vessels,  nerves,  and  the  jirejiectoral  lym])li  glands. 

The  cavity  is  lined  by  the  endothoracic  fascia  and  by  the  pleurae. 

A  longituilinal  septum,  termed  the  mediastinum  (Septum  mediastinale),  ex- 
tends from  the  dorsal  wall  to  the  ventral  and  ])osterior  walls,  and  subdivides  the 
cavity  into  two  lateral  chambers  which  contain  the  lungs.  Ea('h  of  these  chambers 
is  lined  by  a  serous  membrane  called  the  pleura,  and  is  called  a  pleural  cavity 
(Cavum  plcurie).  The  mediastinum  is,  for  the  most  part,  not  median  in  position; 
this  is  largely  due  to  the  fact  that  the  largest  organ  contained  in  it,  the  heart,  is 


THE    PLEUR.E 


451 


placed  more  on  the  left  side;  consequently  the  right  pleural  cavity  and  lung  arc 
larger  than  the  left.  Practically  all  the  organs  in  the  thorax  are  in  the  mediastinal 
space  with  the  exception  of  the  lungs,  the  posterior  vena  cava,  and  the  right  phrenic 
nerve.  The  part  in  which  the  heart  and  the  pericardium  are  situated,  together 
with  that  above  it,  is  usually  called  the  middle  mediastinal  space;  the  parts  before 
and  behind  this  are  termed  the  anterior  and  posterior  mediastinal  spaces  respec- 
tively. 

THE  PLEURA 
The  pleurae  are  two  serous  sacs  which  line  the  pleural  cavities  and  are  reflected 
at  the  roots  of  the  lungs  to  invest  those  organs.     We,  therefore,  distinguish  parietal 
and  visceral  parts  of  the  pleurae. 


Ligamentum  iiuchce 


Scapula 
Spinal  cord 

Disc  between  third 

and  fourth  thoracic 

vertebra: 

Thoracic  duct 

Third  rib 

Left  vagus  nerve 

Left  phrenic  nerve 

Costal  pleura 

Mediastinal 
pleura 

Second  costal 
carlilage 

Internal  thoracic 

vessels 

Sternum 


Sympathetic  nerve 
Subcostal  vessels 

(Esophagus 
Right  vagus  nerve 

Anterior  vena  cava 

Right  phrenic 
nerve 

Pulmonary  pleura 
Costal  pleura 

Brachvd  vessels 


S,  left  brachial  artery;   B,  brachiocephalic  artery;    l.fi., 
line. 


Pleura  indicated  by  red 


The  parietal  pleura  (Pleura  parietalis)  lines  the  cavity  in  which  each  lung  is 
situated  (Cavum  pleurae).  On  the  lateral  thoracic  wall  it  is  adherent  to  the  ribs 
and  intercostal  muscles  and  is  termed  the  costal  pleura  (Pleura  costalis).  Behind 
it  is  closely  attached  to  the  diaphragm,  forming  the  diaphragmatic  pleura  (Pleura 
diaphragmatica).  The  part  which  is  in  apposition  with  the  opposite  sac  or  covers 
the  mediastinal  organs  is  termed  the  mediastinal  pleura  (Pleura  mediastinalis); 


452 


RESPIRATORY    SYSTEM    OF   THE    HORSE 


where  this  layer  is  adherent  to  the  pericardium,  it  is  distinguished  as  pericardiac 
pleura  (Pleura  pericardiaca).' 

The  pleura  is  reflected  at  the  root  of  the  lung,  which  it  covers,  constituting 
the  visceral  or  pulmonary  pleura  (Pleura  pulmonalis).  Behind  the  root  of  the 
lung  a  considerable  triangular  area  is  not  covered  liy  the  pleura,  the  two  lungs  being 
attached  to  each  other  by  connective  tissue  in  this  situation. 

The  ligament  of  the  lung  (Lig.  pulmonale)  is  a  fold  formed  by  the  reflection 
of  the  pleura  from  the  mediastinum  and   the  diaphragm  to  the  lung,  behind  the 


■rV 


Left  vagus  nerve--  /  .VpTr ^^^J^)^-     •:-     ,;      X 


Sympathiiic  trunk 


Riglit  viigus  nerve 


Fifth  rib 
Left  phrenic  nerve 


Right  phrenic  nerve 


I  'i  ncardiac  pleura 


Internal  thoracic  vessels 


'Sternum 


Fig.  359. — CHOSs-SEfTioN-  of  'J"horax  of  New-born  Foal. 
.^,.\orla;    Br.,  bronchi;   /'..I.,  pulmonary  arteries;    (,  lymph  gland;   K..-1.,  right  atrium;    L.A. 
right  ventricle;    L.V.,  left  ventricle  of  heart. 


triangular  area  of  adhesion  just  mentioned.     It  is  seen  when  the  base  of  the  lung 
is  drawn  outward.     It  contains  elastic  tissue,  especially  in  its  posterior  part. 

The  right  pleura  forms  a  special  sagittal  fold  (Plica  venae  cavse)  about  a 
handbreadth  to  the  right  of  the  median  plane,  which  incloses  the  posterior  vena 
cava  in  its  upper  edge  and  gives  off  a  small  accessory  fold  for  the  right  jihrenic 
nerve.  The  fold  arises  from  the  thoracic  floor  and  from  the  diaphragm  below  the 
foramen  vena?  caviB,  and  intervenes  between  the  mediastinal  lobe  and  the  body  of 
the  right  lung.     It  is  delicate  and  lace-like. 

'  Thp  student  shoukl  bear  in  mind  that  tho.so  terms  are  employed  simply  as  a  matter  of 
convenience  in  description;  all  the  parts,  though  differently  named,  form  a  continuous  whole. 


THE    LUNGS 


453 


The  posterior  meiliastinum  is  very  delicate  below  the  ccsophagus,  and  usually 
appears  fenestrated;  when  these  apertures  are  present,  the  two  pleural  cavities 
communicate  with  each  other.' 

The  pleural  sacs  contain  a  serous  fluid,  the  liquor  pleurae ;  in  health  there  is 
only  a  sufficient  amount  to  moisten  the  surface,  but  it  accumulates  rapidly  after 
death. 


Mediaslinal 
pleura 


Mediastinal  lobe 
of  right  lung 


na  azygos 
Thoracic  duct 

Aorta 

Superior  (Esopha- 
geal nerve 
(Esophagus 
Inferior  oesopha- 
geal nerve 

Posterior  vena  cava 


Right  phrenic 
nerve 

Fold  of  pleura  in- 
closing posterior 
vena   cava    and 
right  phrenic 
nerve 


Fig.  360  — Cross-section  of  Thoeax  op  New-born  Foal. 
Ribs  are  numbered. 


THE  LUNGS 

The  lungs  (Pulmones)  occupy  much  the  greater  part  of  the  thoracic  cavity. 
They  are  accurately  adapted  to  the  walls  of  the  cavity  and  the  other  organs  con- 
tained therein.  The  two  lungs  are  not  alike  in  form  or  size,  the  right  one  being 
considerably  larger  than  the  left;  the  difference  is  chiefly  in  width,  in  conformity 
with  the  projection  of  the  heart  to  the  left. 

The  lung  is  soft,  spongy,  and  highly  elastic.  It  crepitates  when  pressed 
between  the  finger  and  thumb,  and  floats  in  water.  When  the  thoracic 
cavity  of  the  unprescrved  subject  is  opened,  the  lung  collapses  immediately 
to  about  one-third  of  its  original  size,  and  loses  its  proper  form;  this  is 
due   to  its  highly  elastic   character  and   the  fact  that  the   tension  of  the  lung 

'  The  apertures  do  not  exist  in  the  fa?tus,  and  are  sometimes  absent  in  the  adult  subject. 
Some  of  them  may  be  produced  in  dissection  by  the  necessary  disturbance  of  the  parts.  Clini- 
cians state  that  a  serous  exudate  formed  in  one  pleural  sac  usually  passes  through  to  the  other 
side  in  the  horse. 


454 


RESPIRATORY    SYSTEM    OF   THE    HORSE 


tissue  caused  by  the  air  pressure  in  its  cavities  has  been  reheved  by  the  external 
air  pressure.' 

The  color  varies  according  to  the  amount  of  blood  contained  in  the  lung. 
During  life  the  lung  has  a  pink  color,  but  in  subjects  which  have  been  bled  for  dis- 
section it  is  light  gray  or  faintl}'  tinged  with  red.  In  unbled  subjects  it  is  dark  red; 
the  de])th  of  color  varies,  and  is  often  locally  accentuated  by  gravitation  of  blood 
to  the  most  deix'ndent  parts  (hypostasis). 

The  foetal  lung,  since  it  contains  no  air  antl  has  a  relativel.y  small  blood-su])]3ly, 
differs  from  that  of  an  animal  which  has  breathed  in  the  following  respects:  (1) 
It  is  much  smaller;  (2)  it  is  firmer  and  does  not  crepitate;  (3)  it  sinks  in  water;  (4) 
it  is  pale  gray  in  color. 

In  form  the  lungs  are  like  casts  of  the  pleural  cavities  in  which  they  are  situated. 
When  well  hardened  in   t<>tu,  their  surfaces  present   impressions  and  elevations 


Fig.  361. — Lkft  Lung  of  Horse,  Costal  Surfac 
Specimen  hardened  /"  situ. 


corresponding  exactly  to  the  structures  with  which  they  are  in  contact.  Each 
lung  presents  two  surfaces,  two  borders,  a  base,  and  an  apex. 

The  costal  (or  external)  surface  (Facies  costalis)  is  convex,  and  lies  against  the 
lateral  thoracic  wall,  to  which  it  is  accurately  adapted. 

The  mediastinal  (or  internal)  surface  (Facies  mediastinalis)  is  less  extensive 
than  the  costal  surface.  It  is  molded  on  the  mediastinum  and  its  contents.  It 
presents  a  large  cavity  adapted  to  the  pericardium  and  heart;  this  is  termed 
the  cardiac  impression  (Impressio  cardiaca),  and  is  larger  and  deeper  on  the 
left  lung  than  on  the  right.  Above  and  behind  this  is  the  hilus,  at  which  the 
bronchus,  vessels,  and  nerves  enter  the  lungs.  The  bronchial  lymph  glands  are 
also  found  here.  Behind  this  the  two  lungs  are  adherent  to  each  other  over  a 
triangular  area.  Above  this  is  a  groove  for  the  oesophagus  (Sulcus  ocsophageus), 
which  is  deepest  on  the  left  lung.  A  groove  for  the  aorta  (Sulcus  aortic)  curves 
upwanl  and  backward  over  the  hilus,  and  passes  backward  near  the  dorsal  border 
of  the  lung;  the  curved  part  of  the  groove  for  the  aortic  arch  is  absent  on  the 
right    lung,  on    which    there  is  a  groove  for  the  vena   azygos.     Anteriorly  there 

'  A  correct  idea  of  the  natural  form  and  size  of  the  lung  cannot  be  obtained  from  a  specimen 
in  this  state.     The  lungs  should  be  hardened  in  situ  for  this  purpose. 


THE    LUNGS 


455 


are    grooves    for  the  traehea,  the  anterior  aorta,  the   anterior   vena  cava,   and 
other  vessels. 


Ligament  of  lunij  (rut] 

or d  p  r 

Groove  for  ^ 
?  for  oesophagus 
fA.r^<i    oF 
odkesion 


Bronchial  artery 
I  Bronchus 
Pulmonarii     I    i  Pulmonary  ,. 

ini  j)ression 


artery 


Line  of  reflect i: 
of  pleura 


Fig.  362. — Left  Lung  of  Horse,  Medi.\stin.\l  and  Diaphr.xgm.vtk:  SiTTtrvrRs. 
Organ  hardened  in  situ.     (Venous  impression  for  common  dorso-cervico-verteljral  .stem.) 


Pulmonary 
Groove  for  artery      Bronchus 

anterior  c.d.         \        \    Groove  for  r<  ua  a:i/;/n 

vena  cava 


Ligamrnt  of  liniq  (cut) 


■    Z3or-s-«/     bofcf'^r 
Cr-ooi^e  Foraori'a 
Groove  /'or  oesopfioQ"^ .^ 

Area  of 
*)^adhesiO' 


Fig.  363. — Right  Lung  of  Horse,  Mediastinal  and  Diaphra 
Organ  hardened  in  situ,     c,  d,  Grooves  for  superior  cervical  and  dorsal  veins.     Arrows  indicate  canal  for  posterior 
vena  cava  between  mediastinal  lobe  and  main  part  of  lung. 


The  dorsal  (or  superior)  border  (Margo  obtusus)  is  long,  thick,  and  rounded; 
it  lies  in  the  groove  alongside  of  the  bodies  of  the  thoracic  vertebrae. 

The  ventral  (or  inferior)  border  (Margo  acutus)  is  thin  and  short.     It  presents, 


456  RESPIRATORY    SYSTEM    OF   THE    HORSE 

opposite  to  the  heart,  the  cardiac  notch  (Incisura  cardiaca).  On  the  left  lung  this 
notch  is  opposite  to  the  third,  fourth,  and  fifth  ribs,  so  that  a  considerable  area  of  the 
pericardium  here  lies  in  direct  contact  with  the  chest-wall.  On  the  right  lung  the 
notch  is  less  extensive,  and  is  an  intercostal  space  further  forward. 

The  base  of  the  lung  (Basis  pulmonis)  is  oval  in  outline;  its  surface  (Facies 
diaphragmatica)  is  deeply  concave  in  adaptation  to  the  thoracic  surface  of  the 
diaphragm.  Laterally  and  posteriorly  it  is  limited  by  a  thin  basal  border  which 
fits  into  the  narrow  recess  (Sinus  phrenico-costaHs)  between  the  diajihragm  and 
the  chest-wall.  The  position  of  this  border,  of  course,  varies  during  respiration. 
In  the  deepest  inspiration  it  may  reach  the  bottom  of  this  recess;  in  ordinary 
inspiration  it  lies  about  four  or  five  inches  (ca.  10  to  12  cm.)  from  the  costal  arch, 
to  which  it  is  nearly  parallel;  in  ordinary  expiration  it  lies  about  twice  as  far  from 
the  costal  arch. 

The  apex  of  the  lung  (Apex  pulmonis)  is  prismatic,  narrow,  and  flattened 
transversely.  It  is  partially  marked  off  from  the  rest  of  the  lung  by  the  cardiac 
notch.  It  curves  downward,  and  is  related  internally  to  the  anterior  mediastinum 
and  behind  to  the  anterior  part  of  the  pericardium. 

In  the  horse  the  lungs  are  not  divided  into  distinct  lobes  by  deep  fissures,  as 
in  mo.st  mammals.  In  the  case  of  the  left  lung  there  is  no  lobation,  but  the  right 
lung  presents  a  mediastinal  lobe,  separated  from  the  body  of  the  lung  by  a  fissure 
which  forms  in  its  dorsal  part  a  canal  for  the  posterior  vena  cava  and  the  right 
phrenic  nerve,  inclosed  in  a  special  fold  of  the  right  pleura.' 

The  root  of  the  lung  (Radix  pulmonis)  is  composed  of  the  structures  which 
enter  or  leave  the  lung  at  the  hilus  on  the  mediastinal  surface.  These  are:  (1) 
The  bronchus;  (2)  the  pulmonary  artery;  (3)  the  pulmonary  veins;  (4)  the  bron- 
chial artery;  (.5)  the  pulmonary  nerves;  (G)  the  lymph  vessels,  which  open  into 
the  bronchial  lymph  glands.  The  bronchus  is  situated  dorsally,  with  the  bronchial 
artery  on  its  upper  surface  and  the  pulmonary  artery  immediately  below  it.  The 
pulmonary  veins  lie  chiefly  below  and  behind  the  artery. 

The  lobulation  of  the  lungs  is  not  very  evident  on  account  of  the  small  amount 
of  interlobular  tissue.  The  lobules  appear  on  the  surface  or  on  sections  as  irregular 
polygonal  areas  of  different  sizes. - 

Bronchial  Branches. — Each  bronchus  at  its  entrance  into  the  lung  gives  off  a 
branch  to  the  apex  of  the  lung.  It  is  then  continued  backward  as  the  main  stem 
bronchus,  parallel  with  the  dorsal  border  of  the  lung,  giving  off  branches  (Rami 
bronchiales)  in  monopodic  fashion;  these  branch  similarly  and  reach  all  parts  of 
the  lung.     The  right  bronchus  giv^es  off  a  special  branch  to  the  mediastinal  lobe. 

The  arrangement  of  the  larger  bronchi  is  not  the  same  in  the  two  lungs.  The  right  bronchus, 
after  detaching  the  apical  branch,  gives  off  a  large  ventral  branch  which  shortly  bifurcates.  One 
of  the  divisions  passes  ventrally  into  the  part  of  the  lung  behind  the  cardiac  notch  (homologue 
of  cardiac  lobe),  while  the  other  passes  downward  and  Inickwanl  into  tljc  lower  part  of  the  base. 
The  stem  bronchus  then  gives  off  the  branch  to  the  niediiu'^tinal  lobe,  and  dixides,  about  six  inches 
from  the  hilus  of  the  lung,  into  two  nearly  equal  branches;  the  dorsal  branch  is  a  direct  con- 
tinuation of  the  stem,  the  ventral  one  passes  into  the  middle  part  of  the  base.  The  left  bronchus, 
after  a  short  course,  divides  into  two  nearly  equal  branches.  The  dorsal  branch  may  be  regarded 
as  the  continuation  of  the  stem;  it  passes  backward  parallel  with  the  dorsal  border  of  the  lung, 
giving  off  a  ventral  branch  much  further  back  than  in  the  right  lung.  The  ventral  division  of 
the  stem  bronchus  divides,  after  a  very  short  course,  into  two  branches;  the  anterior  one  passes 
ventrally  into-the  homologue  of  the  cardiac  lobe,  wliile  the  posterior  one  passes  downward  and 
backward  into  the  base  of  the  lung. 

The  structure  of  the  larger  bronchial  tubes  is,  in  general,  similar  to  that  of  the 
trachea.     Their  walls  contain  irregular  plates  of  cartilage  instead  of  rings.     There  is 

'  Some  authors  consider  each  lung  to  be  divided  into  anterior  and  posterior  lobes  by  the 
cardiac  notch,  so  that  the  right  lung  would  have  three  lobes  and  the  left  lung  two  lobes. 

■  In  fcL'tal  lung  the  lobulation  is  much  more  distinct.  Pigmentation  of  the  lung  is  sometimes 
seen  in  horses,  and  in  such  cases  the  pigment  is  deposited  mainly  in  the  interlobular  tissue,  thus 
mapping  out  the  lobules. 


THE   THYROID    GLAND  457 

a  continuous  layer  of  unstripetl  muscle,  composed  of  circ'ularly  arranged  bundles. 
The  mucous  membrane  presents  numerous  longitutlinal  folds;  it  contains  many 
elastic  fibers,  mucous  glands,  and  lymph  nodules,  and  is  lined  by  ciliated  columnar 
epithelium.  As  the  tubes  diminish  in  size  the  coats  become  thinner  and  the  car- 
tilages smaller;  in  tubes  about  1  mm.  in  diameter  the  cartilages  and  mucous  glands 
are  absent. 

By  repeated  liranching  the  interlobular  bronchi  are  formed,  and  from  these 
arise  the  lobular  bronchioles.  Thi'  latter  enter  a  lolnile  and  branch  within  it, 
forming  the  respiratory  bronchioles ;  these  give  off  the  alveolar  ducts,  tlie  walls  of 
which  are  pouched  out  to  form  hemispherical  diverticula,  the  alveoli  or  air-cells. 

A  lobule  of  the  lung,  the  unit  of  lung  structure,  is  made  up  of  a  lobular  bronchi- 
ole with  its  branches,  and  their  air-cells,  blood-  and  lymph-vessels,  and  nerves. 
Between  the  lol:)ules  is  the  interlobular  tissue,  which  forms  the  supporting  frame- 
work of  the  lung. 

Vessels  of  the  Lungs. — The  branches  of  the  pulmonary  artery  carry  venous 
blood  to  the  lungs.  They  accompany  the  bronchi,  and  form  ricli  capillary  plexuses 
on  the  walls  of  the  alveoli.  Here  the  blood  is  arterialized,  and  is  returned  to  the 
heart  by  the  pulmonary  veins.  Tlie  bronchial  arteries  are  relatively  small  vessels 
which  carry  arterial  blood  for  the  nutrition  of  the  lungs.  The  branches  of  these 
arteries  accompany  the  bronchial  ramifications  as  far  as  the  alveolar  ducts,  but 
do  not  extend  to  the  alveoli.  The  oesophageal  artery  also  supplies  pulmonary 
branches  (in  the  horse)  which  reach  the  lung  by  way  of  the  ligament  of  the 
latter.  These  branches  vary  much  in  size,  and  ramify  chiefly  in  the  subpleural 
tissue  of  the  basal  part  of  the  lung.'  The  lymph  vessels  are  numerous,  and  are 
arranged  in  two  sets.  The  superficial  set  forms  close  networks  in  and  under  the 
pleura,  while  the  deep  set  accompanies  the  bronchi  and  pulmonary  vessels.  All 
converge  to  the  root  of  the  lung  and  enter  the  bronchial  lymph  glands. 

Nerve-supply. — The  pulmonary  nerves  come  from  the  vagus  and  sympathetic 
nerves.  They  enter  at  the  hilus  and  supply  branches  to  the  bronchial  arteries  and 
the  air-tubes. 

THE  THYROID  GLAND 

The  thyroid  gland  (C.Iandula  thyreoidea)  is  a  very  vascular  ductless  gland, 
situated  on  the  trachea  close  to  the  larynx.  It  is  red  brown  in  color,  and  consists 
of  two  lateral  lobes  and  a  connecting  isthmus  (Fig.  .354). 

The  lateral  lobes  are  situated  on  either  side  of  the  first  and  second  or  second 
and  third  rings  of  the  trachea,  to  which  they  are  loosely  attached.  Each  is  about 
the  size  of  a  walnut,  and  has  a  convex  superficial  face  which  is  related  to  the  parotid 
gland  and  the  omo-hyoid  muscle,  and  a  slightly  concave,  deep  face,  applied  to  the 
trachea. 

The  isthmus  in  the  adult  horse  is  usually  very  ruchmentary.  It  may  occur  as  a 
very  narrow  glandular  band  which  connects  the  posterior  extremities  of  the  lateral 
lobes,  extending  across  the  ventral  surface  of  the  trachea,  but  it  is  frequently  only 
a  small  strand  of  connective  tissue,  and  sometimes  is  entirely  absent.  It  may  be 
represented  by  a  small  tail-like  process  of  one  lobe. 

The  lateral  lobes  vary  in  size  and  position,  and  are  often  dissimilar  on  the  two  sides.  The 
anterior  extremity  is  the  larger;  it  is  rounded  and  usually  lies  about  a  finger's  breadth  behind 
the  laiynx,  but  may  be  in  contact  with  it.  The  posterior  extremity  is  often  produced  to  form  a 
narrow  tail-like  process,  which  is  continuous  with  the  isthmus  when  one  is  present.  In  the  ass 
and  mule  the  isthmus  is  usually  well  developed.     There  is  sometimes  a  narrow  band  of  thyroid 

1  It  must  not  be  inferred  from  the  necessarily  brief  account  here  given  that  the  two  sets  of 
vessels  are  quite  distinct.  On  the  contrary,  competent  observers  state  that  numerous  small 
branches  of  the  bronchial  arteries  anastomose  with  pulmonary  vessels.  Part  of  the  blood  con- 
veyed to  the  lungs  by  the  bronchial  arteries  is  returned  by  the  pulmonary  veins.  In  the  horse 
bronchial  veins  are  absent  or  inconstant. 


458  RESPIRATORY    SYSTEM    OF    THE    HORSE 

tissue  which  extends  forward  from  the  isthmus  for  a  variable  distance;  this  is  termed  the  pyra- 
midal lobe.  The  position  of  the  lateral  lobe  is  indicated  approximately  by  the  junction  of  the 
external  maxillary  and  jugular  veins. 

Structure. — The  gland  is  enveloped  hj  a  thin,  filirous  capsule,  from  which 
trabeculae  pa.s.s  into  the  gland,  tlividing  it  into  lobules.  The  lobules  consist  of 
non-ct)inmunicating  alveoli  or  follicles  of  varying  form  and  size.  The  alveoli  are 
lined  by  cubical  epithelium,  and  contain  a  viscid  colloid  substance. 

Blood-supply. — The  arteries  are  relatively  very  large;  there  are  usually  two 
thyroid  arteries,  which  arise  from  the  carotid  and  enter  each  extremity  of  the  gland. 

Nerve-supply. — The  nerves  are  derived  from  the  sympathetic  system. 

Nodules  of  thyroid  tissue  of  variable  size,  sometimes  as  large  as  a  pea,  may  be 
found  near  the  anterior  extremity  of  the  lateral  lobes,  on  the  course  of  the  anterior 
thjToid  artery  or  on  the  trachea,  even  at  a  considerable  distance  from  the  thyroid 
region.     They  are  ternieil  accessory  thyroids  (Glandulte  thyreoidae  accessorise). 

The  parathyroids  are  small  glandular  bodies  found  in  the  thyroid  region. 
They  are  paler  and  not  so  dense  as  the  thyroid  tissue,  but  often  cannot  be  differen- 
tiated by  their  naked-eye  appearance.  In  the  horse  there  is  usually  only  one  on 
each  side  in  the  connective  tissue  over  the  anterior  extremity  of  the  lateral  lobe  of 
the  thyroid.     They  resemble  in  structure  embryonic  thyroid  tissue. 


THE  THYMUS  GLAND 

The  thymus  is  a  ductless  gland  which  has  a  close  resemblance  to  the  lymphoid 
tissues.  It  is  well  developed  only  in  late  foetal  life  and  for  a  few  months  after  birth. 
After  this  it  undergoes  rapid  atrophy,  fatty  infiltration,  and  amyloid  degeneration, 
so  that  in  the  adult  it  is  represented  by  a  thin  remnant  in  the  lower  part  of  the 
anterior  mediastinum  or  has  entirely  disajijiearcd.  In  the  new-born  foal  it  is  of  a 
grayish-pink  color,  and  consists  of  two  lateral  lobes  (Fig.  358).  The  greater  part 
of  the  gland  is  situated  in  the  anterior  mediastinum,  but  the  two  lobes  are  con- 
tinued into  the  neck  by  a  chain  of  lobules  which  lie  along  the  course  of  the  carotid 
artery,  extending  sometimes  as  far  as  the  thyroid  gland.' 

Structure. — The  thymus  is  inclosed  in  a  thin,  connective-tissue  capsule,  and 
consists  of  secondary  lobules  (Lobuli  thymi),  of  varying  shape  and  size,  held  to- 
gether by  areolar  tissue  and  fat,  and  all  attached  to  a  cord  of  adenoid  tissue  termed 
the  tractus  centralis.  These  lolniles  are  subdivided  into  polyhedral  primary 
lobules,  which  arc  composed  of  lymphoid  tissue,  and  present  a  dark  vascular  cortex, 
and  a  lighter  medulla  that  contains  Hassal's  corpuscles. 

Blood-supply. — Internal  thoracic  and  carotid  arteries. 

Nerve-supply. — Sympathetic  and  vagus  nerve. 


RESPIRATORY  SYSTEM  OF  THE  OX 

THE  NASAL  CAVITY 

The  nostrils,  situated  on  either  side  of  the  muzzle,  are  relatively  small,  and  are 

much  less  dilatable  than  those  of  the  horse.     The  alse  are  thick  and  firm.     The 

superior  commissure  is  narrow.     There  is  no  false  nostril  or  diverticulum  nasi. 

The  skin  is  smooth,  bare,  and  moist,  and  there  is  no  clear  line  of  demarcation  be- 

'  The  cervical  part  of  the  gland  is  very  variable.  The  thoracic  lobe  of  one  side  may  ha\'e 
no  cervical  continuation;  the  other  lobe  may  then  give  off  a  single  prolongation  which  Ijifurcates. 
The  thoracic  part  in  the  new-born  foal  occupies  most  of  the  space  which  is  later  taken  up  liy  the 
apices  of  the  lungs.  Its  two  lobes  are  in  contact,  and  its  deep  surface  is  molded  on  the  anterior 
part  of  the  pericardium  and  the  large  vessels. 


THE    LARYNX 


459 


tween  it  and  the  nasal  mucosa.  The  opening  of  the  naso-lacrimal  (kict  is  not  visi- 
ble, as  it  is  on  the  outer  wall  of  the  nostril,  and  is  concealed  l)y  the  cartilaginous 
prolongation  of  the  inferior  turhinal.  There  are  two  parietal  or  lateral  cartilages 
on  either  side,  united  hy  fibrous  tissue.  The  dorsal  cartilages  ar<'  thin  laminae 
which  curve  outward  and  downward  from  the  dorsal  margin  of  the  sejrtal  cartilage; 
they  are  prolongations  of  the  nasal  bones,  and  carry  the  alar  cartilages  on  their 
anterior  extremities.  The  ventral  pair  are  lateral  continuations  of  the  basal 
lamelliE  of  the  inferior  turbinals.  They  lie  along  the  nasal  processes  of  the  pre- 
maxillse;  anteriorly,  they  become  thicker,  turn  a  little  upward,  and  each  blends 
with  the  cartilaginous  prolongation  of  the  upper  coil  of  the  inferior  turbinal.  The 
alar  cartilages  are  of  peculiar  form.  The  lamina  is  oblong,  and  curves  outward  and 
downward  from  the  anterior  extremitj-  of  the  dorsal  parietal  cartilage,  with  which 
it  is  connected.  The  cornu  springs  from  the  outer  part  of  the  lamina  and  curves 
outward  and  upward  into  the  outer  wing  of  the  nostril;  it  carries  on  its  extremity 
a  small  transverse  bar,  thus  having  some  resemblance  to  the  fluke  of  an 
anchor. 

The  nasal  cavity  is  short,  wide  anteriorly,  narrow  behind.  It  is  not  com- 
pletely (Uvided  by  the  septum,  which  in 
its  posterior  third  is  separated  from  the 
floor  of  the  cavity  by  an  interval  that  in- 
creases from  before  backward.  The  midcOe 
meatus  is  very  narrow,  and  divides  pos- 
teriorly into  two  branches;  the  upper  divi- 
sion leads  to  the  ethmoidal  meatuses,  and 
communicates  with  the  frontal  sinus  and  the 
cavity  of  the  superior  turbinal.  Anterior  to 
the  di\'ision  are  commiuiications  with  the 
upper  cavit}'  of  the  ventral  turliinal  and 
the   maxillary   sinus.     The    main    facts   in 

regard  to  the  sinuses  were  stated  in  the      L!BiSBB^I^BilC«i9Eiii_J_ 
osteology. 

THE  LARYNX 
The  larynx  is  more  compact  than  in 
the  horse,  and  presents  numerous  differ- 
ential features.  The  cricoid  cartilage  is 
compressed  laterally.  The  lamina  is  not 
distinctly  marked  off  from  the  arch;  it 
slopes  downward  and  backward  and  has  a 
large  median  ridge.  The  thyroid  cartilage  is  complete  ventrally, /.  e.,  the  lamime 
are  united  throughout  to  form  a  long  jjlate  which  is  notched  in  front  and  behind; 
the  laryngeal  prominence  is  small  and  is  situated  posteriorly.  The  height  and 
thickness  of  the  cartilage  increase  from  before  backward.  The  posterior  cornua 
are  about  an  inch  long,  and  form  syndesmoses  with  the  cricoid  cartilage;  the 
short  anterior  cornua  unite  similarly  with  the  hj'oid  bone.  The  epiglottis  is  oval 
in  outline  and  its  apex  is  rounded;  its  base  rests  on  the  thjTo-hyoid  membrane, 
to  which  it  is  rather  looselj'  attached.  The  cuneiform  cartilages  are  absent. 
The  arytenoid  cartilages  present  only  slight  differences.  The  muscular  process 
is  well  developed,  and  the  vocal  process  is  narrow  and  long.  The  vocal  cords 
project  very  little  from  the  wall,  so  that  the  rima  glottidis  is  wide;  the  vocal 
ligament  is  attached  ventrally  to  the  crico-thyroid  membrane;  it  has  the  form  of 
a  half  tube,  open  laehind.  The  lateral  ventricles  are  extremely  shallow,  and  the 
saccules  are  absent.  The  thyro-ar>-tenoideus  muscle  is  not  divided;  it  is  fan- 
shaped,  thick,  and  narrow  dorsally;    ventrally,  it  is  attached  to  the  base  of  the 


Fig.  364. — Muzzle  of  Ox. 

49,  Nasolabial  region;  4S,  lower  lip.    (.4fterEllen- 

berger-Baum,  Anat.  fiir  Kunstler.) 


460 


RESPIRATORY    SYSTEM    OF   THE    OX 


epiglottis,  the  angle  of  the  union  of  the  thyroid  lamina,  and  the  crico-thjToid 
membrane.     The  hyo-epiglotticus  muscle  is  large  and  bifid. 


THE  TRACHEA 
The  caliber  of  the  trachea  is  relatively  small,  its  width  being  about  an  inch 
and  a  half  (ca.  4  cm.)  and  its  height  one  and  a  half  to  two  inches  (ca.  4  to  5  cm.). 
The  rings  are  smaller,  and  number  about  fifty.     In  the  neck  their  free  ends  are  sep- 


Frontal  eminence 


Great  ethmo-lurhiiml 


Superior  turhinal 

Superior  maitiis 
Middle  meatus 


Inferior 
turhinal 


Inferior 
mealaf: 


Naso- 
labial 
glands 


Gcnio-    Mylo-hy-      Genio- 
glossu^     oideus      hyoideus 


Thyroid  cartilage 


Body  of 

mandible 

Fig.  365. — Sagittal  Section  of  Head  of  Cow. 
;,  Cerebral  hemisphere;  S,  lateral  ventricle;  S,  thalamus;  .(,  corpora  quadrigemina;  5,  optic  chiasmal 
e,  pituitary  body;  7,  pons;  S,  medulla  oblongata;  9,  cerebellum;  JO,  spinal  cord;  17,  ventral  straight  muscles; 
/a,  pharyngeal  lymph  gland;  75,  arytenoid  cartilage;  i4,  epiglottis;  JS,  cricoid  cartilage;  / 6,  vocal  cord;  17, 
palatine  sinus;  18,  soft  palate;  19.  Eustachian  opening;  Ci,  Cj,  C'a,  first,  second,  and  third  cervical  vertebrae;  B.o.. 
basioccipital;   Sp.,  presphenoid. 


arated  by  a  varying  interval,  so  that  the  tube  is  flattened  and  membranous  dor- 
sally.  In  the  thorax  the  ends  are  in  apposition,  so  that  they  form  a  ridge  dorsally. 
The  trachea  is  adherent  to  the  right  lung  from  the  second  rib  backward.  The 
bifurcation  is  opposite  the  fourth  intercostal  space. 


THE  BRONCHI 
There  are  three  chief  bronchi.     The  l)ron(hus  for  the  apical  and  the  anterior 
cardiac  lobe  of  the  right  lung  is  detached  from  the  trachea  at  a  considerable  dis- 
tance anterior  to  the  bifurcation. 


THE    THORACIC    CAVITY    AND    PLEURA 


461 


THE  THORACIC  CAVITY  AND  PLEURA 
The  thoracic  cavity  i;s  relativelj'  small;    it  is  especially  short  dorsally,  and  is 
diminished  laterally  by  the  mode  of  attachment  of  the  diaphragm  to  the  ribs  {vide 
Myology).     The  endothoracic  fascia  is  better  developed  than  in  the  horse,  and  is 


Fig.  366. — Choss-section  of  Thorax  of  Sheep.  Passing  THROunH  Middle  op  Fifth  Pair  of  Ribs,  Posterior 

View. 
/,;',  Lungs;   S,  3',  bronchi;   S,  3',  pulmonary  arteries;    4,  tlioracic  aorta;   5,  oesophagus;   ff,  lymph  gland; 
7,  vena  hemiazygos;   8,  posterior  vena  cava;    9,  large  pulmonary  vein;    10,  left  atrium,    //,  vena    hemiazygos; 
2.2,  left  ventricle;  icS,  right  ventricle;   /4,  sternum;  /5,  internal  thoracic  vessels;  iff,  six' n  joracic  vertebra. 


distinctly  elastic.  The  pleura  is  also  thick,  and  there  are  no  perforations  of  the 
mediastinum.  The  pleural  sacs  are  more  unequal  in  extent  than  in  the  horse,  and 
the  ventral  part  of  the  mediastinum  is  further  to  the  left;  in  front  of  the  pericar- 
dium it  lies  for  the  most  part  on  the  left  wall  of  the  chest. 


462 


RESPIRATORY    SYSTEM    OF   THE    OX 


THE  LUNGS 
The  difference  in  size  between  the  two  lungs  is  greater  than  in  the  horse,  the 
right  lung  weighing  about  half  as  much  again  as  the  left  one.     The  average  weight 


harrlrr- 


FlG.  3G7- — Right  Lung  of  Ox,  Costal  Surfack. 
Organ  hardened  in  situ. 


lobe 

Fig.  368. — -Right  Lung  of  Ox,  Mkdiastixal  .\spect. 
hardened  in  situ,     i,  Left  bronchus;   3,  pulmonary  veins;   S,  pulmonary  artery. 

of  the  lungs  is  about  7}4  pounds  (ca.  3  to  4  kg.);    they  form  about  j]-^  of  the 
body  weight. 

They  are  divided  into  lol)os  liy  dccj)  fissures  (Incisurse  interlobares).     The 
left  lung    is    divided    into    three    lobes,  named   from   before   backward   apical, 


THE    LUXGS 


463 


cardiac,  and  diaphragmatic.  The  right  lung  has  four  or  five  lobes;  the  apical 
lobe  is  much  largiT  than  that  of  tlie  loft  hing,  and  occupies  the  s|)acc  in  front  of 
the  pericardium,  pushing  the  mediastinum  against  the  left  wall;'  the  mediastinal 
lobe  resembles  that  of  the  horse,  while  the  cardiac  lobe  is  often  divided  by  a  fissure 
into  two  parts.  The  apical  lobe  of  the  right  lung  receives  a  special  broncluis  from 
the  trachea  opposite  the  third  rib.  The  right  lung  is  adherent  to  the  trachea  from 
the  second  rib  backward. 


Apical  lobe 


, Cardiac  lobe 


Alediaslinal  lobe 


Diaphragmatic  lobe 

linnl  lymph  gland 
Fig.  369. — Lungs  and  He.^rt  of  Sheep,  Ventral  View. 
Specimen  hardened  in  situ.     Space  between  heart  and  lungs  was  occupied  by  pericardium  and  fat. 


The  interlobar  iissures  begin  at  the  ventral  margin  of  the  lung  and  pass  toward  the  root. 
Those  of  the  left  lung  he  opposite  to  the  fourth  and  sixth  ribs.  The  diaphragmatic  lobe  is  the 
largest,  and  has  the  form  of  a  thrcc-siilcd  p\r:imid  with  its  base  resting  on  the  diaphragm.  The 
cardiac  lobe  is  prismatic  and  forms  thr  iidstciior  margin  of  the  cardiac  notch;  its  long  a.xis  corre- 
sponds to  the  fifth  rib.  The  apical  Inl.r  of  the  left  lung  is  small  and  pointed;  its  ventral  margin 
lies  on  the  pulmonary  artery  and  the  anterior  aorta;  below  this  the  space  in  front  of  the  heart 
is  occupied  by  the  apical  lobe  of  the  right  lung.  The  cardiac  lobe  of  the  right  lung  is  much  larger 
than  that  of  the  left  lung,  and  covers  the  right  face  of  the  pericardium,  .so  that  the  latter  has  no 
contact  with  the  lateral  wall  of  the  thorax. 

The  lobulation  is  very  distinct  on  account  of  the  extremely  large  amount  of 
interlobular  tissue. 

'  It  is  therefore  often  termed  the  precardiac  lobe. 


464  RESPIRATORY    SYSTEM    OF   THE    PIG 

In  the  sheep  the  costal  attachment  of  the  diaphragm  resembles  that  of  the 
horse,  and  the  basal  part  of  the  lung  corresponds  thereto.  The  lobation  of  the 
lungs  resembles  that  of  the  ox,  but  the  lobulation  is  very  indistinct.  The  pleural 
sacs  extend  under  the  first  lumbar  vertebra. 


THE  THYROID  GLAND 

The  lobes  of  the  thyroid  glantl  are  more  extensive  and  paler  in  color  than  in 
the  horse;  they  extend  further  forward,  overlajiping  the  crico-pharyngeus  muscle 
to  a  small  extent,  and  come  in  contact  dorsally  with  the  oesophagus.  They  are 
flattened,  and  have  an  irregular,  lol)ulated  surface.  In  the  young  subject  the  isth- 
mus is  well  developed,  being  about  half  an  inch  (ca.  1  to  1.5  cm.)  in  width. 

Accessory  thyroids  may  be  found,  and  parathyroids  also  occur  near  the  pos- 
terior extremity  or  inner  surface  of  the  lateral  lobes  of  the  thjroid. 

A  pical  lobe  JlorS^  I     border 


"^'^^^--^c  ^,^ 


oesophagus 


■""-  Diaphragmatic  surface 


Apex  \  I 

Cardiac  notch 

Fig.  370. — Rlonx  Lung  of  Sheep,  Mediastinal  Aspect. 

Hardened  in  situ.     B,  Bronchus;    P.a.,  pulmonary  artery;    P.v.,  pulmonary  vein;    T'.c,  posterior  vena  cava; 

L.g.,  bronchial  lymph-gland. 


THE  THYMUS  GLAND 
The  thjTBus  is  pale  and  distinctly  lobulated.  It  is  much  larger  in  the  calf 
than  in  the  foal,  weighing  at  five  or  six  weeks  about  15  to  25  ounces  (ca.  425  to  GOO 
grams).  The  cervical  part  is  specially  large,  thick,  and  compact;  it  extends 
to  the  thyroid  gland.  It  undergoes  atrophy  slowly  and  remnants  of  the 
thoracic  part  often  remain  even  in  advanced  age. 


RESPIRATORY  SYSTEM  OF  THE  PIG 
THE  NASAL  CAVITY 
The  nostrils  are  small,  and  are  situated  on  the  flat  anterior  surface  of  the 
rostrum  or  ,^n()ut  (Rostrum  suis).  The  latter  is  a  short  cylindrical  projection, 
with  which  the  upper  lip  is  fused,  and  is  circumscribed  by  a  prominent  circular 
margin.  The  skin  on  the  snout  is  thin  and  highly  sensitive;  it  presents  small 
pores,  and  scattered  over  it  are  fine  short  hairs.  In  the  snout  between  the  nostrils 
is  the  OS  rostri,  which  is  to  be  regarded  as  a  special  development  of  the  extremity  of 


THE    LARYNX  465 

the  septum  nasi  in  adaptation  to  the  habit  of  rooting.  A  plate  of  cartilage, 
representing  the  lamina  of  the  alar  cartilage  of  the  horse,  curves  outward  and 
downward  from  the  upper  part  of  the  os  rostri  and  a  pointed  bar  of  cartilage 
curves  upward  from  the  lower  ])art  of  the  bone  in  the  outer  wing  of  the  nostril. 
The  notch  between  the  nasal  bone  and  the  prcmaxilla  is  closetl  in  by  jjarietal 
cartilages  which  resemble  those  of  the  ox. 

The  nasal  cavity  is  long  and  narrow.  It  is  divided  behind  by  a  horizontal 
plate  into  an  upper  olfactory  part,  which  leads  to  the  ethmoidal  meatuses, 
and  a  lower  respiratory  part,  which  is  a  direct  continuation  of  the  inferior  meatus. 
The  posterior  jiart  of  the  sejitum  is  membranous. 

The  turbinal  bones  resemble  in  general  those  of  the  ox.  The  superior  meatus 
is  exceedingly  small.  The  middle  meatus  is  a  deep  fissure  between  the  two  turbinals: 
it  diviiles  posteriorly  into  two  branches;  one  of  these  extends  upward  and  back- 
ward Isetween  the  lateral  mass  of  the  ethmoid  bone  and  the  superior  turbinal; 
the  other  widens  and  joins  the  inferior  meatus.  The  opening  l)etween  the  maxillary 
sinus  and  the  middle  meatus  lies  in  a  plane  through  the  last  cheek  teeth.  The 
middle  meatus  is  continuous  with  the  space  inclosed  by  the  dorsal  part  of  the  in- 
ferior turbinal  and  with  the  cavitj'  of  the  superior  turbinal.  The  dorsal  division 
of  the  middle  meatus  presents  several  opening.?  into  the  frontal  sinus.  The  in- 
ferior meatus  is  relatively  roomy;  it  communicates  with  the  space  inclosed  by 
tlie  ventral  coil  of  the  inferior  turbinal.  The  opening  of  the  naso-lacrimal  duct  is 
found  in  the  posterior  part  of  the  inferior  meatus.  The  naso-palatine  duct  and 
the  vomero-nasal  organ  (of  Jacobson)  resemble  those  of  the  ox. 


THE  LARYNX 
The  larynx  is  remarkaljle  for  its  great  length  and  mobility.  The  cartilages 
are  more  loosely  attached  to  each  other  than  in  the  other  animals.  The  cricoid 
cartilage  is  thick  and  comi^ressed  laterally;  its  lamina  is  long  and  narrow;  its 
arch  is  tlirected  obliquely  downward  and  backward.  Tiie  thyroid  cartilage  is  very 
long;  its  laminae  are  unitefl  ventrally  and  form  a  median  ridge.  The  anterior 
cornua  being  absent,  there  are  no  joints  formed  with  the  hyoid  bone.  The  po.?- 
terior  cornua  are  broad,  bent  inward,  and  articulate  with  the  cricoid  cartilage. 
The  epiglottis  is  relatively  very  large,  and  is  more  closely  attached  to  tlie  hyoid 
bone  than  to  the  rest  of  the  larynx.  The  middle  part  of  its  base  is  turned  forward, 
and  rests  on  the  thyro-hyoid  membrane;  it  is  closely  connected  with  the  body  of 
the  hyoid  bone  by  the  hyo-e]iiglottic  ligament  and  the  strong  hyo-epiglottic  muscle.' 
The  apex  of  the  arytenoid  cartilage  is  very  large,  and  is  divided  into  two  parts  at 
its  extremity;  the  inner  jiart  is  fused  with  that  of  the  opposite  cartilage.  There  is 
a  small  interarytenoid  cartilage  in  the  transverse  ligament.  The  rima  glottidis 
is  very  narrow.  The  vocal  cords  are  directed  obliquely  downward  and  liackwartl; 
and  each  is  pierced  by  a  long,  slit-like  opening,  which  leads  into  the  large  laryngeal 
saccule.  The  thjTO-arytenoid  or  vocal  ligament  is  similarly  divided  into  a  larger 
anterior  and  a  smaller  posterior  part.  There  is  a  middle  ventricle  near  the  jja.se  of 
the  epiglottis.  The  thyro-arytenoid  muscle  is  very  strong  and  is  undivided.  The 
arytenoideus  is  very  small.  The  crico-thyroid  consists  of  two  strata;  the  super- 
ficial layer  corresponds  to  the  muscle  of  the  other  animals;  the  deep  part  consists 
of  transverse  fibers. 

'  The  arrangement  here  is  one  of  the  most  striking  features  of  the  pig's  larynx.  The  short, 
thick  middle  hyo-epiglottic  ligament  and  the  anterior  part  of  tlie  thyro-hyoid  membrane  are 
inelastic,  while  the  posterior  part  of  the  membrane  is  thin  and  elastic  and  allows  the  epiglottis 
to  lie  separated  by  a  considerable  interval  from  the  thyroid  cartilage.  Morever,  the  borders  of 
the  epiglottis  are  "connected  with  the  thyroid  cornua  of  the  hyoid  bone  by  lateral  hyo-epiglottic 
ligaments. 
30 


466 


RESPIRATORY    SYSTEM    OF   THE    DOG 


TRACHEA  AND  BRONCHI 
The  trachea  is  circular  in  cross-section,  and  contains  thirty  or  more  rings 
which  almost  meet  dorsally.     A  special  bronchus  is  detached  for  the  apical  lobe 
of  the  right  lung,  as  in  the  ox. 

THE  LUNGS  (Figs.  324,  325) 
The  right  lung  has  four  or  five  lobes,  according  to  whether  the  apical  is  sub- 
divided or  not.     The  left  lung  reseml)lcs  that  of  the  ox  in  form  and  loliation.     The 
lobulation  is  distinct,  but  the  interlolmlar  septa  are  thinner  than  in  the  ox. 


Groove  for  resophagua 


Dorsal      border 


Trachea  _ 


Apical  lobe 


Cardiac  lobe 

Mediastinal  lobe 
Fig.  371. — Right  Lung  of  Pig,  Mediastinal  .\p 
Hardened  m  situ.     B,  Left  bronchus;     V'.,  pulmonary  veins;    .1..  pulinon 


pkragniatic  lube 
(base) 


artery;     /.   Uinpli  plands 


THE  THYROID   GLAND 
The  two  lobes  of  the  thyroid  are  long  ami  flattened;   they  are  situated  close 
together,  on  the  ventral  surface  of  the  trachea,  extending  as  far  forward  as  the 
cricoid  cartilage.     The  gland  is  dark  red  in  color. 


THE  THYMUS 
The  thymus  is  very  large,  extending  to  the  larynx  or  even  to  the  submaxillary 
space  in  young  subjects. 


RESPIRATORY  SYSTEM  OF  THE  DOG 
THE  NASAL  CAVITY 
The  nostrils  are  situated  on  the  muzzle,  with  which  the  upper  lip  blends.  They 
are  shaped  somewhat  like  a  comma,  with  the  broad  part  next  to  the  septum  and 
the  narrow  part  directed  backward  and  outward.  The  skin  around  the  nostrils 
is  bare,  usually  black,  and  in  health  moist  and  cool.  The  muzzle  is  marked  by  a 
median  furrow  (philtrum)  or  a  deep  fissure  in  some  breeds.  The  cartilaginous 
framework  is  formed  essentially  by  the  septal  cartilage  and  the  parietal  cartilages 
which  proceed  from  it.  The  septal  cartilage  projects  beyond  the  premaxilla,  and 
is  much  thickened  at  its  extremity;   it  gives  off  from  its  upper  and  lower  margins 


THE    LARYNX 


467 


the  two  parietal  cartilages,  which  curve  laterally  and  toward  each  other.  A 
grooved  plate  extends  outwartl  from  the  septal  cartilage  in  the  floor  of  the  nostril, 
and  another  lamina  supports  the  alar  fold  of  the  inferior  turbinal  Ijone. 

The  length  of  the  nasal  cavity  varies  greatly  in  tlifferent  breetls,  correspond- 
ing, of  course,  to  the  length  of  the  face.  The  cavity  is  roomy,  but  is  very 
largely  occupied  by  the  turbinals  and  the  lateral  masses 
of  the  ethmoiil  bone.  The  middle  meatus  is  short  and 
narrow,  and  divides  posteriorly  into  two  branches;  the 
upper  branch  leads  to  the  ethmoidal  meatuses;  the 
lower  branch  joins  the  inferior  meatus.  The  inferior 
meatus  is  very  small  in  its  middle  ]3art,  owing  to  the 
great  development  here  of  the  inferior  turbinal.  The 
posterior  jjart  of  the  nasal  cavity  is  divided  by  a  hori- 
zontal plate,  the  lamina  transversalis,  into  an  upper 
olfactory  part  and  a  lower  respiratory  part.  The 
sinuses  have  been  described  (vide  Osteology). 


Cartilages  of 


6,  lower 
cartilage 
Leiserin 


Upper  parietal  cartilage; 
parietal  cartilage:  c,  alar 
.     (.\fter  EUenberger,   in 

c's  Alias) 


The  laminae  of  the  thyroid 


THE  LARYNX 
The  larynx  is  relatively  short.  The  lamina  of  the 
cricoid  cartilage  is  wide;  the  arch  is  grooved  laterally, 
cartilage  are  high,  but  short;  they  unite  ventrally  to  form  the  liody,  on  which  there 
is  anteriorly  a  marked  prominence,  and  posteriorly  a  deep  notch.  The  oblique  line 
on  the  outer  surface  of  the  lamina  is  prominent.  There  is  a  rounded  notch  (Fissura 
thyreoidea)  below  the  short  anterior  cornua  for  the  passage  of  the  superior  laryngeal 
nerve.    The  jiosterior  coi-nu  is  strong,  and  has  a  rounded  surface  for  articulation  with 


Fig.  .37.3.— Sagittal  Section  op  Nasal  Region  op  Dog. 
/.Skin;  2,  parietal  cartilage;  .i,  floor  of  nasal  cavity;  4,  lamina  transversalis;  5,  mucous  membrane  of  hard 
palate;  6.  upper  lip;  7,  frontal  bone;  S,  frontal  sinus;  9.  cranial  plate  of  front-al  bone;  /O,  cranial  cavity;  II,  dotted 
line  indicating  anterior  limit  of  olfactory  region;  a.  superior  turbinal;  b,  inferior  turbinal;  h',  b",  inferior  turbinal 
fold:  c,  e.  ethmoturbinals;  d,  cribriform  plate  of  ethmoid;  /,  superior  meatus;  »,  middle  meatus:  h,  inferior 
meatus;   i,  naso-pharyngeal  meatus,     (.\fter  EUenberger,  in  Leisering's  .\tlas.) 


the  cricoid  cartilage.  The  arytenoid  cartilages  are  relatively  small,  and  have  between 
them  a  small  interarytenoid  cartilage.  The  epiglottis  is  ciuadrilateral :  its  lower  part 
or  stalk  is  narrow,  fitting  into  the  angle  of  the  thyroid  cartilage.  The  cuneiform 
cartilages  are  large  and  somewhat  crescent-shaped;  they  are  not  blended  with  the 
epiglottis. 

The  false  vocal  cords  extend  from  the  cuneiform  cartilages  to  the  thyroid. 


468  RESPIRATORY    SYSTEM    OF    THE    DOG 

The  true  vocal  cords  arc  large  and  prominent.  The  entrance  to  the  large  lateral 
ventricle  and  saccule  is  a  long  slit  parallel  with  th(>  anterior  margin  of  the  true 
vocal  cord. 

The  crico-thyroid  muscle  is  thick.  The  hyo-epiglotticus  is  well  developed, 
and  is  double  at  its  hyoid  attachment.  The  anterior  part  of  the  thyro-arytenoideus 
arises  on  the  cuneiform  cartilage.  Hence  Lesbre  has  suggested  the  name  cuneo- 
arytenoideus  for  it. 

THE  TRACHEA  AND  BRONCHI 

The  trachea  is  very  slightly  flatteneil  dorsally.  It  contains  forty  to  forty-five 
U-shaped  rings;  the  ends  of  the  rings  do  not  meet  dorsally,  so  that  here  the  wall  of 
the  trachea  is  membranous  and  is  composed  of  a  layer  of  transverse  smooth 
muscle-fibers  outside  of  the  rings,  the  fibrous  membrane,  and  the  mucous  membrane. 

The  stem  bronchi  diverge  at  an  obtuse  angle,  and  each  divides  intotwo branches 
before  entering  the  lung.  The  anterior  branch  goes  to  the  apical  and  cardiac 
lobes,  the  posterior  one  to  the  diaphragmatic  lobe,  supplying  also  the  mediastinal 
lobe  of  tiie  right  lung.  The  anterior  branch  of  the  left  bronchus  crosses  under  the 
pulmonary  artery. 

THE  LUNGS 
The  lungs  (Figs.  342,  343)  dift'er  in  shape  from  those  of  the  horse  and  ox  in 
conformity  with  the  shape  of  the  thorax,  which  is  relatively  very  wide  in  the  dog; 
the  lateral  thoracic  walls  are  strongly  curved,  and  the  co.stal  surface  of  the  lungs 
is  corresjiondingly  convex.  There  is  no  cardiac  notch  on  the  left  lung,  although 
a  small  jjart  of  the  jioricardiura  is  not  covered  by  the  lung  at  the  lowest  part  of 
the  fifth  and  sixth  intercostal  spaces.  On  the  right  side  the  cardiac  notch  is 
opposite  the  fourth  and  fifth  intercostal  spaces.  Each  lung  is  divided  by  deep 
fissures  into  three  lobes — apical,  cardiac,  and  diaphragmatic ;  the  right  lung  has 
in  addition  a  mediastinal  lobe.  The  apical  lolje  of  the  right  lung  is  considerably 
larger  than  that  of  the  left.  The  latter  is  often  more  or  less  fused  with  the  cardiac 
lobe.  Variable  accessory  lobes  maj-  be  found.  On  account  of  the  small  amount  of 
interlobular  tissue  the  lobulation  is  not  distinct. 

THE  THYROID  GLAND 

Th(^  lateral  lobes  of  the  thyroid  gland  are  long  and  narrow,  and  have  a  flat- 
tened, eiliijsoiilai  form;  they  are  placed  on  the  lateral  surfaces  of  the  trachea  near  the 
larynx.  The  extremities  are  .small,  the  posterior  one  often  Ix'ing  pointed.  The 
isthmus  is  inconstant  and  varialjle;  in  large  dogs  it  usually  has  the  form  of  a  glandu- 
lar Ijand  which  may  l)e  nearly  half  an  inch  (ca.  1  cm.)  wide;  in  small  dogs  it  is 
usually  absent. 

Accessory  thyroids  are  frequently  present;  thre(>  or  four  may  be  found  on 
eith(^r  side,  as  well  as  a  median  one  near  the  hyoid  lionc. 

The  parathyroids,  al)Out  the  size  of  millet  or  hem])  seed,  are  four  in  number 
usually.  Two  are  ])laced  on  the  deep  face  of  the  thyroid  loljcs;  the  others  are 
placed  laterally  near  the  anterior  extremity  of  the  thyroid. 

THE  THYMUS 
The  thymus  is  relatively  small,  and  is  situated  almost  entirely  in  the  thorax. 
The  left  lol)e  is  much  larger  than  the  right,  and  extends  back  as  far  as  the  sixth 
rib  at  the  time  of  its  greatest  size.  Accortling  to  Baum  tlie  gland  increases  in  size 
during  the  first  two  weeks  after  birth,  and  atroi)hies  rapidly  in  the  next  two  or 
three  months.  Traces  of  it  are  present  at  two  or  three  years  of  age,  and  may  be 
found  even  in  old  subjects. 


THE  UROGENITAL  SYSTEM 

This  system  (Apjiaratvis  urogenitalis)  includes  two  groups  of  organs,  the  uri- 
narj-  and  the  genital.    The  urinary  organs  elaborate  and  remove  the  chief  excretory 
fluid,  the  urine.     The  genital  organs  siTve 
for  the  formation,  development,  and  expul- 
sion of  the  products  of   the  reproductive 
glands.     In  the  higher  vertebrates  the  two 
apparatus  are  independent   except  at  the 
terminal  part,  which  constitutes  a  urogeni- 
tal tract,  and  includes  the  vulva  in  the 
female  and  the  greater  part  of  the  urethra  . 
in  the  male. 


THE  URINARY  ORGANS 

The  urinary  organs  (Organa  uropoie- 
tica)  are  the  kidneys,  ureters,  bladder,  and 
urethra.  The  kidneys  are  the  glands  which 
secrete  the  urine;  they  are  red-brown  in 
color,  and  are  situated  against  the  dorsal 
wall  of  the  abdomen,  being  in  most  animals 
almost  .symmetrically  placed  on  either  side 
of  the  spine.  The  ureters  are  tubes  which 
convey  the  urine  to  the  bladder.  The  latter 
is  an  ovoid  or  pjTiform  sac,  situated  on  the 
pelvic  floor  when  empty  or  nearly  so;  it  is 
a  reservoir  for  the  urine.  The  urine  ac- 
cumulates in  the  bladder  until  that  organ 
is  full,  and  is  then  expelled  through  the 
urethra. 


Fig.  374. — General  Dorsal  View  of  Ubisary 
Organs  of  Horse. 
1,  Right  kidney;  V ,  left  kidney;  2.  «'.  ad- 
renal bodies;  S.  S' ,  ureters;  4.  urinary  bladder;  4', 
anterior  end  of  bladder  with  cicatricial  remnant  of 
urachus;  4".  urethra:  5,  aorta;  6,  6,  renal  arteries; 
7,  7,  external  iliac  arteries;  S,  S,  internal  iliac 
arteries;  9,  9,  umbilical  arteries,  (.\fter  Leisering's 
Atlas.) 


THE   URINARY   ORGANS   OF  THE 
HORSE 

THE  KIDNEYS 

Each  kidney  (Ren)  presents  two  sur- 
faces, two  borders,  and  two  extremities  or 

poles,  but    they  differ   so   much   in   form  and  position  as  to  require  a  separate 
description  of  each  in  these  respects.' 

The  right  kidney  (Ren  dexter)  in  outline  resembles  the  heart  on  a  playing 
card,  or  an  equilateral  triangle  with  the  angles  rounded  off.     It  lies  ventral  to  the 

'  The  kidneys  are  soft,  plastic  organs,  and  hence  an  accurate  knowledge  of  their  form  can 
be  gained  only  from  a  study  of  specimens  which  have  been  hardened  in  situ.  The  description 
here  given  is  based  on  this  method.  For  this  purpose  subjects  should  be  hardened  in  the  standing 
position  to  avoid  artefacts. 

469 


470 


THE  URINARY  ORGANS  OF  THE  HORSE 


upper  parts  of  the  last  two  or  three  ribs  and  the  tip  of  the  first  lumbar  transverse 
process.  The  dorsal  (or  superior)  surface  (Facies  dorsalis)  is  strongly  convex; 
it  is  related  chiefly  to  the  diaphragm,  but  also  to  a  small  extent  posteriorly 
to  the  psoas  muscles.  In  well  hardened  specimens,  especially  those  from  thin 
subjects,  impressions  of  the  last  two  ribs  and  the  tip  of  the  first  lumbar  transverse 
process  are  usually  visible.  The  ventral  (or  inferior)  surface  (Facies  ventralis)  is 
in  general  slightly  concave,  and  is  related  to  the  liver,  pancreas,  caecum,  and  right 
adrenal;  it  either  has  no  peritoneal  covering,  or  only  a  narrow  area  externally  is  so 
covered.  The  internal  border  (Margo  medialis)  is  convex  and  rounded;  it  is 
related  to  the  right  adrenal  and  the  posterior  vena  cava.  It  presents  about  its 
middle  a  deep  notch,  the  hilus  (Hilus  renalis):  this  is  bounded  by  rounded 
margins,  and  leads  into  a  space  termed  the  renal  sinus  (Sinus  renalis).     The  ves- 


/'"■'^    L.I.      J 

0 

i 

CJ     L.IT 

—  _   0 

0 

Gh 

^^"^^^^z.izr, i 

Fit:.  .375. — DiAf.RAM  of  Position  and  Dorsal  Relations  of  Kidni:ys  of  Horse. 
Areas  of  direct  relations  are  inclosed  by  continuous  lines;  parts  of  skeleton  which  overlie  the  kidneys  but  are  i 
contact  with  them  are  indicated  by  dotted  lines.     L.I-IU,  lumbar  transverse  processes. 


sels  and  nerves  reach  the  kidney  at  the  hilus,  and  the  sinus  contains  the  ]K'lvis  or 
dilated  origin  of  the  ureter.  The  external  border  (Margo  lateralis)  is  rounded, 
and  is  thinner  than  the  internal  one.  It  consists  of  two  parts,  anterior  and 
posterior,  which  meet  at  an  external  angle;  the  anterior  part  fits  into  the  renal 
impression  of  the  liver.  The  duodenum  curves  around  the  external  border.  The 
anterior  extremity  (Extremitas  cranialis),  thick  and  rounded,  lies  in  the  renal 
impression  of  the  liver.  The  posterior  extremity  (Extremitas  caudalis)  is  thinner 
and  narrower. 

The  left  kidney  (Ren  sinister)  is  bean-shaped.  It  is  considerably  longer  and 
narrower  than  the  right  one,  and  is  situated  nearer  the  median  plane  and  further 
back,  so  that  the  hilus  of  the  left  kidney  is  about  opposite  to  the  posterior  extremitj- 
of  the  right  one.  It  lies  usually  under  the  upper  ])art  of  the  last  ril)  and  the  fir.st 
two  or  three  lumbar  transverse  processes.     The  dorsal  surface  is  convex,  and  is 


THE    KIDNEYS 


47] 


related  to  the  left  crus  of  the  diaphragm,  the  psoas  muscles,  and  the  base  of  the 
spleen.  The  ventral  surface  is  convex  and  irregular;  the  greater  part  of  it  is 
covered  by  the  peritoneum.     It  is  in  relation  with  the  origin  of  the  small  colon,  the 


liiyht  adrenal 


Left,  adrenal 


Left  ureter 
Fig.  376 — Kidnevs  and  Adren.\ls  of  Horse,  Dors.\l  View. 
Hardened  in  situ.     Impression  of  seventeenth  rib  on  right  kidney  is  indicated  by  small  cross. 


Anterior  mesenteric 
artery  (stump) 


Renal  arteries 


Fig.  ."ir?. — KiDNETs  .\n-d  .\drex.4i.5  of  Horse,  Ventral  View. 
Hardened  in  situ.     Left  renal  vein  (not  marked)  is  seen  curving  round  posterior  end  of  left  adrenal. 


terminal   part   of  the  duodenum,  the  left  adrenal,  and  the   left   extremity  of  tlie 
pancreas.    The  internal  border  is  longer,  straighter,  and  thicker  than  that  of  the  right 


472 


THE    URINARY    ORGANS    OF   THE    HORSE 


kidney.  It  is  related  to  the  ])ostcrior  aorta,  the  adrenal,  and  the  ureter.  The 
external  border  is  related  chiefly  to  the  ba.se  of  the  spleen.  The  anterior  extremity 
extends  almost  to  the  saccus  CiECUs  of  the  stomach;  it  is  related  to  the  left  end  of 
the  pancreas,  and  the  splenic  vessels.  The  posterior  extremity  is  usually  larger 
than  the  anterior  one. 

The  form  of  the  left  kidney  is  variable.  In  some  cases  its  outline  is  similar  to  that  of  the  right 
kidney,  but  its  ventral  surface  is  convex  and  is  often  marked  by  several  furrows  which  diverge 
from  the  hilus.  In  well-hardened  specimens  the  three  areas  of  the  dorsal  surface  are  often  dis- 
tinct. The  psoas  area  is  flat,  parallel  with  the  inner  border,  and  widens  behind.  The  diaphrag- 
matic area  is  small  and  convex;  it  is  crescentic  and  is  confined  to  the  anterior  pole.  The  splenic 
area,  convex  and  external,  is  often  so  extensive  antl  distinct  as  really  to  constitute  a  third  surface. 

Fixation. — The  kidneys  are  held  in  position  chiefly  by  the  pressure  of  adjacent 
organs  and  by  the  renal  fascia.  The  latter  is  a  special  development  of  the  sub- 
peritoneal tissue,  which  splits  into  two  layers  to  inclose  the  kidney,  together  with 
the  perirenal  fat  or  capsula  adiposa.     On  account  of  its  relations  with  the  liver. 


Renal  crest 


Cortical  substance 


Medullary  substance 


Renal  artery 


Fig.  378. — Frontal  (Horizontal)  Section  of  Kid.n-ey  of  Horse. 
removed.     \  large  accessory  renal  artery  entered  the  posterior  pole.     Sectii 
liiiiitiiig  layer  between  cortical  and  medullary  substance  are  white  in  figure. 


pancreas,  and  the  base  of  the  ctecum,  the  right  kidney  is  much  more  strongly 
attached  than  the  left  one.  It  is,  therefore,  not  surprising  that  the  latter  varies 
somewhat  in  position;  its  posterior  jjole  may  be  found  ventral  to  the  third  or  fourth 
lumbar  transverse  process.  The  position  of  the  right  kidnej'  seems  to  be  very 
constant,  excluding  its  movements  during  respiration. 

Weight  and  Size. — The  right  kidney  is  usually  one  or  two  ounces  heavier  than 
the  left.  The  average  weight  of  the  right  kidney  is  about  23  to  24  ounces  (ca. 
700  gm.);  that  of  the  left,  about  22  to  23  ounces  (ca.  670  gm.).  The  relation  of 
the  weight  of  both  kidneys  to  the  body-weight  is  about  1  :  300-350. 

Chauveau  gives  as  an  average  750  grams  for  the  right  kidney,  antl  710  grams  for  the  left. 
Ellenlierger  and  Baum  (24  cases)  give  the  right  kidney  as  varying  between  430  and  840  grams; 
and  the  left  between  42.5  and  780;  this  is  an  average  of  635  grams  (about  22'.)  ounces)  for  the 
right  kidney,  and  ()02.5  grams  (about  21 'o  oimces)  for  the  left.  They  give  the  relation  of  the 
weight  of  both  kidneys  to  the  body-weight  as  1:  25.5-344.  In  a  Percheron  mare  weigliing  about 
2000  pounds  the  right  kidney  weighed  4  potmds  3  ounces,  and  the  left  one  4  potmds.  In  a  horse 
of  medium  size  the  right  kidney  is  about  six  inches  (ca.  15  cm.)  in  length,  about  the  same  in  width, 
and  about  two  inches  (ca.  5  cm.)  thick.  The  left  kidney  is  about  seven  inches  (ca.  IS  cm.)  long, 
four  to  five  inches  (ca.  10  to  12  cm.)  wide,  and  two  to  two  and  a  half  inches  (ca.  5  to  6  cm.)  thick. 


THE    KIDNEYS  473 

Structure. — The  surface  of  the  kidney  is  covered  by  a  thin  but  strong  fibrous 
capsule  (Tunica  fibrosa),  which  is  in  general  easily  stripped  off  the  healtiiy  ki(hiey. 
It  is  continued  along  the  hilus  and  lines  the  renal  sinus.  Sections  through  tiie 
kidney  show  it  to  consist  of  an  external  cortical  substance  and  an  internal  metlullary 
substance.'  The  cortical  substance  (Substantia  corticalis)  is  red  brown  in  color 
and  has  a  granular  appearance.  It  is  dotted  over  with  minute  dark  points;  these 
are  the  renal  (or  Malpighian)  corpuscles  (Corpuscula  renis),  each  consisting  of  the 
dilated  origin  of  a  uriniferous  tubule  (Capsula  glomeruli),  with  an  invaginated  tuft 
of  capillaries  (Glomerulus)  inclosed  by  it.  The  medullary  substance  (Substantia 
medullaris)  is  more  resistant  and  presents  a  tlistinct  radial  striation.  Its  central 
part  is  pale,  but  its  periphery,  the  intermediate  zone,  is  of  a  deep  red  color;  in 
the  latter  are  seen,  at  fairly  regular  intervals,  sections  of  the  relatively  large  arci- 
form  vessels,  which  are  taken  to  represent  the  demarcation  between  the  jirimitive 
lobes.-  Between  the  vessels  the  medulla  is  prolonged  somewhat  toward  the  per- 
iphery, forming  the  bases  of  the  renal  (or  Malpighian)  p3n"amids.  These  are  not 
very  pronounced  in  the  kidney  of  the  horse,  especially  as  the  gland  is  not  papillated. 


Renal  crest         Peleis  lUmil     Branches       Ureter 

vein  of  renal  artery 

Fig.  379. — Traxsverse  .Sectiox  of  Right  Kidxey  of  Horse  Through  thf-  Hii.us. 
Posterior  portion  of  organ  hardened  in  situ.      Note  cur\-ature  of  dorsal  surface. 

Between  the  leases  of  tlie  pyramids  processes  of  the  cortex  dip  in  toward  the  sinus, 
forming  the  renal  columns.^  The  inner  central  part  of  the  medulla  forms  a  concave 
ridge  or  cre.st  which  projects  into  the  pelvis  of  the  kidney;  the  crest  is  marked  by 
numerous  small  openings  at  which  the  renal  tubules  terminate. 

Examination  with  a  pocket  lens  shows  that  the  cortex  is  imperfectly  divided 
into  lobules  (Lobuli  corticales).  Each  lobule  consists  of  an  axial  radiate  part  (Pars 
radiata),  surrounded  bj'  a  convoluted  part  (Pars  convoluta).  The  former  (formerly 
termed  pyramids  of  Ferrein)  a])])ear  as  ray-like  prolongations  from  the  bases  of 
the  pyramids  (hence  also  termed  medullary  raj's),  and  consist  largely  of  narrow, 
straight  or  slightl.v  flexuous,  tubules  (limbs  of  the  loops  of  Henle).  The  convoluted 
part  (formerly  termed  the  labyrinth)  is  granular  in  appearance,  and  consists  lurgel}- 
of  the  renal  corpuscles  and  convoluted  tubules. 

The  pelvis  of  the  kidney  (Pelvis  renalis)  is  the  dilated  origin  of  the  excretory 

'  The  most  instructive  sections  are  those  made  in  the  horizontal  and  transverse  planes, 
through  the  pelvis  in  each  case. 

-  The  foetal  kidney  is  divided  bj'  furrows  into  a  number  of  polygonal  areas,  each  of  which 
is  the  base  of  a  pyramidal  lobe  or  renculus.  These  furrows  usually  disappear  before  or  soon  after 
birth  in  the  foal,  although  traces  of  them  are  sometimes  seen  in  the  adult. 

'  In  the  kidney  of  the  horse  the  renal  columns  dip  in  between  the  pyramids  very  super- 
ficially as  compared  ^\'ith  the  arrangement  in  the  human  kidney.  Breuer  states  that  the  pyra- 
mids are  40  to  64  in  number,  and  are  arranged  in  four  rows.     Only  the  middle  ones  are  distinct. 


474 


THE  URINARY  ORGANS  OF  THE  HORSE 


duct.  It  lies  in  the  sinus  of  the  kidney,  and  it  is  funnel-shaped,  l)ut  flattened  dorso- 
ventrally.  The  renal  crest'  (Pai)illa  communis)  projects  into  the  outer  part  of 
the  pelvis  in  the  form  of  a  horizontal  ridge  with  a  concave  free  edge.  The  tubules 
of  the  middle  part  of  the  medullary  substance  open  on  this  crest  into  the  pelvis. 
The  tubules  from  each  end  of  the  kidney  do  not  open  into  the  pelvis  proper  (Rcces- 
sus  medius),  but  into  two  long,  narrow  diverticula  (Recessus  terminales),  which 
proceed  from  it  toward  the  poles  of  the  kidney.  The  wall  of  the  pelvis  consists 
of  three  layers.  The  external  fibrous  coat  or  adventitia  is  continuous  with  the 
supporting  tissue  of  the  kidney.  Tlie  muscular  coat  consists  of  longitudinal  and 
circular  fibers.     The  mucous  coat  does  not  cover  the  renal  crest,  nor  is  it  continued 


Arched  collecting 
tubule 
Siriiight  colhcl- 
ing  liihiilc 
Distal  coiiro- 
liUed  tubule 
Renal  (Malpig- 
hinri)  corpuscle 
Proximal  convo- 
luted tubule 
Loup  of  Henle 

Collecting  tubule 


Arteria  arci-    . 
formis 


Large  collecting 
tubule 


Papillary  duct 


Artery  of  capsule 

Interlobvlar 
artery 


Capillary  net- 
irork.  Vas 
afferens 

Artcriola  recta 
apuria 


.M Glomerulus 


Vetia  arciformis 


"Z_J: 


Fig.  380. — Dhorammatic  Scheme  of  Uriniferou.s  Tubules  and  Blood-vessels  of  Kidney. 
Drawn  in  part  from  the  desrriptions  of  Golubew  (Bohm.  Davidoff.  ami  Huber). 

into  the  diverticula  of  the  pelvis.  It  has  a  yellowish  tinge,  and  presents  numerous 
folds.  It  contains  glands  (Cdandulse  pelvis  renalis)  which  secrete  the  thick  mucus 
always  found  in  the  pelvis. 

Renal  Tubules— The  parenchyma  or  proper  substance  of  the  kichiey  i.s  eoniposed  of  the 
small  renal  or  uriniferous  tubules  ('rnlmli  renalcs),  which  are  very  close  together  ami  have  a 
complicated  course.  Each  tubule  begins  in  a  thin-walled,  spherical  dilatation  or  capsule,  which  is 
invajiinated  to  receive  a  tuft  of  looped  capillaries  termed  a  glomerulus;  these  two  structures 
constitute  a  renal  (or  Malpighian)  corpuscle;  the  corpuscles  are  visible  as  minute  red  or  dark 
spots  in  th:;  convoluted  part  of  the  cortex.  Succeeding  this  is  a  short  narrow  neck,  beyond 
which  the  tubule  becomes  wide  and  convoluted,  forming  the  proximal  convoluted  tubule,  .and 
enters  the  radiate  portion  of  the  cortex.  It  then  gradually  narrows  and  enters  the  intermediate 
zone;  becoming  very  narrow  antl  nearly  straight,  it  descends  for  a  variable  distance  into  the  medul- 
lary substance,  turns  sharply  upon  itself,  and  returns  to  the  cortex,  forming  thus  the  loop  of 
Henle,  with  its  descending  and  ascending  limbs.     In  the  convoluted  part  of  the  cortex,  it  widens 

'  The  crest  is  the  result  of  fu.sion  of  the  papilla;  or  apices  of  the  pyramids  in  the  embryo. 


THE    URETERS ^THE    URINARY    BLADDER  475 

and  liccomes  tortuous,  I'onstituting  the  distal  convoluted  tubule.  The  tubule  then  narrows, 
enters  a  medullary  ray,  and  opens  with  other  tubules  into  a  straight  collecting  tubule;  this  passes 
axially  through  a  pyramid,  and  unites  with  other  collecting  tubules  to  form  the  relatively  large 
papillary  ducts,  which  open  into  the  renal  pelvis. 

Stioma. — The  interstitial  tissue  forms  a  reticulum  throughout  which  supports  the  tubules 
and  blood- ve.s.sels.  It  is  very  scanty  in  the  cortex,  much  more  abundant  in  the  medulla,  in  which 
it  incrc:iscs  in  amount  toward  the  pelvis. 

Blood-supply. — The  kidneys  receive  a  large  amount  of  lilood  through  the 
renal  arteries.  Branches  of  these  enter  at  the  hilus  and  on  the  ventral  surface  of 
the  gland,  and  reach  the  intermediate  zone,  where  they  form  anastomotic  arches 
lArteriae  arciformes).  P'rom  these  arciform  arteries  branches  pass  into  the  cortex 
and  medulla.  The  cortical  branches  (Arterise  interlobulares)  have  in  general  a 
radial  course  between  the  cortical  lobules,  and  give  off  short  lateral  branches,  each 
of  which  ends  as  the  afferent  vessel  (Vas  afferens)  of  a  renal  corpuscle.  The  blood 
is  carried  from  the  glomerulus  liy  a  smaller  efferent  vessel,  which  breaks  up  im- 
meiliately  into  capillaries  which  form  networks  around  the  tubules.  The  medul- 
lary branches  descend  in  the  pyramids,  forming  in  them  bundles  of  straight  twigs 
(Arteriolae  rectae). 

The  veins  correspond  in  general  to  the  arteries.  In  the  superficial  part  of 
the  cortex  the  veins  form  star-like  figures  (\'enre  stellatte)  by  the  convergence  of 
several  small  radicles  to  a  common  trimk. 

Lymph  Vessels. — These  maj^  be  divided  into  two  sets,  capsular  or  superficial, 
and  parenchymatous  or  deep. 

Nerve-supply. — The  nerves  are  derived  from  the  renal  plexus  of  the  sym- 
pathetic, and  form  a  plexus  around  the  vessels. 


THE  URETERS 

The  ureters  are  the  narrow  part  of  the  excretory  ducts  of  the  kidneys.  Each 
l)egins  at  the  renal  pelvis  and  terminates  at  the  bladder.  It  is  about  ^  to  ^  inch  (ca. 
()to8  mm.)  in  diameter,  and  its  average  length  is  about  28  inches  (ca.  70  cm.).  The 
abdominal  part  ( Pars  abdominalis)  of  each  ureter  emerges  ventrally  from  the  hilus 
of  the  kidney,  and  curves  backward  and  inward  towartl  the  lateral  face  of  the 
posterior  vena  cava  (right  side)  or  the  posterior  aorta  (left  side).  They  then  pass 
almost  straight  backward  in  the  subperitoneal  tissue  on  the  surface  of  the  psoas 
minor,  cross  the  external  iliac  vessels,  and  enter  the  pelvic  cavity.  The  pelvic 
part  (Pars  pelvina)  passes  backward  and  a  little  downward  on  the  lateral  wall  of 
the  pelvic  cavity,  tiu-ns  inward,  and  pierces  the  dorsal  wall  of  the  bladder  near  the 
neck. 

In  the  male  the  pelvic  part  enters  the  urogenital  fold  and  crosses  the  vas 
deferens.  In  the  female  the  ureter  is  situated  in  the  greater  part  of  its  cour-se  in 
the  dorsal  part  of  the  broad  ligament  of  the  uterus. 

The  wall  of  the  ureter  is  composed  of  three  coats.  The  outer  fibrous  coat 
(Tunica  adventitia)  is  composctl  of  loose  fibrous  tissue.  The  muscular  coat 
(Tunica  muscularis)  consists  of  inner  and  outer  layers  of  longitudinal  fil)ers,  with 
a  stratum  of  circular  fibers  between  them.  The  mucous  membrane  (Tunica 
mucosa)  is  covered  with  transitional  epithelium;  glands  (Glandulffi  mucosa 
ureteris)  resembling  those  of  the  renal  pelvis  occur  in  the  first  three  or  four  inches 
of  the  ureter. 

THE  URINARY  BLADDER 

The  urinary  bladder  (\esica  urinaria)  (Figs.  270,  271,  272)  differs  in  form,  size, 

and  position  according  to  the  amount  of  its  contents.     When  empty  and  contracted, 

it  is  a  dense,  pyriform  mass,  about  the  size  of  a  fist,  lies  on  the  ventral  wall  of  the 

pelvic  cavit}',  and  does  not  reach  to  the  inlet.     AVhen  moderately  filled,  it  is  ovoid 


476  THE    URINARY    ORGAN'S    OF   THE    HORSE 

in  form,  and  extends  a  variable  distance  along  the  ventral  al)(Iominal  wall.  Its 
physiological  capacity  varies  greatly,  but  may  be  estimated  approximately  at 
about  three  or  four  quarts. 

The  anterior  rounded  blind  end  is  termed  the  vertex ; '  on  its  middle  is  a  mass 
of  cicatricial  tissue  (Centrum  verticis),  a  vestige  of  the  urachus,  which  in  the  foetus 
forms  a  tubular  connection  between  the  bladder  and  the  allantois.  The  body  or 
middle  part  (Corpus  vesicae)  is  rountled,  and  is  .somewhat  flattened  dorso-ventrally, 
except  when  distended.  It  presents  two  surfaces,  dorsal  and  ventral,  the  former 
being  the  more  strongly  convex,  especially  in  its  posterior  part  in  front  of  the  en- 
trance of  the  ureters."  The  posterior  narrow  extremity,  the  neck  (Collum  vesicse), 
joins  the  urethra. 

The  relations  of  the  bladder  vary  according  to  the  degree  of  fullness  of  the 
organ,  and  also  differ  in  important  respects  in  the  two  sexes.  The  ventral  surface 
lies  on  the  ventral  wall  of  the  pelvis,  and  extends  forward  on  the  abdominal  wall  as 
the  bladder  fills.  The  dorsal  surface  in  the  male  is  related  to  the  rectum,  the 
urogenital  fold,  the  terminal  parts  of  the  vasa  deferentia,  the  vcsiculae  seminales, 
and  the  prostate;  in  the  female  it  is  in  contact,  instead,  with  the  body  of  the 
uterus  and  the  vagina.  The  vertex  of  the  full  bladder  is  related  to  coils  of  the  small 
intestine  and  small  colon,  and  to  the  pelvic  flexure  of  the  large  colon. 

Fixation. — Displacement  of  the  bladder  is  limited  chiefly  bj-  three  iioritoneal 
folds,  termerl  the  middle  and  lateral  ligaments  (Figs.  257,  272).  The  middle  liga- 
ment (Plica  umbilicalis  media)  is  a  median  triangular  fold,  formed  by  the  reflection 
of  the  peritoneum  from  the  ventral  surface  of  the  bladiler  on  to  the  ventral  wall  of  the 
pelvis  and  alidomen.  In  the  new-born  animal  it  is  extensive  and  reaches  to  the  um- 
bilicus; in  the  adult  it  is  usually  much  reduced  in  length  relatively.  It  contains  ela.s- 
tic  and  muscular  fillers  in  its  posterior  part.  The  lateral  ligaments  (Plica-  uniliilicales 
laterales)  stretch  from  the  lateral  aspects  of  the  l)ladder  to  the  lateral  jjchir  walls. 
Each  contains  in  its  free  edge  a  round,  firm  banil.  the  round  or  umbilical  ligament 
(Lig.  umbilicale  s.  teres);  this  is  the  remnant  of  the  large  Uv\a\  umbilical  artery, 
the  lumen  of  which  in  the  adult  is  verj'  small.  The  retroperitoneal  jiart  of  the 
bladder  is  attached  to  the  surrounding  parts  by  loose  connective  tissue,  in  which 
there  is  a  quantity  of  fat.  It  is  evident  that  the  posterior  part  of  the  bladder 
has  a  definite  fixed  position,  while  its  anterior  part  is  movatile. 

Structure. — The  wall  of  the  bladder  consists  of  a  partial  ])criton(>al  investment, 
the  muscular  coat,  and  the  mucous  lining. 

The  serous  coat  (Tunica  serosa)  covers  the  greater  part  of  the  dorsal  surface, 
from  which  it  is  reflected  in  the  male  to  form  the  urogenital  fokl;  in  the  female 
it  passes  on  to  the  vagina,  forming  the  vesico-genital  pouch.  \'entrally  the  peri- 
toneum covers  only  the  anterior  half  or  less  of  the  Isladtler,  and  is  reflected  posteri- 
orly on  to  the  ]ielvic  floor. 

The  muscular  coat  (Tunica  muscularis)  is  relatively  thin  when  the  bladder  is 
full.  It  is  unstriped,  pale,  and  not  clearly  divided  into  layers,  but  has  rather  a 
plexiform  arrangement.  Longitudinal  fibers  occur  on  the  dorsal  and  ventral  sur- 
faces, but  laterally  they  become  oblique  and  decussate  with  each  other.  A  dis- 
tinctly circ'ular  arrangement  is  found  at  the  neck,  where  the  fibers  form  a  sphincter 
(Annulus  urethralis). 

The  mucous  coat  (Tunica  nuicosa)  is  pale  and  thin.  It  is  in  general  attached 
by  a  highly  elastic  submucosa  to  the  muscular  coat,  and  forms  numerous  folds 
when  the  organ  is  empty  and  contracted.  It  is  motlified  dorsally  in  the  vicinity 
of  the  neck  over  a  triangular  area,  termed  the  trigonum  vesicae ;  the  angles  of  this 
space  lie  at  the  orifices  of  the  two  ureters  and  the  urethra,  which  are  close  together. 

'  This  is  commonly  termed  the  fundus  by  veterinarians,  but  is  not  the  homologue  of  tlie 
fundus  of  tlie  human  Ijladdcr. 

'  This  would  correspond  to  the  fundus  vesicae  of  man. 


THE    ADRENAL    BODIES  477 

Here  the  mucous  membrane  is  closely  attacheil  and  does  not  form  fokls.  From 
each  ureteral  oriiice  (Orificium  ureteris)  a  fokl  of  mucous  membrane  (Plica  urctcr- 
ica)  passes  backward  and  inward,  uniting  with  its  fellow  to  form  a  median  crest 
(Crista  urethralis)  in  the  first  part  of  the  urethra.  The  ureteral  orifices  arc  a  little 
more  than  one  inch  (ca.  3  cm.)  apart.  The  terminal  part  of  the  ureter,  after  pierc- 
ing the  muscular  coat  of  the  bladder,  passes  for  a  distance  of  about  an  inch  (ca. 
2  to  3  cm.)  between  the  muscular  and  mucous  coats  before  piercing  tlie  latter;  this 
arrangement  constitutes  a  valve  which  prevents  absolutely  the  return  of  the  urine 
from  the  bladder  into  the  ureter.  The  internal  urethral  orifice  (Orificium  urethrse 
internum)  lies  at  the  apex  of  the  trigonum,  and  is  about  an  inch  and  a  half  (ca. 
4  cm.)  behind  the  ureteral  orifices.  The  mucous  membrane  is  covered  with  transi- 
tional epithelium  like  that  of  the  ureter  and  renal  pelvis.  It  contains  lymph 
nodules. 

Blood-supply. — This  is  derived  chiefiy  from  the  vesico-prostatic  branch  of 
the  internal  pudic  artery.  It  is  also  supplied  by  small  twigs  from  the  obturator 
and  umbilical  arteries.  The  veins  terminate  chiefly  in  the  internal  pudic  veins. 
They  form  plexuses  i^osteriorl.y. 

Lymph  Vessels. — These  form  plexuses  on  both  surfaces  of  the  muscular  coat. 
They  go  to  the  internal  iliac  and  lumbar  glands. 

Nerves. — The  nerves  are  derived  from  the  pelvic  plexus  (sympathetic  and 
ventral  branches  of  third  and  fourth  sacral  nerves).  Thej'  form  a  plexus  in  the 
submucosa  which  presents  microscopic  ganglia. 

In  the  foetus  and  new-born  animal  the  bladder  is  situated  chiefly  in  the  abdomen.  It  is 
long,  narrow,  and  fusiform.  Its  aljdominal  end  lies  at  the  umbilicus,  through  which  it  is  con- 
tinued by  the  urachus  to  the  extra-embryonic  part  of  the  allantois.  As  the  pelvis  increases  in 
size  and  tlie  large  intestine  grows,  the  bladder  retract.s  into  the  pelvis  and  changes  its  form. 

The  urethra  will  be  described  with  the  genital  organs. 


THE  ADRENAL  BODIES 

The  adrenal  bodies  or  suprarenal  glands  (Glandulfe  suprarenales)'  are  two 
small,  flattenetl  organs,  which  lie  in  contact  with  the  anterior  part  of  the  inner 
border  of  the  kidneys  (Figs.  376,  377).     Thej'  are  ductless. 

In  the  horse  they  are  red-brown  in  color,  about  three  and  a  half  to  four  inches 
(ca.  9  to  10  cm.)  long,  one  to  one  and  a  half  inches  (ca.  3  to  4  cm.)  wide,  and  abotit 
half  an  inch  or  more  ( ca.  1  to  5  cm.)  in  thickness.  The  weight  varies  from  one  to  two 
ounces  (ca.  28  to  oG  gm.). 

The  right  adrenal  is  related  internally  to  the  posterior  vena  cava,  to  which  it  is 
atlherent.  Its  anterior  part  curves  dorsally  around  the  inner  border  of  the  right 
kidney.  Its  posterior  part  is  flattened  and  is  related  ventrally  to  the  pancreas 
and  ciecum.  dorsally,  to  the  right  renal  vessels.  The  anterior  extremity  is  con- 
cealed in  the  renal  impression  of  the  liver;    the  posterior  is  related  to  the  ureter. 

The  left  adrenal  is  a  little  shorter  than  the  right  one,  and  its  extremities  are 
rounded;  it  is  usually  curved,  so  that  its  internal  border  partly  embraces  the 
anterior  mesenteric  artery.  Its  dorsal  surface  is  related  to  the  kidney,  the  renal 
artery,  the  aorta,  and  the  left  coeliaco-mesenteric  ganglion.  The  ventral  surface 
is  in  relation  with  the  left  extremity  of  the  pancreas  and  the  root  of  the  great 
mesentery.  The  posterior  extremity  often  curves  inward  behind  the  anterior 
mesenteric  artery;  it  is  related  behind  to  the  left  renal  vein. 

When  hardened  in  mlu  tlie  adrenals  present  se\-eral  features  not  e\'ident  in  the  soft  organs. 
The  anterior  part  of  the  riglit  adrenal  is  tmsted  upward  and  outward  over  the  inner  margin  of 
the  kidney,  so  tliat  this  part  is  prismatic  and  has  three  surfaces;  of  these,  the  concave  outer  one 
is  applied  to  the  kidney,  the  dorsal  one  is  related  to  the  right  crus  of  the  diaphragm  and  tlie  liver, 

■From  the  standpoint  of  comparative  anatomy  the  term  "adrenal"  seems  decidedly 
preferable  to  "suprarenal." 


478 


URINARY    ORGANS    OF   THE    OX 


and  the  inner  one  is  in  contact  with  the  posterior  vena  cava.  The  anterior  mesenteric  artery 
is  nearly  always  more  or  less  enlarged  as  a  result  of  verminous  arteritis,  and  the  form  and  degree 
of  curvature  of  the  left  adrenal  seem  to  vary  in  conformity  with  the  condition  of  the  artery. 

Structure. — The  fibrous  capsule  adheres  intimately  to  the  surface  of  the  organ. 
It  contains  elastic  fibers,  and  in  its  deep  part  unstriped  muscle-fibcr.s.  From  it 
trabecular  pass  radially  into  the  substance,  blending  with  the  fine  supporting  reti- 
culum. The  parenchyma  consists  of  a  cortical  and  a  medullary  portion.  The 
cortical  substance  (Sul)stantia  corticalis)  is  red-brown  in  color,  and  is  clearly 
distinguishable  from  the  yellow  medullary  substance  (Substantia  medullaris). 
A  large  central  vein  ( N'ena  centralis)  is  visible  on  cross- 
sections. 

The  cells  of  the  corte.x  are  arranged  in  chains  of  one  or  two 
rows.  In  the  peripheral  portion  the  cells  are  of  high  cylinilrical 
shape,  and  the  chains  form  connecting  loops;  Giinther  has  pro- 
posed the  name  zona  arcuata  for  this  part,  instead  of  the  usual 
term  zona  glomerularis.  More  deeply  the  chains  are  distinctly 
palisade-like,  and  this  region  is  called  the  zona  fasciculata.  Next 
to  the  medulla  is  the  zona  reticularis,  in  which  the  chains  form 
a  network.  The  cells  in  these  two  zones  are  polygonal  and  con- 
tain a  brown  pigment. 

The  cells  of  the  medulla  are  arranged  in  irregular  groups  or 
form  sheaths  around  the  veins.  They  react  to  chromic  salts  by 
assuming  a  yellow  or  yellow-brown  color,  and  are  termed  chromaf- 
fin cells;  they  share  this  peculiarity  with  certain  cells  of  the  sym- 
pathetic ganglia  and  paraganglia,  with  which  they  are  probably 
related  genetically.  The  alkaloid  adrenalin  appears  to  be  formed 
in  the  medullary  cells. 

Vessels  and  Nerves. — The  adrenals  receiv(>  a  rela- 
tively large  bloixl-siipply  through  the  adrenal  arteries 
(Aa.  suprarenales),  which  arise  from  the  renal  arteries 
or  from  the  aorta  directly.  The  veins  terminate  in  the 
posterior  vena  cava  and  the  left  renal  vein.  The  lymph 
vessels  go  to  the  renal  hinjih  glands.  The  numerous 
nerves  are  derived  from  the  sympathetic  system 
through  the  solar  and  renal  plexuses.  Tlie  fillers 
form  a  rich  interlacement,  especially  in  the  medullary  sub.stance.  Ganglion  cells 
are  fountl  chiefly  in  the  medulla,  but  also  occur  in  the  deeper  part  of  the  cortex. 


Fig.    381. — .\dhenal    Body     of 
Horse;    Horizont.\l  Sec- 
tion, Reduced. 
/,  Capsule;    £,   2\  cortical 

substance;  3,  medullary  substance; 

4,  blood-vessel  in  section.     (From 

Leisering's  Atlas,  reduced.) 


URINARY  ORGANS  OF  THE  OX 

The  kidneys  are  superficially  divided  into  polygonal  lobes  by  fissures  of  vari- 
able depth.  The  lobes  vary  in  size,  and  are  commonly  about  twentj'  to  twenty- 
five  in  nuniljer.     The  fissures  are  filled  with  fat. 

The  right  kidney  has  an  elongated  elliptical  outline,  and  is  flattened  dorso- 
ventrally.  It  lies  ventral  to  the  last  rib  and  the  first  two  or  three  hnubar  transverse 
processes.  The  dorsal  surface  is  rounded,  and  is  in  contact  chiefly  with  the  sub- 
lumbar  muscles.  The  ventral  surface  is  less  convex,  and  is  related  to  the  liver, 
pancreas,  duodenum,  and  terminal  part  of  the  colon.  The  hilus  is  situated  on  the 
anterior  part  of  this  surface  near  the  inner  border.  The  internal  border  is  nearly 
straight,  and  lies  parallel  with  the  ])osterior  vena  cava.  The  external  liorder  is 
convex.  The  anterior  extremity  occupies  the  renal  impression  of  the  liver,  and  is 
capped  l)y  the  adrenal  body. 

The  left  kidney  occupies  a  remarkable  position,  and  when  hardened  in  situ, 
differs  strongly  in  form  from  the  right  one.  When  the  rumen  is  full,  it  pushes  the 
kidney  backward  and  across  the  median  plane,  so  that  it  is  situated  on  the  right 


VRIXARY    ORGANS    OF   THE    OX 


479 


side,  behind  and  at  a  lower  level  than  the  right  kidney.  It  then  lies  usuallj-  under 
the  third,  fourth,  and  fifth  hnnbar  vertehrie.  When  the  rumen  is  not  full,  the  left 
kidney  may  lie  partly  to  the  left  of  the  median  plane.  It  has  three  surfaces.  The 
dorsal  surface  is  convex,  and  presents  on  its  antero-external  part  the  hilus,  which 
opens  outward.     The  ventral  surface  is  related  to  the  intestine.     The  third  face 

External  border 


Anterior  extremity 


Ureter        Renal  artery 
Fill.  382. — Right  Kidney  of  Ox,  Ventral  Face. 
Organ  hanienetl  in  situ.     Fat  has  been  removed  from  fisvures  herween  lobes. 

is  often  more  or  less  flattened  by  contact  with  the  rumen,  and  may  be  termetl  the 
ruminal  surface.     The  anterior  extremity  is  small,  the  posterior  large  and  rounded. 

The  preceding  stateraent.s  refer  to  the  adult  subject,  and  are  based  on  investigations  made  on 
living  subjects,  and  studies  of  frozen  sections  and  material  hardened  in  situ.  In  the  young 
calf  the  kidneys  are  almost  symmetrically  placed,  but  as  the  rumen  grows  it  pushes  the  left  kidney 
to  the  right  and  backward  pari  passu.  It  also  usually  causes  a  rotation  of  the  kidney,  so  that  the 
primary  dorsal  surface  comes  to  lie  almost  in  a  sagittal  plane.  Further,  the  gland  is  bent  so  that 
the  hilus  is  largely  closed  up  and  faces  outward  (to  the  right).  In  very  fat  subjects  the  three- 
sided  appearance  of  the  kidney  may  be  absent,  and  about  one-third  or  more  may  remain  to  the  left 
of  the  median  plane,  even  where  the  rumen  is  pretty  well  filled. 

The  kidneys  are  embedded  in  a  large  amount  of  perirenal  fat.     The  weight 


Renal  artery 
Fig.  383. — Frontal  Section  op  Kidnet  of  Ox. 
L,  Lobes  of  cortex:   P.  papillse;   C,  calyx  major;    c*,  calyces  minores. 


of  a  kidney  is  about  20  to  2.5  ounces  (ca.  570  to  700  gm.),  the  left  one  being  usuallj' 
an  oimce  or  more  the  heavier.     The  two  form  about  34  P^r  cent,  of  the  laody-weight. 

The  right  kidney  measures  about  S  to  10  inches  (ca.-20  to  25  cm.)  in  length,  4  to  .5  inches  (ca. 
10  to  12  cm.)  in  width,  and  2I2  to  .3  inches  (ca.  7  cm.)  in  thickness.  The  left  kidney  is  one  or 
two  inches  (ca.  2  to  .5  cm.)  shorter,  but  its  posterior  part  is  much  thicker  than  the  right  one. 

Structure. — The  hilus  is  equivalent  to  the  hilus  and  sinus  of  the  kidney  of  the 
horse;  in  the  right  kidnej'  it  is  an  extensive  elliptical  cavity,  in  the  left,  a  deep 
fissure.     The  pelvis  is  absent.     The  ureter  begins  at  the  junction  of  two  wide, 


480 


URINARY    ORGANS    OF   THE    OX 


thiii-wallod  tulies,  the  calyces  majores ;  tho  anterior  cal>-x  is  usually  the  larger. 
Each  calyx  major  sivcs  off  a  number  of  branches,  and  these  divide  into  several 
funnel-shaped  calyces  minores,  each  of  which  embraces  a  renal  papilla.  The 
space  not  occupied  by  tlie  calyces  and  vessels  is  filled  with  fat. 

On  .section  through  the  kidney  tlio  renal  pyramids  are  easily  made  out.  The 
blunt  apex  of  each  pyramid,  the  papilla  renalis,  projects  into  a  calyx  minor.  On 
each  papilla  are  small  orifices  (Foramina  papillaria)  by  which  the  terminal  renal 
tubules  (Ductus  papillares)  open  into  the  calj-x.  The  renal  columns  are  much 
more  distinct  than  in  the  horse. 

At  the  hilus  the  renal  artery  is  dorsal,  the  vein  in  tlie  middle,  and  the  ureter 
ventral;   a  quantity  of  fat  surrounds  these  structures  in  the  hilus. 

The  kidneys  of  the  sheep  are  bean-shaped  antl  smooth,  without  any  superficial 
lobation.  The  soft  organ  is  regularly  elliptical  in  form,  with  convex  dorsal  and 
ventral  surfaces  and  rounded  e.xtremities;  its  length  is  about  2J/2  to  3  inches  (ca. 
5  to  8  cm.),  its  width  about  13^2  to  2  inches  (ca.  4  to  5  cm.),  and  its  thickness  a  little 


Fig.  385.— Kidney  oi    -ii 
/,  Cortical  substanc 
S,  renal  crest;  It,  renal  pelv 
ing's  .\tla.s.  reduced.) 


2,  ineLluUary   substance; 
5,  ureter.     (From  Leiser- 


more  tlian  1  inch  (ca.  3  cm.).  In  ])osition  tliey  resemble  those  of  the  ox,  excejit  that 
the  right  one  is  usually  a  little  further  back,  and  lies  under  the  first  three  huubar 
transverse  processes.  The  average  weight  of  each  is  about  four  ounces.  The 
hilus  is  in  the  middle  of  the  inner  border.  There  is  a  renal  crest  or  common  papilla 
formed  by  the  fusion  of  twelve  to  sixteen  pyramids. 

When  tho  rumen  is  full,  the  left  kidney  (which  is  attuehed  by  a  short  nie.sentery)  usually 
lies  entirely  to  tlic  right  of  tho  median  plane,  under  the  third,  fourth,  and  fifth  lumbar  trans- 
verso  processes.  The  primitive  dorsal  surface  has  become  ventro-m.edial,  and  is  sonienh:U 
flattened  by  contact  with  the  rumen. 

The  ureters  are,  in  general,  like  those  of  the  horse,  except  in  regartl  to  tlie 
first  part  of  the  left  one,  which  has  a  peculiar  course,  in  conformity  with  the  remark- 
al)le  position  of  the  kidney.  It  l)egins  at  the  ventral  part  of  the  hilus  (which  faces 
toward  the  right),  cinves  upward  and  inward  over  the  outer  aspect  of  the  kidney 
to  its  dorsal  surface,  crosses  the  median  plane,  and  runs  backward  on  the  left  side. 

The  bladder  is  longer  and  narrower  than  that  of  the  horse,  and  extenils  further 
forward  on  the  abdominal  floor.  The  peritoneal  coat  extends  backward  further 
than  in  the  horse. 


URINARY    ORGANS    OF   THE    PIG 


481 


THE  ADRENAL  BODIES 

The  right  adrenal  lies  again.st  the  inner  part  of  the  anterior  pole  of  the  right 
kidney.  When  hardened  in  situ  it  is  pyramidal  in  form.  Its  inner  surface  is 
flattened  and  is  in  contact  with  the  right  crus  of  the  diaphragm.  The  outer  sur- 
face is  convex  and  lies  in  the  renal  impression  of  the  liver.  The  ventral  surface  is 
grooved  for  the  po.sterior  vena  cava;  on  this  surface  a  relatively  large  vein  emerges 
near  the  apex.  The  base  is  concave  and  rests  obliquely  against  the  anterior  pole 
of  the  kidney.  The  apex  fits  into  the  angle  between  the  posterior  vena  cava  and 
the  dorsal  liorder  of  the  liver. 

The  left  adrenal  lies  on  the  inner  face  of  the  posterior  vena  cava  just  behind 
the  anterior  mesenteric  artery,  and  is  therefore  practically  median  in  position. 
It  is  flattened,  and  irregularly  triangular  or  heart-shaped  in  outline.     Its  left  face 


Posterior  pole 


Groove  for  vena  cava 
J 


Anterior  pole 

Fig.    386. — Left    .\drenal   of   Ox.  Ventral  View: 
Hardened  in  situ. 


_   Anterior  pole 


Fig.  387. — Right   .\drenal   of  Ox,   Ventral  View: 


is  related  to  the  dorsal  sac  of  the  rumen.     Its  right  face  is  related  to  the  vena  cava, 
and  presents  a  large  emergent  vein.     The  posterior  border  or  base  is  deeply  notched. 

It  is  interesting  to  note  that  the  left  adrenal  does  not  migrate  with  the  kidney,  but  retains 
its  primitive  position;  it  lies  usually  about  two  inches  (ca.  5  cm.)  in  front  of  a  transverse  plane 
through  the  anterior  pole  of  the  left  kidney. 

The  adrenals  of  the  sheep  are  both  bean-shaped.  The  right  one  lies  along 
the  anterior  part  of  the  inner  border  of  the  kidney,  at  the  angle  of  the  junction  of 
the  right  renal  vein  and  the  posterior  vena  cava.  It  is  a  little  over  an  inch  (ca. 
3  cm.)  long,  and  about  an  inch  (ca.  12  to  15  mm.)  ^^ide.  The  left  adrenal  is  longer, 
flatter,  and  somewhat  bent.  It  lies  across  the  left  renal  vein,  to  which  it  is  attached, 
but  is  not  in  contact  with  the  kidney. 


URINARY  ORGANS  OF  THE  PIG 
The  kidneys  are  smooth  and  bean-shaped;    they  are  more  flattened  dorso- 
ventrally,  more  elongated,  and  smaller  at  the  extremities  than  those  of  the  dog. 
The  length  is  about  twice  the  width.     They  are  usually  almost  sjonmetrically  placed 
31 


482 


URINARY    ORGANS    OF   THE    PIG 


pKrag 


tiki  A    •' 

Fig.  3sS. — KinKETS  OF  Pin  m  sidi,  Vicntrai 
C.a.,  Hepatic  artery:    Ma.,  gastro-splenic  ai 


Cortical  s^tbslance 


Medullary  substance 


Papilla: 


^  Calyces  minores 


Via.  3Sa — Ibontal  Section  oi    Kidney  of  Pig. 


DRINARY    ORGANS    OF   THE    DOG  483 

on  either  side  of  the  first  four  lumbar  vertebrae.  (Variations  in  position  are  not  rare, 
and  involve  the  left  kidnej^  oftener  tlian  the  right.  The  former  has  been  found 
near  the  pelvic  inlet.)  The  external  border  lies  against  the  flank  parallel  with  the 
edge  of  the  longissimus  muscle.  The  posterior  extremity  usually  lies  about  mid- 
way between  the  last  rib  and  the  external  angle  of  the  ilium.  The  anterior  ex- 
tremity of  the  right  kidney  usually  extends  as  far  forward  as  the  last  rib,  liut  has 
no  contact  with  the  liver. 

The  weight  of  the  kidney  of  a  medium-sized  pig  is  about  seven  to  nine  ounces 
(200  to  2.30  grams).  The  ratio  of  their  combined  weight  to  that  of  the  body  is 
about  1  :  1.50-200. 

Structure. — The  hilus  is  about  in  the  middle  of  the  inner  border.  The  pelvis 
is  funnel-shapetl,  anil  diviilcs  into  two  calyces  niajores,  which  pass  in  a  curve  for- 
ward and  backward  respectively,  and  give  off  some  eight  to  twelve  short  calyces 
minorcs;  each  of  the  latter  contains  a  papilla  Some  papillse  are  narrow  and  coni- 
cal, and  correspond  to  a  single  pyramid;  others  are  wide  and  flattened,  and  result 
from  the  fusion  of  two  or  more  pjTamids;  some  project  directly  through  the  wall 
of  the  pelvis  without  the  formation  of  a  calyx.  The  renal  pyramids  are  distinct, 
but  it  is  apparent  that  some  are  compound,  i.  c,  formed  by  fusion  of  primitively 
separate  pyramids.  The  renal  artery  enters  the  ventral  part  of  the  hilus,  and  the 
ureter  leaves  it  dorsally. 

The  only  special  feature  in  regard  to  the  ureter  is  that  it  is  at  fir.st  relatively 
wide  and  gradually  tliminishes  in  caliber. 

The  bladder  is  relatively  very  large;  when  full,  it  lies  chiefly  in  the  abdomi- 
nal cavity.     It  is  almost  completely  covered  with  peritoneum. 


URINARY  ORGANS  OF  THE  DOG 

The  kidneys  are  relatively  large,  forming  about  j^jt  to  ^^^  of  the  body-weight; 
the  weight  of  the  kidney  of  a  medium-sized  dog  is  about  two  ounces  (ca.  50  to  60 
grams).  They  are  both  bean-shaped,  thick  dorso-ventrally,  with  a  rounded  ven- 
tral surface  and  a  less  convex  dorsal  surface;   the  surfaces  are  smooth. 

The  right  kidney  (Fig.  343)  is  not  subject  to  much  variation  in  position;  it 
is  situated  usually  under  the  last  rib  and  the  first  three  lumbar  transverse  processes. 
Its  anterior  part  lies  in  the  deep  renal  impression  of  the  liver;  its  posterior  part  is 
related  to  the  sublumbar  muscles  dorsally,  and  the  pancreas  and  duodenum 
ventrally. 

The  left  kidney  (Fig.  342)  is  subject  to  some  variation  in  position;  this  is  due 
to  the  fact  that  it  is  loosely  attached  by  the  peritoneum,  and  is  aiTected  by  the  de- 
gree of  fullness  of  the  stomach.  When  the  stomach  is  nearly  empty,  the  kidney 
usually  lies  under  the  transverse  processes  of  the  second,  third,  and  fourth  lumbar 
vertebrje,  so  that  its  anterior  pole  is  opposite  to  the  hilus  of  the  right  kidney.  As 
the  stomach  fills  it  pushes  the  left  kidney  backward,  so  that  the  anterior  pole  of 
the  latter  may  be  opposite  the  posterior  pole  of  the  right  kidney.  The  dorsal 
surface  is  related  to  the  sublumbar  muscles.  The  ventral  surface  is  in  contact 
with  the  terminal  part  of  the  colon  (Colon  descendens).  The  external  border  is 
related  to  the  spleen  and  the  flank.  The  anterior  extremity  touches  the  stomach 
and  the  left  extremity  of  the  pancreas. 

The  external  border  of  the  left  kidney  has  considerable  contact  with  the  flank,  and  hence 
it  may  be  palpated  more  or  les.s  distinctly  in  the  living  animal  about  half-way  between  the  last 
rib  and  the  crest  of  the  ilium. 

Structure. — The  hilus  is  in  the  middle  of  the  inner  border  and  is,  relatively 


484  URINARY    ORGANS    OF   THE    DOG 

wide.  Cortex,  limiting  zone,  and  medulla  are  clearly  defined.  On  frontal  sections 
it  is  seen  that  the  medullary  substance  forms  a  horizontal  renal  crest  like  that  of 
the  horse,  but  with  the  important  difference  that  curved  ridges  proceed  dorsally 
and  ventrally  from  the  crest  somewhat  like  buttresses.  Sections  above  or  below 
the  renal  crest  often  cut  these  ridges  in  such  a  manner  as  to  give  the  appearance 
of  conical  papillse,  and  thus  tend  strongly  to  produce  a  false  impression.  The 
pelvis  is  adapted  to  this  arrangement  of  the  medullary  substance.  It  incloses  a 
central  cavity  into  which  the  renal  crest  projects,  and  is  prolonged  outward 
between  the  ridges,  forming  cavities  for  the  latter,  thus  simulating  the  appearance 
of  calyces  which  do  not  e.xist. 

The  ureters  i)resent  no  special  features. 

The  bladder  is  abdominal  in  position,  the  neck  lying  at  the  anterior  I)order  of 
the  pubic  bones.  It  is  relativelj'  large,  and  when  full,  the  vertex  may  reach  to  the 
umbilicus.     It  has  a  practically  complete  peritoneal  coat. 


THE  ADRENALS 

The  right  adrenal  lies  between  the  anterior  part  of  the  inner  border  of  the  kid- 
ney and  the  posterior  vena  cava.  It  is  somewhat  prismatic,  and  is  pointed  at 
either  end. 

The  left  adrenal  lies  along  the  posterior  aorta,  from  the  renal  vein  forward, 
but  is  not  in  contact  with  the  kidney.  It  is  elongated  and  flattened  dorso-ventrally. 
(There  is  a  furrow  on  the  ventral  surface  for  the  vein  which  crosses  it;  the  part  in 
front  of  this  furrow  is  discoid,  and  may  be  taken  for  the  entire  organ  in  a  fat 
subject.) 

The  cortex  is  pale  yellow  in  color,  the  medulla  dark  brown. 


THE  MALE  GENITAL  ORGANS 

The  male  genital  organs  (Organa  genitalia  masculina)  are:  (1)  The  two 
testicles,  the  essential  reproductive  glands,  with  their  coverings  and  appendages; 
(2)  the  vasa  deferentia,  the  ducts  of  the  testicles;  (3)  the  vesiculae  seminales; 
(4)  the  prostate,  a  musculo-glandular  organ;  (5)  the  two  bulbo-urethral  (or  Cow- 
per's)  glands;  (ti)  the  male  urethra,  a  canal  which  transmits  the  generative  and 
urinary  secretions;  (7)  the  penis,  the  male  copulatory  organ.  The  vesicula 
seminales,  the  prostate,  and  the  bulbo-urethral  glands  discharge  their  secretions 
into  the  urethra,  where  they  mix  with  the  seminal  fluid  secreted  by  the  testicles; 
hence  they  are  often  termed  the  accessory  sexual  glands. 


MALE  GENITAL  ORGANS  OF  THE  HORSE 
THE  TESTICLES 
The  testicles  (Testes)  are  situated  in  the  inguinal  region,  inclosed  in  a  diverti- 
culum of  the  abdomen  termed  the  scrotum.  Their  long  axes  are  nearly  longitu- 
dinal. They  are  ovoid  in  form,  but  considerably  compre.ssed  from  side  to  side. 
Each  presents  two  surfaces,  two  borders,  and  two  extremities.  The  internal  and 
external  surfaces  (Fades  medialis,  lateralis)  are  convex  and  smooth.  The  free 
or  ventral  border  (Margo  liber)  is  convex  in  both  directions.  The  attached  or 
dorsal  border  (iVIargo  epididymidis)  is  nearly  straight,  and  is  the  one  by  which  the 
gland  is  suspended  in  the  scrotum  by  the  spermatic  cord;  the  epididj'mis  is  at- 
tached to  this  border  and  overlies  it  externally.  The  anterior  and  posterior 
extremities  (Extremitas  capitata,  caudalis)  are  rounded. 

At  the  anterior  extremity  there  is  often  a  sessile  or  pedunculated  sac  which  contains  a  clear 
fluid;  this  is  the  appendix  testis  or  hydatid  of  Morgagni,  from  which  a  thread-like  process 
extends  backward  toward  the  vas  deferens.  It  is  regarded  as  a  remnant  of  the  ^Nlullerian  duct 
of  the  embryo. 

A  testicle  of  average  size  of  an  adult  stallion  is  aliout  four  or  five  inches  (ca. 
10  to  12  cm.)  long,  two  and  a  half  inches  (ca.  6  to  7  cm.)  high,  and  one  and  a  half  to 
two  inches  (ca.  -4  to  5  cm.)  wide;  it  weighs  about  ten  and  one  half  ounces  (ca.  300 
grams).  They  vary  much  in  size  in  different  subjects,  and  are  commonh'  of  un- 
equal size,  the  left  one  being  more  often  the  larger. 

The  epididymis  is  adherent  to  the  attached  border  of  the  testicle,  and  overlaps 
somewhat  the  e.xternal  surface.  Its  anterior  enlarged  end  is  termed  the  head 
or  globus  major  (Caput  epididymidis),  and  its  posterior,  slightly  enlarged  end  is 
the  tail  or  glolius  minor  (Cauda  epididymidis) ;  while  the  intermediate  narrow  part 
is  the  body  (Corpus  epididymidis).  The  head  is  closely  connected  with  the  testicle 
by  the  efferent  ducts  of  the  latter,  by  connective  tissue,  and  by  the  serous  memlirane. 
The  body  is  less  closely  attached  bj-  the  serous  covering,  which  forms  externally  a 
pocket  beneath  the  epididymis  termed  the  digital  fossa  (Sinus  epididymidis). 
The  tail  is  firmly  attached  to  the  posterior  extremity  of  the  testicle  by  a  short 
ligament  (Lig.  epididjTiiidis),  formed  by  a  thick  fold  of  the  tunica  vaginalis,  which 
contains  smooth  muscle-fibers;   it  is  continued  by  the  vas  deferens. 

Structure  of  the  Testicle  and  Epididymis. — The  greater  part  of  the  surface 
of  the  testicle  is  covered  by  a  serous  membrane,  the  tunica  vaginalis  propria,  which 

485 


486 


THE  MALE  GENITAL  ORGANS  OF  THE  HORSE 


is  the  visceral  layer  of  the  serous  envelop  of  the  cord  and  testicle;  this  is  reflected 
from  the  attached  border  of  the  gland,  leaving  an  uncovered  area  at  which  the  vessels 
and  nerves  in  the  spermatic  cord  reach  the  testicle.  Beneath  this  serous  covering  is 
the  tunica  albuginea,  a  strong  capsule  composed  of  dense  white  inelastic  fibrous  tissue 
and  unstriped  muscle-filiers.  From  the  deep  surface  of  this  tunic  delicate  mem- 
branous septa  (Septula  testis)  pass  into  the  glantl,  dividing  it  into  pjTamidal 
spaces,  the  bases  of  which  are  peripheral.  At  the  anterior  part  of  the  attached 
border  of  the  testicle  connective  tissue  and  smooth  muscle-fibers  jiass  into  the 
substance  of  the  glantl,  forming  the  mediastinum  testis;  from  this  the  septa 
radiate.     The  mediastinum  contains  a  network  of  fine  canals,    the  rete  testis; 


/ 


^Vs.^ 


Fir,.  390. — Ingtinal  Reoion  of  Stallion,  with  Testicles  Exposed. 
a.  a'.  Testicles;  6,  scrotum,  opened  and  reflected;  c.  tunica  vaginalis  communis,  opened  and  reflected; 
rf,  ligament  of  epididymis;  e,  tunica  vaginalis  propria  (mesorchium);  /,  vas  deferens;  {7,(7',  tail  of  epididymis;  /t,  body 
of  same;  i,  head  of  same;  k,  digital  fossa  or  sinus  epididymidis;  /,  spermatic  vessels  showing  through  tunica 
vaginalis  propria;  m,  spermatic  artery;  n,  prepuce;  n',  raph6;  o,  preputial  orifice.  (After  EUenberger-Baum, 
Toi).  .\nat.  d.  Pferdes.) 


it  is  traversed  by  blood-vessels,  which  radiate  on  the  septa  to  the  deep  face  of  the 
tunica  albuginea,  forming  a  delicate  network — the  so-called  tunica  vasculosa. 
The  spaces  imperfectly  marked  off  by  the  septa  contain  the  parenchyma  testis, 
which  consists  of  seminiferous  tubules  (Tubuli  seminiferi),  su])ported  by  loose 
intertubular  connective  tissue.  The  tubules  are  collected  into  small  masses  or 
lobules  (Lobuli  testis).  They  arc  at  first  very  tortuous  (Tubuli  contorti);  to- 
wartl  the  a])ex  of  the  lobule  they  unite  with  other  tubules,  forming  larger  straight 
tubules  (Tubuli  recti);  these  pass  into  the  mediastinum  testis,  where  they  form 
the  rete  testis.  From  the  latter  a  number  (ca.  15  to  20)  of  larger  efferent  tubules 
(^'asa  efferent ia)  ])iercc  the  albuginea  and  enter  the  head  of  the  epiflidymis. 

The  epididymis  is  covered  by  the  tunica  vaginalis  propria  and  a  thin  albuginea. 


THE    SCROTUM 


487 


Its  head  consists  of  lobules  iLdhuli  cpididymidis),  each  of  which  consists  of  a 
coiled  tubule  or  conus  vasculosus,  wliich  succeeds  a  vas  efferens.  By  the  union 
of  these  tubules  is  formed  a  siuolc  tulie,  tiic  duct  of  the  epididymis  (Ductus  ei^ididy- 
midis),  which,  by  its  coiu])lex  coils,  forms  tlic  body  and  tail  of  the  epididymis  antl 
terminates  in  the  vas  deferens.  The  tubules  and  the  coils  of  the  duct  of  the 
epididymis  are  held  together  by  connective  tissue  and  unstriped  musclc-fil)ers. 
The  tubules  and  duct  are  lined  with  ciliated  epithelium,  and  the  duct  has  a  mus- 
cular coat  which  consists  of  longitudinal  and  circular  fibers. 

Vessels  and  Nerves. — The  testicle  is  richly  supplied  with  blood  by  the  sper- 
matic artery,  a  l)ran(h  of  the  posterior  aorta.  The  artery  descends  in  the  anterior 
part  of  the  spermatic  cord,  and  is  very  tortuous  near  the  testicle;  on  reaching  the 
attached  border  of  the  gland  it  passes  backward  in  a  flexuous  manner,  giving 
branches  to  the  testicle  and  epididymis,  turns  around   the   posterior  extremity, 


Fig.   391. — Right  Testicle  axd  Spermatic  Cord  of 
Horse,  Inclosed  in  Tcnic.\  Vaginalis. 
c.  Tunica    vagioalis   communis;    g,    prominence 
caused  by  tail  of  epididymis;  p,  cremaster  externus  mus- 
cle.    (.A.fter  Ellenberger-Baura,  Top.  .\nat.  d    Pferdes.) 


Fig.  392. — Right  Testicle  and  Sperm.vtic  Cord  of 
Horse,  E.xposed. 
a'.  External  surface  of  testicle;  c.  tunica  vagin- 
alis, cut  and  reflected;  d,  ligament  of  epididymis;  e, 
mesorchium;  g,  tail,  A,  body,  f',  head  of  epididymis;  k, 
digital  fossa  or  sinus  epididymidis;  I.  spermatic  vessels 
showing  through  tunica  vaginalis  propria;  m,  end  of 
spermatic  artery.  Dotted  line  indicates  position  of  vas 
deferens  on  other  side  of  mesorchitun.  (After  EUen- 
berger-Baum,  Top.  Anat.  d.  Pferdes.) 


and  runs  forward  on  the  free  border  to  the  anterior  extremity.  It  is  partially 
embedded  in  the  tunica  albuginea,  and  detaches  lateral  branches  \\hich  ascend  in 
a  tortuous  fashion  on  each  surface  of  the  testicle;  these  give  off  small  branches 
which  enter  the  gland  on  the  septa. 

The  spermatic  veins  on  leaving  the  testicle,  form  the  pampiniform  plexus 
around  the  artery  in  the  spermatic  cord.  The  vein  which  issues  from  this  plexus 
usually  joins  the  posterior  vena  cava  on  the  right  side,  the  left  renal  vein  on  the 
left  side. 

The  nerves,  derived  from  the  renal  and  posterior  mesenteric  plexuses,  form 
the  spermatic  plexus  around  the  vessels. 


THE   SCROTUH 
The  scrotum,  in  which  the  testicles  and  the  lower  parts  of  the  spermatic  cords 
are  situated,  is  somewhat  globular  in  form,  but  is  commonly  a.symimetrical,  since 


488  THE  MALE  GENITAL  ORGANS  OF  THE  HORSE 

one  testicle — more  often  the  left — is  the  larger  and  more  dependent.  It  varies 
in  form  and  appearance  in  the  same  subject,  according  to  the  condition  of  its  sub- 
cutaneous muscular  tissue.  The  latter  contracts  on  exposure  to  cold,  so  that  the 
scrotum  is  drawn  up  and  becomes  thicker  and  \\Tinkled;  when  relaxed  under  the 
influence  of  heat  or  fatigue,  or  from  debility,  it  becomes  smooth  and  pendulous, 
with  a  constriction  or  neck  superiorly.  It  consists  of  layers  which  correspond 
with  those  of  the  abdominal  wall;   considered  from  without  inward  these  are: 

(1)  The  skin,  which  is  thin,  elastic,  usually  black  in  color,  and  smooth  and  oily 
to  the  touch.  It  presents  scattered  short  fine  hairs,  and  is  abundantly  supplied 
with  very  large  sebaceous  and  sweat  glands.  It  is  marked  centrally  by  a  longitu- 
dinal furrow,  in  which  is  a  line,  the  raphe  scroti ;  this  is  continued  forward  on  the 
prepuce  and  behind  on  the  perineum. 

(2)  The  dartos  (Tunica  dartos)  is  reddish  in  color  and  is  closely  adherent  to 
the  skin  except  superiorly.  It  consists  of  fibro-elastic  tissue  and  unstriped  muscle. 
Along  the  raphe  it  forms  a  median  partition,  the  septum  scroti,  which  divides  the 
scrotum  into  two  pouches.  Dorsally  the  septum  divides  into  two  layers  which 
diverge  on  either  side  of  the  penis  to  join  the  abdominal  tunic.  At  the  bottom 
of  the  scrotum  fibers  connect  the  dartos  closely  with  the  tunica  vaginalis  and  the 
tail  of  the  epididymis,  constituting  the  scrotal  ligament.'  Elsewhere  the  dartos 
is  loosely  connected  with  the  underlying  tunic  liy  areolar  tissue  which  contains 
no  fat. 

(3)  The  scrotal  fascia,  which  is  apparently  derived  from  the  oblique 
abdominal  muscles. 

It  has  been  customary  to  describe  three  layers  of  fascia,  in  conformity  with  the  accounts 
given  in  text-boolis  of  human  anatomy.  Tlie.se  are:  (1)  the  intercolumnar  or  spermatic  fascia, 
derived  from  the  margin  of  the  external  inguinal  ring;  (2)  the  cremasteric  fascia,  derived  from  the 
internal  oblique  muscle;  (3)  the  infundibuliform  fascia,  derived  from  the  fascia  transversalis. 
The  first  two  cannot  be  distinguished  by  dissection  and  the  third  is  (in  the  scrotum)  fused  with 
the  parietal  peritoneum  of  the  tunica  vaginalis. 

(4)  The  parietal  layer  of  the  tunica  vaginalis. — This  is  a  fibro-serous  sac  which 
is  continuous  with  the  jiarietal  peritoneum  of  the  abdomen  at  the  internal 
inguinal  ring.  It  is  thin  above,  but  is  thick  in  its  scrotal  part,  where  it  is  strength- 
ened by  fibrous  tissue  (Lamina  fibrosa)  derived  from  the  transversalis  fascia.  It 
will  be  described  further  under  the  caption  tunica  vaginalis." 


THE  VAS  DEFERENS 
This  tube  (Ductus  deferens)  extends  from  the  tail  of  the  epididymis  to  the 
ejaculatory  duct.  It  passes  upward  in  the  inguinal  canal,  inclosed  in  a  fold  de- 
tached from  the  inner  surface  of  the  mesorchium,  near  the  posterior  (attached) 
border  of  the  latter.  At  the  vaginal  ring  it  separates  from  tlie  other  constituents 
of  the  spermatic  cord,  and  turns  back\\ard  and  inward  into  the  pelvic  cavity 
(Fig.  272).  For  some  distance  it  lies  in  the  free  edge  of  the  urogenital  fold,  by 
which  it  is  attached  to  the  lower  part  of  the  lateral  wall  of  the  pelvis.  In  its 
further  course  (over  the  dorsal  surface  of  the  liladder)  it  leaves  the  edge  of  the  fold 
and  inclines  inward  between  its  layers,  coming  in  contact  with  the  inner  face  of 
the  vesicula  seminalis.  Over  the  neck  of  the  bladder  the  two  vasa  lie  very 
close  together,  flanked  laterally  bj^  the  necks  of  the  vesiculse  seminales,  and 
having  the  uterus  masculinus  between  them.  They  then  disappear  under  the 
isthmus  of  the  prostate,  and  are  continued  through  the  wall  of  the  urethra  Ijy  the 
ejaculatory  ducts.     The  latter  are  formed  in  the  urethral  wall  by  the  union  of  the 

'  This  is  a  remnant  of  the  gubernaculum  testis  of  the  foetus. 

■  The  tunica  vaginalis  is  not  a  part  of  the  scrotum  in  the  strict  or  narrow  sense  of  that  term, 
but  is  included  here  on  practical  grounds. 


THE    SPERMATIC    CORD — THE    TINICA    VAGINALIS  489 

vas  deferens  with  the  duct  (or  neck)  of  the  corresponding  vesicula  seminalis; 
they  are  thin-walled  tubes,  about  2  to  3  mm.  long  and  6  to  7  mm.  wide,  which 
open  into  the  urethra  on  either  side  of  the  colliculus  seminalis.  In  about  15  per 
cent,  of  subjects  the  vas  deferens  and  duct  of  the  seminal  vesicle  do  not  unite,  but 
open  side  by  side  into  the  urethra.  From  its  origin  until  it  reaches  the  dorsal 
surface  of  the  bladder  the  vas  deferens  has  a  uniform  diameter  of  about  a  ciuarter 
of  an  inch  (ca.  6  mm.).  It  then  forms  a  fusiform  dilatation,  the  ampulla  ductus 
deferentis  (Fig.  394);  this  part  is  about  six  to  eight  inches  (ca.  15  to  20  cm.)  long, 
and  in  its  largest  part  nearly  an  inch  (ca.  2  cm.)  in  diameter  in  the  stallion;  in 
geldings  the  dilatation  is  usually  not  very  pronounced.  Bej'ond  the  ampulla  the 
duct  abruptly  contracts. 

Structure. — The  wall  of  the  vas  deferens  is  thick  and  the  lumen  relatively 
small,  so  that  the  tube  has  a  firm  and  cord-like  character.  It  is  covered  with  peri- 
toneum, except  in  the  last  few  inches  of  its  course.  The  loose  adventitia  contains 
numerous  vessels  and  nerves.  The  thick  muscular  coat  consists  of  longitudinal 
and  circular  layers.  The  mucous  membrane  has  an  epithelium  of  short  columnar 
cells.  In  the  posterior  part  of  the  tube,  and  especially  in  the  ampulla,  there  are 
numerous  tulmlo-alveolar  glands. 

Blood-supply. — Spermatic  and  umbilical  arteries. 

Nerve-supply. — Spermatic  and  pelvic  plexuses. 


THE  SPERMATIC  CORD 
The  spermatic  cord  (Funiculus  spermaticus)  consists  of  the  structures  carried 
down  by  the  testicle  in  its  migration  through  the  inguinal  canal  from  the  abdominal 
ea^^ty  to  the  scrotum.  It  begins  at  the  internal  inguinal  ring,  where  its  constituent 
parts  come  together,  extends  obliciuely  downward  through  the  inguinal  canal, 
passes  over  the  side  of  the  penis,  and  ends  at  the  attached  border  of  the  testicle. 
It  consists  of  the  following  structures; 

(1)  The  spermatic  artery. 

(2)  The  spermatic  veins,  which  form  the  pampiniform  plexus  around  the 
artery. 

(3)  The  lymphatics,  which  accompany  the  veins. 

(4)  Sympathetic  nerves,  which  run  with  the  artery. 

(5)  The  vas  deferens. 

(6)  The  internal  cremaster  muscle,  which  consists  of  bundles  of  unstriped 
muscular  tissue. 

(7)  The  visceral  layer  of  the  tunica  vaginalis  or  mesorchium. 

The  first  four  of  these  constituents  are  gathered  into  a  rounded  mass  which 
forms  the  anterior  part  of  the  cord;  they  are  united  by  connective  tissue,  inter- 
spersed with  which  are  bundles  of  the  cremaster  internus.  The  vas  deferens  is 
situated  posteriorly,  inclosed  in  a  special  fold  detached  from  the  inner  surface  of 
the  mesorchium;   hence  it  is  not  \asible  externallj'. 

The  term  .spermatic  cord  is  to  a  certain  extent  misleading  as  applied  to  most  animals,  while 
in  man  the  structure  is  distinctly  cord-like.  In  the  horse,  when  the  tunica  vaginahs  is  sht  open 
and  the  ''cord"  stretched  out.  the  latter  is  seen  to  have  the  form  of  a  wide  sheet,  the  mesorchium, 
which  has  a  thick,  rounded  anterior  edge,  the  so-called  "vascular  part"  of  the  cord.  The  posterior 
edge  of  the  mesorchium  is  continuous  with  the  parietal  layer  of  the  tunic;  its  inner  surface  pre- 
sents posteriorly  the  deferential  fold  (Plica  ductus  deferentis).  Between  the  two  lajers  of  the 
mesorchium  are  bundles  of  imstriped  muscle  (cremaster  internus)  and  small  vessels. 


THE  TUNICA  VAGINALIS 
The  tunica  vaginalis  is  a  somewhat  pjTiform  serous  sac  which  extends  from  the 
internal  inguinal  ring  through  the  inguinal  canal  to  the  bottom  of  the  scrotum. 


490 


THE  MALE  GENITAL  ORGANS  OF  THE  HORSE 


Like  the  abdominal  peritoneum,  of  which  it  is  an  cvagination,  it  consists  of  two 
layers — parietal  and  visceral.  The  parietal  layer,  or  tunica  vaginalis  communis 
(s.  refliexa),  lines  the  scrotum  below;  its  narrow,  tubular  part  lies  in  the  inguinal 
canal  and  is  directly  continuous  with  the  parietal  peritoneum  of  the  abdomen 
at  the  internal  inguinal  ring.  The  cavity  of  the  tunica  vaginalis  (C'avum  vaginale) 
is  a  diverticulum  of  the  general  peritoneal  cavity,  with  which  it  communicates 
through  the  vaginal  ring  (Annulus  vaginalis).  It  contains  normally  a  small  quan- 
tity of  serous  fluid.  The  jwrietal  layer  is  reflected  from  the  posterior  wall  of  the 
inguinal  canal  arountl  the  structures  of  the  cord,  forming  tlie  mesorchium,  a  fold 
analogous  to  the  mesentery  of  the  intestine.  The  visceral  layer,  or  tunica 
vaginalis  propria,  covers  the  spermatic  cord,  testicle,  and  epididymis. 

The  external  cremaster  muscle  (M.  cremaster  externus)  lies  on  the  outer  and 
posterior  part  of  the  tunic,  to  the  scrotal  part  of  which  it  is  attached. 

Confusion  has  arisen  from  the  use  of  the  term  internal  abdominal  or  inguinal  ring  in  two 
senses.  The  term  is  used  to  designate  the  upper  or  abdominal  opening  of  tlie  inguinal  canal, 
but  it   is  also  applied  to  the  upper  opening  of  the  cavity  of   tlie   tunica   vaginalis.     It   should 


Spermatic  vessels  and  nerves 


Parietal  layer  of  tunica 
vaginalis 


Visceral  layer  of  tunica 
vagiiialis  or  mesorchium 

Cremaster  inlernus 
Vas  deferens 


Fig.  393.— Di 


'  Cross-section 


4l,is:    Latter  Rkpre 


only  bf  applied  to  the  abdominal  opening  of  the  canal,  the  subperitoneal  ring.  The  peritoneal 
ring  at  which  tlir  i-avily  of  the  tunica  vaginalis  opens  into  the  general  peritoneal  sac  is  distin- 
gui.slird  li\  I  lie  iiauLc  vaginal  ring.  It  is  placed  about  four  or  five  inches  (ca.  10  to  12  cm.)  from 
the  liiica  allia,  and  about  two  or  three  inches  (ca.  6  to  S  cm.)  in  front  of  the  ilio-pectineal  eminence. 
In  stallions  it  will  usually  admit  the  end  of  the  finger  readily,  but  it  may  be  abnormally  large  and 
allow  a  loop  of  bowel  to  enter  the  cavity  of  the  tunica  vaginalis.  In  the  gelding  it  is  smaller  and 
sometimes  partially  occluded.  In  man  the  cavity  is  almost  always  obliterated  early,  except  in 
its  scrotal  portion,  thus  abolishing  the  vaginal  ring. 


DESCENT  OF  THE  TESTICLES 
During  early  fatal  life  the  testicle  is  situated  against  the  dorsal  wall  of  the 
abdominal  cavity,  in  contact  with  the  ventral  surface  of  the  corresponding  kidney. 
As  growth  jiroceeds  it  gradually  migrates  from  this  primitive  position,  and  finally 
passes  down  the  inguinal  canal  into  the  scrotum.  Previous  to  its  descent  through 
the  abdominal  wall  the  testicle  is  suspended  by  a  fold  of  peritoneum,  termed 
the  mesorchium.  This  fold  contains  the  vessels  and  nerves  of  the  testicle  in  its 
anterior  hordcT.  In  its  po.sterior  edge  is  the  elongated  tail  of  the  epididymis, 
and  two  cords  of  filirous  tissue  and  unstriped  muscle.  One  of  these  cortls  is  short 
and  connects  the  tail  of  the  epididymis  with  the  testicle ;   later  it  becomes  shorter, 


THE    VESICUL^    SEMINALES  491 

and  is  termed  the  ligament  of  the  epididymis.  The  other  cord,  the  gubemaculum 
testis,  extends  from  the  tail  of  the  epididymis  to  the  sul)))eritoneal  tissue  in  the 
vicinity  of  the  future  vaginal  ring.  The  deferential  fold  (Plica  ductus  deferentis) 
is  given  off  from  the  inner  face  of  the  mesorchium,  and  joins  the  urogenital  fold 
I)osteriorl}-.  The  body  of  the  epididymis  at  this  time  lies  in  the  edge  of  an  ohlique 
fold  formed  bj'  the  outer  layer  of  the  mesorchium.  After  the  middle  of  fo'tal  life, 
a  pouch  or  diverticulum  of  the  peritoneum,  the  processus  vaginalis,  grows  ilowmvard 
through  the  inguinal  canal,  carrying  with  it  cremaster  fibers  derived  from  the 
internal  oblique  muscle  and  a  layer  from  the  transversalis  fascia.  It  is  accom- 
panied by  an  inguinal  extension  of  the  gubernaculum  testis.  The  latter  blends 
below  with  the  subcutaneous  tissue  which  later  becomes  the  dartos.  The  tail  of 
the  epididymis  first  enters  the  processus  vaginalis,  followed  by  the  testicle  with  its 
mesorchium,  which  descends  within  this  diverticulum  of  the  peritoneum  until  it 
reaches  the  scrotum.  The  vas  deferens  and  its  fold  descend  synchronously  with 
the  epididymis  and  testicle. 

The  mechanical  factors  concerned  in  tlie  migration  of  the  testicle  are  matters  on  which 
much  uncertainty  still  exists.  That  the  gul)ernaculum  exerts  sufficient  traction  to  guide  the 
epididymis  and  testicle  to  the  inguinal  canal  seems  plausible.  The  internal  inguinal  ring  may 
constitute  a  locus  minoris  resistentia;  in  the  abdominal  wall,  especially  after  the  descent  of  the 
processus  vaginalis.  Progressive  shortening  of  the  gubernaculum  was  formerly  considered  to  be 
the  chief  cause  of  the  descent  through  the  abdominal  wall.  Increase  in  the  intra-abdominal 
pressure  is  probably  an  important  factor. 

In  the  foal  the  descent  of  the  testicles  is  often  complete  at  birth,  but  it  fre- 
quently happens  that  one  testicle  or  both  may  be  retained  in  the  inguinal  canal  or 
in  the  abdonten  for  some  months.  In  other  cases  the  testicle  may  return  into  the 
canal  or  abdomen,  since  in  the  young  foal  the  vaginal  ring  is  large  and  the  testicle 
small  and  soft,  and  not  yet  closely  anchored  by  the  scrotal  ligament.  In  rare  cases 
the  descent  may  be  completed  as  late  as  the  fourth  year  (personal  observation). 

Indefinite  retention  of  one  testicle  or  both  in  the  abdominal  cavity  or  inguinal  canal  is  not  rare 
in  horses;  this  condition  is  termed  cryptorchism.  Abdominal  retention  is  the  more  usual  form 
of  crj-ptorchism  in  adult  horses,  inguinal  retention  being  usually  temporary.  The  retained 
testicle  is  usually,  but  not  always,  small,  thin,  soft,  and  flabby,  and  is  non-spermiogenic.  The 
processus  vaginalis  and  the  inguinal  part  of  the  gubernaculum  are  usually  present,  but  may  be 
rudimentary.  The  ligament  of  the  epididymis  and  the  corresponding  part  of  the  mesorchium 
are  often  so  long  that  the  tail  of  the  epididymis  may  be  several  inches  distant  from  the  testicle. 
The  abdominal  part  of  the  gubernaculum  may  be  8  to  10  inches  (ca.  20  to  2.5  cm.)  long,  and  the 
ligament  of  the  epididymis  much  elongated  (10  to  1.5  cm.  in  length  according  to  Vennerholm) ; 
thus  the  testicle  may  have  a  wide  range.     The  vaginal  ring  is  sometimes  closed. 

In  many  mammals  the  testicles  normally  remain  in  the  abdominal  cavity;  such  animals  are 
termed  testiconda,  and  include  the  elephant,  some  insectivora,  hyrax,  sloths,  ant-eaters,  armadillos, 
and  cetacea.  In  others  the  testicles  descend  periodically  during  the  period  of  oestrum,  and  then 
return  into  the  abdomen,  or  they  may  be  extruded  and  retracted  voluntarily;  this  is  true  of  most 
rodents,  many  insectivora  (moles,  shrews,  hedgehog),  and  bats. 


THE  VESICULAE   SEMINALES 

The  vesiculae  seminales  (  Fig.  394 )  arc  two  elongated  and  somewhat  pyriform 
sacs,  which  lie  on  either  side  of  the  posterior  part  of  the  dorsal  surface  of  the  blad- 
der. They  are  partly  inclosed  in  the  urogenital  fold,  and  are  related  to  the  rectum 
dorsally.  Their  long  axes  are  parallel  with  the  vas  defercntia  and  converge  pos- 
teriorly. Each  consists  of  a  rounded  l)lind  end,  the  fundus,  a  middle,  slightly 
narrower  part,  the  body,  and  a  posterior  constricted  part,  the  neck  or  duct. 

In  the  stallion  they  are  about  six  to  eight  inches  (ca.l5to20cm.)  long,  and  their 
greatest  diameter  is  about  two  inches  (ca.  5  cm.);  in  the  gelding  they  are  usually 
much  smaller.' 

'  Sometimes  one  vesicula  or  both  are  very  large  in  the  gelding.  The  writer  has  seen  four 
cases  in  the  dissecting  room,  three  of  which  were  bilateral,  the  other  unilateral.  The  vesicula  re- 
sembled the  urinary  bladder  in  appearance  and  contained  about  a  quart  of  thick,  amber-colored 
secretion. 


492 


THE  MALE  GENITAL  ORGANS  OF  THE  HORSE 


The  vesiculse  are,  for  the  most  part,  retroperitoneal,  but  the  fundus  extends 
forward  into  the  urogenital  fokl  anil  hence  has  a  serous  covering.  The  neck  or 
duct  (Ductus  excretorius)  dips  untler  the  prostate,  and  usually  unites  with  the 
end  of  the  vas  deferens  to  form  the  ejaculatory  duct. 

Structure. — The  wall,  exclusive  of  the  partial  serous  coat,  consists  of  a  fibrous 


Bulbo-uretliral  (Cowpcr's)  gland  — 


On  left  aide  urethriil 


304. — Internal  Genital  Organs  of  Stallion.  Dorsal  View. 
cle  has  been  removed  over  bulbo-urethral  gland.     Corriua  of  uterus  masculinus 
dicated  in  urogenital  fold. 


adventitia,  a  mirldle  muscular  coat,  and  a  mucous  lining.  The  muscular  coat 
is  thickest  at  the  fundus,  and  consists  of  two  planes  of  longitudinal  fibers  with  a 
circular  layer  between  them.  The  mucous  membrane  is  thin,  and  is  arranged  in 
numerous  folds  which  form  a  network;  the  spaces  so  inclosed  present  the  open- 
ings of  tubulo-alveolar  glands.  The  epithelium  is  columnar.  The  blood-supply 
is  derived  from  the  internal  pudic  artery. 


THE    PROSTATE — THE    BULBO-URETHRAL    GLANDS  493 

THE  PROSTATE 

The  prostate  (Prostata)  is  a  musculo-glaiuhilar  organ  which  lies  on  the  neck 
of  the  blacldcr  and  the  beginning  of  the  uretlira,  beneath  the  rectum.  It  consists 
of  two  lateral  lobes  and  a  connecting  isthmus. 

The  lateral  lobes,  right  and  left  (Lobus  dexter  et  sinister),  are  somewhat 
prismatic  in  form,  and  are  directed  forward,  outward,  and  somewhat  upward. 
The  antero-internal  surface  of  each  lobe  is  concave  and  partly  embraces  the  cor- 
responding vesicula  seminalis.  The  dorsal  surface  is  concave  and  is  in  relation 
with  the  rectum.  The  ventral  surface  is  convex  and  lies  on  the  obturator  internus 
muscle  and  fat.  The  apex  is  pointed  and  lies  near  the  posterior  end  of  the 
superior  ischiatic  spine. 

The  isthmus  is  a  thin,  transverse  band,  about  four-fifths  of  an  inch  (ca.  2  cm.) 
wide.  It  lies  over  the  junction  of  the  bladder  with  the  urethra,  the  uterus  mascu- 
linus,  the  terminal  parts  of  the  vasa  deferentia,  and  the  necks  of  the  vesiculse 
seminales.  Dorsally  it  is  partly  covered  by  transverse  fibers  of  the  urethral 
(Wilson's)  muscle. 

Structure. — The  prostate  is  inclosed  in  a  fibro-muscular  capsule,  which  sends 
thick,  somewhat  radially  arranged  trabeculse  into  the  gland  substance,  dividing 
it  into  spheroidal  or  ovoid  lobules.  Tlie  lobules  contain  a  central  space  in  which 
the  prostatic  secretion  (Succus  prostaticus)  collects.  The  walls  of  these  spaces 
are  pouched  out  to  form  tubular  diverticula,  and  the  latter  present  saccular 
dilatations.  These  cavities  are  all  lined  by  cubical  epithelium.  There  are  15  to 
20  prostatic  ducts  (Ductus  prostatici)  on  either  side,  which  perforate  the  urethra 
and  open  lateral  to  the  colliculus  seminalis.  The  blood-supply  is  derived  from 
the  internal  pudic  artery. 

The  surface  of  the  prostate  is  commonly  tuberculate  in  old  subjects,  and  amyloid  bodies 
and  calcareous  concretions  may  be  found  in  it. 


THE  UTERUS  MASCULINUS 
The  uterus  masculinus  or  prostatic  utricle  is  a  rudimentary  structure  of  vari- 
able size  and  form,  situated  centrally  on  the  posterior  part  of  the  dorsal  surface  of 
the  bladder.  When  well  developed,  it  consists  of  a  median  flattened  tube,  some 
three  or  four  inches  (ca.  7.5  to  10  cm.)  long,  and  about  half  an  inch  (ca.  1  to  1.5  cm.) 
wide,  the  anterior  part  of  which  lies  in  the  urogenital  fold  and  gives  off  two  slender 
processes  or  cornua;  the  latter  curve  forward  and  outward  in  the  fold  a  variable 
distance,  being  sometimes  traceable  as  far  as  the  anterior  end  of  the  ampulla  of 
the  vas  deferens.  The  posterior  extremity  of  the  tube  passes  under  the  isthmus 
of  the  prostate,  and  opens  into  the  urethra  on  the  summit  of  the  colliculus  or  joins 
an  ejaculatory  duct.  It  has  a  muscular  coat  and  a  mucous  lining.  In  many  cases 
it  consists  merely  of  a  very  small  central  tubule  with  a  blind  anterior  end,  or  a 
band,  not  at  all  sharply  marked  off  from  the  adjacent  tissue;  in  other  cases  it 
cannot  be  recognized.  It  is  interesting  chiefly  as  being  a  remnant  of  the  ducts  of 
Miiller  and  the  homologue  of  the  uterus  and  vagina. 


THE  BULBO-URETHRAL  GLANDS 
The  bulbo-urethral  (or  Cowper's)  glands  (Glandulae  bulbourethrales)  are  two 
in  number,  and  are  situated  on  either  side  of  the  pelvic  part  of  the  urethra  close  to 
the  ischial  arch  (Fig.  452).  They  are  covered  by  the  urethral  (Wilson's)  muscle. 
They  are  ovoid  in  form,  somewhat  depressed  dorso-ventrally,  and  their  long  axes 
are  directed  obliquely  forward  and  outward.     In  the  stallion  they  may  measure 


494 


THE  MALE  GENITAL  ORGANS  OF  THE  HORSE 


about  two  inches  (ca.  5  cm.)  in  lengtli,  antl  an  inch  or  more  (ca.  3  cm.)  in  width. 
In  the  geliUns  they  are  aliout  the  size  of  an  average  hazel  nut. 

Structure. — They  resemble  the  prostate  in  general  structure,  but  the  inter- 
stitial tissue  is  much  less  abundant,  especially  in  regard  to  its  muscular  elements. 
In  the  peri]iheral  ])art  there  are  striped  muscle-fibers.  Each  gland  has  six  to 
eight  excretory  ducts  (Ductus  excretorii)  which  open  into  the  urethra  on  a  series 
of  small  i^apiihe  liehind  the  prostatic  ducts  and  close  to  the  median  plane.  The 
blood-supply  comes  from  the  internal  pudic  artery. 


THE  PENIS 

The  penis,  the  male  organ  of  copulation,  is  composed  essentially  of  erectile 

tissue,  and  incloses  the  extrapelvic  part  of  the  urethra.     It  extends  from  the  ischial 

arch  forward  between  the  thighs  on  to  the  umbilical  region  of  the  abdominal  wall. 

It  is  supported  by  the  fascia  penis  and  the  skin,  and  its  prescrotal  portion  is  situated 


Deep  arU'rij  (Jro/n  internal  pudic) 


Dorsal  artery  (from  Corona  glandis 

external  pudic)  Collum  (ihinrlis 

Proc.  doriiuli.^  :/hnr!i..  i.^^ 

^    4B     Ure- 
thral 
proems 


Retractor  penis  muscle 


BODY 
Fig.  395. — Penis  of  Horse,  L-\ter-kl  View. 


in  a  cutaneous  pouch,  the  prepuce  or  sheath.     It  is  cylindrical  in  form,  but  much 
compressed  laterally  in  the  greater  part  of  its  extent. 

In  the  quiescent  state  it  is  about  20  inches  (ca.  50  cm.)  long;  of  thi.s,  about  6  to  S  inches 
(ca.  1.5  to  20  cm.)  is  free  in  the  prepuce.     In  erection  it  increases  50  per  cent,  or  more  in  length. 

It  may  be  divided  into  a  root,  a  body,  and  a  terminal  enlargement,  the  glans. 

The  root  (Radix  penis)  is  attached  to  the  lateral  parts  of  the  ischial  arch  by 
two  crura,  which  converge  and  unite  below  the  arch  (Fig.  452).  The  urethra  passes 
over  the  ischial  arch  between  the  crura,  and  curves  forward  to  become  incorpor- 
ated with  the  penis. 

The  body  (Corpus  penis)  begins  at  the  junction  of  the  crura  and  constitutes 
the  bulk  of  the  organ.  At  its  origin  it  is  attached  to  the  symphysis  ischii  by  two 
strong  flat  bands,  the  suspensory  ligaments  of  the  penis  (Ligamenta  suspensoria 
penis),  which  blend  with  the  tendon  of  origin  of  the  graciles  muscles  (Figs.  451, 
456).  This  part  of  the  jienis  is  flattened  laterally  for  the  most  part,  but  becomes 
rounded  and  smaller  anteriorh'.  It  presents  four  surfaces.  The  dorsal  surface  or 
dorsum  penis,  is  narrow  and  rounded;  on  it  are  the  dorsal  arteries  and  nerves 
of  the  penis  and  a  rich  venous  plexus.  The  ventral  or  urethral  surface  (Facies 
urethralis)  is  rounded,  and  along  it  runs  the  urethra,  embeddeil  in  the  deep 
urethral  groove  of  the  corpus  cavernosum.  The  lateral  surfaces  are  high  and 
flattened,  except  anteriorly,  where  they  are  lower  and  rounded. 


THE    PENIS 


495 


The  glans  penis  is  tlio  culargod  free  einl  of  the  organ.  It  is  marked  off  from 
the  bod}'  liy  a  faintlj-  iiiarl^cd  neck  iColhini  glandis).  In  front  of  this  is  a  promi- 
nent circular  ridge,  tlie  corona  glandis,  which  is  notched  below.  The  base  of  the 
glans  is  rounded  and  extentls  further  backward  dorsally  than  vontrally;  it  i.s 
marked  in  its  lower  part  by  a  deep  depression,  the  fossa  glandis,  in  which  the 
urethra  protrudes  for  about  an  inch  (ca.  2.5  cm.)  as  a  free  tul)e,  the  urethral 
process  (Processus  urethra>),  covered  by  a  thin  integument.  The  urethra  is  thus 
surroundeil  by  a  circular  fossa,  which  opens  superiorly  into  the  urethral  sinus,  a 
bilocular  diverticulum  lined  bj-  thin  black  skin.  This  diverticulum  is  filled  some- 
times with  a  caseous  mass  of  sebaceous  matter  and  epithelial  debris. 

Structure. — The  penis  consists  essentially  of  two  erectile  Ixxlies,  the  corpus 
cavernosum  penis  and  the  corpus  spongiosum. 

The  corpus  cavernosum  penis  forms  the  greater  part  of  the  Inilk  of  the  penis 
except  at  its  free  extremity.  It  arises  from  each  side  of  the  ischial  arch  bj-  a  cms, 
which  is  embedded  in  the  ischio-cavernosus  muscle.  Belowthe  ischial  archthe  crura 
fuse  completelj'  to  form  the  laterally  compressed  bodj'  of  the  corpus  cavernosum; 
this  presents  ventralh'  the  urethral  groove  (Sulcus  urethralis),  which  contains  the 
urethra  and  corpus  spongiosum.     An- 


Dorsum  penis 


Corpus 
cavernosum 


Corpus 
spongiosum 


Trabecules 


Tunica 

albuginea 


—  Bulhn- 

carcrnosus 
m  uscle 


Retractor  penis  muscle 
Fig.  396. — Cross-section  of  Boi>i  or  Pf.nis  of  Ho 


teriorly,  the  corpus  cavernosmn  divides 
into  three  processes,  a  long  central  one, 
which  is  capped  by  the  glans  penis, 
and  tw-o  short  blunt  lateral  ones.  The 
corpus  cavernosum  is  inclosed  by  the 
tunica  albuginea,  a  thick  capsule  of 
fibrous  tissue  which  contains  many 
elastic  fibers  and  some  unstriped 
muscle.  Externally  the  fibers  are 
chiefly  longitudinal;  internally  they 
are  mainly  circular  and  are  looser  in 
arrangement.  Numerous  trabeculae 
pass  inward  from  the  tunic  and  form 
a  sponge-like  framework  in  the  in- 
terior of  the  corpus  cavernosum, 
which  is  thus  di\nded  into  numerous 
spaces  (Cavernse).  These  spaces  may 
be  regarded  as  greatly  enlarged  capil- 
laries; they  contain  blood,  are   lined 

with  flat  endothelial  cells,  antl  are  directly  continuous  with  the  veins  of  the  penis. 
Their  walls  are  composed  very  largely  of  unstriped  muscle.  Erection  is  produced  by 
distention  of  these  spaces  with  blood;  at  other  times  the  spaces  are  mere  slits. 

In  man  there  are  two  distinct  corpora  cavernosa,  separated  by  a  complete  septum  penis, 
except  in  the  middle  part  of  the  organ,  where  the  septum  is  composed  of  vertical  trabecular,  be- 
tween which  are  slit-like  intervals;  through  the  latter  the  blood-spaces  of  the  two  corpora  caver- 
nosa communicate.  In  the  horse  no  distinct  septum  exists  except  near  the  root,  but  m  the  pro.xi- 
mal  and  distal  parts  of  the  corpus  cavernosum  there  are  vertical  trabecute. 

The  corpus  spongiosum  or  corpus  cavernosum  urethrae  forms  a  tube  around 
the  urethra,  and  is  inucli  enlargetl  at  its  free  end  to  form  the  bulk  of  the  glans  penis; 
throughout  the  remainder  of  its  cour.se  it  is  practically  uniform  in  size,  and  does 
not  form  any  very  distinct  bulb  (Bulbus  urethra?)  at  its  origin,  as  in  man  and 
many  animals.  The  glans  has  been  described  in  part;  it  should  be  noted  that 
the  corpus  spongiosum  extends  backward  dorsally  a  distance  of  about  four  mches 
(ca.  10  cm.)  on  the  middle  process  of  the  corpus  cavernosum  penis,  forming  the 
processus  dorsalis  glantlis.  The  urethral  process  is  covered  by  a  thin  layer  of 
corpus  spongiosum. 


496  THE  MALE  GENITAL  ORGANS  OF  THE  HORSE 

In  structure  the  corpus  spongiosum  has  a  general  resemblance  to  the  corpus 
cavernosum,  but  the  trabeculse  are  finer  and  more  clastic.  In  the  glans  the  trabe- 
culffi  are  highly  elastic,  and  the  spaces  are  large  and  very  extensible;  the  latter  are 
continuous  at  the  extremity  of  the  processus  dorsalis  with  large  veins  on  the  dorsum 
penis.  There  is  a  partial  septum  glandis.  The  skin  covering  the  glans  is  thin, 
destitute  of  glands,  and  richly  supplied  with  nerves  and  .special  nerve-endings. 

Vessels  and  Nerves. — The  penis  is  supplied  with  blood  by  three  arteries,  viz., 
the  internal  pudic,  obturator,  and  external  pudic.  The  veins  form  a  rich  jilexus 
on  the  dorsum  and  sides  of  the  penis,  which  is  drained  by  the  external  pudic  and 
obturator  veins ;  from  the  root  the  blood  is  carried  by  the  internal  pudic  veins. 
The  lymphatics  run  with  the  veins  and  go  to  the  inguinal  and  liiiiihar  glands. 
The  nerves  are  derived  chiefly  from  the  pudic  nerves  and  the  pelvic  plexus  of  the 
sympathetic. 

MUSCLES   OF   THE   PENIS  (Figs,  183,  451,  452,  456) 

1.  The  ischio-cavemosus  (or  erector  penis)  is  a  short  but  strong  paired  muscle, 
which  arises  from  the  tuber  ischii  and  the  adjacent  part  of  the  sacro-sciatic  ligament, 
and  is  inserted  on  the  crus  and  adjacent  part  of  the  body  of  the  penis.  It  is  some- 
what fusiform,  incloses  the  crus  as  in  a  sheath,  and  is  situated  in  a  deep  depression 
in  the  semimembranosus  muscle.  It  pulls  the  penis  against  the  pelvis,  and  assists 
in  producing  and  maintaining  erection  by  compressing  the  dorsal  veins  of  the  penis. 
Its  blood-supply  is  derived  from  the  obturator  artery,  and  the  nerve-supply  from 
the  pudic  nerve. 

2.  The  retractor  penis  is  an  unstriped  muscle  which  arises  on  the  ventral  sur- 
face of  the  first  two  or  three  coccygeal  vertebrae.  It  chvides  into  two  flat  bands, 
half  an  inch  or  more  (ca.  1.5  cm.)  in  width,  which  pass  downward  over  the  sides  of 
the  rectum  to  meet  below  the  anus.  Here  there  is  a  decussation  of  fibers,  thus  form- 
ing a  sort  of  suspensory  apparatus  for  the  posterior  part  of  the  rectum  and  the  anus. 
From  the  decussation  the  muscle  passes  for  a  short  distance  between  superficial 
and  deep  layers  of  the  bulbo-cavernosus,  and  then  along  the  ventral  surface  of  the 
penis,  to  which  it  is  loosely  attached.  Near  the  glans  penis  it  splits  up  into  bundles 
which  pass  through  the  bulbo-cavernosus  and  arc  attached  to  the  tunica  albuginea. 
Below  the  anus  the  muscle  is  attached  to  the  sphincter  ani  externus.  On  the 
penis  the  two  muscles  are  intimately  united  to  each  other.  Their  action  is  to 
withdraw  the  penis  into  the  sheath  after  erection  or  protrusion.  The  proximal 
part  would  draw  the  anus  upward  and  forward  and  support  it  during  defecation. 


THE  PREPUCE 
The  prepuce  (Prseputium),  popularly  calleil  the  "sheath,"  is  a  doul)le  in- 
vagination of  the  skin  which  contains  and  covers  the  free  or  prescrotal  portion  of 
the  penis  when  not  erect.  It  consists  of  two  parts,  external  and  internal.  The 
external  part  or  sheath  extends  from  the  scrotum  forward  close  to  the  umbilicus, 
where  the  external  layer  is  reflected  ventrally  and  laterally,  forming  the  thick 
margin  of  the  preputial  orifice  (Ostium  pripputiale) ;  dorsally  it  is  directly  continu- 
ous with  the  integument  of  the  abdominal  wall.  It  is  marked  by  a  median  raphe 
praeputii,  a  continuation  of  the  scrotal  raphe.  At  the  lower  margin  of  the  pre- 
putial orifice  there  are  often  in  the  stallion  two  papilla*,  which  arc  rudimentary 
teats  or  nipples.  The  internal  layer  passes  backward  from  the  preputial  orifice 
a  distance  of  about  six  to  eight  inches  (ca.  15  to  20  cm.),  lining  the  cavity  of  the  ex- 
ternal prepuce,  and  is  then  reflected  forward  until  it  approaches  the  orifice,  where 
it  is  again  reflected  backward.  It  thus  forms  within  the  cavity  of  the  sheath  a  sec- 
ondary tubular  invagination,  the  prepuce  proper,  in  which  the  anterior  part  of 


THE    MALE    URETHRA 


497 


the  penis  lies.  Tliis  tuljular  cavity  is  closed  behind  by  the  reflection  of  the  internal 
layer  on  to  the  penis  to  form  the  jx'nilc  layer  of  the  prepuce.  Its  orifice  is  sur- 
rounded by  a  thick  margin,  the  preputial  ring  (Annulus  pra^putialis),  which  is 
connected  ventrally  with  the  outer  part  of  the  sheath  by  the  preputial  frenum 
(Frenulum  pnejiutii). 

The  arrangement  differs  from  that  found  in  man  in  the  fact  that  the  inner  part  of  the  pre- 
puce as  described  above  is  equivalent  to  the  entire  human  prepuce.  Thi.s  part,  tlie  prepuce 
projier,  is  well  seen  on  .sagittal  sections,  and  can  be  demonstrated  by  pulling  the  penis,  inclosed 
ill  tliis  prepuce,  out  of  the  cavity  of  the  sheath;  the  arrangement  of  the  free  part  of  the  penis  and 
prepuce  is  then  like  that  in  man.  (In  paraphimosis  the  penis  is  strangulated  by  tlie  preputial 
i-ing.) 

Structure. — The  external  skin  of  the  prepuce  resembles  that  of  the  scrotum. 
The  inner  layers  of  skin  are  hairless,  variable  in  color,  and  often  irregularly  pig- 
mented; they  form  irregular  folds,  and  are  supplied  with  numerous  large  sebaceous 
glamls  anel  coil  glands,  which  reach  their  greatest  size  at  the  preputial  ring.     Be- 


FiG.  397. — .Saoittal  Section  of  Prepuce  and  Part  of  Penis  of  Horse. 

P,  Internal  part  of  prepuce  or  prepuce  proper;    P' ,    external  part  of  prepuce  or  sheath;    c.p.,  preputial    cavity; 

F.O-t  fossa  glandis;   D,  diverticulum  of  fossa  glandis:    p.w.,  processus  urethra?. 

yond  this  the  glands  are  absent,  and  the  skin  resembles  a  non-glandular  mucous 
membrane.  The  secretion  of  the  preputial  glands  (Cdanduhr  pra?])iitiales),  to- 
gether with  desquamated  epithelial  cells,  forms  the  fatty  smegma  prseputii,  which 
has  a  strong  unpleasant  odor,  and  often  accumulates  in  considerable  amount. 
Beneath  the  skin  is  a  large  amount  of  loose  connective  tissue,  except  over  the  glans 
penis,  where  the  skin  is  closely  attached  to  the  tunic  of  the  corpus  spongiosum. 
The  external  part  of  the  prepuce  is  strengthened  by  a  laj'er  of  elastic  tissue,  derived 
from  the  abdominal  tunic,  and  termerl  the  stispensory  ligament. 

Vessels  and  Nerves. — The  arteries  are  branches  of  the  external  pudic  artery, 
antl  the  veins  go  chiefly  to  the  external  pudic  vein.  The  lymphatics  go  to  the  sujicr- 
ficial  inguinal  and  lumbar  lymph  glands.  The  nerves  are  derivetl  from  the  pudic, 
ilio-hypogastric,  and  ilio-inguinal  nerves. 


THE  MALE  URETHRA 
The  urethra  of  the  male  (Urethra  masculina)  is  the  long  mucous  tube  which 
extends  from  the  bladder  to  the  glans  penis.     It  passes  backward  on  the  floor  of 
32 


498 


THE  MALE  GENITAL  ORGANS  OF  THE  HORSE 


the  pelvis,  turns  around  the  ischial  arch,  forming  an  acute  angle,  and  passes  forward 
inclosed  in  the  corpus  spongiosum.  It  may,  therefore,  he  iliviiled  into  two  seg- 
ments, pelvic  and  extrapelvic. 

The  pelvic  part  (Pars  pelvina)  is  four  or  five  inches  (ca.  10  to  12  cm.)  long. 
At  its  origin  it  is  not  distinguishablefromthe  neck  of  the  bladder  in  size  or  structure; 
in  fact  no  line  of  tlcniarcation  exists  between  the  two.  Behind  the  prostate  the 
tube  dilates  to  a  potential  width  of  two  inches  or  more  (ca.  5  to  6  cm.).  Near  the 
ischial  arch,  between  the  bulbo-urethral  (Cowper's)  glands,  it  contracts  again, 
forming  the  isthmus  urethras.  It  is  related  dorsally  to  the  rectum  and  the  prostate, 
ventrally  to  the  internal  obturator  muscles,  and  laterally  to  the  bulbo-urethral 


Lateral  lobe  of  prostate 


Orifice  of  vierus  mascvlinus 


Ducts  of  urethral  glands 


Collie  111  us  seininalis 


Duets  of  h^dho-urethral 
(Cowper's)  glands 


Fig.  398. — Pelvic  Urethra 


Posterior  Part  op  Bladder  i 
e.d.,  Ejaculatory  ilucts 


Slit  Ventrally  and  Laid  Open. 


glands.     It  is  inclosed,  except  at  its  origin,  by  the  urethral   (^^'ilson's)  muscle. 
Beneath  this  is  a  rich  venous  plexus,  forming  a  sort  of  erectile  tissue." 

The  extrapelvic  part  (Pars  cavernosa)  passes  between  the  two  crura  of  the 
penis  and  runs  along  the  groove  on  the  ventral  surface  of  the  corpus  cavernosum 
penis,  inclosed  by  the  corpus  spongiosum  and  the  bulbo-cavernosus  muscle.  It 
passes  through  the  glans  penis  and  projects  forward  aliout  an  inch  in  the  fossa 
glandis  as  a  free  tube,  the  processus  urethrse;  this  jiart  is  covered  by  a  delicate 
integument,  under  which  there  is  a  thin  layer  of  erectile  tissue. 

'  It  has  been  customary  to  divide  the  pelvic  part  of  the  urethra  into  prostatic  and  mem- 
branous parts.  These  terms  apply  well  in  human  anatomy,  but  have  no  special  value  in  com- 
parative anatomy.  In  the  horse  a  prostatic  part  hardly  exists,  unless  we  assume  that  it  and  the 
neck  of  the  bladder  together  are  only  about  an  inch  in  length.  There  is  no  membranous  part  in 
the  sense  in  wliich  that  term  is  used  in  regard  to  man. 


THE    MALE    URETHRA  499 

The  himon  of  tho  tulio  is  liirfjely  obliterated  in  the  inactive  condition  of  the  parts.  When 
moderately  distended  its  dimensions  in  a  horse  of  medium  size  are  as  follows:  At  its  origin  the 
diameter  is  al)0Ut  half  an  inch  (1  to  1.5  cm.)-  The  pelvic  dilatation  at  its  widest  part  measures  one 
and  a  half  to  two  inches  (ca.  3.5  to  5  cm.)  transversely,  and  about  an  inch  (2  to  3  cm.)  vertically;  it 
is  elliptical  in  cros.s-seetion  when  fully  distended.  The  isthmus  at  the  ischial  arch  is  a  little 
smaller  than  the  initial  part.  Beyond  this  the  lumen  is  about  one-half  to  three-fourths  of  an 
inch  (ca.  1.5  cm.)  in  diameter,  and  is  fairly  tmiform  to  the  glans  penis.  Here  there  is  a  .slight 
fu.siform  dilatation  (Fo.ssa  navicularis),  beyond  which  the  tube  contracts. 

The  opening  from  the  bladder  into  the  urethra  is  termed  the  internal  urethral 
orifice  (Orificium  urethrse  internum);  it  is  closed  except  during  urination.  The 
terminal  ojiening  is  the  external  urethral  orifice  (Orificium  urethrje  externum)  or 
meatus  urinarius.  The  t\vo  orifices  of  the  ejaculatory  ducts  are  situated  dorsally 
on  either  side  of  the  collieulus  seminalis,  about  two  inches  (ca.  5  cm.)  behind  the 
internal  urethral  orifice;  they  are  slit-like  antl  close  together.  The  small  orifice 
of  the  uterus  masculinus  is  placed  centrally  on  the  collictdus;  it  is  inconstant.  The 
orifices  of  the  prostatic  ducts  are  on  two  groups  of  small  jiapillte,  placed  lateral  to 
the  openings  of  the  ejaculatory  ducts.  The  ducts  of  the  bulbo-urethral  (Cowper's) 
glands  open  on  two  lateral  series  of  small  papillae,  about  an  inch  (ca.  2.5  cm.) 
further  back  and  close  to  the  median  line.  The  small  orifices  of  tlie  urethral 
glands  are  situated  laterally  in  the  wide  pelvic  portion. 

Structure. — The  mucous  membrane  contains  an  unusually  large  amount  of 
fine  elastic  fibers,  ami  in  its  pelvic  jiart  there  are  alveolar  glands  (Glandulse  ure- 
thrales).  The  epithelium  is  at  first  like  that  of  the  bladder,  then  becomes  cylindrical, 
and  in  the  terminal  part  is  .stratified  squamous.  In  the  dorsal  wall  the  membrane 
forms  a  median  ridge,  the  urethral  crest  (Crista  urethralis);  this  terminates  aliout 
two  inches  from  the  internal  urethral  orifice  in  a  rounded  elevation,  the  collieulus 
seminalis,  on  the  sides  of  which  the  ejaculatory  ducts  open. 

At  the  origin  of  the  urethra  there  is  a  layer  of  circular  unstriped  muscle-fibers 
outsitle  of  the  mucous  coat.  Beyond  this  the  latter  is  inclosed  ]>y  a  layer  of  erectile 
tissue,  composed  of  plexuses  of  veins  supported  by  traboculse  of  elastic  and  smooth 
muscular  tissue.  This  is  continued  by  the  corpus  spongiosum.  Outside  of  the 
erectile  tissue  there  is  a  continuation  of  the  intrinsic  unstriped  muscular  coat, 
consisting  of  external  and  internal  longitudinal  strata,  with  a  layer  of  circular 
fibers  between  them. 

Except  at  its  origin  and  termination  the  urethra  is  provided  with  a  continuous 
layer  of  striped  muscle,  placed  outside  of  the  erectile  tissue.  This  is  described  as 
consisting  of  two  parts  or  muscles. 

(1)  The  urethral  (or  Wilson's)  muscle  (M.  urethralis)  consists  of  dorsal 
and  ventral  layers  of  transverse  fibers  on  the  wide  pelvic  part  of  the  ure- 
thra, and  covers  the  bulbo-urethral  (Cowper's)  glands.  It  is  a  compressor  of  the 
pelvic  part  of  the  urethra  and  the  bulbo-urethral  glands.  By  its  forcible  contrac- 
tion it  plays  an  important  role  in  the  ejaculation  of  the  seminal  fluid,  and  also  in 
evacuating  the  last  of  the  urine  in  micturition.' 

(2)  The  bulbo-cavernosus  muscle  (or  accelerator  urinse)  is  the  continuation 
of  the  urethral  muscle  on  the  extrapelvic  part  of  the  urethra;  it  extends  from  the 
ischial  arch  to  the  glans  penis.  At  the  root  of  the  penis  it  is  the  thickest,  and 
forms  a  complete  layer  of  circular  fibers  which  inclose  the  corpus  spongio.sum  and 
the  urethra.  Beyond  this  it  diminishes  very  gradually  in  thickness,  and  consists 
of  fibers  which  arise  on  a  median  ventral  raphe  and  curve  around  the  corpus 
spongiosum  to  end  on  the  tunica  albuginea  of  the  corpus  cavernosum.  Its  action 
is  to  empty  the  extrapelvic  part  of  the  urethra. 

The  ischio-urethral  muscles  (Fig.  452)  are  small  bands  which  arise  on  the  ischial  arch  and 
crura  of  the  penis  and  pass  forward  to  become  lost  on  the  ventral  layer  of  the  urethral  muscle. 
They  may  assist  in  erection  of  the  penis  by  exerting  pressure  on  the  dorsal  veins. 

'  The  statement  often  made  that  it  acts  as  a  sphincter  of  the  bladder  is  a  hypothesis  of 
doubtful  plausibility.  In  material  hardened  in  situ,  in  which  the  internal  urethral  orifice  is 
tightly  closed,  the  urethral  muscle  apparently  takes  no  part  in  the  closure. 


500 


MALE  GENITAL  ORGANS  OF  THE  OX 


HALE  GENITAL  ORGANS  OF  THE  OX 
The  scrotum  is  situated  somewhat  further  forward  than  in  the  horse.  It  is 
long,  pendulous,  and  has  a  well-marked  neck.  The  skin  here  is  usually  flesh-col- 
ored, Ijut  in  some  breeds  is  more  or  less  pigmented;  it  is  sparselj'  covered  with 
short  hairs.  Just  in  front  of  it  are  four  (sometimes  only  two)  rudimentary  teats. 
The  testicles  are  relatively  larger  than  those  of  the  horse,  and  have  an  elon- 
gated, oval  outline.  The  long  axis  is  vertical.  The  inner  surface  is  somewhat 
flattened. 

A  testicle  of  an  adult  bull  measures  on  the  average  about  four  or  five  inches  (10  to  12  cm.) 
in  length,  exclusive  of  the  epididymis;  with  the  latter  the  length  is  about  six  inches  (15  cm.).   The 


Vesicula  seminalis 


Body  of  prostate 


External 
vrctlirtil  orifice 


Tail 
Fig.  399. — Genebat,  View  of  Genital  Ourans  of  Bull. 


width  is  about  two  and  a  half  to  throe  inches  (ca.  0  to  S  cm.),  and  the  antero-postcrior  diam- 
eter about  the  same.     The  weight  is  about  nine  or  ten  ounces  (ca.  250  to  300  grams). 

The  tunica  albuginea  is  thin.  The  parenchyma  is  yellowish  in  color.  The 
mediastinum  testis  descends  from  the  anterior  part  of  the  upper  extremity  deeply 
into  the  gland  as  an  axial  strand  about  5  mm.  in  thickness.  The  vasa  efferentia 
leave  at  the  upper  end  of  the  mediastinum. 

The  epididymis  is  very  closelj'  attached  to  the  testicle.  The  head  is  long; 
it  curves  over  the  upper  extremity  and  nearly  half  way  down  the  anterior  border 
of  the  testicle.  The  body  is  very  narrow,  and  lies  along  the  outer  part  of  the  pos- 
terior border  of  the  testicle,  to  which  it  is  attached  by  a  narrow  peritoneal  fold. 
The  tail  is  larg(>  and  is  closely  attached  to  the  lower  extremity  of  the  testicle. 

The  spermatic  cord  and  the  tunica  vaginalis  are  much  longer  than  in  the  horse; 
the  extra-inguinal  i)art  of  the  cord  is  about  eight  toten  inches  (20to 25  cm.)  in  length. 
The  cremaster  externus  is  well  developed,  and  almost  completely  incloses  the  tunic 
to  the  neck  of  the  scrotum;  it  does  not  extend  so  far  down  as  in  the  horse,  but  is 
inserted  about  at  the  level  of  the  upper  pole  of  the  testicle.     The  vaginal  ring  is 


MALE  GENITAL  ORGANS  OF  THE  OX  SOI 

relatively  very  small,  ami  is  about  four  inches  (ca.  10  cm.)  from  the  linea  alha. 
The  cremaster  internus  is  feeble. 

The  spermatic  cords  emerge  tlirough  tlie  outer  angles  of  the  external  inguinal  ring.s,  and 
curve  downward  and  inward  to  the  neck  of  the  scrotum.  The  e.\ternal  rings  arc  about  four 
inches  (ca.  It)  cm.)  long,  and  are  two  and  a  half  to  three  inches  (6  to  8  cm.)  apart.  In  animals  in 
good  condition  there  is  a  large  mass  of  fat  above  the  neck  of  the  scrotum,  between  the  spermatic 


Vesicula  seminalis 


Urethra  (covered  by  urethral  muscle) 


Bulho-urethral  {Cowper's)  gland 


Fig.  400. — Lvternal  Gknital  Org.ans 
The  right  vesicula  i.s  sectioned  frontally.     The  dutteJ  line  indicate 


te  (body) 


iti.l;  Dors-al  View. 

he  Ijaclvward  extension  of  the  peritoneum. 


cords.     The  me.sorchium  extends  to  the  bottom  of  the  tunica  vaginalis,  forming  a  narrow  fold 
(ca.  1  cm.  wide)  which  attaclics  the  epididymis  to  the  posterior  part  of  the  tunic. 

The  inguinal  canal  presents  .several  special  features  in  the  bull.  The  internal  ring  is  very 
long.  Its  anterior  border,  formed  by  the  edge  of  the  internal  oblique,  is  decidedly  concave  and 
is  tendinous  in  its  inner  part.  The  long  axis  of  the  external  ring  is  directed  outw^ard,  forward,  and 
downward.  The  spermatic  cord  lies  in  its  outer  part,  the  external  pudic  vessels  in  its  middle. 
A  muscular  band  about  an  inch  wide,  detached  from  the  internal  oblique  muscle,  crosses  tlie  outer 
side  of  the  vaginal  ring. 

The  vas  deferens  is  small  in  caliber.  The  urogenital  fold  is  narrow,  so  that 
the  vasa  are  closer  together  in  it  than  in  the  horse.  On  reaching  the  po.sterior 
part  of  the  bladder  they  are  in  apposition  for  a  distance  of  about  four  inches 


502 


MALE  GENITAL  ORGANS  OF  THE  OX 


(10  cm.),  flanked  and  overlapped  by  the  vesiculse  seminales.  They  form  ampullae 
about  four  or  five  inches  (10  to  12  cm.)  long  and  half  an  inch  (1.2  to  1.5  cm.)  wide, 
the  mucous  lining  of  which  is  plicated.  The.y  then  pass  under  the  body  of  the 
prostate  and  unite  with  the  ducts  of  the  vesiculie  seminales  to  form  the  ejaculatory 
ducts.  The  latter  liave  slit-like  openings  on  either  side  of  the  colliculus  seminalis 
The  vesiculae  seminales  are  not  bladder-like  sacs,  as  in  the  horse,  but  are 
compact  glandular  organs-  with  a  lobulated  surface.  In  the  adult  thej' 
measure  about  four  or  five  inches  (ca.  10  to  12  cm.)  in  length,  two  inches 
(5  cm.)  in  width  in  their  largest  part,  and  an  inch  or  more  (ca.  3  cm.)  in 
thickness.      The    dorsal    surface    of    each    faces    upward    and    inward    and    is 

The  ventral  surface  faces  in  the  opposite 
direction  and  is  non-peritoneal.  Each 
may  be  regarded  as  consisting  of  a 
very  thick-walled,  sacculated  tube,  bent 
on  itself  in  a  tortuous  manner.  This 
tube,  if  straightened  out,  would  be 
about  ten  inches  (25  cm.)  in  length. 
They  are  commonlj'  unsymmetrical  in 
size  and  shape.  Short  branches  are 
often    given    off    from    the  chief    tube. 


partially  covered   with  peritoneum. 


Fig.  401.— An 


OF  Penis  of  Bull, 
Bohm.) 


Fig.  402. — Cross-section    of    Pelvic    Urethra    of 
Bull. 
7 ,  Prostate  gland  (pars  disseminata);  5,  urethra: 
S,  urethral  muscle;  4,  aponeurosis.     The  lumen  of  the 
urethra  is  black. 


The  excretory  duct  or  neck  joins  the  outer  side  of  the  vas  deferens  at  an  acute 
angle  to  form  the  ejaculatory  duct. 

The  structure  of  the  vesicula  is  masked  liy  a  tliick  capsule  of  fibrous  tissue  and  uiisfripod 
muscle,  which  maintains  it  in  its  bent  condition  antl  also  sends  trabecular  between  the  alveoli. 
There  is  a  central  canal  into  which  the  secretion  formed  in  the  alveoli  passes.  The  cavities  (central 
canal  and  alveoli)  are  lined  with  columnar  epithelium.  On  account  of  this  structure  the  term 
glanduUe  ve.siculares  is  preferred  by  some  anatomists. 

The  prostate  is  pale  yellow  in  color,  and  consists  of  two  parts.  The  body 
(Corpus  prostatte)  is  a  mass  which  stretches  across  the  dorsal  surface  of  the  neck 
of  the  bhidiler  and  the  origin  of  the  urethra.  It  measurers  about  an  inch  and  a 
half  (ca.  3.5  to  -1  cm.)  transversely,  and  about  half  an  inch  (ca.  1  to  1.5  cm.)  in  width 
and  thickness.  The  pars  disseminata  surrounds  the  pelvic  part  of  the  urethra; 
dorsally  it  forms  a  layer  about  half  an  inch  (ca.  10  to  12  mm.)  thick,  but  ventrally 
it  is  quite  thin.  It  is  concealed  by  the  urethral  (Wilson's)  muscle;  hence  it  often 
escapes  notice,  but  is  very  evident  on  cross-section  (Fig.  402).  The  prostatic 
ducts  ojien  into  the  urethra  in  rows  between  two  folds  of  the  mucous  membrane 
which  proceed. backward  from  the  colliculus  seminalis. 


MALE  GENITAL  ORGANS  OF  THE  OX  503 

The  uterus  masculinus  appears  to  be  absent  fieciueiitly.  Ellenberger 
states  tliat  it  opens  between  the  ejaculatory  ducts,  while  Martin  says  that 
it  usually  has  two  orifices  at  the  collieulus,  but  that  it  often  unites  with 
the  vasa  deferent  ia. 

The  bulbo-urethral  (Cowper's)  glands  arc  somewhat  smaller  than  in  the 
stallion.  They  are  liable  to  escape  notice,  since  they  are  covered  by  a  thick  layer 
of  dense  fibrous  tissue  and  also  partially  by  the  buhbo-cavernosus  muscle.  Each 
has  a  single  tluct  which  opens  into  the  urethra  under  cover  of  a  fold  of  the  mucous 
memlirane. 

The  penis  is  cylindrical,  and  is  longer  and  of  very  much  smaller  diameter 
than  in  th(>  horse.  Just  behind  the  scrotum  it  forms  an  S-shaped  curve,  the 
sigmoid  flexure  ;  thus  about  one  foot  is  folded  up  -when  the  penis  is  fully  retracted. 
The  flexure  is  effaced  during  erection.  The  glans  penis  is  about  three  inches  (ca. 
8  cm.)  in  length.  It  is  flattened  dorso-vcntrally,  and  its  extremity  is  pointed  and 
twisted.  The  external  urethral  orifice  is  situated  at  the  end  of  a  groove  formed 
by  this  twist;  it  is  only  large  enough  to  admit  a  probe  of  medium  size.  Even  in 
the  non-erect  state  the  penis  is  remarkalily  dense  and  firm.  The  tunica  albuginea 
is  very  thick,  and  incloses  the  urethra.  In  the  first  part,  as  far  as  the  first  curve, 
there  is  a  thick  median  septum  penis.  Beyond  this  there  is  a  central  axial  rod  of 
dense  fibrous  tissue  from  which  numerous  strong  trabeculse  radiate.  The  erectile 
tissue  is  small  in  amount,  so  that  the  organ  undergoes  very  little  enlargement  in 
erection. 

The  length  of  the  penis  in  the  adult  is  about  three  feet  (ca.  90  cm.).  The  crura  are  flattened 
laterally.  The  suspensory  ligaments  are  attached  to  the  ventral  ridge  on  the  symphysis.  The 
JDody  is  somewhat  flattened  dorso-vent rally  beyond  the  iirst  curve.  The  extremity  of  the  glans 
is  unsymmetrical,  the  urethral  orifice  being  situated  ventro-laterally.  The  glans  contains  little 
erectile  tissue,  and  hence  undergoes  little  enlargement  in  erection. 

The  bulbo-cavemosus  muscle  presents  several  remarkable  features.  It  is  for 
the  greater  part  an  inch  or  more  (ca.  3  cm.)  in  thickness,  but  its  length  is  only 
six  to  eight  inches  (15  to  20  cm.).  It  is  covered  by  a  strong  aponeurosis,  and  is 
divided  by  a  median  raphe  into  two  lateral  halves  except  at  its  origin.  It  dim- 
inishes in  size  from  behind  forward,  and  its  anterior  extremity  is  pointed. 

The  ischio-cavemosus  muscle  resembles  in  general  that  of  the  horse,  but  is 
flattened  laterally.     It  is  covered  by  a  close  aponeurosis. 

The  retractor  penis  muscle  resembles  that  of  the  horse  in  origin.  Its  two 
parts  arc  about  an  inch  (ca.  2  to  5  cm.)  apart  on  the  root  of  the  penis,  where  they  lie 
in  a  groove  on  either  side  of  the  bulbo-cavernosus.  They  then  come  close  together 
and  pass  on  either  side  of  the  ventral  curve  of  the  sigmoid  flexure.  Further 
forward  they  lie  along  the  ventral  aspect  of  the  penis,  and  end  about  five  or  six 
inches  (ca.  12  to  15  cm.)  behind  the  glans. 

The  prepuce  is  very  long  and  narrow.  Its  orifice  is  about  two  inches  (ca. 
5  cm.)  behind  the  umbilicus;  it  is  only  large  enough  to  admit  a  finger  readily,  and 
is  surrounded  liy  long  hairs.  The  cavity  of  the  sheath  is  about  fifteen  inches 
(35  to  40  cm.)  long,  and  a  little  over  an  inch  (ca.  3  cm.)  in  diameter.  The  lining 
membrane  forms  longitudinal  folds;  it  is  covered  with  squamous  stratified  epithe- 
lium, and  has  coiled  tubular  glands.  The  penile  layer  is  glandless,  and  is  reddish 
in  color.     It  presents  lymph  nodules  in  its  posterior  part. 

There  are  two  pairs  of  preputial  muscles  which  are  derivatives  of  the  pannicu- 
lus  carnosus.  The  anterior  pair,  the  protractors  of  the  prepuce  (Mm.  prseputiales 
craniales),  are  two  flat  bands,  two  inches  or  more  (5  to  6  cm.)  in  width,  which  arise 
close  together  in  the  xiphoid  region,  about  eight  inches  (20  cm.)  in  front  of  the 
preputial  orifice.  Traced  backward  thej'  diverge,  leaving  the  umbilicus  and 
an  area  about  one  and  a  half  inches  wide  free,  and  then  unite  behind  the  preputial 
orifice.     They  draw  the  prepuce  forward.     The  posterior  pair,  the  retractors  of 


504 


MALE  GENITAL  ORGANS  OF  THE  PIG 


the  prepuce  {Mm.  prteputiales  eaudales),  arise  in  the  inguinal,  region  and  converge 
on  the  anterior  part  of  the  prepuce.     They  draw  the  prepuce  backward. 

These  muscles  are  subjeet  to  a  good  deal  of  variation.  The  retractor  may  be  absent .  Many 
fibers  come  in  from  the  pannieulu?  on  either  side,  dip  under  the  protractor,  and  are  inserted  into 
the  skin  just  behind  tlic  preputial  opening.  The  homologuc  of  the  protractor  is  present  in  the 
cow. 

The  urethra  in  its  pelvic  part  is  about  five  inches  (12  cm.)  long,  and  is  of 
relatively  small  and  uniform  caliber.  The  urethral  (AVilson's)  muscle  incloses  the 
tube  ventrally  and  laterally;  it  is  very  thick,  crescentic  in  cross-section,  and  is 
covered  by  an  aponeurosis.  Dorsally,  the  aponeurosis  is  thick  and  the  muscle 
absent.  Inside  of  these  the  pars  di-sseminata  of  the  prostate  surrounds  the  urethra 
as  far  back  as  the  bulbo-urethral  glands.  The  colliculus  seminalis  is  short,  but 
prominent;  frotn  it  the  urethral  crest  extends  forward  to  the  trigonum  vesicae. 
The  extrapelvic  part  has  an  enlargement,  the  bulb,  at  its  origin;  it  then  gradually 


Processus  urethrm 


Galea  glandis 

Corona  (jlandis 
Collum  glandis 


Prepuce 


Processus  urethrm 
Galea  glandis 
Corona  glandis 

Tuhrrcnl'im 
Colhiin  ijhnxHs 

Prepuce 
Raphe  yraputii 


Fig.  403. — -Interior  Part  of  Penis  of  Ram. 

-1.  Right  side;  B,  leftside.     (After  Bohm.) 

diminishes  in  diameter,  and  is  relatively  very  small  at  its  termination.     Other 
features  have  been  mentioned  in  preceding  paragraphs. 

In  the  ram  the  urethra  lies  in  a  groove  on  the  ventral  surface  of  the  corpus 
cavernosum.  Its  terminal  part  projects  commonly  3  to  4  cm.  bej'ond  the  glans 
penis,  forming  a  twisted  processus  urethrse. 


MALE  GENITAL  ORGANS  OF  THE  PIG 
The  scrotum  is  situated  a  short  distance  from  the  anus,  and  is  not  so  sharply 
defined  from  the  surrounding  parts  as  in  the  other  animals. 

The  testicles  are  very  large  and  are  soft  in  texture.  Their  long  axis  is  almost 
vertical,  the  free  border  being  posterior  and  the  tail  of  the  epididymis  dorsal. 
The  mediastinum  testis  is  well  developed.  The  epidiflymis  is  closely  attached  to 
the  testicle  anil  the  tunica  vaginalis;   the  tail  is  specially  large. 

The  spermatic  cord  is  necessarily  very  long  (20  to  25  cm.  in  a  boar  of  meditmi 
size).  The  vas  deferens  in  its  testicular  part  is  flexuous,  and  is  closely  attached 
to  the  tunica  vaginalis;  it  forms  no  ampullae.  The  cremaster  extemus  is  well 
developed,  and  extends  to  about  the  middle  of  the  scrotal  part  of  th.e  tunic. 


MALE    GEN'ITAL    ORGAN'S    OF   THE    PIG 


505 


The  vesiculae  seminales  are  exceedingly  large,  and  extend  into  tlie  abdominal 
cavity.  They  are  three-sided  pjTamidal  masses,  are  in  apposition  with  each  other 
medially,  and  cover  the  posterior  part  of  the  bladder  and  the  ureters,  the  vasa 
deferentia,  the  body  of  the  prostate,  and  the  anterior  part  of  the  urethra.  They 
are  pale  jiink  in  color,  distinctly  lobulated  and  glandular  in  structure,  and  contain 
large  alveoli,  but  no  central  cavity.  There  are  two  excretory  ducts  which  open  into 
the  urethra  close  to  the  vasa  deferentia;  the  two  ducts  frequentlj-  unite. 

In  the  adult  boar  the  vesiculae  are  about  five  to  six  inches  (ca.  12  to  lo  cm.)  long,  two  to 
three  inches  (ca.   .5  to  S  cm.)  wide, 
and  one  and  a  half  to  two  inches 
(ca.  4  to  5  cm.)  thick;  they  weigh 
about  6  to  S  ounces  each. 

The  prostate  consists  of 
two  jiarts.  as  in  the  ox.  The 
body  is  about  an  inch  (2.5 
cm.)  ^-ide,  and  embraces  the 
neck  of  the  bladder  and  the 
urethra  at  their  junction  dor- 
sally  and  laterally.  It  is  con- 
cealed by  the  vesiculir  sem- 
inales. The  pars  disseminata 
forms  a  layer  which  surrountls 
the  pelvic  part  of  the  urethra, 
and  is  covered  l\v  the  urethral 
muscle. 

The  uterus  masculinus  is 
small. 

The  bulbo-urethral  (Cow- 
jjer's)  glands  are  very  large  and 
dense.  They  are  somewhat 
cyliuchical,  and  lie  on  either 
side  of  and  upon  the  pos- 
terior two-thirds  of  the  pelvic 
urethra.  In  a  large  boar  they 
are  about  five  inches  (ca.  12 
cm.)  in  length  and  an  inch  or 
more  (ca.  2.5  to  3  cm.)  in 
diameter.  Thej'  are  partially 
covered  with  a  layer  of  stri- 
ated muscle  (^I.  ischio-glandu- 
laris),  and  have  a  lobulated 
surface.  Each  gland  has  a 
large  excretory  duct  which 
leaves  at  the  posterior  ex- 
tremity, perforates  the  dorsal  wall  of  the  urethra  at  the  ischial  arch,  and  opens  in 
a  cul-de-sac  covered  by  a  fold  of  mucous  membrane. 

It  is  to  be  noted  that  these  accessorj'  glands  are  very  small  in  animals  which  have  been 
castrated  eady. 

The  penis  resembles  in  general  that  of  the  ox.  The  sigmoid  flexure  is,  how- 
ever, prescrotal.  The  anterior  portion  has  no  glans,  and  is  spirally  twisted, 
especially  in  erection.  The  urethral  orifice  is  slit-like  and  is  situated  ventro- 
laterally,  close  to  the  pointed  extfemity.  The  penis  in  the  adult  boar  measures 
about  18  to  20  inches  (ca.  45  to  50  cm.)  in  length.  Its  muscles  resemble  those  of 
the  bull ;   the  bulbo-cavernosus  is  very  strong  but  short. 


Fig.  404— Gi 
.Testicle;  6, epididjT 


Organs  of  Boar. 

35  deferens:  d.  spermatic  artery 
f ,  vesicula  seminalis  reflected  to  show  the  body  of  the  prostate,  /;  e' 
excretory  ducts  of  vesiculse;  (/,  bulbo-urethral  (Cowper's)  gland;  h 
urinary  bladder;  i',  urethral  muscle;  k.  bulbo-cavernosus  muscle;  i 
penis;  /'.  sigmoid  flexure  of  penis;  /",  spiral  anterior  part  of  penis,  ex 
posed  by  slitting  open  prepuce;  m.  orifice  of  preputial  pouch;  n.  re 
tractor  penis  muscle.     (Ellenberger-Batim,  Anat.  d.  Haustiere.) 


506  MALE  GENITAL  ORGANS  OF  THE  DOG 

The  prepuce  has  a  narrow  orifice,  around  which  there  are  a  number  of  stiff  hairs. 
The  cavity  is  partially  divided  by  a  circular  fold  into  a  posterior  narrow  portion 
and  a  much  wider  anterior  portion.  The  lining  membrane  of  the  posterior  part  is 
papillated,  and  is  in  close  contact  with  the  penis.  In  the  dorsal  wall  of  the  wide  part 
there  is  a  circular  opening  which  leads  into  a  cul-de-sac,  the  preputial  diverticulum. 
This  pouch  is  ovoid  in  form  (when  distended),  and  varies  greatly  in  size  in  different 
subjects.  It  extends  for  the  most  part  backward  over  the  narrow  part  of  the 
prepuce.  Its  cavity  is  partially  divided  by  a  narrow  median  septum.  It  contains 
usually  decomposing  urine  and  macerated  epithelium,  which  have  a  characteristic 
and  very  unpleasant  odor.     Concrements  have  been  found  in  it. 

Oehmke  found  that  a  cast  of  the  pouch  in  a  Yorkshire  boar  weighing  about  .500  pounds 
measured  9  cm.  in  length,  12 '2  cm.  in  breadth,  and  6  cm.  in  height.  The  opening  into  the  pre- 
puce will  admit  two  fingers  in  the  adult,  but  is  ordinarily  closed  by  folds  of  the  lining  membrane. 
The  sac  is  much  smaller  in  animals  which  were  castrated  young,  and  the  opening  is  vertical  and 
further  back;  in  them  it  is  often  empty  or  contains  only  a  little  clear  urine.  The  pouch  is  covered 
by  a  layer  of  striped  muscle  which  is  mainly  derived  from  the  homologue  of  the  protractor  of  the 
prepuce  of  ruminants. 

The  urethra  has  a  very  long  pelvic  portion  (ca.  15  to  18  cm.  long  in  the  adult ) ; 
it  is  inclosed  (with  the  pars  disseminata  of  the  prostate)  by  a  thick  urethral  muscle. 
There  is  a  distinct  bulb  at  the  root  of  the  penis.  The  penile  part  is  of  small  caliber, 
and  is  surrounded  by  erectile  tissue  which,  however,  does  not  extend  to  the 
extremity  of  the  penis. 


MALE  GENITAL  ORGANS  OF  THE  DOG 

The  scrotum  is  situated  about  half  way  between  the  inguinal  region  and  the 
anus.  The  skin  covering  it  is  pigmented  and  is  covered  sparsely  with  fine  hairs. 
The  raphe  is  not  very  distinct. 

The  testicles  are  relatively  small,  and  have  a  round-oval  form.  The  long 
axis  is  oblique,  and  is  directed  upward  and  backward.  The  mediastinum  testis 
is  central  and  is  well  developed.  The  epididymis  is  large,  and  is  closely  attached 
along  the  outer  ]iart  of  the  dorsal  border  of  the  testicle. 

The  spermatic  cord  and  the  tunica  vaginalis  are  long;  they  cross  the  side  of 
the  penis  very  obliciuely.  The  upper  entl  of  the  tunic  is  sometimes  closed,  so  that 
there  is  then  no  vaginal  ring.     The  vasa  deferentia  have  very  narrow  ampullae. 

The  vesiculse  seminales  are  absent;    hence  there  are  no  ejaculatory  ducts. 

The  prostate  is  relatively  large;  it  is  yellowish  in  color,  dense  in  structure, 
and  lies  at  the  anterior  border  of  the  pubis.  It  is  globular,  and  surrounds  the 
neck  of  the  bladder  and  the  urethra  at  their  junction.  A  faint  median  furrow 
indicates  a  division  into  two  lateral  lobes.  The  capsule  and  stroma  contain  a  large 
amount  of  unstripcd  muscle.  The  ducts  are  numerous.  Lobules  of  prostatic 
tissue  (pars  disseminata)  are  also  found  on  the  urethra  further  back.  The  gland 
is  subject  to  much  variation  in  size,  and  is  often  enlarged,  especially  in  old  subjects. 

The  uterus  masculinus  is  a  very  small  saccule  (Utriculus  prostaticus),  often 
difficult  to  find. 

The  bulbo-urethral  (Cowper's)  glands  are  absent. 

The  penis  presents  several  special  features.  In  its  posterior  jiart  there  are  two 
distinct  corpora  cavernosa,  separated  by  a  median  septum  penis.  In  its  anterior 
part  there  is  a  bone,  the  os  penis,  which  in  large  dogs  reaches  a  length  of  four 
inches  (ca.  10  cm.)  or  more.  It  is  regarded  as  a  continuation  forward  of  the  corpus 
cavernosum.  Ventrally  it  is  grooved  for  the  urethra;  ilorsally  it  is  convex,  and 
anteriorly  it  becomes  smaller  and  has  a  curved  fibrous  prolongation.  The  glans 
penis  is  very  long,  extending  over  the  entire  length  of  the  os  penis;    posteriorly  it 


MALE  GENITAL  ORGANS  OF  THE  DOG 


507 


forms  a  rounded  enlargement,  the  bulbus  glandis;  anteriorly  it  is  cylindrical, 
smaller,  and  pointed  at  the  extremity.  Just  in  front  of  tlie  l)ull)\is  glandis  there  is 
a  thick  circular  layer  of  glands,  forming  the  annulus  glandularis  (Schmaltz). 
The  two  dorsal  veins  arise  from  the  Ijulbus  glandis,  pass  Ijackward  on  the  dorsum 
penis,  and  unite  at  the  ischial  arch.  A  small  muscle  (M.  compressor  vense  dorsalis 
penis)  arises  from  the  tutjer  ischii  on  either  side;  the  two  converge  on  the  dorsum 
penis  near  the  bulbus  glandis.  They  compress  the  dorsal  veins,  and  may  also  tend 
to  elevate  the  penis  and  thus  assist  in  copulation.  The  other  muscles  offer  no 
features  worthy  of  special  description. 

The  prepuce  forms  a  complete  slieath  around  the  anterior  ])art  of  the  penis. 
The  outer  la3-er  is  ordinary  integument.     The  inner  layer  has  the  character  of  a 


Fig.  405. — External  Genital  Organs  of  Male  Dog,  Ventro- 
lateral View  of  Preparatio.v. 
i,  Scrotum;  1\  tunica  vaginalis;  2,  epididymis;  3,  vascular 
part  of  spermatic  cord;  4.  vas  deferens;  5,  prepuce;  6,  glans  penis; 
&,  corpus  cavemosum  penis;  7.  bulbus  glandis;  7',  contour  of  bul- 
bus in  erection;  S,  ischio-cavernosus  muscle:  a,  acetabulum;  6,  ob- 
turator foramen.       lAfter  Ellenberger,  in  Leisering's  Atlas.) 


Fig 


1,  Urinary  bladder;  2.  ureter;  3,  vas 
deferens;  4.  prostate;  5.  urethral  muscle;  ff, 
bulb  of  urethra;  a,  abdominal  wall;  6.  ilium; 
c,  ischium,  (.\fter  Ellenberger,  in  Leisering's 
Atlas.) 


glandular  mucous  membrane;  it  is  thin  and  reddish  in  color.  The  penile  layer  is 
glandless.  In  the  fundus  of  the  praeputial  cavity  there  are  numerous  Ij-mph 
follicles.  The  protractor  muscles  arise  in  the  xiphoid  region  antl  decussate  pos- 
teriorly around  the  extremity  of  the  penis. 

The  pehdc  part  of  the  urethra  is  relatively  long.  Its  first  part  is  inclosed  in 
the  prostate.'  At  the  ischial  arch  the  urethra  has  a  well-developed  biloljed  bulb, 
formed  by  an  enlargement  here  of  the  corpus  spongiosum.  It  is  covered  by 
the  strong  but  short  bun30-caverno.sus  muscle.  The  other  erectile  bodies  have 
been  described. 

The  urethral  (Wilson's)  muscle  is  very  strong;  it  encircler  the  urethra  and 
has  a  median  raphe  dorsally. 

'  Tliis  is  clinically  important,  since  enlargement  of  the  prostate  may  interfere  with  mic- 


THE  FEMALE   GENITAL  ORGANS 

The  female  genital  organs  (Organa  genitalia  feminina)  are:  (1)  The  two 
ovaries,  the  essential  re]iroiluctive  glands,  in  which  the  ova  are  produced;  (2) 
the  uterine  or  Fallopian  tubes,  which  convey  the  ova  to  the  uterus;  (3)  the  uterus, 
in  whicii  the  ovum  tlevelops;  (4)  the  vagina,  a  dilatable  passage  through  which  the 
fcetus  is  expelled  from  the  uterus;  (5)  the  vulva,  the  terminal  segment  of  the  genital 
tract,  which  serves  also  for  the  expulsion  of  the  urine;  (6)  the  mammary  glands, 
which  are  glands  of  the  skin,  but  are  so  closely  associated  functionaUy  with  the 
generative  organs  proper  as  to  be  described  with  them. 


GENITAL  ORGANS  OF  THE  MARE 
THE   OVARIES 
The   ovaries  (Ovaria)  of  the  mare  are  bean-shapetl,  and  are  much  smaller 
than  the  testicles.     Their  size   varies  much  in  different  subjects,  and  they  are 


Fifi.  407. — Lateral  View  of  Genital  Okgans  and  Adjacent  Strttcti'res  of  Mare. 
The  removal  of  the  ulher  ahilominul  viscera  has  allowe  i  the  ovarie.s  and  uterus  to  sink  down,  whereas  they 
are  normall.v  in  contact  with  the  roof  of  the  cavity  in  the  non-pregnant  subject.  /,  Left  ovary;  S.  Fallopian  tube: 
S,  left  cornu  uteri;  4.  right  cornu  uteri;  5,  corpus  uteri;  5',  portio  vaginalis  uteri,  and  5",  os  uteri,  seen  through 
window  cut  in  vagina;  S,  broad  ligament  of  uterus;  6',  round  ligament;  7,  vagina;  S,  labia  vulva';  9,  rima  vulvsp; 
9*,  superior  commissure,  and  0" ,  inferior  commissure  of  vulva;  JO,  constrictor  vulvae;  //,  position  of  vestibular 
bulb:  /S,  ventral  wall  of  abdomen;  i3,  left  kidney;  /4,  left  ureter;  7.5,  urinary  bladder;  ;C,  urethra;  /7,  rectum; 
is,  anus;  19,  19',  unpaired  and  paired  parts  of  sphincter  ani  externus;  SO,  retractor  ani  cut  at  disappearance 
under  sphincter;  21,  sui?pensory  ligament  of  anus;  32,  longitudinal  muscular  layer  of  rectum;  22' ,  recto-coccj'geus; 
S3,  constrictor  vaginie;  a,  utero-ovarian  artery,  with  ovarian  (a')  and  uterine  (n")  branches;  b,  uterine  artery  ; 
c.  umbilical  artery;  rf,  ischium;  c,  imbis;  /.ilium.     (.After  Ellenberger,  in  Leisering's  .\tlas.) 


normally  larger  in  young  than  in  old  animals;    one  ovary  is  often  larger  than 
the  other.     They  are  about  three  inches  (ca.  7  to  8  cm.)  long  and  an  inch  to  an  inch 

508 


THE    OVARIES 


509 


and  a  lialf  (ca.  3  to  4  cm.)  thick.     The  weight  is  about  two  and  a  half  to  tiirce 
ounces  (ca.  70  to  80  grams). 

Eacii  presents  for  description  two  surfaces,  two  borders,  and  two  extremities 
or  poles.  The  surfaces  are  termed  internal  and  external  (Facies  medialis,  lateralis); 
thej'  are  both  smooth  and  rounded.'  The  attached  or  mesovarial  border  (Margo 
mesovaricus)  is  convex.  It  is  inclosed  in  a  part  of  the  broad  ligament  termed  the 
mesovarium;  the  vessels  and  nerves  reach  the  gland  at  this  border.  The  free 
border  (Margo  liber)  is  marked  by  a  notch  which  leads  into  a  depres.sion,  the 
ovulation  fossa.  The  tubal  or  anterior  extremity  (Extremitastubaria)  is  rounded, 
and  is  relateil  to  the  fimbriated  end  of  the  uterine 
or  Fallopian  tube.  The  uterine  or  posterior  ex- 
tremity (Extremitas  uterina)  is  also  round,  and  is 
connected  with  the  horn  of  the  uterus  by  the 
ovarian  ligament. 

The  ovaries  are  situated  in  the  sublumbar  region 
of  the  alidominal  cavity,  about  a  handbreadth  be- 
hind the  corresponding  kidnej'.  Thcj'  are  in  contact 
with  the  lumbar  wall  of  the  abdomen,  and  are  com- 
monly about  two  or  three  inches  (ca.  5  to  7.5  cm.) 
from  the  median  plane.  The  distance  from  the 
ovaries  to  the  vulvar  orifice  is  about  twenty  inches 
(ca.  50  cm.)  in  a  mare  of  medium  size.  The  at- 
tached (mesovarial)  border  is  commonly  directed 
toward  the  median  plane,  the  free  border  laterally 
and  somewhat  ventrallv. 


The  position  of  the  ovaries  is  not  constant,  but  is  sub- 
ject to  less  variation  than  might  be  expected  from  their  mode 
of  attachment.  The  normal  variations  in  the  non-pregnant 
state  are  chiefly  in  a  transverse  direction,  and  do  not  usually 
exceed  two  or  three  inches  (ca.  5  to  7  cm.).  It  is  not  at  all 
rare  to  find  the  ovary  deflected  medially,  so  that  the  external 
surface  faces  v-entrally.  In  the  longitudinal  direction  little 
variation  appears  to  occur.  The  right  ovary  is  usually  about 
four  or  five  inches  (ca.  10  to  12  cm.),  and  the  left  one  about 
three  or  four  inches  (ca.  8  to  10  cm.),  behind  the  correspond- 
ing kidney.  Thus  they  lie  about  in  a  transverse  plane  tangent 
to  the  external  angles  of  the  ilia,  i.  e.,  through  the  fifth  lumbar 
vertebra.  They  may  be  about  two  inches  (ca.  5  cm.)  from  the 
extremity  of  the  corresponding  cornu  of  the  uterus  or  in  con- 
tact with  it.  The  right  ovary  commonly  lies  a  little  (ca.  2. .5 
cm.)  further  forward  than  the  left  one.  Except  during  preg- 
nancy, they  are  normally  in  contact  with  the  lumljar  ab- 
dominal wall,  and  do  not  hang  down  among  the  adjacent 
viscera. 


Fig.  408. — Eight   Ov.\rt   of   Mare, 

WITH  .\djacext  Structures. 
The    extremity    of    the    cornu 
uteri    is   opened.     /,  Ovary;     2.  Fal- 
lopian tube,  with  its  ostium   abdom- 
inale  (2'),    fimbrire    iS"),  and    ostium 
i2"');  3,  cornu  uteri, with  its 
lining   (3');    4>  ovarian   liga- 
ment:   4\  mesosalpinx.     (After    Ell- 
enberger.    in     I.eisering's     .\tlas,    re- 
duced.) 


The  ovary  is  attached  to  the  sublumbar 
region  by  the  anterior  part  of  the  broatl  liga- 
ment; this  part  of  the  ligament,  the  mesovarium, 

is  about  three  or  four  inches  (ca.  8  to  10  cm.)  wdde,  measured  from  the 
ovary  directly  to  the  parietal  attachment.  The  uterine  or  posterior  extremity 
of  the  ovary  is  connected  with  the  extremity  of  the  cornu  of  the  uterus  by 
the  ovarian  ligament  (Ligamentum  ovarii  proprium);  this  is  a  band  of  unstriped 
muscle  inclosed  between  the  layers  of  the  broad  ligament. 

Structure. — The  greater  part  of  the  surface  of  the  o\'ary  has  a  covering  of 
peritoneum.     The  peritoneal  investment  is  absent  at  the  attached  border  where 

'  These  terms  apply  properly  only  when  the  adjacent  viscera  are  removed  and  the  ovaries 
are  actually  "suspended"  by  the"  broad  ligaments.  When  the  ovary  is  in  its  natural  position, 
the  surfaces  are  tlorsal  and  ventral,  the  former  corresponding  to  the  "external"  surface  if  the 
free  border  is  directed  outward,  to  the  "internal"  if  the  free  edge  is  medial. 


510 


GENITAL  ORGANS  OF  THE  MARE 


the  vessels  and  nerves  enter;  this  area  is  termeil  the  hilus.  The  ovulation  fossa 
is  covered  liy  a  layer  of  columnar  cells,  a  remnant  of  the  ])rimitive  germinal  epithe- 
lium. The  stroma  of  the  ovary  (Stroma  ovarii)  is  a  network  of  connective  tissue 
and  unstriped  muscular  fibers.  In  the  deeper  or  medullary  portion  of  the  stroma 
(Zona  vasculosa)  the  meshes  are  largely  occupieil  by  the  numerous  blood-vessels. 
In  the  peripheral  or  cortical  portion  (Zona  parenchymatosa)  are  numerous  ova 
(Ovula)  in  various  stages  of  development.  The  immature  ova  are  surrounded  by 
follicle  cells;  those  more  advanced  in  development  are  inclosed  also  by  a  condensa- 
tion of  the  stroma  termed  the  theca  f olliculi ;  within  the  theca  is  a  quantity  of 
fluid,  the  liquor  f olliculi.  These  constitute  the  Graafian  follicles  (Folliculi  oojihori), 
which  enlarge  as  they  mature,  becoming  visible  to  the  naked  eye  as  vesicles  with  a 
diameter  of  a  centimeter  or  more.  When  fully  developed,  the  follicles  are  super- 
ficially situated,  and  often  project  slightly  from  the  surface  of  the  ovary.     At 

intervals  follicles  rupture  and 
their  contents  escape.  This 
process,  which  sets  free  the 
ovum,  is  termed  ovulation; 
it  takes  place  in  the  mare 
only  at  the  ovulation  fossa, 
and  occurs  during  the  periods 
of  oestrum. 

After  rupture  of  a  follicle  its 
cavity  is  partly  occupied  by  a 
blood-clot,  constituting  what  may 
be  termed  a  corpus  rubrum.  By 
proliferation  and  enlarKcnient  and 
fatty  changes,  the  follicle  cells  are 
transformed  into  lutein  cells,  form- 
ing a  yellow  mass  known  as  a  cor- 
pus luteum.  If  impregnation  takes 
place,  the  accompanying  increase  in 
vascularity  of  the  organs  may  cause 
the  corpus  luteum  to  reach  a  large 
size;  if  impregnation  does  not  occur, 
it  is  much  smaller,  and  is  sooner 
replaced  by  scar  tissue,  the  corpus 
albicans. 

In  the  young  foal  the  ovaries 
are  large  and  oval  in  form.  The 
free  border  is  convex  and  is  covered 
by  germinal  epithelium,  which  ex- 
tends over  part  of  the  surfaces  also. 
This  area  is  distinguishable  by  its 
dull  gray  appearance  from  the  peritoneal  surface,  which  has  the  usual  smooth  glistening 
character.  As  growth  proceeds  the  ovary  gradually  becomes  bent  until  it  assumes  its 
definitive  curved  shape.  The  germinal  epithelium  is  then  limited  to  the  ovulation  fossa. 
The  ovary  migrates  somewhat  during  development  from  its  primitive  position,  which  is  the 
same  as  that  of  the  testicle. 

In  old  animals  the  ovaries  commonly  consist  largely  of  filjrous  tissue,  in 
which  there  are  often  cj'sts  of  various  sizes.  The  ova,  present  in  enormous  num- 
ber at  birth,  have  then  been  extruded,  or  destroyed  by  phagocytic  action  or  de- 
generation. 

Vessels  and  Nerves. — The  arteries  of  the  ovary  are  derived  from  the  ovarian 
artery.  The  artery  is  relatively  large  and  is  fle.xuous;  it  reaches  the  attached  i)order 
of  the  ovary  by  passing  between  the  layers  of  the  mesovarium.  The  veins  are 
large  and  numerous.  They  form  a  plexus  somewhat  like  that  of  the  spermatic 
cord.  The  lymph  vessels  pass  to  the  lumbar  glands.  The  nerves  are  derived  from 
the  sympathetic  system  through  the  renal  and  aortic  plexuses.  They  accompany 
the  arterial  branches. 


Fig.  409. — Schematic  Represent.ation  of  Change.s  in  Ovary  of 
Mare  fro.m  Fcetal  to  .\dult  State,  (.\fter  Born.) 
The  changes  alTect  chiefly  the  free  border  (upper  in  figure)  and 
the  extent  and  form  of  the  area  covered  by  germinal  epithelium  (4). 
/,  Peritoneum  (broad  ligament);  S.  ligament  of  ovary;  S,  fimbria  of 
Fallopian  tube:  4,  germinal  eijitheliuin;  5.  vessels,  which  reach  the 
ovary  at  the  attached  border  (ff).  The  latter  represents  the  hilus, 
while  the  deep  ilepression  at  the  free  border  is  the  ovulation  fossa. 
(EUenberger.  in  Leisering's  .\tlas.) 


THE    UTERINE    OR    FALLOPIAN    TUBES — THE    UTERUS  511 

THE  UTERINE  OR  FALLOPIAN  TUBES 
The  uterine  or  Fallopian  tubes  (Tubts  uterinse)  act  as  excretory  ducts  of  the 
ovaries,  since  they  convey  tlie  ova  from  the  repiochictive  glands  to  the  uterus. 
They  are  not,  however,  in  tlirect  continuity  with  the  glands,  hut  rather  partly  in 
contiguity  with,  and  partly  attached  to,  thcni.'  They  are  two  flexuous  tubes, 
about  ten  to  twelve  inches  (ca.  25  to  30  cm.)  long,  which  extend  from  the  extremities 
of  the  uterine  cornua  to  the  ovaries.  Each  is  inclosed  in  a  peritoneal  fold,  derived 
from  the  external  laj'er  of  the  broad  ligament,  and  termed  the  mesosalpinx.  This 
largely  covers  the  outer  aspect  of  the  ovary,  and  forms  with  it  and  the  broad  liga- 
ment a  pouch  called  the  bursa  ovarica.  The  uterine  extremity  of  the  tube  com- 
municates with  the  cavity  of  the  cornu  bj'  a  minute  orifice,  the  ostium  uterinum. 
The  ovarian  or  fimbriated  extremity  is  expanded  into  a  funnel-shaped  infundibulum. 
The  margin  of  the  latter  is  slit  into  irregular  processes  or  fimbriae,  some  of  which, 
the  fimbriae  ovaricae,  are  attached  in  the  ovulation  fossa.  In  the  center  of  the 
fimbriated  extremity  is  a  small  opening,  the  ostium  abdominale,  lij-  which  the  tube 
communicates  with  the  peritoneal  cavity.  The  tube  ajipears  normally  to  be 
applied  to  the  ovary,  so  that  the  extrudetl  ova  pass  into  it  and  are  conveyed  to  the 
uterus.' 

Pedunculated  cysts,  the  hydatids  of  Morgagni,  are  often  found  on  one  or  more  of  the 
fimbriiE.  In  the  mesosalpinx  are  bUnd  flexuous  tuljules,  which  constitute  the  paroophoron,  a 
remnant  of  the  Wolffian  body.  They  are  most  evident  in  the  young  adult,  and  tend  to  disappern- 
with  increasing  age.     Not  uncommonly  they  give  rise  to  cysts. 

Structure. — The  tube  is  covered  externally  by  a  serous  coat  formed  by  the 
mesosalpinx.  The  serous  memljrane  is  continued  on  the  fimbria^,  and  meets  the 
mucous  lining  on  them.  The  fibrous  coat  or  adventitia  is  continuous  with  the 
filjrous  lamina  of  the  broad  ligament.  The  muscular  coat  consists  chiefly  of  circu- 
lar fil)ers,  although  longitudinal  fibers  occur  externally.  The  mucous  coat  is 
thin  and  is  much  plicated.  The  folds  (Plicse  tubarite)  are  chiefly  longitinlinal,  but 
in  the  wide  part  of  the  tube  (Ampullse  tuba?)  they  are  very  complex,  .so  that  on 
cross-sections  the  spaces  between  the  folds  may  be  mistaken  for  brancheil  tubular 
glands.  The  folds  are  continued  on  to  the  findiria.  The  epithelium  is  a  single 
layer  of  columnar  ciliated  cells,  the  cilia  producing  a  current  directed  toward  the 
uterus.  At  the  fimbriated  extremity  this  epithelium  passes  gradually  into  the 
scjuamous  type  of  the  serous  coat. 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  utero-ovarian  artery. 
The  veins  are  satellites  of  the  arteries.  The  lymphatics  pass  with  the  ovarian 
vessels  to  the  lumbar  glands.  The  nerves  have  a  similar  origin  to  those  of  the 
ovary. 

THE  UTERUS 

The  uterus  is  a  hollow  muscular  organ,  which  receives  the  Fallopian  tubes 
anteriorly  and  opens  into  the  vagina  posteriorh'.  It  is  situated  chieflj'  in  the  ab- 
dominal cavity,  Ijut  extends  a  short  distance  into  the  pelvic  cavity.  It  is  attached 
to  the  lumljar  wall  of  the  abdomen  and  the  lateral  walls  of  the  pelvic  cavity  by 
two  folds  of  peritoneum  termed  the  broad  ligaments.  It  consists  of  two  cornua 
or  horns,  the  body,  and  the  neck. 

The  cornua  or  horns  of  the  uterus  (Cornua  uteri)  are  situated  entirely  in 
the  aljdomen.     They  appear  to  varj-  considerably  in  position;    commonly  thej- 

'  The  Fallopian  tubes  may  be  regarded,  both  in  structure  and  morphology,  as  prolongations 
of  the  uterus  (McMurrieh). 

-  The  arrangement  is  the  only  exception  to  the  general  rule  that  the  serous  cavities  are 
closed.  In  this  case  the  mucous  memlirane  of  the  fiml)riated  extremity  is  continuous  with  the 
adjacent  peritoneum,  a  persistence  of  the  embryonic  relations  of  the  Miillerian  duct. 


512 


GENITAL  ORGANS  OF  THE  MARE 


are  pressed  up  against  the  sublumhar  muscles  by  the  intestine  (left  portions  of 
large  colon,  small  colon,  and  small  intestine).  They  are  cj'lindrical,  and  are 
about  ten  inches  (ca.  25  cm.)  in  length.  The  anterior  extremity  of  each  forms  a 
blunt  point  which  receives  the  Fallopian  tube.  Posteriorly  they  increase  some- 
what in  caliber,  converge,  ami  unite  with  the  body.  The  dorsal  (or  attached) 
border  is  slightly  concave  and  is  attached  to  the  broad  ligament.  The  ventral 
border  is  convex  and  free. 


Fio.  410.— Gkn-itai.  ORnAN-s  OF  Maff.  Dobsal  View. 
The  left  cornu  and  adjacent  jjart  of  the  botly  of  the  uterus  and  the  vagina  and  vulva  are  opened  up.  U 
Ovary;  2.  Fallopian  tube,  with  S' ,  its  timbriated  end;  S,  cavity  of  corpus  uteri;  J,,  cavity  of  left  cornu;  5,  right 
cornu,  with  5',  its  communication  with  the  body;  (7,  portio  vaginalis  uteri;  6',  os  uteri;  7,  broad  ligament  of  uterus; 
8,  ligament  of  ovary;  9,  vagina;  10,  vulva;  /O',  glandula-  vestibulares  majores;  10".  glandulte  vestibulares  niinores; 
11,  transverse  fold;  12,  external  urethral  opening;  IS,  13',  labia  vulva?:  14,  glans  clitoridis;  14',  jtmction  of 
crura  to  form  corpus  clitoridis  indicated  by  tlotteil  lines:  15,  urinary  bladder:  a,  utero-ovarian  artery  with 
ovarian  (a')  antl  uterine  (a")  branches;    6   ute'"'"" '""*°'"''       t  xftar  v\\at\\^arrrar  ',„  r  Qico,-i,^.T't  Atloc^ 


irtery.     (.\fter  EUenberger,  in  Leisering's 


When  a  soft  utori;,s  is  distpndeil,  the  cornua  are  strongly  curved,  but  this  does  not  represent 
tlie  natiu-al  form.  Wlien  fixed  in  .litii  tlie  liorns  are  eitlier  sliglitly  curved  or  nearly  straight. 
The  two  horns  are  commonly  unsymmetrical  in  length  and  diameter  in  mares  which  hiive  borne 
young. 

The  body  of  the  uterus  (Corpus  uteri)  is  situated  partly  in  tin-  abdomen, 
partly  in  the  pelvic  cavity.  It  is  cylindrical,  but  considerably  flattened  dorso- 
vcntrally,  so  that  in  cross-section  it  is  elliptical.  Its  average  length  is  about  six 
inches  (15  cm.),  and  its  diameter,  when  moderately  distended,  about  four  inches 
(10  cm.).     Its  dorsal  surface  (Facies  rcctalis)  is  related  to  the  small  colon  and  rec- 


THE    UTERUS  513 

turn.  Its  ventral  surface  (Facies  vesicalis)  is  in  contact  with  the  bladder,  and  has 
inconstant  relations  with  various  parts  of  the  intestine.  The  term  fundus  uteri 
is  applied  to  the  anterior  wide  part  from  which  the  cornua  diverge. 

The  position  of  the  liody  of  the  uterus  is  variable,  especially  in  regard  to  its  anterior  part. 
It  is  often  pressed  up  against  the  rectum,  and  may  be  deflected  to  either  side — most  frequently 
to  the  left — by  the  pelvic  flexure  of  the  colon  or  coils  of  the  small  colon. 

The  cervix  or  neck  of  the  uterus  (Cervix  uteri)  is  the  constricted  posterior 
part  which  joins  the  vagina.  Part  of  it  (Portio  vaginalis  uteri)  projects  into  the 
cavity  of  the  vagina;  it  is  therefore  not  visible  externally,  but  may  be  felt 
through  the  vaginal  wall.  It  is  about  two  inches  (5  cm.)  in  length,  and  an  inch 
and  a  half  1 3.5  to  4  cm.)  in  diameter. 

Attachments. — The  body  and  cornua  are  attached  to  the  abrlominal  and  pelvic 
walls  by  two  extensive  peritoneal  folds,  the  broad  ligaments  (Ligamenta  lata). 
These  extend  on  either  side  from  the  sulihmibar  region  and  the  lateral  pelvic  walls 
to  the  dorsal  border  of  the  cornua  and  the  lateral  margins  of  the  bod.y  of  the  uterus. 
They  contain  the  vessels  and  nerves  of  the  uterus  and  ovaries,  connective  tissue, 
and  unstriped  muscular  fibers.  The  ureters  are  situated  along  their  parietal 
margins.  The  outer  layer  of  each  forms  a  fold,  the  round  ligament  of  the  uterus 
(Ligamentum  teres  uteri),  which  blends  with  the  parietal  peritoneum  over  the 
internal  inguinal  ring;  its  anterior  extremity  is  .situated  above  the  extremitj'  of 
the  cornu  and  is  rounded  and  free.  It  contains  muscular  tissue,  vessels,  and 
nerves,  and  is  the  homologue  of  the  gubernaculum  testis.  The  anterior  part  of 
the  neck  is  continuous  with  the  vagina,  and  thus  has  a  more  fixed  position  than 
the  rest  of  the  organ. 

The  cavity  of  the  uterus  (C'avum  uteri)  is  largely  obliterated  in  the  non- 
pregnant state  by  the  contraction  of  the  wall  and  by  folds  of  the  mucous  lining. 
At  the  extremity  of  each  cornu  it  communicates  by  a  minute  opening  with  the 
Fallopian  tube.  The  cavity  of  the  neck  is  termed  the  cervical  canal  (Canalis 
cervicis);  it  is  closed  ordinarily  by  mucous  folds  and  a  plug  of  mucus.  It  o])ens 
into  the  vagina  by  the  os  uteri  externum,  and  into  the  liody  by  t he  os  uteri  internum. 

Structure. — The  wall  of  the  uterus  consists  of  three  coats — an  external  serous, 
a  middle  muscular,  and  an  internal  mucous.  The  serous  coat  (Perimetrium)  is, 
for  the  most  part,  closely  adherent  to  the  muscular  coat.  It  is  continuous  with 
the  broad  ligaments.  The  muscular  coat  consists  essential^  of  two  layers,  a  thin 
external  stratum  of  longitudinal  fibers,  and  a  thick  layer  of  circular  fibers. 
Between  these  is  a  very  vascular  layer  (Stratum  vasculare)  of  connective  tissue 
with  circular  and  oblique  muscular  fibers  in  it.  The  circular  coat  is  very  thick 
in  the  neck,  where  it  forms  a  sphincter  half  an  inch  or  more  (ca.  1.5  cm.)  in 
thickness.  The  mucous  membrane  rests  directly  on  the  muscular  coat.  It  is 
thick,  and  is  covered  by  columnar  epithelium.  It  contains  numerous  long  tubu- 
lar uterine  glands  (Glandula?  utcrinse).  It  is  brownish-red  in  color,  except  in  the 
neck,  where  it  is  pale. 

Vessels  and  Nerves. — The  chief  arteries  are  the  uterine  and  the  uterine 
branch  of  the  utero-ovarian,  which  have  a  flexuous  course  in  the  broad  ligaments; 
tliere  is  also  a  branch  from  the  internal  pudic  artery.  The  veins  form  pam- 
jjiniform  plexuses  and  accompany  the  arteries.  The  lymphatics  are  numerous 
and  go  to  the  internal  iliac  and  lumbar  glands.  The  nerves  are  derived  from  the 
sjTnpathetic  through  the  uterine  and  peh-ic  plexuses. 

The  foregoing  statements  refer  to  the  non-g^a^^d  uterus.  In  the  pregnant  state  it  under- 
goes important  changes  in  size,  position,  and  structure.  The  increase  in  size  affects  chiefly  the 
gravid  cornu  (except  in  the  case  of  twins)  and  the  body.  The  cornu  attains  a  length  of  about 
two  and  a  half  to  three  feet  (ca.  SO  to  90  cm.),  and  a  corresponding  diameter;  intliis  process  it 
extends  much  bevond  the  ovarv,  and  the  broad  ligament.  The  gravid  uterus  is  entirely  abdominal 
in  position,  and  extends  alongthe  ventral  wall,  chiefly  to  the  left  of  the  median  plane.  It  weighs 
about  nine  pounds  (ca.  -1  kg.),  according  to  Ellenberger.  The  broad  ligaments  increase  greatly 
33 


514  GENITAL  ORGANS  OF  THE  MARE 

in  size  and  contain  more  muscular  tissue.  Tlie  vessels  are  greatly  enlarged  and  form  new  branches. 
The  muscular  coat,  in  spite  of  the  increase  in  size  and  number  of  the  fibers,  is  somewhat  thinner, 
except  in  the  neck.  The  mucous  membrane  is  thicker  and  more  vascular;  the  epithelium  be- 
comes non-ciliated  and  stratified. 

THE  VAGINA 

The  vagina  i.s  tlie  i);issage  which  extends  horizontally  through  the  pelvic 
cavity  from  the  neck  of  the  uterus  to  the  vulva.  It  is  tubular,  is  about  six  to  eight 
inches  (ca.  15  to  20  cm.)  in  length,  and,  when  slightly  distended,  about  four  or  five 
inches  (ca.  10  to  12  cm.)  in  diameter.  Its  dilatability  appears  to  be  limited  only  by 
the  pelvic  wall.  There  is  no  external  line  of  demarcation  between  the  vagina 
and  the  uterus  or  the  vulva. 

It  is  related  dorsally  to  the  rectum,  vcntrally  to  the  liladder  and  urethra,  and 
laterally  to  the  pelvic  wall.  The  recto-genital  pouch  of  the  peritoneum  extends 
between  the  vagina  and  rectum  for  a  distance  of  about  two  inches  (5  cm.),  and 
ventrally  the  vesico-genital  jiouch  passes  backward  somewhat  less  between  the 
vagina  and  bladder.  Thus  most  of  the  vagina  is  retroperitoneal  and  is  sur- 
rounded by  a  quantity  of  loose  connective  tissue,  a  venous  plexus,  and  a  variable 
amount  of  fat. 

Structure. — With  the  exception  of  the  .short  peritoneal  part,  as  indicated  above, 
the  jiroj^er  wall  of  the  vagina  is  composed  of  muscular  and  mucous  coats.  The 
muscular  coat  is  composed  of  a  thin  layer  of  longitudinal  fibers,  and  a  thicker  laj'er 
of  circular  fibers;  it  contains  also  many  elastic  fibers.  The  mucous  coat  is  highly 
elastic,  and  is  covered  with  a  stratified  epithelium.     It  has  no  glands. 

Under  u.sual  conditions  the  cavity  is  practically  obliterated  by  apposition  of 
the  walls,  so  that  the  lumen  is  a  transverse  slit;  this  condition  is  pronounced  when 
the  ampulla  of  the  rectum  is  full.  The  anterior  end  of  the  vagina  is  largely  occupied 
by  the  intravaginal  part  of  the  neck  of  the  uterus,  so  that  the  cavity  is  here  reduced 
to  an  annular  recess  termed  the  fornix  vaginae.  The  posterior  part  is  directly 
continuous  with  the  vulva  without  anj'  line  of  demarcation  except  the  valvular 
fold,  which  covers  the  external  urethral  orifice;  in  very  young  subjects  this  fold  is 
continued  on  either  side,  forming  the  hymen,  which  narrows  the  entrance  to  the 
vagina  (Introitus  vaginte).' 

Vessels  and  Nerves. — The  l)lood-supply  is  derived  from  the  branches  of  the 
internal  pudic  arteries.  The  veins  form  a  jjJexus  which  is  drained  bj-  the  internal 
pudic  veins.  The  lymphatics  pass  to  the  internal  iliac  lymph  glands.  The  nerves 
are  derivetl  from  the  symitathetic  through  the  pelvic  plexus. 


THE  VULVA 
The  vulva  or  urogenital  sinus  is  the  terminal  part  of  the  genital  tract.-  It  is 
continuous  in  front  with  the  vagina,  and  opens  externally  at  the  vulvar  cleft 
below  the  anus.  There  is  no  external  line  of  demarcation  between  the  vagina  and 
vulva.  The  tube  is  about  five  inches  (ca.  12  cm.)  in  length,  measured  from  the 
external  urethral  orifice  to  the  inferior  commissure;  dorsally  it  is  considerably 
shorter.  It  is  related  dorsally  to  the  rectum  and  anus,  ventrally  to  the  pelvic  floor, 
and  laterally  to  the  sacro-sciatic  ligament,  the  semimembranosus  muscle,  and  the 
internal  pudic  artery.  The  external  orifice  or  vulvar  cleft  (Rima  vuIvsb)  has  the 
form  of  a  vertical  slit,  about  four  to  six  inches  (ca.  10  to  15  cm.)  high,  and  is  margined 

'  In  formalin-hardened  subjects  there  is  frequently  a  pronounced  ring-like  constriction  at  the 
beginning  of  the  vulva. 

-  The  term  vulva  is  used  here  in  the  sen.se  in  which  it  is  understood  generally  by  English 
and  French  veterinarians.  In  the  (lerman  works  it  is  applied  only  to  the  labia  and  other  struc- 
tures around  the  external  orifice  of  the  urogenital  sinus,  while  the  sinus  itself  is  termed  the  vestibule 
of  the  vagina  (Vestibulum  vagina>). 


THE    FEMALE    URETHRA  515 

by  two  prominent  roundwl  folds,  the  labia.  The  labia  of  the  vulva  (Labia  vul- 
vae) meet  above  at  an  acute  angle,  forming  the  superior  commissure  {C'ommissura 
dorsalis),  which  is  about  two  inches  (ca.  5  cm.)  below  the  anus.  Below  they  unite 
to  form  the  thick  rountled  inferior  commissure  (C'ommissura  ventralis),  which  lies 
about  two  inches  (ca.  5  cm.)  behind  and  below  the  ischial  arch.  When  the  labia 
are  drawn  apart,  a  rounded  body,  about  an  inch  (ca.  2.5  cm.)  wide,  is  seen  in  the  in- 
ferior commissure;  this  is  the  glans  clitoridis,  the  homologue  of  the  glans  penis. 
Overlying  it  is  a  thin  fold,  the  prepuce  of  the  clitoris  (Prceputium  clitoridis).  At 
the  anterior  extremity  of  the  ventral  wall  of  the  vulva,  /.  c,  about  four  or  five 
inches  (ca.  10  to  12  cm.)  from  the  inferior  commissure,  is  the  external  urethral 
orifice  or  meatus  urinarius  (Orificium  urethrae  externum).  It  readily  admits  the 
finger  and  is  very  dilatable.  It  is  covered  by  a  fold  of  mucous  membrane,  the 
free  edge  of  which  is  directed  backward. 

Structure. — The  labia  are  covered  by  thin,  pigmented,  smooth  skin,  which  is 
richly  supplied  with  seliaceous  and  sweat  glands.  This  is  continuous  at  a  distance  of 
about  half  an  inch  (ca.  1  to  1.5  cm.)  from  the  free  edge  with  a  thin  glandless  nuicous 
membrane.  Between  these  is  a  layer  of  striped  muscle,  the  constrictor  vulvae; 
this  fuses  above  with  the  sphincter  ani,  and  embraces  the  clitoris  below,  spreading 
out  laterally  at  the  inferior  commissure.  It  constricts  the  vulvar  orifice  and  ele- 
vates the  clitoris.  The  constrictor  vestibuli  muscle  embraces  the  vulva  in  front 
of  the  preceding;  it  is  joined  on  either  side  bj'  a  band  of  unstriped  muscle  which 
arises  from  the  first  and  secontl  coccygeal  vertebrae,  and  is  homologous  with  the 
proximal  part  of  the  retractor  penis.  It  constricts  the  vulva.  Under  this  muscle 
in  the  lateral  wall  is  a  flattened,  oval  body,  the  bulbus  vestibuli  (Fig.  453) ;  this  is 
an  erectile  structure,  homologous  with  the  corpus  spongiosum  urethrae  of  the 
male.  It  is  about  two  and  a  half  to  three  inches  (ca.  6  to  8  cm.)  long,  and  an  inch 
or  more  (ca.  3  cm.)  wide.  It  consists  of  a  venous  network  inclosed  in  a  fibrous 
capsule,  and  is  supi)lied  with  blood  bj'  a  large  branch  of  the  internal  pudic  artery. 
The  mucous  membrane  of  the  vulva  is  reddish  in  color,  and  forms  longitudinal 
and  transverse  folds.  It  presents  ventrally  two  linear  series  of  small  papilhe 
which  converge  toward  the  inferior  commissure;  these  mark  the  orifices  of  the 
ducts  of  the  glandulae  vestibulares  minores.  On  either  side  of  the  dorsal  wall  is  a 
grou]i  of  eight  to  ten  larger  prominences  on  which  the  ducts  of  the  glandulae 
vestibulares  majores  (of  Bartholin)  open. 

Quite  exceptionally  there  may  be  found  on  either  side  of  the  urethral  orifice  tlic  opening  of 
the  canals  of  Gartner  (Ductus  epoophori  longitudinales). 

The  clitoris  is  the  homologue  of  the  penis.  It  arises  from  the  ischial  arch  by 
two  crura,  which  unite  to  form  a  body  as  large  as  one's  little  finger.  This  projects 
backward  into  the  inferior  commissure  of  the  vulva,  capped  bj^  a  small  rounded 
glans.  The  organ  is  composed  of  erectile  tissue  similar  to  the  corpus  cavernosum 
penis.  The  ischio-cavemosus  (or  erector  clitoridis)  is  a  very  feeble  muscle  which 
depresses  the  clitoris.  The  veins  of  the  clitoris  communicate  by  an  intermediate 
plexus  on  either  side  with  the  bullous  vestibuli. 


THE  FEMALE  URETHRA 
The  female  urethra  (Urethra  ferainina)  represents  only  that  part  of  the  canal 
of  the  male  which  lies  between  the  internal  urethral  orifice  and  the  openings  of 
the  ejaculatory  ducts.  Its  length  is  about  two  inches  (5  cm.),  and  its  lumen  is 
sufficient  to  admit  of  the  introduction  of  the  finger;  it  is,  however,  capable  of 
remarkable  dilatation  if  sufficient  care  and  patience  are  exercised  in  the  process. 
It  lies  centrally  on  the  pelvic  floor,  and  is  related  and  attached  dorsally  to  the 
vagina. 


516  GENITAL  ORGANS  OF  THE  MARE 

Structure. — The  intrinsic  muscular  coat  consists  of  longitudinal  and  circular 
layers  of  unstri]^ed  fibers.  Between  these  is  a  laj-er  of  areolar  tissue  which  contains 
a  rich  venous  plexus.  The  mucous  membrane  is  thrown  into  longitudinal  folds 
when  the  canal  is  closed:  it  is  highly  elastic,  and  is  covered  with  stratified  epithe- 
lium. 

The  urethral  muscle  {M.  compressor  urethrte)  embraces  the  urethra  and  is 
continued  backwartl  for  some  distance  under  the  constrictor  vestibuli.  It  is 
covered  by  a  fibro-elastic  membrane. 


THE  MAMMARY  GLANDS 

The  mammary  glands  (Glanduhr  lactifera>)  are  motlifietl  cutaneous  glands 
which  are  so  closely  associated  functionallj'  with  the  genital  organs  as  to  be  con- 
sidered accessory  to  them. 

In  the  mare  they  are  two  in  numl)er,  and  are  placed  on  either  side  of  the  median 
plane  in  the  inguinal  region.  Each  gland  has  the  form  of  a  short  cone,  much  com- 
pressed transversely,  and  having  a  flat  inner  surface.  It  consists  of  the  glandular 
mass  or  body  of  the  gland  (Corpus  mammae)  and  the  teat  or  nipple  { Papilla  mam- 
mse).  The  base  is  related  to  the  abdominal  wall,  to  which  it  is  attached  by  areolar 
tissue,  which  contains  a  venous  plexus,  the  superficial  inguinal  Ij'mph  glands, 
and  a  variable  amount  of  fat.  The  apex  is  constituted  by  the  teat,  which  is  also 
flattened  transversely  and  varies  in  length  from  one  to  two  inches  (ca.  2.5  to  5  cm.). 
Between  the  bases  of  the  teats  is  the  intermammary  groove.  On  the  apex  of  each 
teat  two  or  three  small  orifices  are  placed  close  together;  these  are  the  openings 
of  the  lactiferous  ducts. 

Structure. — The  skin  over  the  glands  is  thin,  pigmented,  ehieflj-  hairless,  and 
supplietl  with  numerous  large  sebaceous  and  sweat  glands.  Under  this  are  two 
layers  of  fascia  except  on  the  teats.  The  superficial  fascia  presents  no  special 
features.  The  deep  fascia  consists  of  two  lamina?  detached  from  the  abdominal 
tunic  which  ilescend  on  either  side  of  the  median  plane,  forming  a  septum  between 
the  two  glands,  and  constituting  their  ligamentum  suspensorium. 

These  lamina?  are  separated  by  a  layer  of  areolar  tissue,  so  that  it  is  possible  to  remove  one 
gland  if  diseased  by  careful  dissection  between  the  layers  of  the  septum. 

The  gland  substance  or  parench5rma  is  jiinkish  gray  in  color,  and  of  firmer 
consistence  than  the  fat  which  is  found  around  and  within  the  gland.  It  is  inclosed 
by  a  fibro-elastic  capside  which  sends  inward  numerous  tralieeulse;  these  form  the 
interstitial  tissue,  and  ilivide  the  gland  into  lobes  antl  lobules.  In  the  latter  are 
the  secretory  tubules  and  alveoli,  which  unite  to  form  the  larger  ducts.  Each  lobe 
has  a  duct,  which  opens  at  the  base  of  the  teat  into  a  space  called  the  lactiferous 
sinus  (Sinus  lactiferus);  this  is  lined  with  mucous  memlirane,  and  from  it  t^^'0 
(or  three)  lactiferous  ducts  (Ductus  lactiferi)  pass  through  the  extremity  of  the 
nipple.  Tliese  ducts  are  lined  with  a  non-glandular  mucous  membrane,  which  is 
covered  with  stratified  scjuamous  epithelium.  They  are  surrounded  by  unstriped 
nuisctdar  tissue,  the  bulk  of  the  fibers  being  arranged  in  a  circular  manner  to  form 
a  sphincter. 

The  .size  and  form  of  the  mammary  glands  are  subject  to  much  variation.  In  the  young 
subject,  before  pregnancy,  they  are  small  and  contain  little  gland  tissue.  During  the  "latter 
part  of  gestation,  and  especially  during  lactation,  they  increase  greatly  in  size,  and  the  gland 
tissue  is  highly  developed.  After  lactation  tlic  .secretory  structures  undergo  marked  involution, 
and  the  gland  is  much  reduced  in  size.  The  relative  amounts  of  gland  substance  and  interstitial 
tissue  vary  greatly;  in  some  cases  a  gland  of  considerable  size  contains  little  secretory  tissue  and 
is  consequently  functionally  deficient. 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  external  pudic 
artery,  which  enters  the  gland  at  the  posterior  part  of  its  base.     The  veins  form  a 


GENITAL  ORGANS  OF  THE  COW 


517 


plexus  on  either  side  of  the  base  of  the  gland,  which  is  drained  by  the  external 
pudic  vein  chiefly.  The  lymphatics  are  numerous  and  pass  chiefly  to  the  superficial 
inguinal  (or  supramammary i  lyinpli  glands.  The  nerves  are  derived  from  the 
inguinal  nerves  and  the  posterior  mesenteric  plexus  of  the  sympathetic  system. 


GENITAL  ORGANS  OF  THE  COW 

The  ovaries  of  the  cow  are  much  smaller  than  tliose  of  the  marc,  measuring 
usually  about  one  to  one  and  a  half  inches  (ca.  3  to  4  cm.)  in  length,  and  a 
little  less  than  an  inch  (ca.  2  cm.)  in  thickness  in  their  largest  part.  They  are 
oval  in  form,  pointed  at  the  uterine  end,  and  have  no  ovulation  fossa.  They  are 
situated  usually  a  little  above  the  middle  of  the  lateral  margin  of  the  pelvic  inlet 
in  the  non-pregnant  subject,  but  may  be  found  a  little  further  forward.  They  are 
thus  about  16  to  18  inches  (ca.  -10  to  45  cm.)  from  the  vulva  in  a  cow  of  medium  size. 


Fig.  411. — Ovart  of  Cow. 
i.  Broad  ligament  of  uterus;  2,  ligament  of 
ovar>';  5,  fimbria  ovarica;  4.  attachment  of  broad 
ligament;  5,  surface  of  ovarj'  covered  with  ger- 
minal epithelixmi;  6,  corpora  lutea;  7,  Graafian 
follicle.     (From  Leisering's  Atlas.) 


Fig.  412. — Uterus  of  Cow,  Contr.\cted,  Dors.^l  View. 
a,  Body  of  uterus;  6,  fc',  horn  of  uterus;  c.  ovar>-;  rf,  d', 
triangular  folds  connecting  horns  of  uterus    (Lig.  intercomu- 
alia).     (.\fter  Zieger.) 


The  greater  part  of  the  surface  of  the  gland  is  covered  with  germinal  epithelium, 
the  peritoneal  epithelium  being  limited  to  a  narrow  zone  along  the  attached  border. 
Follicles  of  various  sizes  are  often  seen  projecting  from  the  surface,  as  well  as  cor- 
pora lutea:  a  corpus  luteum  verum  has  a  pronounced  yellow  color,  and  may  reach 
a  width  of  half  an  inch  or  more  (ca.  1  to  1.5  cm.). 

The  Fallopian  or  uterine  tubes  are  long  and  less  fiexuous  than  in  the  mare. 
The  junction  witli  the  cornu  of  the  uterus  is  not  so  abrupt  as  in  the  mare,  since  the 
extremities  of  the  horns  are  pointed.  The  uterine  orifice  of  the  tube  is  rather 
large  and  funnel-shaped.     The  fimbrise  are  not  so  extensive  as  in  the  mare. 

The  uterus  lies  almost  entirely  within  the  abdominal  cavity  in  the  adult. 
The  body  is  only  about  one  inch  (ca.  2  to  3  cm.)  in  length,  although  externally  it 
appears  to  be  much  longer.  This  false  impression  is  due  to  the  fact  that  the  pos- 
terior parts  of  the  cornua  are  united  by  connective  and  muscular  tissue  and  have 
a  common  peritoneal  covering.  The  cornua  are.  therefore,  really  longer  than  they 
appear  externally.  They  taper  gratlually  toward  the  free  end,  so  that  the  junction 
with  the  Fallopian  tubes  is  not  abrupt,  as  in  the  mare.  The  free  part  of  the  horn 
curves  at  first  downward,  forward,  and  outward,  and  then  turns  upward,  forming 
a  spiral   coil.     The  cervix  is  about  four  or  five  inches  (ca.  8  to  10  cm.)   long; 


518 


GENITAL  ORGANS  OF  THE  COW 


its  wall  is  rcnuirkahly  dense,  and  may  he  nearly  an  inch  (ca.  2  em.)  in  thickness. 
Its  lumen,  the  cervical  canal,  is  sjiiral,  and  is  ordinarily  tightly  closed  and  very 
difficult  to  dilate.  The  muscular  coat  of  the  uterus  is  thicker  than  in  the  mare. 
It  consists  of  an  external  longitudinal  layer  and  two  circular  strata.  The  inner 
circular  layer  is  about  a  fourth  of  an  inch  (ca.  6  mm.)  thick  in  the  cervix.  The  other 
layers   are   continued  in  the  vagina.     The 

mucous  membrane  of  the  horns  and  body  ," 

presents    as    a    characteristic    feature    the  ^^_ 

uterine  cotyledons   (Cotyledones   uterinse).  ^tflPife  z^V 

The.se  are  oval  prominences,  about  a  hun-  OSlCQI^f^kli     ' 

dred  in  number,  which  are  either  irregularly 
scattered  over  the  surface  or  arranged  in 
rows  of  about  a  dozen. 

In  the  non-gravid  uterus  they  average  al)out 
}4  to  ?4  inch  (ca.  1.5  to  IS  mm.)  in  length,  j  inch 
(ca.  S  mm.)  in  width,  and  '  s  inch  (ca.  2  to  4  mm.) 
in  thickness.  During  pregnancy  they  become  greatly 
enlarged  and  pedunculated.  The  larger  one.s  then 
measure  about  4  to  .5  inches  (10  to  12  cm.)  in  length, 
1  to  1  Jo  inches  (3  to  4  cm.)  in  \\-idth,  and  1  inch  (2 
to  2.5  cm.)  in  thickness.  The  deep  face  has  a  hilus 
at  which  the  vessels  enter.  The  rest  of  the  surface 
has  a  spongy  appearance,  due  to  numerous  crypts 
which  receive  the  villi  of  the  chorion. 

The  uterine  glands  are  long  and 
branched.  The  mucous  membrane  of  the 
cervix  is  pale  and  forms  numerous  folds. 
The  latter  are  arranged  in  several  scries 
which  obliterate  the  lumen.  At  the  ex- 
ternal orifice  (os  uteri)  the  folds  (Plicae 
palmata?)  form  rounded  prominences  ar- 
ranged circularly,  which  project  into  the 
cavity  of  the  vagina.  There  are  no  glands 
in  the  cervix,  but  a  thick  mucus  is  secreted 
by  goblet  cells. 


Fig.  414 


ITAL  Organs  of  Cow.  Dorsal 


Fig.  41^. — Uterine  Cotyledon  of  Cow. 

The  figure  repre.seiits  a  cotyledon   of  medium  size.    (Afte 

Ellenberger,  in  Leisering's  .\tlaa.) 


The  right  uterine  cornu  and  the  vagina  and 
vulva  are  opened  up:  /,  Labium  vulvae;  $,  ventral 
commissure:  S,  glans  clitoridis;  4,  glandula  vesti- 
bularis major,  exposed  by  slit  in  mucous  mem- 
brane; 5,  opening  of  duct  of  preceding;  6,  sub- 
urethral diverticulum;  7.  external  urethral  open- 
ing; 8,  openings  of  canals  of  Ciartner;  9,  os  uteri; 
10,  corpus  uteri:  //,  cornu  uteri;  13,  cotyledons: 
13,  Fallopian  tube;  14,  oslimn  abdominale  tubic; 
15,  ovary      (FroTU  Leisering's  Atlas,  reduced.) 


The  broad  ligaments  are  not  attached  in  the  sulilumbar  region  as  in  the  mare, 
but  to  the  u]ip('r  part  of  the  flanks,  aliout  a  handbreadth  below  the  level  of  the 
external  angle  of  the  ilium.  They  contain  a  conspicuous  amount  of  unstriped 
muscle.  The  round  ligaments  are  well  tleveloped,  and  can  he  traced  distinctly 
to  the  vicinity  of  the  internal  inguinal  ring. 

The  vagina  is  somewhat  longer  and  more  roomy  than  that  of  the  mare;    its 


GENITAL  ORGANS  OF  THE  COW 


519 


wall  is  also  thicker.  Its  average  length  in  the  non-pregnant  animal  is  at)out  eight 
inches  (ca.  20  cm.);  liut  in  the  pregnant  cow  the  length  increases  to  twelve  inches 
(30  cm.)  or  more.  The  recto-genital  pouch  of  peritoneum  extends  backward  about 
five  inches  (ca.  12  cm.)  on  the  dorsal  surface,  while  ventrally  the  serous  coat  only 
extends  backward  about  two  inches  (ca.  5  cm.). 

This  gives  ample  space  dorsally  for  the  incision  of  the  forni.\  vagina;  in  oophorectomy. 

In  the  ventral  wall  of  the  vagina,  between  the  muscular  and  mucous  coats, 
there  are  frequentl.v  present  the  two  canals  of  Gartner  (Ductus  epoophori  longitu- 
dinales).  When  well  developed  they  may  attain  the  diameter  of  a  goose  quill, 
and  may  be  traced  forward  to  the  anterior  part  of  the  vagina  or  even  further. 
They  open  posteriorly  near  the  external  uretliral  orifice. 

These  tubes  are  remnants  of  the  Wolffian  ducts,  and,  like  other  foetal  vestiges,  are  very 
variable.  Roder  states  that  the  right  canal  was  absent  in  over  52  per  cent.,  the  left  in  only  22  per 
cent.,  of  the  cows  examined  by  him.  In  some  cases  they  may  be  traced  in  the  broad  hgaments  for 
a  variable  distance  toward  the  ovary.  They  are  of  clinical  interest  in  that  cy.sts  frequently  form 
along  their  course. 


\L  Section  of  Part  of  Urogexita 

DrVERTICCLUM. 


Cow,  Showing  Scbcrethral 


The  vulva  has  thick  wrinkled  labia,  and  both  commissures  are  acute;  the 
lower  one  is  pointed,  and  has  on  it  a  number  of  long  hairs;  it  lies  about  two  inches 
(.5  cm.)  behind,  and  about  the  same  distance  below,  the  level  of  the  ischial  arch. 
The  glans  clitoridis  is  small;  the  crura  are  about  four  inches  (ca.  10  cm.)  long  and 
are  flexuous.  The  external  urethral  orifice  or  meatus  urinarius  is  four  or  five 
inches  (10  to  12  cni.i  from  the  ventral  commissure.  Beneath  it  is  a  blind 
pouch,  the  suburethral  diverticulum,  which  is  more  than  an  inch  (ca.  3  to  4  cm.) 
long,  and  reailily  admits  the  end  of  a  finger. 

The  form  and  position  of  this  pouch  should  be  carefully  noted  on  account  of  the  difficulty 
it  causes  in  catheterizing  the  bladder.  If  the  catheter  is  passed  along  the  ventral  wall  of  the 
vulva  (as  in  the  mare),  it  will  always  enter  the  pouch  instead  of  the  urethra. 

The  glandulae  vestibulares  majores  (or  glands  of  Bartholin)  are  situated  on 
the  lateral  walls  of  the  vulva,  under  the  constrictor  vulva".  They  are  little  over 
an  inch  (ca.  3  cm.)  long  and  about  half  an  inch  (ca.  1..5  cm.)  in  width.  Each  has 
a  single  duct  which  opens  about  an  inch  and  a  half  (ca.  3  to  4  cm.)  lateral  to  and 
behind  the  external  urethral  orifice. 

The  urethra  of  the  cow  is  about  four  inches  (10  cm.)  in  length ;  it  is  narrower  and 
much  less  dilatable  than  that  of  the  mare.  It  is  fused  dorsally  with  the  wall  of  the 
vagina,  while  laterally  and  ventrally  it  is  covered  by  the  constrictor  vagina^  muscle. 

The  mammary  glands,  normally  two  in  number,  are  popularly  termed  the 
udder.     They  are  very  much  larger  than  in  the  mare,  and  the  body  of  each  is 


520 


GKXITAL  ORGANS  OF  THE  COW 


somewhat  ellipsoidal  in  form,  hut  flattened  transversely.  The  base  (or  dorsal 
surface)  of  each  gland  is  slightly  concave  and  slopes  obliquely  downward  and  for- 
ward in  adaptation  to  the  alxlominal  wall,  to  which  it  is  adherent;  posteriorly  it 
is  in  relation  to  the  large  supramammary  lymph  glands  and  a  quantity  of  fat. 
The  inner  surface  is  flat,  and  is  separated  from  the  other  gland  by  a  well-developed 
double  septum.  The  outer  surface  is  convex.  Four  well-developed  teats  are 
present ;  they  average  aliout  three  inches  (ca.  7  to  8  cm.)  in  length.     It  is  customary 


a,  Body  of  Klarid;  b,  Lactiferous 


— Cross-section  op  Mammary  Glands  of  Cow. 
Ills;  c,  cavity  of  teat;  J,  duct  of  teat;  r,  intennammary  groove;  /.septum 
between  glands;  {/,  supramammary  fat. 


to  consider  the  udder  to  consist  of  four  "quarters."  There  is  no  septum  nor  visible 
division  between  the  two  quarters  of  the  same  side,  but,  on  the  other  hand,  in- 
jections of  fluids  of  different  colors  into  the  two  teats  of  the  gland  demonstrate  that 
the  cavities  drained  by  them  do  not  communicate. 

The  size  and  form  of  the  glands  vary  greatly;  in  the  highly  .^specialized  dairy  breeds  (p.  g., 
Holsteins)  they  often  attain  enormmis  dimensions.  The  size  of  the  udder  is  not  a  certain  index 
of  its  productivity,  .since  .some  so-called  "fleshy"  udders  contain  a  very  large  amount  of  inter- 
stitial tissue  and  relatively  little  parenchyma.  Small  accessory  teats  often  occur  posteriorly; 
commonly  these  are  rudimentary  and  imperforate  (polythelia),  but  sometimes  they  drain  a  small 
amount  of  gland  suljstancc  (polymastia).  Sanson  described  a  case  in  which  there  were  seven 
teats,  all  giving  milk. 


GENITAL  ORGANS  OF  THE  SOW 


521 


Each  teat  has  a  single  duct  which  widens  superiuriy  and  opens  free!}-  into  a 
roomy  lactiferous  sinus  or  milk  cistern  (Sinus  lactiferusj.  The  lactiferous  duct 
or  teat  canal  is  lined  by  a  glandless  mucous  membrane  which  is  covered  with 
stratified  squamous  epithelium;  the  lower  part  (ca.  1  cm.)  of  the  canal  is  narrow, 
and  is  closed  by  a  sphincter  of  unstriped  muscle.  The  mucous  membrane  of 
the  sinus  forms  numerous  folds  which  render  the  cavity  multilocular. 

Vessels  and  Nerves. — The  blood-supply  is  derived  from  the  external  pudic 
arteries.  The  veins  form  a  circle  at  the  base  of  the  udder,  from  which  the  blood 
is  drainetl  by  three  trunks,  viz.,  the  very  large  subcutaneous  abdominal  ("milk 
vein"),  the  external  pudic,  and  the  perineal  vein.  Tlie  lymphatics  are  numerous, 
and  [Dass  to  the  supramammary  glands  chictly.  The  nerves  are  derived  from  the 
inguinal  nerves  and  the  posterior  mesenteric  plexus  of  the  sympathetic. 


GENITAL  ORGANS  OF  THE  SOW 

The  ovaries  are  concealed  in  the  bursa  ovarii,  owing  to  the  large  extent  of  the 
mesosalpinx.     They  are  more  rounded  than  in  the  bitch,  and  have  a  distinct  hilus. 


Fig.  417. — Genital  Organs  of  Sow,  Dorsal  View.     The  Vagina  and  Cervix  Uteri  are  Slit  Open. 
1,  Labia  vulva?;    2,  glans  clitoridis;    3,  vulva;    4,  external  urethral  orifice;    3,  vagina:    5',  cervix  uteri;   6, 
corpus  uteri;   7,  cornua  uteri,  one  of  which  is  opened  at  7'  to  show  folds  of  mucous  membrane;   S,  Fallopian  tube; 
5^,  abdominal  opening  of  tube;   P.  ovaries;    70,  ovarian  bursa;    ii,  broad  ligaments  of  uterus;    75,  urinary  bladder, 
(From  Leisering's  .\tlas.) 


They  are  situated  usually  as  in  the  cow,  but  their  position  is  quite  variable  in 
animals  which  have  borne  young.     The  surface  commonly  presents  rounded  promi- 


522  GENITAL    ORGANS    OF   THE    BITCH 

nences,  so  t!mt  soinetinK's  tlu'  filand  lias  an  irregulai',  nuiUicrry-like  aspect;  this 
is  due  to  tlie  fact  that  there  is  veiy  Httle  stroma  and  the  hirger  Graafian  follicles 
project  from  the  surface. 

The  Fallopian  or  uterine  tubes  are  long  ( ca.  15  to  80  cm.),  and  less  flexuous  than 
in  the  mare.  The  fimbriated  extremity  forms  an  amjjulla  anil  has  a  large  abdominal 
opening.  The  uterine  end  shatles  inseusiblj-  into  the  small  extremity  of  the  cormi 
of  the  uterus. 

The  uterus  presents  several  striking  features.  The  body  is  only  about  two 
inches  (ca.  5  cm.)  long.  The  horns  are  extremely  long  and  flexuous,  and  are  freely 
movable,  on  account  of  the  large  extent  of  the  broad  ligaments.  The  extremities 
of  the  horns  taper  to  about  the  diameter  of  the  Fallopian  tubes.'  The  neck  is 
remarkable  for  its  length  (ca.  15  to  20  cm.)  and  the  fact  that  it  is  directly  continued 
by  the  vagina  without  forming  any  intravaginal  projection  (os  uteri).  It  can  be 
distinguished  by  the  transverse  folds  of  its  mucous  membrane  and  the  thickness 
of  its  wall. 

Tlie  changes  in  form  and  position  of  the  uterus  during  pregnancy  are  similar  to  those  men- 
tioned later  in  the  case  of  the  bitch. 

The  vagina  is  about  four  or  five  inches  (ca.  10  to  12  cm.)  long  in  a  sow  of  medium 
size.  It  is  small  in  caliber,  and  has  a  thick  muscular  coat  which  consists  mainly 
of  circular  fibers.  The  mucous  membrane  is  plicated,  and  is  intimately  united 
with  the  muscular  coat. 

The  vulva  is  relatively  long.  The  inferior  commissure  is  jiointed  and  dejien- 
dent.  The  mucous  lining  is  plicatetl.  There  is  a  small  suburethral  diverticulum. 
The  vestibular  glands  are  small  and  variable  in  number.  The  vestibular  bullis 
are  little  developed.  The  canals  of  Gartner  may  sometimes  be  traced  as  far  as 
the  ovary,  but  are  often  difficult  to  find. 

The  clitoris  is  long,  flexuous,  anil  pointed;   beneath  it  is  a  cul-de-sac. 

The  urethra  is  very  long;  its  vulvar  orifice  is  not  concealed  by  a  valvular  fold. 

The  mammary  glands  are  usually  ten  or  twelve  in  number,  and  are  arranged 
in  two  rows,  as  in  the  l)itch.     Each  teat  has  commonly  two  excretorj-  ducts. 


GENITAL  ORGANS  OF  THE  BITCH 

The  ovaries  (Fig.  33(5)  are  small,  elongated-oval  in  outline,  and  flattened. 
Each  ovary  is  situated  clo.se  to  or  in  contact  with  the  posterior  pole  of  the  corre- 
sponding kidney,  and  thus  lies  ventral  to  the  third  or  fourth  lumbar  vertebrijp, 
or  about  half  way  between  the  last  rib  and  the  crest  of  the  ilium.  Each  is  concealed 
in  a  peritoneal  pouch,  the  bursa  ovarii,  which  has  a  slit-like  opening  ventrally. 
The  two  folds  which  form  this  pouch  contain  a  quantity  of  fat  and  unstriped  muscle. 
They  are  continued  to  the  cornu  of  the  uterus,  constituting  the  mesosalpinx  and 
the  ovarian  Ugament.  The  surface  of  the  ovary  presents  ])rominences  caused  by 
projecting  tiraafian  follicles.     There  is  no  distinct  hilus. 

The  Fallopian  or  uterine  tubes  are  small  and  average  two  or  three  inches  (ca. 
5  to  8  cm.)  in  length.  Each  jiasses  at  first  forward  and  then  turns  backward,  hav- 
ing a  straight  or  only  slightly  flexuous  cour.se.  The  fimbriated  extremity  lies  in 
the  bursa  ovarii,  and  has  a  rather  large  ojiening.  The  uterine  orifice  is  very 
small. 

The  uterus  has  a  very  short  body  and  two  long  narrow  horns.  In  a  bitch  of 
medium  size  the  body  is  about  an  inch  (ca.  2  to  3  cm.)  and  the  cornua  five  or  six 

'  Lesbre  states  that  the  cornua  may  attain  a  length  of  45  to  50  cm. 


GENITAL    ORt5ANS    OF    THE    BITCH 


523 


inches  (ca.  12  to  15  cm.)  long.  The  horns  are  of  viniform  diameter,  are  nearly 
straight,  and  lie  entirely  within  the  abdomen.  They  diverge  from  the  bodj'  in  the 
form  of  a  V  toward  each  kichiej".  Their  posterior  parts  are  united  by  the  peri- 
toneum. The  neck  i.s  very  short  and  is  fused  dorsally  with  the  vagina.  It  has  a 
thick  muscular  coat.  The  mucous  mem- 
brane of  the  uterus  has  long  uterine  glands 
and  also  short  tubular  crypts. 

The  broad  ligaments  contain  fat  and 
imstriped  nuisfje.  They  are  much  longer  in 
the  mitldle  than  at  either  enil.  The  posterior 
part  is  attached  tn  the  anterior  part  of  the 
vagina.  The  roiind  ligaments  are  very  long, 
extending  through  the  inguinal  canals,  and 
traceable  almost  to  the  vulva. 

The  horns  of  the  graviil  uterus  present  dilata- 
tions or  ampullae,  which  contain  the  fa?tuseS|  and 
are  separated  by  constrictions.  The  gravid  uterus 
lie.s  on  the  ventral  abdominal  wall,  and  toward  the 
end  of  gestation  extends  forward  to  the  stomach 
and  liver. 

The  vagina  is  relatively  long.  It  is  nar- 
row anteriorly,  and  has  no  distinct  fornix. 
The  muscular  coat  is  thick  and  consists 
chiefly  of  circular  fibers.  The  mucous  mem- 
brane forms  longitudinal  folds.  The  canals 
of  Gartner  are  usually  absent. 

The  vulva  has  thick  labia  which  form 
a  pointed  inferior  commissure.  The  mucous 
lining  is  smooth.  On  either  side  of  the  ure- 
thral orifice  there  is  a  small  depression.  The 
glandulse  vestibulares  majores  are  absent, 
but  the  smaller  glands  are  present,  and 
their  ducts  open  ventrallj-  on  either  side 
of  a  mechan  ridge.  The  vestibular  bulbs 
are  relatively  large  and  join  dorsally.  The 
clitoris  has  a  small  pointed  glans,  beneath 
which  is  a  diverticulum.  The  corpus  caver- 
nosum  is  a  little  more  than  an  inch  (ca.  3  to 
4  cm.)  long  in  a  subject  of  medium  size,  and 
is  infiltratetl  with  fat. 

The  mammary  glands  are  usually  ten  in 
number,  and  are  arranged  in  two  series  extending  from  the  posterior  part  of  the 
pectoral  region  to  the  inguinal  region:   they  are,  therefore,  designated  according  to 
location  as  pectoral,  abdominal,  and  inguinal.     The  teats  are  .short,  and  present 
on  their  apices  six  to  twelve  small  orifices  of  the  excretory  ducts. 


Fig.  418. — GE^^TAL  Org.a 

Vulva,  vagina,  and  uteri 

open,     a.  Ovarian  bursa;  b,  sar 

the  right  o 


OF  Bitch. 
iin  part)  are  slit 
opened  to  show 
rf.rf,  horns  of  uterus;  e.e'.body 
of  uterus;  /,  neck  of  uterus;  /',  OS  uteri;  g,  vagina; 
h,  hymen;  i,  vulva;  k.  e.xterna!  urethral  orifice;  I, 
urinary  bladder;  m,  urethra:  rt,  n,  labia  vulva-;  o, 
fossa  clitoridis;  p,  clitoris.  .(After  Ellenberger,  in 
Leisering's  Atlas.) 


ANGIOLOGY:  THE  VASCULAR  SYSTEM 

Angiology  is  the  description  of  the  organs  of  circulation  of  the  blood  and 
lymph — the  heart  and  vessels.  The  heart  is  the  central  hollow  muscular  organ 
which  functions  as  a  suction  and  force  pump;  the  differences  in  pressure  caused 
by  its  contraction  and  relaxation  determine  the  circulation  of  the  blood  and  lymph. 
It  is  situated  in  the  middle  mediastinal  space  of  the  thorax,  between  the  two  lungs, 
and  is  inclosed  in  a  fibro-serous  sac — the  pericardium.  The  vessels  are  tubular 
and  run  through  almost  all  parts  of  the  body.  They  are  designated  according  to 
their  contents  as  blood-  and  lymph-vessels. 

The  blood-vascular  system  consists  of:  (1)  the  arteries,  which  convey  blood 
from  the  lieart  to  the  tissues;  (2)  the  capillaries,  microscopic  tubes  in  the  tissues 
which  ]5ermit  of  the  necessary  interchange  between  the  blood  and  the  tissues; 
(3)  the  veins,  which  convey  the  blood  back  to  the  heart. 

The  blood-vessels  are  divided  into  the  pulmonary  and  the  systemic.  The 
pulmonary  artery  conveys  the  blood  from  the  right  ventricle  of  the  heart  to  the 
lungs,  where  it  is  arterialized,  and  is  returned  by  the  pulmonary  veins  to  the  left 
atrium  of  the  heart,  and  passes  into  the  left  ventricle.  The  systemic  arteries 
convey  the  lilood  from  the  left  ventricle  all  over  the  body,  whence  it  is  returned  by 
the  venje  cavae  to  the  right  atrium,  and  passes  into  the  right  ventricle. 

It  .should  be  noted,  however,  that  the  lungs  receive  arterial  blood  through  the  systemic 
bronchial  arteries.  This  blood  is  returned  in  part  by  the  bronchial  veins  to  the  right  atrium 
(indirectly),  in  part  by  the  pulmonary  veins  to  the  left  atrium. 

The  term  portal  system  is  often  applied  to  the  portal  vein  and  its  tributaries 
which  come  from  the  stomach,  intestine,  pancreas,  and  spleen.  The  vein  enters 
the  liver,  where  it  branches  like  an  artery,  so  that  the  blood  in  this  subsidiary 
system  passes  through  a  second  set  of  capillaries  before  being  conveyed  to  the  heart 
by  the  hepatic  veins  and  the  posterior  vena  cava. 

The  arteries  (Arteriae),  as  a  rule,  divide  at  an  acute  angle,  giving  off  finer 
and  finer  branches.  In  some  cases  branches  come  off  at  a  right  angle,  and  others 
are  recurrent,  ?'.  e.,  run  in  a  direction  opposite  to  that  of  the  parent  stem.  The 
intercommunication  of  branches  of  adjacent  arteries  is  termed  anastomosis.  Most 
commonly  the  connections  are  made  by  a  network  of  numerous  fine  branches 
(Plexus  vasculosus).  Relatively  large  communicating  branches  (Kami  connnuni- 
cantes)  occur  in  certain  places;  they  may  be  transverse  or  in  tlie  form  of  arclies. 
Wide-meshed  networks  of  A'essels  are  termed  Retia  vasculosa.  Terminal  or  end  ar- 
teries are  such  as  form  isolated  networks,  /.  c,  do  not  anastomose  with  adjacent  ar- 
teries. A  rete  mirabile  is  a  network  intercalated  in  the  course  of  an  artery.  A 
collateral  vessel  (Vas  collaterale)  is  one  which  pursues  a  course  near  and  similar 
to  that  of  a  larger  vessel. 

The  veins  (Venae)  are  in  general  arranged  like  the  arteries,  but  are  usually  of 
greater  caliber.  When  a  vein  accompanies  an  artery,  it  is  termed  a  vena  comitans 
or  sateUite  vein ;  in  many  places  two  veins  accompany  a  single  artery.  The  primi- 
tive venous  trunks  do  not  run  with  the  arteries,  and  most  of  the  superficial  veins 
(VeniE  cutanea?)  pursue  independent  courses.  They  anastomose  even  more  freely 
than  the  arteries,  and  large  communicating  branches  are  very  common.  The  veins 
form  very  rich  plexuses  (Plexus  venosi)  in  many  places.  Some  veins  which  are 
without  independent  walls  and  are  inclosed  by  dense  membranes  and  run  usually 

524 


THE    PERICARDirM  525 

in  bony  grooves  are  termed  (venous)  sinuses;  examples  of  tills  are  tiie  sinuses  of 
tiie  dura  mater  of  the  brain. 

Structure  of  Arteries.—  Tlie  wall  consists  of  three  coats.  The  external  coat 
(Tunica  externa)  consi.sts  chiefly  of  fibrous  connective  tissue.  In  the  deeper  part 
are  some  elastic  fibers,  and  in  some  arteries  there  are  also  longitudinal  unstriped 
muscle-fibers.  The  middle  coat  (Tunica  media)  is  composed  of  unstriped  muscle 
and  elastic  tissue  in  medium-sized  arteries.  In  small  vessels  there  is  onh'  the 
muscular  tissue,  and  in  the  largest  trunks  only  elastic  tissue.  The  internal  coat 
or  intima  (Tunica  intima)  consists  of  a  layer  of  endothelial  cells,  resting  on  an  elastic 
membrane.  The  sheath  (\'agina  vasis)  is  a  condensation  of  the  surrounding  con- 
nective tis>ue,  and  is  attached  more  or  less  closely  to  the  external  coat. 

Structure  of  Veins. — The  walls  of  veins  are  similar  in  structure  to  those  of 
the  arteries,  but  are  very  much  thinner,  so  that  veins  collapse  more  or  less  com- 
pletely when  empt.v,  while  arteries  do  not.  The  middle  coat  is  very  thin  and  con- 
sists to  a  large  extent  of  ordinar\'  connective  tissue.  The  intima  is  also  less  elastic 
than  in  the  arteries.  In  many  veins  this  coat  forms  semilunar  valves,  the  free 
edges  of  which  are  cUrected  toward  the  heart.  They  are  most  numerous  in  the 
veins  of  the  skin  and  the  deep  veins  of  the  extremities  (except  the  foot),  while  in 
most  veins  of  the  body  cavities  and  viscera  they  are  absent  or  occur  only  where  the 
veins  open  into  larger  ones  or  where  two  veins  join. 

The  walls  of  the  vessels  are  supplied  with  blood  bj-  numerous  small  arteries, 
called  vasa  vasorum.  These  arise  from  branches  of  the  arterj-  which  they  supply 
or  from  adjacent  arteries,  ramify  in  the  external  coat,  and  enter  the  middle  coat 
also. 

The  nerves  of  the  vessels  consist  of  both  medullated  and  non-meduUated  fibers. 
They  form  plexuses  around  the  vessels,  from  which  fibers  pass  mainh'  to  the  muscu- 
lar tissue  of  the  middle  coat. 


BLOOD-VASCULAR  SYSTEM  OF  THE  HORSE 
THE  PERICARDIUM  1 

The  pericardium  is  the  fibro-serous  sac  which  sui'rounds  the  heart,  and  also 
the  great  vessels  in  connection  with  it  to  a  greater  or  less  extent.  Its  form  is 
in  general  similar  to  that  of  the  heart.  The  fibrous  layer  is  relatively  thin,  but 
strong  and  inela.stic.  It  is  attached  dorsally  to  the  large  vessels  at  the  base  of  the 
heart,  and  is  continued  in  part  up  to  the  longus  colli  muscle.  \'entrally  it  is  firmly 
attached  to  the  middle  of  the  posterior  half  of  the  thoracic  surface  of  the  sternum. 
The  serous  layer  is  a  closed  sac,  surrounded  by  the  fibrous  pericardium,  and  invag- 
inated  liy  the  heart.  It  is  smooth  and  glistening,  and  contains  a  small  amount  of 
clear  serous  fluid,  the  liquor  pericardii.  Like  other  serous  membranes,  it  may  be 
regarded  as  consisting  of  two  parts,  jiarietal  and  visceral.  The  parietal  part  lines 
the  fibrous  layer,  to  which  it  is  closely  attached.  The  visceral  layer  covers  the 
heart  and  parts  of  the  great  vessels,  and  is  therefore  also  termed  the  epicardiimi. 
The  serous  pericardium  is  composed  of  a  connective-tissue  membrane,  rich  in 
elastic  fibers,  and  covered  on  its  free  surface  by  a  laj'er  of  flat  endothelial  cells. 

The  pericardium  is  covered  by  the  mediastinal  jjleura  (Pleura  pericardica) 
and  is  crossed  laterallj'  by  the  phrenic  nerves.  Its  lateral  surfaces  are  related 
chieflj'  to  the  lungs,  but  the  lower  part  is  in  partial  contact  with  the  chest-wall. 
On  the  left  side  the  area  of  contact  is  from  the  third  to  the  fifth  intercostal  space 
inclusive.     On  the  right  side  the  contact  is  smaller  and  is  at  the  third  and  fourth 

'  The  pericardium  is  described  before  the  heart  since  it  must  be  examined  first  in  the  labor- 
atory. 


526 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


ribs.  The  anterior  border  of  the  base  is  opposite  to  the  second  intercostal  space, 
and  the  posterior  l)ordcr  is  opposite  to  the  sixth  rib  or  space.  The  base  is  related 
to  the  great  vessels,  the  trachea  and  its  bifurcation,  the  bronchial  lyni])li  glands, 
the  cesophagus,  and  the  vagus,  left  recurrent,  and  cardiac  nerves. 

The  two  parts  of  the  serous  pericardium  are,  of  course,  continuous  with  each  other  at  the 
hne  of  reflection  on  to  the  great  vessels.  The  latter  are  covered  in  varying  degree  by  the  \'isceral 
layer.  The  aorta  and  pulmonary  arterv  are  inclosed  in  a  complete  common  sheath  as  far  as  the 
bifurcation  of  the  latter.  A  pouch  paiises  inward  lietweon  tlie  pulmonary  artery  and  the  left 
auricle,  and  is  connected  with  another  pouch  which  passes  backward  between  the  right  auricle 
and  the  aorta,  thus  forming  the  great  transverse  sinus  of  the  pericardium.  The  posterior  vena 
cava  is  covered  on  the  riglit  ami  below  for  a  distance  of  an  inch  or  a  little  more  (ca.  3  cm.).  The 
pulmonary  veins  receive  practicallv  no  serous  covering.  The  epicardium  is  closely  adherent  to 
the  muscular  tissue  of  the  heart,  but  is  attached  to  the  vessels  by  loose  tissue  and  fat,  and  hence 
is  easily  dissected  off  them. 

THE  HEART 
The  heart  (Cor)  occupies  the  greater  part  of  the  middle  mediastinal  space. 
Its  shape  is  that  of  an  irregular  antl  somewhat  flattened  cone.     It  is  attached  at 


Brachiocephalic  trunk    / 


Pulmonary  reins 


Lift 

nur,rlr 


,/i.r) 


Ventricle 


_Coronary 
'groiirc 


Posterior 
border 


Left  longitudinal  groove 


Fig.  419. — He,\bt  of  Horsi:,  Left  View.     Hardened  in  situ 
The  dotted  line  indipjitcs  the  line  of  reflection  of  the  serous  pericardium.     The  epicardii 
have  not  been  removed  from  the  heart. 


id  subepicardial  fat 


its  base  by  the  great  vessels,  but  is  otherwise  entirely  free  in  the  pericardium.     It 
presents  two  surfaces,  two  borders,  a  base,  and  an  apex  for  description. 

In  position  the  heart  is  decidedly  asymmetrical,  about  two-fifths  being  to  the 


THE    HEART 


527 


right  of  till'  median  iilanc  and  three-fifths  to  the  left.  The  long  axis  (from  the 
middle  of  th(>  hase  to  the  apex)  is  directed  downward,  Ijackward,  and  somewhat  to 
the  left.  The  base  (Basis  cordis)  is  directed  dorsally  and  lies  a  little  above  the 
middle  of  the  ilorso-ventral  diameter  of  the  thorax.  It  is  opposite  to  the  riijs  from 
the  third  to  the  sixth  inclusive.  The  apex  (Apex  cordis)  lies  above  the  last  segment 
of  the  sternum,  and  is  separated  by  a  very  short  interval  from  the  sternal  part  of 
the  diaphragm.  The  anterior  border  (Margo  cranialis)  is  strongly  convex  and  is 
directed  ol>liquely  downward  and  backward;  its  lower  part  is  parallel  with  the 
sternum.     The  posterior  border  (Margo  caudalis)  is  much  shorter,  nearly  vertical, 


Pulmonary  (        right  branch 
Pulmonar,/ reins  '"''"^    Heft  branch 


\  vna  iizygos 


Line  of  reflecti' 


Fig.  420. — He.\rt  of  Horse,  Right  View.  H.\rdened  in  situ. 
:rous  pericardium  dotted.     Epicardium  and  subepicardial  fat  have  not  been  removed  from 
heart.      Left  ventricle  is  considerably  contracted. 


and  is  opposite  to  the  sixth  rib  or  intercostal  space.  The  surfaces,  right  and  left 
(Fades  dextra,  sinistra),  are  convex  and  are  marked  by  grooves  which  indicate 
the  division  of  the  heart  into  four  chambers,  the  two  atria  al>ove  and  two  ven- 
tricles below.  The  left  surface  (covered  by  the  pericardium)  is  in  contact  wdth 
the  lower  third  of  the  chest-wall  from  the  third  to  the  fifth  intercostal  space.  On 
the  right  side  the  cardiac  notch  of  the  lung  is  smaller  and  further  forward,  so  that 
the  area  of  contact  is  at  the  third  and  fourth  riljs. 

The  coronary  or  atrio-ventricular  groove   (Sulcus  coronarius)   indicates  the 
division  between  the  atria  and  tlie  ventricles.     It  almost  completely  encircles  the 


528 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


heart,  but  is  interrupted  liy  the  origin  of  the  pulmonary  artery.  The  longitudinal 
or  interventricular  grooves,  right  and  left  (Sulci  longitudinales  sinister  et  dexter), 
correspond  to  the  septum  between  the  ventricles.  The  left  groove  is  left-anterior 
in  position.  It  begins  at  the  coronary  groove  behind  the  origin  of  the  pulmonary 
artery,  and  passes  downward  almost  parallel  to  the  posterior  border,  but  does  not 
reach  the  apex.  The  right  groove  is  right-posterior  in  position.  It  begins  at  the 
coronary  groove  below  the  termination  of  the  posterior  vena  cava  and  passes 
downward  and  a  little  backward,  ending  about  an  inch  and  a  half  (ca.  3  to  4  cm.) 


'Honary  veins 


fe. — 

Pulmonary 
veins 


Fig.  421.— Base  of  Hkart  of  Horse 


Posterior  vena  eara 
Left  atrium  (sinus  venosus) 


Large  Vessels,  Dorsal  View.       Specimen  Hardened  in  situ. 


above  the  apex.     The  grooves  are  occupied  by  the  coronary  vessel  ami  a  variable 
quantity  of  fat. 

Size  and  Weight. — In  horses  of  meflium  size  the  heart  usually  weighs  about 
seven  or  eight  jjounds  (ca.  3.5  kg.),  or  about  0.7  per  cent,  of  the  body-weight. 
There  is,  liouever,  great  range  of  variation  in  apparently  normal  specimens. 

The  following  measurements  were  obtained  in  medium-sized  hearts  in  diastole: 

Sagittal  diameter  of  base 2.5  cm. 

Greatest  width  of  base IS  to  20  em. 

Cireumference  at  coronary  groove 6.5  to  70  cm. 

Distance  between  origin  of  puhiionary  artery  and  apex 2.5  cm. 

Distance  between  termination  of  posterior  vena  cava  and  apex 18  to  20  cm. 


THE    RIGHT    ATRIUM 


529 


The  Right  Atrium 

The  right  atrium  (Atrium  dcxtrum)  or  auricle  forms  the  right-anterior  part 

of  the  base  of  the  heart,  aiul  lies  above  the  right  ventricle.     It  consists  of  a  sinus 

venosus,  into  which  the  veins  open,  anil  an  auricle  or  auricular  appendix.     The 

latter  is  a  conical  diverticulum  which  curves  around  the  right  and  anterior  surfaces 


[iilirior  vena  cava 


Orifice  of  vena  azygos 


Pulmonary  I'dn": 


Fossa 
ovalii 


Right  ventri- 
cle {septal 
wall) 


Fig.  422. — Right  Side  of  He.\rt  of  Horse  Open-ed  up  b 

Hardened  in  situ. 
The  right  ventricle  wa^  in  diastole,     r,  Intervenous  crest;    v,  v,  tricuspid  valve;      p.  p,  papill 
moderator  bands.     Arrow  points  into  origin  of  pulmonary  artery. 


Part  of  Right  W.\ll.     Organ 


of  the  aorta,  its  blind  end  appearing  on  the  left  side  in  front  of  the  origin  of  the 
pulmonary  artery. 

There  are  five  chief  openings  in  the  right  atrium.  The  opening  of  the  anterior 
vena  cava  (Ostium  vente  cavte  cranialis)  is  in  the  upper  and  fore  part.  The 
opening  of  the  posterior  vena  cava  (O.stium  vense  cava?  caudalis)  is  at  the  lower 
posterior  part.  Between  the  two  the  wall  pouches  upward  somewhat,  forming 
what  is  sometimes  termed  the  sinus  venosus  or  sac  of  Lower.  In  the  anterior  part 
of  this  the  vena  azygos  opens.  The  coronary  sinus  opens  immediately  below  the 
34 


530  BLOOD-VASCILAR    SYSTEM    OF   THE    HORSE 

posterior  vena  cava;  the  orifice  is  jirovidcd  with  a  small  semilunar  valve  or  valve 
of  Thebesius  (Valvula  sinus  coronarii).  The  middle  coronary  vein  has  a  scjiarate 
opening  in  some  cases  close  to  that  of  the  coronary  sinus.  The  atrio-ventricular 
opening  is  in  the  lower  part,  and  leads  into  the  right  ventricle.  In  addition  to 
the  foregoing  there  are  several  small  orifices  of  the  venae  cordis  parva^i  these 
arc  concealed  in  the  depressions  between  the  musculi  pectinati. 

The  atrium  is  linetl  with  a  glistening  membrane,  the  endocardium.  Its  walls 
are  smooth  except  on  the  right  and  in  the  auricle  (or  apjx'ndi.x),  where  it  is  crossed 
in  various  directions  by  muscular  ridges,  the  musculi  pectinati.  Small  bands 
extend  across  some  of  the  spaces  inclosed  by  the  musculi  pectinati.  The  latter 
terminate  above  on  a  curved  crest,  the  crista  terminales,  which  indicates  the 
junction  of  the  primitive  sinus  venosus  of  the  embryo  with  the  atrium  proper, 
and  corresponds  with  the  sulcus  terminalis  externally.  The  openings  of  the  venae 
cavse  are  without  valves.  A  ridge,  the  intervenous  crest,'  projects  downward  and 
forward  from  the  roof  just  in  front  of  the  opening  of  the  posterior  vena  cava;  it 
tends  to  direct  the  flow  of  blood  from  the  anterior  vena  cava  to  the  atrio-ventricular 
opening.  The  fossa  ovalis  is  an  oval  depression  in  the  septal  wall  at  the  point  of 
entrance  of  the  posterior  vena  cava,  bounded  internally  by  a  tliick  margin  (Limlnis 
fossae  ovalis).  The  fossa  is  the  remains  of  an  opening,  the  foramen  ovale,  through 
which  the  two  atria  communicate  in  the  fo'tus. 

The  Left  Atrium 
The  left  atrium  (Atrium  sinistrum)  or  auricle  forms  the  posterior  part  of  the 
base  of  the  heart.  It  lies  behind  the  pulmonary  artery  and  the  aorta  antl  above 
the  left  ventricle.  The  auricle  (or  appendix)  extends  outward  and  forward  on  the 
left  side,  anfl  its  blind  end  is  behind  the  origin  of  the  pulmonary  artery.  The 
pulmonary  veins,  usually  seven  or  eight  in  number,  open  into  the  atrium  behind 
and  on  the  right  side.  The  cavit.y  of  the  atrium  is  smooth,  with  the  exception  of 
the  auricle  (or  appendix),  in  which  the  musculi  pectinati  are  present.  In  some 
cases  there  is  a  depression  on  the  sejital  wall  op])osite  the  fossa  ovalis,  bounded 
above  by  a  fold  which  is  the  remnant  of  the  valve  of  the  foramen  ovale  of  the  fcetus. 
The  atrio-ventricular  opening  is  situatetl  below  and  in  front;  it  usually  appears 
smaller  than  the  right  one  on  account  of  the  contraction  of  the  left  ventricle  in  the 
dead  subject.  The  apertures  of  small  veins  of  the  heart  are  found  in  the  spaces 
inclosed  bj'  the  musculi  pectinati. 

The  number  and  the  arrangement  of  tlie  pulmonary  veins  are  \-ariable.  They  may  be 
five  to  nine  in  number.  The  large.st  oriiiee  is  posterior.  I'sually  three  vein.s  of  considerable  size 
enter  close  together  on  the  right  above  th(>  posterior  vena  cava,  and  three  or  four  open  close 
to  tlie  ridge  wliich  projects  from  the  roof  at  tlic  liase  of  the  auricle  (appendix). 

The  Right  Ventricle 
The  right  ventricle  (Ventriculus  dexter)  constitutes  the  right-anterior  part  of 
the  ventricular  mass.  It  forms  almost  all  of  the  anterior  border  of  the  heart,  but 
does  not  reach  the  apex,  which  is  formed  entirely  by  the  left  ventricle.  It  extends 
from  the  third  rib  to  the  fourth  intercostal  space  on  the  left  side,  to  the  fifth  rib 
and  space  on  the  right  side.  It  is  somewhat  triangular  in  outline,  and  is  semilunar 
in  cross-section.  Its  base  faces  upward  and  a  little  to  the  right  and  is  connected 
largely  with  the  right  atrium,  with  which  it  communicates  through  the  atrio- 
ventricular orifice;  but  its  left  jiart  projects  higher  and  forms  the  conus  arteriosus, 
from  which  the  iiulmonary  artery  arises.  Its  apex  is  two  inches  or  more  (ca.  5  to 
6  cm.)  above  the  apex  of  the  heart.  On  opening  the  cavity  it  is  seen  that  the  two 
openings   are   separated   by   a   thick   rounded   ridge    (Crista   supraventricularis). 

'  This  is  termed  the  tubercle  of  Lower  in  human  anatomy  and  the  tuberculum  intervenosum 
by  German  veterinary  anatomists. 


THE    RIGHT   VENTRICLE 


531 


The  axis  of  the  cavity,  taken  from  this  ridge  to  the  apex  forms  a  spiral  curve  down- 
ward and  to  the  right.  The  septal  wall  is  convex  and  faces  obliquely  forward 
and  to  the  right. 

The  right  atrio-ventricular  orifice  (Ostium  venosum  dextrum)  is  oval  and  is 
situated  opposite  to  the  lower  jjarts  of  the  third  and  fourth  ribs.  It  is  guarded  by 
a  tricuspid  valve  (\'alvula  trieuspidalis);  of  the  three  large  cusps  of  this  valve,  one 
is  between  the  atrio-ventricular  opening  and  the  conus  arteriosus,  one  is  septal, 
and  the  third  is  on  the  right  margin.  .Small  intermediate  cusps  intervene  between 
the  large  ones.  The  peripheral  edges  of  the  cusps  are  attached  to  the  fibrous  ring 
at  the  atrio-ventricular  opening.     The  central  edges  are  irregular  and  hang  down 


Anterior  j'ena  cara  — 


Right  coronary    '    9^ 
artery 


Modcmtu, 
band 

Right  venlriclc— 


Rigid  coronary  urkr'j 


Great  coronary 
-^(      ^    vein 
U'"      Left  coronary 
■---.^_  _;)*>'—.._  artery  {circuni- 
■'V''--^^        flex  branch) 
/'        "   Bicuspid  valve 
Chordw  tendinecE 

Musculu^  papillaris 

^'^  Moderator  band 
Left  ventricle 


Specimen  hardened  i 


Fig.  423. — Section  op  Heart  of  Horse. 
n'lii  and  cut  nearly  at  right  angles  to  the  ventricular  septum.     The  left  ventricle  is  contracted. 


but  not  ad  maxin 


V .  a.,  Segmeot  of  aortic  valve. 


into  the  ventricle;  they  give  attachment  to  chordre  tendinea?.  The  auricular 
surfaces  are  smooth.  The  ventricular  surfaces  are  rough  and  furnish  attachment 
to  interlacing  branches  of  the  chordae  tendines.  The  valves  are  folds  of  the  endo- 
cardium, strengthened  by  fibrous  tissue  and  at  the  periphery  liy  muscular  fibers 
also.  The  chordae  tendineae  are  attached  below  to  the  three  musculi  papillares, 
which  project  from  the  ventricular  wall;  .superiorh-  they  divide  into  branches 
which  are  inserted  into  the  ventricular  surfaces  and  the  free  edges  of  the  valves. 
Each  segment  of  the  valve  receives  chordae  tendineae  from  two  papillary  muscles. 
Of  the  latter,  two  are  on  the  septum  and  the  third  and  largest  springs  from  the 
anterior  wall. 

The  pulmonary  orifice  (O.-^tium  arteria^  pulmonalis)  is  circular  and  is  situated 


532 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


at  the  summit  of  the  conus  arteriosus,  opposite  to  the  lower  part  of  the  third 
intercostal  space.  It  is  guarded  by  the  pulmonary  valve,  composed  of  three  semi- 
lunar cusps  (Valvulae  semilunares  arteria-  pulmoiialis) ;  of  these,  one  is  internal,  one 
external,  and  the  third  posterior.  The  convex  peripheral  border  of  each  cusp  is 
attached  to  the  fibrous  ring  at  the  junction  of  the  pulmonary  artery  and  the  conus 
arteriosus.  The  central  border  is  free  and  slightly  concave.  Each  cusp  consists 
of  a  layer  of  endocardium  on  its  ventricular  surface,  a  continuation  of  the  inner  coat 
of  the  artery  on  its  arterial  surface,  and  an  intermediate  layer  of  fibrous  tissue. 
The  upper  edge  of  the  conus  arteriosus  forms  three  arches  with  intermediate 
projecting  angles  or   horns,  to   all   of   which  the  cusps   are  attached;    and   the 


Musculi  peclinati 


Pulmonary  artery  ^^ 


Musculi  ^^ 
■peclinati  '\ 


Aortic  valve  -- 

Great  coronary 
vein 
Left  coronary 

artery 
Bicuspid  valve 

Chorda:  tenrtincw 
Papillary  muscle 


^S-—  Right  coronary 
>    j  artery 

'"'--Tricuspid  valve 

— ^__  Papillary 
m  uscle 


Trahecula: 
'    carnecE 


Fig.  424. — Section  of  Heart  of  Horse.     Specimen  Ha 

;  is  cut  nearly  at  right  angles  to  the  ventricular  septum,  and  is  viewed  from  the  right  and  posteriorly. 


artery  forms  opposite  each  cusp  a  pouch,  the  sinus  of  the  pulmonary  artery  (or 
of  Valsalva). 

The  walls  of  the  ventricle  (except  in  the  conus  arteriosus)  bear  muscular  ridges 
and  bands,  termed  trabeculse  cameae.  These  are  of  three  kinds,  viz.,  (1)  ridges  or 
columns  in  relief;  (2)  musculi  ]iapill:ires,  somewhat  conical  flattened  projections, 
continuous  at  the  base  with  the  wall  and  giving  off  the  chordtp  tendinea;  to  the 
tricuspid  valve;  (3)  moderator  bands  (Musculi  transversi  cordis)  which  extend 
from  the  septum  to  the  opposite  wall.  The  latter  arc  partly  nuiscular,  partly 
tendinous,  and  vary  in  different  subjects.  The  strongest  one  is  usually  about 
midway  between  the  Ijase  and  apex  and  extends  from  the  septum  to  the  base  of 
the  anterior  musculus  papillaris.  It  is  considered  that  they  tenil  to  prevent 
overdistention. 


THE    LEFT    VENTKICLE 


533 


The  Left  Ventricle 

The  left  ventricle  (\'entriculus  sinister)  forms  the  left  posterior  part  of  the 
ventricuhxr  mass.  It  is  more  regularly  conical  than  the  right  ventricle  and  its 
wall  is  much  thicker  except  at  the  apex.  It  forms  all  of  the  posterior  border  of 
the  ventricular  part  anil  the  apex  of  the  heart.  Its  base  is  largely  continuous  with 
the  left  atrium,  with  which  it  communicates  through  the  left  atrio-ventricular 
opening,  but  in  front  it  opens  into  the  aorta.  The  cavity  usually  appears  smaller 
than  that  of  the  right  ventricle  in  the  dead  subject,  on  account  of  the  greater  con- 
traction of  its  wall.     It  is  almost  circular  in  cross-section. 

The  left  atrio-ventricular  orifice  (Ostium  venosum  sinistrum)  is  opposite  to 
the  fifth  rib  and  intercostal  si)ace.     It  is  almost  circular  and  is  guarded  by  the 


Origin  of  right  coronary  urttj-/ 


Conus  arteriosus 


Pulmonary  opening 


Origin  of  left  coram iry 
artery 


Left  atrio-ventricular 
opening. 


Fig.  425.— 1 
!  been  removed  : 


[E  Bases  of  the  Ventricles  of  the  Heaht  of  the  Horse. 
\d  the  aorta  and  pulmonary  artery  cut  off  sfiort.     The  left  ventricle 
V.V.,  Pulmonary  valve;   a. v.,  aortic  valve. 


bicuspid  or  mitral  valve  (Valvula  bicuspidalis).  The  two  segments  of  this  valve 
are  larger  and  thicker  than  those  of  the  right  side  of  the  heart.  One  is  placed  in 
front  and  separates  the  atrio-ventricular  and  aortic  openings.  The  other  is  placed 
behind  and  laterally  and  is  usually  divided  into  two  or  three  flaps. 

The  aortic  orifice  (Ostium  aorticum)  is  directed  upward  and  slightly  forward. 
It  is  situated  opposite  to  the  fourth  rib.  It  is  guarded  by  the  aortic  valve,  composed 
of  three  semilunar  cusps  (Valvute  semilunares  aortae) ;  one  cusp  is  anterior,  the 
others  right  and  left  posterior.  They  are  similar  to  those  of  the  pulmonary  valve, 
but  are  much  .stronger.  The  free  edge  of  each  contains  a  central  nodule  of  fibrous 
tissue,  the  corpus  Arantii  (Nodulus  valvulsp  semilunaris). 

The  chordae  tendineae  are  fewer  but  larger  than  those  of  the  right  ven- 
tricle. 

There  are  two  large  musculi  papillares,  one  on  each  side;    they  are  usually 


534  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

compound.  The  moderator  hands  are  variable.  Commonly  two  or  three  larger 
ones  (which  are  often  branched)  extend  from  the  musculi  papillares  to  the  septum. 
Smaller  ones  may  be  found  in  various  places,  especially  at  the  apex.  The  other 
trabeculip  are  fewer  and  less  prominent  than  in  the  right  ventricle. 

The  interventricular  septum  (Septum  ventriculorum)  is  the  musculo-memliran- 
ous  partition  which  separates  the  cavities  of  the  two  ventricles.  It  is  placet!  ol)- 
liquely.  One  surface  is  convex,  faces  forward  and  to  the  right,  and  bulges  into 
the  right  ventricle.  The  other  surface,  which  faces  into  the  left  ventricle,  is  con- 
cave and  looks  backward  and  to  the  left.  The  greater  part  of  the  septum  is  thick 
and  muscular  (Septum  musculare),  but  the  upper  part  is  thin  and  membranous 
(Septum  membranaceum).  The  latter  intervenes  between  the  left  ventricle,  on 
the  one  hand,  and  the  right  ventricle  and  atrium  on  the  other. 


Structure  of  the  Heart 

The  heart-wall  consists  mainly  of  peculiar  striped  muscle,  the  myocardium, 
which  is  covered  externally  by  the  visceral  part  of  the  serous  pericardium  or 
epicardium,  and  is  lined  by  the  endocardium. 

The  epicardium  is  in  general  closely  attached  to  the  muscular  wall,  but  is 
loosely  attached  over  the  coronary  vessels  and  the  associated  subepicardial  fat. 
It  consists  of  a  layer  of  flat  polygonal  cells,  resting  on  a  membrane  of  white  and 
elastic  fibers. 

The  myocardium  consists  of  planes  of  fibers  arranged  in  a  somewhat  compli- 
cated manner.  The  muscular  tissue  of  the  atria  is  almost  completely  separated 
from  that  of  the  ventricles  by  the  fibrous  rings  around  the  atrio-ventricular  orifices. 

In  the  atria  the  muscle  Ijands  fall  naturally  into  two  groups — superficial  and 
deep.  The  former  aic  common  to  both  atria,  the  latter  special  to  each.  The 
superficial  or  common  fibers  for  the  most  part  begin  and  end  at  the  atrio-ventricular 
rings,  but  some  enter  the  interatrial  septum.  The  deep  or  special  bundles  also 
form  two  sets.  Looped  fibers  pass  over  the  atria  from  ring  to  ring,  wliile  annular 
or  spiral  fibers  surround  the  ends  of  the  veins  which  open  into  the  atria,  the  auricles, 
and  the  fossa  ovalis. 

The  muscular  wall  of  the  ventricles  is  much  stronger  than  that  of  the  atria. 
That  of  the  left  ventricle  is  in  general  about  three  times  as  thick  as  that  of  the  right 
one,  but  is  thin  at  the  apex.  The  superficial  fibers  are  attached  above  to  the  atrio- 
ventricular fibrous  rings  and  pass  in  a  spiral  toward  the  apex.  Here  they  bend 
upon  themselves  and  pass  deeply  upward  to  terminate  in  a  papillary  muscle  of  the 
ventricle  opposite  to  that  in  which  they  arose.  The  loops  so  formed  at  the  apex 
constitute  a  whorl,  the  vortex  cordis.  The  deep  fibers,  although  they  appear  to 
l)e  jjroper  to  each  ventricle,  have  been  shown  by  MacCallum  to  be  in  reality  almost 
all  conunon  to  both.  Their  arrangement  is  scroll-like.  They  begin  on  one  side, 
curve  around  in  the  wall  of  that  ventricle,  then  pass  in  the  septum  to  the  opposite 
side,  and  curve  around  the  other  ventricle.  There  is  a  layer  of  deep  fibers  which  is 
confined  to  the  basal  part  of  the  left  ventricle;  it  is  attachetl  to  the  left  atrio- 
ventricular ring. 

Four  fibrous  rings  (Annuli  fibrosi)  surround  the  orifices  at  the  bases  of  the 
ventricles.  The  atrio-ventricular  rings  separate  the  musculature  of  the  atria  from 
that  of  the  ventricles.  Tho.se  which  surround  the  origins  of  the  pulmonary  artery 
and  aorta  are  festooned  in  confoi'mity  with  the  attached  borders  of  the  valves. 
The  aortic  ring  contains  on  the  right  .side  a  ])late  of  cartilage  (Cartilago  cordis), 
which  frequently  becomes  more  or  less  calcified  in  old  animals.  Sometimes  a 
smaller  plate  is  present  on  the  left  side. 

The  endocardium  lines  the  cavities  of  the  heart  and  is  continuous  with  the 
internal  coat  of  the  vessels  which  enter  and  leave  the  organ.     Its  free  surface  is 


THE    PVLMOXARY    ARTERY THE    SYSTEMIC    ARTERIES  535 

smooth  and  glistening  and  is  formed  by  a  layer  of  endothelial  cells.  The  latter 
rest  on  a  thin  layer  of  connective  tissue,  which  is  connected  with  the  myocardium 
by  a  subenilocardial  elastic  tissue  containing  vessels  and  nerves. 

Vessels  and  Nerves. — The  heart  receives  its  blood-supply  through  the  two 
coronary  arteries  which  arise  from  the  aorta  opposite  to  the  anterior  and  left  cusps 
of  the  aortic  valve.  IMost  of  the  blood  is  returned  by  the  coronary  veins,  which 
open  into  the  right  atrium  by  the  coronarj-  sinus.'  A  few  small  veins  open  directly 
into  the  right  atrium,  and  others  are  said  to  open  into  the  left  atrium  and  the 
ventricles.  The  lymph-vessels  form  a  suliepicardial  network  which  communicates 
through  stomata  with  the  cavity  of  the  pericardium.  There  is  a  less  distinct 
subendocardial  network.  The  vessels  converge  usually  to  two  trunks  which  ac- 
company the  l)lood-vessels  in  the  atrio-ventricular  grooves  and  enter  the  glands  at 
the  bifurcation  of  the  trachea.  The  nerves  are  derived  from  the  vagus  and 
sympathetic  through  the  cardiac  plexus. 


The  Arteries 
the  pulmonary  artery 
The  pulmonary  artery  (A.  pulmonalis)  springs  from  the  conus  arteriosus  at  the 
left  side  of  the  ijase  of  the  right  ventricle.  It  curves  upward,  backward,  and 
inward,  and  tlivides  behind  the  arch  of  the  aorta  into  right  and  left  branches.  It  is 
related  in  front  to  the  right  auricle  (appendix),  behind  to  the  left  auricle  (appendix), 
and  internally  to  the  aorta.  It  is  enveloped  with  the  latter  in  a  common  .sheath 
of  the  visceral  layer  of  the  serous  pericardium.  Near  the  bifurcation  it  is  connected 
with  the  arch  of  the  aorta  by  a  fibrous  band  about  half  an  inch  (ca.  1.2  cm.)  in 
width;  this  is  the  ligamentum  arteriosum,  a  remnant  of  the  large  ductus  arteriosus, 
which  conducts  most  of  the  blood  from  the  pulmonarj-  artery  to  the  aorta  in  the 
foetus.  The  artery  is  bulbous  at  its  origin,  and  forms  three  sinuses  or  pouches, 
which  correspond  to  the  cusps  of  the  semilunar  valve.  Beyond  this  it  gradually 
diminishes  in  caliber. 

In  a  horse  of  medium  size  the  arterj'  is  about  seven  inches  (ca.  17  to  IS  cm.)  long.  At  the 
origin  it  is  about  two  and  a  half  inches  (ca.  6  to  6.5  cm.)  in  width;  at  the  bifurcation  its  caliber 
is  about  one  and  a  half  inches  (ca.  3.5  to  4  cm.).  The  wall  is  relatively  thin,  especially  at  the 
origin. 

The  right  branch  (Ramus  dexter)  of  the  pulmonary  arterj'  is  a  little  longer  and 
wider  than  the  left  one.  It  passes  over  the  fore  part  of  the  left  atrium  and  below 
the  bifurcation  of  the  trachea  to  the  hilus  of  the  right  lung,  and  enters  the  latter 
below  the  right  bronchus.  In  the  lung  it  passes  to  the  outer  and  lower  side  of  the 
stem-bronchus  and  accompanies  it  to  the  base  of  the  organ.  The  branches 
correspond  to  the  ramification  of  the  bronchi.  The  left  branch  (Ramus  sinister) 
is  very  short.  It  passes  backward  and  enters  the  lung  below  the  left  bronchus. 
Its  branches  within  the  lung  are  arranged  like  that  of  the  right  one. 


THE  SYSTEMIC  ARTERIES 
The  aorta  is  the  main  sj'stemic  arterial  trunk.  It  begins  at  the  base  of  the  left 
ventricle  and  is  practically  median  at  its  origin.  It  pa.sses  upward  and  slightly 
forward  between  the  pulmonary  artery  on  the  left  and  right  atrium  on  the  right. 
It  then  curves  sharply  l)ackward  and  upward  and  inclines  somewhat  to  the  left, 
forming  the  arch  of  the  aorta  ( Arcus  aortse),  and  reaches  the  ventral  surface  of  the 
spine  at  the  eighth  or  ninth  thoracic  vertebra.  After  passing  backward  along  the 
ventral  aspect  of  the  bodies  of  the  vertebrte  between  the  lungs  it  traverses  the  hiatus 

'  These  vessels  will  be  described  later  in  their  systematic  order. 


536 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


aorticus  and  enters  the  abdominal  cavity,  where  it  lies  below  the  vertebral  bodies 
and  the  psoas  minor,  just  to  the  left  of  the  median  plane.  It  divides  under  the 
fifth  lumbar  vertebra  into  the  two  internal  iliac-  or  hypogastric  arteries. 

From  the  bifurcation  a  small  vessel,  the  middle  sacral  artery  (A.  sacralis  media),  sometimes 
passes  backward  on  the  pelvic  surface  of  the  .sacrum.  It  becomes  lost  in  the  periosteum  or  joins 
the  coccygeal  artery,  or  in  exceptional  cases  is  traceable  to  the  sphincter  ani  externus. 

The  caliber  of  the  aorta  is  greatest  at  its  origin,  which  is  termed  the  bulbus 
aortae.  Here  it  forms  three  pouch-like  dilatations,  the  sinuses  of  the  aorta  (or  uf 
Valsalva).  These  correspond  to  the  cusps  of  the  aortic  valve,  and  the  coronary 
arteries   arise   from   the   left  posterior  and   anterior  sinuse.s.     At  the  arch  the 


Ri(,hl 
Pidmnyiari/  rcitis     pulntonari/ 
artery 


Great  coronary  rein 


Small  corumiry  vein 


l!ig}d  coronary  artery 


Fig.  426. — Cahdiac  Vessels  of  Horse,  Right  Side. 
Veins  are  black,  arteries  white. 


diameter  is  about  two  inches  (ca.  5  cm.),  and  beyond  this  it  diminishes  gradually 
in  width. 

It  is  convenient  to  divide  the  aorta  into  thoracic  and  abdominal  parts.  The 
thoracic  aorta  (Aorta  thoracica)  lies  within  the  pericardium  to  the  point  of  attach- 
ment of  the  ligamentum  artcriosum,  and  is  inclosed  with  the  pulmonary  artery 
in  a  prolongation  of  the  epicardium.  Beyond  this  it  is  between  the  two  pleural 
sacs.  It  is  crossed  on  the  right  l)y  the  ocsophagits  and  trachea,  on  the  left  by  the 
left  vagus  nerve.  The  left  recurrent  nerve  winds  around  the  concavity  of  the  arch 
from  left  to  right,  and  the  vena  azygos  and  thoracic  duct  lie  along  the  dorsal  part 
of  its  right  face.  The  trachea  causes  it  to  deviate  to  the  left;  but  beyond  this  it 
becomes  median.  The  abdominal  aorta  (Aorta  abdominalis)  (Fig.  450)  is  related 
above  to  the  lumbar  v('rt('i)r;p,  the  inferior  common  ligament,  and  the  left  psoas 
minor  muscle;  in  the  hiatus  aorticus  it  is  related  to  the  cisterna  chyli.  On  its 
right  is  the  posterior  vena  cava,  and  on  its  left  the  left  kidney  and  ureter. 


COMMON    BRACHIOCEPHALIC    THUXK    OR   ANTERIOR   AORTA 


537 


BRANCHES  OF  THE  THORACIC  AORTA 
I.  CORONARY  ARTERIES 

The  two  coronary  arteries,  riglit  and  left,  are  distributed  almost  entirely  to 
the  heart,  but  send  some  small  twigs  to  the  origins  of  the  great  vessels. 

The  right  coronary  artery  (A.  coronaria  dextra)  arises  from  the  anterior  sinus 
of  the  aorta.  It  passes  forward  between  the  conus  arteriosus  and  the  right  auricle 
(appendix)  to  the  coronary  groove,  in  which  it  curves  around  to  the  right  and  back- 
ward. It  then  descends  in  the  right  ventricular  groove  almost  to  the  apex  of  the 
heart. 

The  left  coronary  artery  (A.  coronaria  sinistra)  arises  from  the  left  posterior 


Pulmonary  veins 


Great  coronary 

rein 
Left  coronary 
artery,  circumflex 
brancli. 


Descending  branch  of 
left  coronary  artery 

Great  coronary  vein 


Fig.  427. — C.^rdiac  Vessels  of  Horse,  Left  Side. 
The  dotteti  lines  indicate  part  of  the  left  coronary  artery  which  is  concealed  by  the  left  auricle. 

sinus  of  the  aorta,  passes  to  the  left  lieliind  tlie  origin  of  the  pulmonary  artery, 
and  divides  into  two  branches.  The  descending  branch  (Ramus  descendens) 
passes  down  the  left  ventricular  groove  toward  the  apex.  The  circumflex  branch 
(Ramus  circumflexus)  runs  backward  in  the  coronary  groove,  in  which  it  winds 
around  to  the  right  side. 


2.  COMMON  BRACHIOCEPHALIC  TRUNK  OR  ANTERIOR  AORTA 
The  common  brachiocephalic  trunk  f)r  anterior  aorta  (Truncus  brachiocephali- 
cus  communis)  is  a  very  large  vessel  which  arises  from  the  convexity  of  the  arch 
of  the  aorta  within  the  pericardium.  It  is  directed  forward  and  upward.  Its 
length  in  horses  of  medium  size  is  usually  about  two  inches  (ca.  5  to  6  cm.),  but 
it  is  sometimes  only  half  an  inch  or  less  (ca.  1  cm.).  It  is  crossed  on  the  left  bj-  the 
left  vagus  and  cardiac  nerves,  and  the  left  recurrent  nerve  runs  between  it  and 


538 


BLOOD-VASCVLAR    SYSTEM    OF   THE    HORSE 


the  trachea.  It  divides  opposite  to  the  second  intercostal  space  or  tiiird  ril)  into 
the  lirachiocephalir  and  left  brachial  arteries. 

The  brachiocephalic  artery  (A.  Ijrachiocephalica)  is  directed  forward  and  a 
little  iii)\vard  in  the  anterior  media.stinum,  beneath  the  trachea.  Opposite  the 
first  ril)  it  gives  off  the  bicarotid  trunk  and  is  continued  as  the  right  brachial  artery. 
The  latter  (A.  subclavia  dextra)  turns  downward  and  bends  around  the  anterior 
border  of  the  first  rib  and  the  insertion  of  the  scalenus  muscle  above  the  brachial 
vein.  Its  course  and  branches  beyond  this  point  will  he  described  with  the  vessels 
of  the  thoracic  linil). 

The  left  brachial  artery  (A.  subclavia  sinistra)  is  longer  than  the  right  one  and 
ri.ses  to  a  higher  level.     It  forms  an  almost  semicircular  curve,  the  concavity  being 


Fio.  428. — TopoGRAPnT  of  Thoracic  Cavity  of  Horse,  Xept  Side,  after  Removal  of  Left  Li'ng. 
The  ninth,  fifteenth,  and  eighteenth  ribs  are  retained,  a,  Pericardium;  h,  thoracic  aorta;  c.  brachio- 
cephalic trunk;  rf,  rf",  dorsal  artery;  rf',  subcostal  artery;  e,  e',  superior  or  deep  cervical  artery;  /,  vertebral  artery; 
0,  (/',  left  brachial  artery;  h,  inferior  cervical  artery;  i,  internal  thoracic  artery;  k,  common  carotid  artery;  I, 
jURular  vein;  m,  brachial  vein;  m',  inferior  cervical  vein;  n,  anterior  vena  cava;  o.  thoracic  duct;  ;),  rrsophagus; 
Q,  costal  part  of  diaphragm;  (/,  tendinous  center  of  same;  q",  left  crus  of  same;  r,  anterior  mediastinal  lymph- 
glands;  ».  trachea;  /,  bronchial  lymph-glands;  u,  root  of  left  lung;  r,  anterior  mediastinum;  v' ,  posterior  medi- 
astinum; w,  longus  colli;  x,  sterno-cephalicus;  't,  scalenus;  z,  transversalis  costarum;  /,  longissimus;  2.  splenius:  B, 
spinalis  et  semispinalis;  4.  4'.  rhomboideus;  5,  left  i>hrenic  nerve:  6,  left  vagus;  6' ,  6",  oesophageal  continuations 
of  vagi;  7,  dorsivl  branch  of  right  vagus;  <9,  cardiac  nerve;  9,  left  recurrent  nerve;  10,  cervical  trunk  of  sympathetic; 
//,  first  thoracic  ganglion  of  sympathetic;  IS,  thoracic  trunk  of  sympathetic;  IS,  brachial  plexus,  (.\fter  Ellen- 
berger-liauin.  Tojj.  .\iiat.  d.  Pferdes.) 


ventral.  It  is  related  internally  to  the  oesophagus,  trachea,  and  thoracic  duct, 
and  the  left  vagus,  phrenic,  and  cardiac  nerves  cross  under  its  origin.  It  emerges 
from  the  thorax  like  the  artery  of  the  right  side.  There  is  thus  a  difference  at  first 
between  the  trunks  of  opposite  sides,  but  iDeyond  tliis  their  course  and  distribution 
are  similar. 

The  brachial  and  brachioce])halic  arteries  within  the  thorax  give  off  the  dorsal, 
superior  cervical,  vertebral,  and  internal  thoracic  arteries.  At  the  first  rib  they 
give  off  the  external  thoracic  and  inferior  cervical  arteries. 

1.  The  left  dorsal  or  dorso-intercostal  artery  (A.  costo-cervicalis)  passes 
dorsally  across  the  left  face  of  the  trachea  anil  oesophagus  toward  the  second 
intercostal  sjiace.     The  right  artery  arises  usually  by  a  common  trunk  with  the 


COMMON    BRACHIOCEPHALIC    TRUNK    OR    ANTERIOR    AORTA 


539 


superior  cervical,  crosses  the  right  face  of  the  trachea  and  has  no  contact  with  the 
oesophagus.  Both  detach  small  branches  to  the  trachea,  lymph  glands,  and 
pleura,  and  divide  on  reaching  the  longus  colli  into  two  branches.  Of  these  the 
subcostal  artery  (A.  intercostalis  suprema)  is  the  smaller.  It  passes  backward 
under  the  costo-vertebral  joints  with  the  sympathetic  trunk.  It  gives  off  the 
second,  third,  and  fourth  intercostal  arteries,  and  ends  at  the  fifth  space,  where  it 
anastomoses  with  the  first  aortic  intercostal  artery,  or  constitutes  the  fifth  inter- 
costal artery,  or  dips  into  the  longissimus  muscle.  It  also  gives  off  spinal  branches 
and  twigs  to  the  longus  colli  and  the  pleura.  The  other  branch  (A.  transversa 
colli)  is  the  direct  continuation  of  the  trunk.     It  emerges  through  the  upper  end  of 


Fig.  429. — Topography  of  TiioRAnr  Cavity  of  Horsf,  Right  View. 
The  ninth,  fifteenth,  ami  eighteenth  ribs  are  retained,  a,  Pericardium;  6,  posterior  vena  cava;  c,  vena 
azygos;  c'.  oesophageal  vein;  rf,  e,  anterior  vena  cava;  /,  brachial  vein;  g,  inferior  cervical  vein;  h,  jugular  vein; 
I,  vertebral  vein;  k,  superior  cervical  vein;  I,  dorsal  vein;  7?i.  trachea;  n,  root  of  right  lung;  o,  trsophagus;  p, 
mediastinal  lobe  of  right  lung;  g,  mediastinum;  r,  bronchial  Ijmph  glands;  s,  mediastinal  lymph  glands;  (,  costal 
part  of  (liaphragm;  i',  tendinous  center  of  same;  w,  intercostal  muscle;  r,  longus  colli;  u',  po.sterior  deep  pectoral 
muscle;  w' ,  anterior  deep  pectoral  muscle;  i,  superficial  pectoral  muscle;  y,  sterno-cephalicus;  z,  scalenus;  /,  6, 
right  brachial  artery;  2,  dorso-cer\-ical  trunk;  3',  superior  or  deep  cer\-ical  artery;  3,  dorsal  artery  (cut);  3', 
subcostal  artery:  4.  internal  thoracic  artery;  6,  external  thoracic  artery;  7.  inferior  cervical  artery;  S,  bicarotid 
trunk;  10,  aorta;  11,  oesophageal  artery;  12,  thoracic  duct;  13,  right  phrenic  nerve;  14,  brachial  plexus;  15, 
right  vagus;  15',  IS",  esophageal  continuations  of  vagi;  IB,  right  recurrent  nerve;  17,  cervical  trunk  of  sympa- 
thetic; l,i.  thoracic  trunk  of  sympathetic;  SO,  inferior  cervical  ganglion;  SI,  first  thoracic  ganglion  of  sympathetic; 
S3,  right  cardiac  nerve;  23,  longissimus;  24,  transversalis  costarura;  2d,  spinaUs;  26,  multifidus;  27,  ligamentum 
nuciia?.     (After  EUenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


the  second  intercostal  space,  passes  across  the  transversalis  costarum  and  longissi- 
mus toward  the  withers,  and  divides  into  several  diverging  branches.  An  anterior 
branch  passes  upward  and  forward  Ijetween  the  splenius  and  complexus  and  anas- 
tomoses with  branches  of  the  superior  cervical  artery;  the  others  are  directed 
upward  under  the  serratus  magnus  and  rhomlioideus  to  the  withers,  supplying 
the  muscles  and  skin  of  this  region. 

The  left  dorsal  artery  sometimes  arises  with  the  superior  cervical  by  a  common  trunk.  On 
the  right  side  there  may  be  a  common  stem  for  the  dorsal,  superior  cervical,  and  vertebral  ar- 
teries. Occasionally  the  artery  arises  from  the  anterior  aorta.  Sometimes  it  emerges  through 
the  third  space.  The  subcostal  may  arise  independently  behind  the  dorsal  or  from  the  superior 
cervical  artery. 


540  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

2.  TliP  superior  or  deep  cervical  artery  (A.  cervicalis  profunda)  arises  in  front 
of  the  dorsal  or  liy  a  common  trunk  with  it.  It  crosses  the  cesophgaus  (left  side), 
the  trachea  (right  side),  and  the  longus  colli,  and  emerges  from  the  thoracic  cavity 
l)y  passing  through  the  space  behind  the  first  cost o-trans verse  articulation.  In  the 
thorax  it  gives  off  a  small  branch  (A.  mediastini  cranialis)  to  the  mediastinum  and 
the  pericardium;  also  the  first  intercostal  arterj'  (A.  intercostalis  prima),  a  very 
small  vessel  which  passes  down  in  the  first  intercostal  space.  After  leaving  the 
thorax  the  artery  passes  upward  and  forward  on  the  spinalis  muscle  and  the  lamellar 
part  of  the  ligamentum  nuchiB,  covered  by  the  complexus.  Its  terminal  branches 
anastomose  with  branches  of  the  occipital  and  vertebral  arteries  in  the  region  of  the 
axis.  Numerous  collateral  branches  are  detached  to  the  extensor  muscles  of  the 
head  and  neck,  the  ligamentum  nuclue,  anil  the  skin,  and  anastomoses  occur  with 
the  dorsal  artery  above  and  the  vertebral  artery  below. 

The  artery  sometimes  emerges  throush  the  seeond  intercostal  space. 

3.  The  vertebral  artery  (A.  vertebralis)  arises  from  the  brachial  for  brachio- 
cephalic) opposite  the  first  intercostal  space  and  passes  upward  and  forward. 
On  the  left  side  it  crosses  the  oesophagus,  on  the  right  the  trachea.  Emerging  from 
the  thorax  it  passes  between  the  longus  colli  internally  and  the  scalenus  externally, 
under  the  transverse  process  of  the  seventh  cervical  vertebra,  and  continues  along 


Verlebral  arterij 


Fig.  430. — Vertebr 


the  neck  through  the  series  of  foramina  transversaria,  between  which  it  is  covered 
by  the  intertransversales  colli.  Emerging  from  the  foramen  of  the  axis,  it  crosses 
the  capsule  of  the  atlanto-axial  joint,  and  joins  the  retrograde  branch  of  the  occi- 
pital artery  under  cover  of  the  great  oblique  muscle  of  the  head.  At  each  inter- 
vertebral foramen  a  spinal  branch  ( Ramus  spinalis)  is  given  off  which  enters  the 
vertebral  canal  and  reinforces  tlic  \cntral  spinal  artery.  It  also  gives  off  series 
of  dorsal  and  ventral  muscular  branches  'Rami  nuisculares).  The  dorsal  branches 
are  the  larger;  they  supply  the  deep  exten.sor  muscles  of  the  head  and  neck,  and 
anastomose  with  the  deep  cervical  and  occipital  arteries.  The  ventral  liranches 
supply  chiefly  the  scalenus,  longus  colli,  intertransversales,  and  rectus  capitis 
anterior  major.  The  artery  is  accompanied  by  the  vertebral  vein  and  a  sym- 
])athetic  nerve  trunk. 

In  some  oases  the  last  cervical  transverse  process  has  a  foramen  transversarium,  through 
whicli  the  artery  [Kusses. 

4.  The  internal  thoracic  artery  (A.  thoracica  s.  mammaria  interna)  is  a  large 
vessel  which  arises  from  the  ventral  side  of  the  brachial  opposite  the  first  rib.  It 
curves  downward  and  backward,  being  at  first  on  the  inner  surface  of  the  rib,  and 
then  crosses  the  lower  part  of  the  first  intercostal  space  and  passes  under  the  trans- 
versus  thoracis  muscle.  It  runs  backward  tmder  cover  of  that  muscle  over  the 
chondro-sternal  joints  to  the  eighth  costal  cartilage,  where  it  divides  into  asternal 
and    anterior    abdominal    branches.     At    each    intercostal    space    two    collateral 


THE    COMMON    CAROTID    ARTERY  541 

branches  arc  dctachod.  The  intercostal  branches  (Rami  intorrostales)  pass 
upward  in  tlio  intercostal  sjiaces  and  anastomose  witii  liomonymous  descending 
arteries.  Tlie  lower  branches  detach  small  twigs  to  the  transvers\is  thoracis,  ])lcura, 
and  pericardium,  and  pass  out  between  the  costal  cartilages  as  perforating  branches 
(Rami  perforantes)  to  supply  the  pectoral  muscles  and  skin,  anastomosing  with 
the  external  thoracic  artery.  A  very  small  pericardiaco-phrenic  artery  ascends  in 
the  mediastinum  on  the  left  side,  in  the  caval  fold  of  pleura  on  the  right  side;  it 
supplies  fine  twigs  to  the  pericardium  and  pleura  and  accompanies  the  phrenic 
nerve  to  the  diaphragm.  In  the  young  subject  it  gives  small  branches  (Aa. 
thymicse)  to  the  thymus  gland.  The  asternal  artery  (A.  musculophrenica)  passes 
along  the  ninth  costal  cartilage  and  continues  along  the  costal  attachment  of  the 
transversus  abdominis  (Fig.  185).  It  gives  off  intercostal  branches  which  anas- 
tomose with  those  descending  from  the  thoracic  aorta,  and  twigs  to  the  diaphragm 
and  transversus  abdominis.  The  anterior  abdominal  artery  (A.  epigastrica 
cranialis)  is  the  direct  continuation  of  the  internal  thoracic.  It  passes  be- 
tween the  ninth  costal  cartilage  and  the  xiphoid  cartilage,  runs  backward  on  the 
abdominal  sia-face  of  the  rectus  abdominis  and  then  becomes  embedded  in  it 
(Fig.  466).  It  supplies  the  ventral  wall  of  the  abdomen  and  anastomoses  with 
the  posterior  alxlominal  artery. 

5.  The  external  thoracic  artery  (A.  thoracica  externa)  is  given  off  from  the 
ventral  aspect  of  the  brachial,  usually  at  the  inner  surface  or  anterior  border  of 
the  first  rib.  It  turns  around  the  first  rib  below  or  behind  the  brachial  vein  (when 
given  off  within  the  thorax)  and  passes  backward  under  the  deep  pectoral  muscle; 
it  is  continued  as  a  small  vessel  in  the  panniculus  carnosus,  where  it  accompanies 
the  external  thoracic  ("spur")  vein.  It  sends  branches  to  the  pectoral  muscles 
and  the  axillary  lymph  glands. 

This  artery  varies  in  origin  and  size.  Not  rarely  it  arises  from  the  internal  thoracic  or 
from  the  brachial  outside  of  the  thorax.  In  other  cases  it  arises  by  a  common  trunk  witli  the 
inferior  cervical.  It  may  be  very  small  or  even  absent,  in  which  case  the  perforating  branches 
of  the  internal  thoracic  compensate. 

6.  The  inferior  cervical  artery  (Truncus  omo-cervicalis)  arises  usually  from 
the  dorsal  surface  of  the  brachial  opposite  the  first  rib  or  where  that  vessel  winds 
around  the  rib.  It  is  directed  downward  and  a  little  forward  across  the  external 
surface  of  the  jugular  vein  and  the  deep  face  of  the  scalenus  among  the  lymph 
glands  at  the  thoracic  inlet,  and  cUvides  into  ascending  and  descending  branches. 
The  ascending  branch  (A.  cervicalis  ascendens)  passes  upward  and  forward  along 
the  external  surface  of  the  jugular  vein,  then  turns  sharply  backward  and  runs 
upward  along  the  anterior  border  of  the  anterior  deep  pectoral  muscle,  between  the 
omo-hyoideus  and  mastoido-humeralis  and  in  relation  to  the  jjrescapular  lymph- 
glands;  it  gives  branches  to  these  muscles  and  the  prepectoral  and  prescapular 
lymph  glands.  The  descending  branch  (A.  transversa  scapulae)  passes  downward 
and  outward  across  the  surface  of  the  anterior  deep  pectoral  and  then  runs  in  the 
groove  between  that  muscle  and  the  mastoido-humeralis  in  company  with  the 
cephalic  vein.     It  supplies  branches  to  these  muscles  and  the  skin  of  the  breast. 


THE  COMMON  CAROTID  ARTERY 
These  two  vessels  (Arteriae  carotides  communes)  arise  from  the  brachio- 
cephalic artery  by  a  common  trunk.  This  stem,  the  truncus  bicaroticus  or  cephalic 
artery,  is  detached  from  the  inner  face  of  the  brachiocephalic  opposite  the  first  rih 
and  passes  forward  in  the  median  plane  beneath  the  trachea.  It  is  related  ventrally 
to  the  prepectoral  lymph  glands,  the  terminal  parts  of  the  jugular  veins,  and  the 
anterior  vena  cava,  anrl  laterally  to  the  vagus  and  recurrent  nerves.     It  is  commonly 


542 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


two  or  three  inches  (ca.  5  to  7  cm.)  in  length,  liut  it  may  varj-  between  one  and 
eight  inches  (ca.  2.5  to  20  cm.). 

The  right  common  carotid  artery  passes  obhquely  from  the  ventral  face  of 
the  trachea  to  its  right  side.  In  this  position  it  runs  upward  and  forward  and 
divides  at  the  crico-pharyngeus  muscle  and  under  the  submaxillary  gland  into 
external  carotid,  internal  carotid,  and  occipital  arteries.  It  is  inclosed  in  a 
fibrous   sheath,    and   is   accompanied    dorsally    by    the   vagus   and   sympathetic 


Fig.  431. — Vessels  and  Nerves  of  Neck  of  Horse. 
a,  Mastoido-huraeralis;  6,  sterno-cephalicus;  c,  omo-hyoideus;  d,  sterno-thyro-hyoideua;  c,  trachea;  /,  posi- 
tion of  cariniform  cartilage:  fl.  anterior  superficial  pectoral  muscle;  A,  scalenus;  i',  intertransversales;  A:,  insertion 
of  serratus  cervicis;  /.  origin  of  trapezius;  m,  rhomboideus;  n,  splenius;  o,  complexus;  p.  i^,  trachelo-mastoideus: 
p',  ^,  tendons  of  same;  r,  longissimus;  s,  obliquus  capitis  posterior;  (,  wing  of  atlas;  u,  parotid  gland;  v,  supra- 
spinatus;  w,  anterior  deep  pectoral;  j,  spine  of  scapula;  .y,  prescapular  lymph  glands;  /,  external  maxillary  vein; 
S.  S,  jugular  vein;  4,  carotid  arter.v,  exposed  by  drawing  jugular  vein  aside;  5.  6,  ascending  anil  descending  branches 
of  inferior  cervical  artery;  T,  cephalic  vein;  S,  branches  of  superior  or  deep  cervical  arter.v;  9-14.  ventral  branches 
of  second  to  seventh  cervical  nerves;  to,  branches  of  dorsal  divisions  of  cervical  nerves.  (Ellenberger-Baum, 
Top.  Anat.  rl.  1'ferde.s.) 


nerves,  ventrally  by  the  recurrent  nerve.  At  the  last  two  cervical  vertebrae 
it  is  in  contact  superficially  with  the  jugular  vein,  but  further  forward  the 
omo-hyoideus  muscle  intervenes  between  the  artery  and  vein.  Near  its  ter- 
mination the  artery  becomes  more  deeply  placed  and  is  related  externally  to 
the  submaxillary  and  parotid  glands,  internally  to  the  oesophagus.  In  some 
cases  it  is  in  contact  ventrally  with  the  thyroid  gland,  especially  when  the 
latter  is  larger  than  usual. 


THE    COMMON    CAROTID    ARTERY 


543 


Tlir  left  common  carotid  artery  diftVrs  from  the  right  one  in  that  it  is  related 
deeply  to  the  a'sophagus,  which  separates 
it  from  the  trachea  in  the  greater  part  of 
its  course. 

The  collateral  branches  of  the  common 
carotids  are  in  the  main  small.  They  com- 
prise: 

1.  Muscular  branches  (Rami  muscu- 
lares)  of  variable  size,  which  go  to  the 
ventral  mnscles  of  the  neck  and  the  skin. 

2.  (Esophageal  and  tracheal  branches 
(Rami  ocsophagei  et  trachoales).  Small 
twigs  go  to  the  cervical  lymi:)h  glands  also. 

3.  The  parotid  artery.  This  comes  off 
near  the  termination  and  enters  the  ventral 
part  of  the  parotid  gland.  It  also  supplies 
the  subparotid  lymph  glands,  and  sometimes 
sends  a  branch  to  the  submaxillary  gland. 
It  is  inconstant. 

4.  The  thyro-laryngeal  artery  (A.  thy- 
reoidea  cranialis).  This,  the  largest  col- 
lateral branch  of  the  carotid,  arises  from 
the  latter  two  or  three  inches  before  it 
divides.  It  curves  over  the  anterior  end 
of  the  thjToid  gland,  into  which  it  sends 
several  branches.  It  gi\es  off  a  lar3mgeal 
branch  (A.  laryngea),  which  sends  tAxigs  to 
the  external  muscles  of  the  larynx  and  the 
constrictors  of  the  pharynx,  passes  between 
the  cricoid  and  thyroid  cartilages,  and  sup- 
plies the  internal  muscles  and  the  mucous 
membrane  of  the  larynx.  A  small  phar3ni- 
geal  branch  (A.  pharyngea  ascendens)  runs 
upward  antl  forward  to  the  crico-pharyn- 
geus,  and  supplies  twigs  to  the  posterior 
part  of  the  pharynx  and  the  origin  of  the 
oesophagus.  Small  innominate  twigs  are 
given  off  to  the  trachea,  the  oesophagus, 
and  the  sterno-thyro-hyoideus  anil  omo- 
hyoideus  muscles. 

In  some  cases  the  thxroid  anil  laryngeal 
arteries  arise  from  the  carotid  separately  or  by 
a  short  common  stem.  A  laryngeal  branch  is 
often  detached  from  the  carotid  in  front  of  the 
thyro-laryngeal  and  enters  the  larj-nx  with  the 
superior  laryngeal  nerve.  The  pharyngeal  branch 
frequently  comes  directly  from  the  carotiil. 

5.  The  accessory  thyroid  artery  (A. 
thjTeoidea  caudalis)  is  an  inconstant  vessel 
which  arises  from  the  carotid  at  a  vari- 
able distance  liehind  the  thyro-laryngeal — 
sometimes  from  the  latter  or  from  the  i)aro- 

tid  arterJ^  It  sends  branches  into  the  posterior  part  of  the  thyroid  gland  and 
detaches  small  tracheal  and  muscular  twigs.  In  some  cases  it  is  distributed 
chiefly  or  entirely  to  the  adjacent  muscles. 


Fig.  432. — Choss-section  of  Neck  of  Horse, 
Passing  through  Fifth  Cervic.\l  A'er- 
TEBR.\;  .\nterior  View. 
a.  Branches  of  cer\'ical  nen'es;  a',  nuchal 
fat;  b,  intertransversalis  muscle;  c,  longissimus 
muscle;  d,  vertebral  artery;  e,  vertebral  vein;  /, 
vertebral  nerve;  g,  spinal  accc-s-^ory  nerve  (upper 
division);  h,  recurrent  nerve;  /,  vago-sympa- 
thetic  trunk;  ^^  tracheal  lymph  duct;  /,  body  of 
fifth  cervical  vertebra;  /',  transverse  process  of 
same;  m,  carotid  artery;  n,  jugular  vein;  o, 
superior  cer\'ical  arterj-;  o' ,  satellite  vein  of  o, 
p,  spinal  cord;  q.  dura  mater;  r,  spinal  vein;  s 
ligamentum  nuchte;  /,  rhomboideus  muscle 
u,  splenius;  v,  complexus;  w,  niultifidus;  x 
serratus  cervicis;  y,  mastoido-humeralis;  z 
sterno-cephalicus;  1,  rectus  capitis  ant.  major; 
■2,  omo-hyoideus;  S,  panniculus;  4.  sterno- 
thyro-hyoideus;  5,  longus  colli;  6,  7,  trachelo- 
mastoideus;  S,  trapezius;  9.  spinalis;  10, 
cesophagus;  //,  trachea,  with  cartilaginous 
ring  {II'),  mucous  membrane  ill"),  and  mus- 
cular layer  {il'").  (After  Ellenberger.  in  Leiser- 
ing's  Atlas.) 


544 


BLOOD-VASCULAU    SYSTEM    OF   THE    HORSE 


THE  OCCIPITAL  ARTERY 
The  occipital  artery  (A.  occipitalis)  is  the  second  in  size  of  the  terminals  of 
the  carotid.     It  arises  usually  just  in  front  of  the  internal  carotid,  but  in  some  cases 


Fig.  433. — Deep  Dissection  op  Neck  op  Horse. 
a,  a,  Ends  of  sterno-cephalicus;  6,  anterior  part  of  omo-hyoideus;  c,  sterno-thyro-hyoideus;  d,  trachea; 
c,  OESophaRUs;  /,  cariniform  cartilage;  g,  rectus  cap.  ant.  major;  h,  stump  of  trachelo-mastoideus;  i,  iotertraris- 
versales;  /.-,  multifidus;  f,  m,  scalenus;  n,  serratus  cer\icis;  o,  o,  stumps  of  splenius,  j?,  longissimus.  g,  complexus 
(most  of  which  is  removed) ;  r,  rhomboideus;  s,  trapezius;  (,  spinalis  et  semispinalis;  u,  lamellar  part  of  lig.  nuchip; 
V,  mastoido-humeralis;  w,  anterior  deep  pectoral;  x,  supraspinatus;  y,  anterior  superficial  pectoral;  z,  scapular 
tuberosity;  /,  /,  articular  processes  of  cervical  vertebrse;  2,  2,  transverse  processes  of  same;  ^,  atlas;  5',  axis; 
4,  A.  jugular  vein  (remainder  removed;;  5.  common  carotid  artery,  from  which  a  piece  is  removed  to  show  the  ac- 
companying nerves;  6,  vago-sympathetic  trunk;  7,  7,  tracheal  and  muscular  branches  of  carotid  artery;  S,  re- 
current ner\-e;  10,  left  tracheal  lymph-duct;  //,  12,  ascending  and  descemling  branches  of  inferior  cervical  artery 
(/3);  14,  cephalic  vein;  13-20,  ventral  branches  of  second  to  seventh  cervical  ner\'es;  21,  roots  of  phrenic  nerve; 
22,  thoracic  or  pectoral  nerves;  22' ,  nerve  to  serratus  magnus;  2S,  musculo-cutaneous  nerve;  24,  median  nerve; 
25,  ulnar  nerve;  26,  radial  nerve;  27,  axillary  nerve;  2S,  dorsal  branches  of  cervical  nerves;  28' ,  accessory  nerve 
(cut);  29,  superior  or  deep  cervical  artery;  SO,  muscular  branch  of  vertebral  artery;  31,  posterior  (anastomotic) 
branch  of  occipital  artery;  32,  vertebral  artery;  55,  muscular  branches  of  occipital  artery;  34,  obliquus  capitis 
post.;  35,  obi.  cap.  ant.;  36,  twig  from  dorsal  branch  of  third  cervical  nerve.  (After  Ellenberger-Baum,  Top. 
Anat.  des  Pferdes.) 


with  that  artery  by  a  common  trunk  of  variable  length.  It  pursues  a  somewhat 
fiexuous  course  to  the  fossa  atlantis,  where  it  divides  into  anterior  and  posterior 
branches.  It  is  related  superficially  to  the  submaxillary  gland  and  the  mastoido- 
humeralis,   and  deeply  to   the  guttural    pouch  and  the  rectus    capitis  anterior 


THE    OCCIPITAL    ARTERY 


545 


major.'  Tlie  internal  carotid  artery,  the  inferior  cerebral  vein,  and  the  accessory, 
vagus,  and  sympathetic  nerves  cross  its  deep  face.  It  gives  twigs  to  the  sub- 
maxillary gland,  the  anterior 
straight  muscles,  the  guttural 
pouch  and  the  adjacent  lymph 
glands,  and  two  named  collateral 
branches.  The  condyloid  or  pre- 
vertebral artery  (A.  condyloidea) 
is  a  small  vessel  which  passes  up- 
ward and  forward  on  the  guttural 
pouch,  and  divides  into  muscular 
and  meningeal  branches.  The 
latter  enter  the  cranium  through 
the  foramen  lacerum  and  hj'po- 
glossal  foramen  and  are  dis- 
tributed to  the  dura  mater.  This 
artery  is  very  variable  in  its 
origin.  The  posterior  meningeal 
or  mastoid  artery  (A.  nieningea 
caudalis)  is  a  much  larger  vessel 
which  runs  upward  and  forward 
between  the  small  olilique  muscle 
and  the  paramastoid  process, 
passes  through  the  mastoid  fora- 
men  into    the    parieto-temporal 

canal,  enters  the  cranial  cavity, 

and  is   distributed  to  the  dura 

mater. 

The  posterior  or  retrograde 

branch   (Ramus    dcscendens)    of 

the  occipital  passes  up  through 

the   foramen    transversarium   of 

the  atlas  and  joins  the  vertebral 

artery.     It  gives  branches  to  the 

great  oblique  muscle  of  the  head, 

which  covers  it. 

The    anterior    or    occipital 

branch  (Ramus  occipitalisj  passes 

through     the     alar     (antero-ex- 

ternal)  foramen  of  the  atlas  and 

supplies   the    muscles    and   skin 

of  the    poll,    anastomosing  with 

the  deep  cer\'ical  artery  and  its 

fellow  of  the  opposite  side.     In 

the  alar  furrow  it   gives  off  the 

cerebrospinal   artery,  which  en- 
ters   the    s]iinal    canal    through 

the      intervertebral      (antero-in- 

ternal)    foramen     of    the    atlas, 

perforates  the  dura  mater,  and  divides  into  cerebral  and  spinal  branches.     The 

cerebral   branch    unites    with    that   of  the   opposite   side  to   form  the  basilar 


.  434. — Vessels  t 


iNe 


OF  Base  of  Brain  of  Horse. 
IS,  Cerebro-spinal  artery;  14,  middle  spinal  artery;  15, 
basilar  artery;  16,  posterior  cerebellar  artery;  17,  anterior 
cerebellar  artery;  18,  internal  auditory  artery;  19,  posterior 
cerebral  artery;  20,  deep  cerebral  artery;  Bl ,  stump  of  internal 
carotid  artery;  22,  anterior  choroid  artery;  23,  anterior  menin- 
geal artery;  24,  middle  cerebral  artery;  25,  artery  of  corpus 
callosum;  26,  anterior  communicating  artery;  /,  /',  1",  ol- 
factory tracts;  1'" ,  olfactory  peduncle;  2-12,  cranial  nerves; 
a,  olfactory  bulb;  b,  trigonum  olfactorium;  c,  lamina  perforata 
anterior;  d,  fossa  transversa;  e,  pyriform  lobe;  /.  cerebral 
peduncle;  g,  tractus  transversus;  h,  corpus  mammillare;  i,  tuber 
cinereum;  k,  lateral  fissure  (of  .Sylvius);  /,  presylvian  fissure; 
m.  pons;  o.  pyramid;  p,  facial  eminence;  q,  corpus  restifornie; 
r,  cerebellum;  s,  middle  peduncle  of  cerebellum,  (.\fter  Ellen- 
berger  Baum.  Top.  .\nat.  d.  Pferdes.) 


^The  relation  to  the  guttural  pouch  is  not  constant.     In  some  cases — especially  when  the 
head  and  neck  are  extended — the  artery  lies  behind  the  pouch.     The  backward  extension  of  the 
latter  is  variable. 
3.5 


546  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

artery,  and  the  spinal  branch  similarly  forms  by  union  with  its  fellow  the  middle 
spinal  artery. 

The  basilar  artery  (A.  basilaris  cerebri)  passes  forward  in  the  median  groove 
on  the  ventral  surface  of  the  medulla  and  pons  and  divides  into  the  two  posterior 
cerebral  arteries.     The  collateral  branches  of  the  basilar  are: 

1.  ]\Iedullarj'  branches  (Rami  medullares),  ten  or  twelve  in  numlier,  dis- 
tributed to  the  medulla  oblongata. 

2.  Posterior  cerebellar  arteries  (Aa.  cerebelli  caudales)  which  pass  outward 
around  the  medulla  behind  the  pons  to  the  cerebellum,  to  which  they  are  distributed 
after  giving  twigs  to  the  medulla  and  pons. 

3.  The  small  auditory  artery  (A.  auditiva  interna)  accompanies  the  eighth 
nerve  to  the  internal  car.     It  often  arises  from  the  posterior  cerebellar. 

4.  Anterior  cerebellar  arteries  (Aa.  cerebelli  nasales).  These  are  very  variable 
in  immbcr  and  origin.  There  are  often  two  or  three  on  either  side  and  they  fre- 
quentlj'  arise  from  the  posterior  cerebrals.  They  pass  outward  in  front  of  the 
pons  and  supply  the  anterior  part  of  the  cerebellum. 

The  posterior  cerebral  arteries  (Aa.  conimunicantes  caudales)  diverge  at  an 
acute  angle  and  join  the  posterior  communicating  branches  of  the  internal  carotid 
arteries  on  the  inferior  surface  of  the  cereliral  peduncles.  They  are  connected  by  a 
transverse  branch  and  by  a  network  of  fine  twigs  which  form  often  a  rete  mirabile. 


THE  INTERNAL  CAROTID  ARTERY  (Figs.  434,  436,  437) 

This  artery  (A.  carotis  interna)  is  somewhat  smaller  than  the  occipital.  It 
usually  arises  just  behind  that  artery,  crosses  its  deep  face,  and  runs  upward  and 
forward  on  the  guttural  pouch  to  the  foramen  lacerimi.  It  is  closely  related  to 
the  vagus  nerve  and  the  superior  cervical  ganglion  of  the  sympathetic  nerve,  fibers 
from  which  accompany  it.  It  is  crossed  externally  by  the  ninth  and  twelfth 
cranial  nerves  and  the  pharyngeal  branch  of  the  vagus.  It  passes  through  the 
inferior  petrosal  sinus  and  enters  the  cavernous  sinus,  within  which  it  forms  an 
S-shaped  curve.  It  is  connected  with  the  opposite  artery  by  a  transverse  branch 
(A.  intercarotica),  which  lies  behind  the  pituitary  body  in  the  intercavernous 
sinus.  A  branch  (A.  caroticobasilaris)  sometimes  connects  it  with  the  basilar  artery. 
It  then  perforates  the  dura  mater,  gives  off  the  posterior  conimiuiicating  branch, 
and  passes  forward  and  divides  at  the  side  of  the  optic  chiasma  into  anterior 
and  middle  cerebral  arteries. 

The  posterior  communicating  artery  (A.  communicans  jiostcrior)  turns  back- 
ward and  joins  the  posterior  cerel)ral.  It  gives  off  the  deep  cerebral  artery  (A. 
cerebri  profunda)  which  winds  around  the  cerebral  peduncle  and  is  distriluited 
chiefly  to  the  mid-brain.  A  smaller  collateral  branch  is  the  anterior  choroid 
artery  (A.  chorioidea  nasalis)  which  passes  along  the  optic  tract  and  is  distributed 
in  the  choroid  plexus  of  tho  lateral  ventricle. 

The  anterior  cerebral  artery  (A.  cerebri  anterior)  unites  with  the  corresponding- 
branch  of  the  opposite  artery  above  the  optic  chiasma.  From  this  junction  pro- 
ceeds the  artery  of  the  corpus  callosum  (A.  corporis  callosi),  which  turns  around  the 
genu  of  the  corpus  callosum,  enters  the  great  longitudinal  fissure,  divides  into  two 
branches,  and  is  distributed  to  the  inner  aspect  of  the  cerebral  hemispheres.  A 
small  anterior  meningeal  branch  (A.  meningea  nasalis)  of  the  anterior  cerebral  is 
distributed  to  the  anterior  part  of  the  dura,  and  assists  in  forming  a  network 
in  the  ethmoidal  fossa  (Rete  ethmoidale),  anastomosing  with  the  ethmoidal  branch 
of  the  ophthalmic  artery. 

The  middle  cerebral  artery  (A.  cerebri  media)  jiasses  outward  in  the  lateral 
fissure  (of  Sylvius)  and  divides  into  branches  on  the  outer  surface  of  the  hemisphere. 

The  arterial  circle  of  AVillis  (Circulus  arteriosus)  (Fig.  434)  is  formed  at  the 


THE  EXTERNAL  CAROTID  ARTERY  547 

interpeduncular  space  of  the  base  of  the  brain  by  the  union  of  the  anterior  cere- 
liral  arteries  in  front,  l)y  the  diverging  posterior  cerebral  arteries  behind,  and 
is  completed  laterally  by  the  junction  of  the  latter  with  the  posterior  communi- 
cating arteries  and  by  the  internal  carotid.  It  is  irregularly  polygonal  in  out- 
line. 

The  ci'reliral  arteriog  are  vory  variable  in  arrangement,  and  the  foregoing  account  is  a  brief 
statement  of  the  more  usual  disposition  of  the  larger  vessels.  Tlie  internal  carotid  artery  often 
arises  with  the  occipital  by  a  common  trunk  of  variable  length. 


THE  EXTERNAL  CAROTID  ARTERY  (Figs.  436,  437) 
This  artery  (A.  carotis  externa)  by  its  size  and  direction  constitutes  the  con- 
tinuation of  the  common  carotid.  It  passes  forward  on  the  lateral  wall  of  the 
pharynx  at  the  lower  border  of  the  guttural  pouch,  covered  by  the  submaxillary 
gland  and  the  stylo-maxillaris,  digastricus,  and  stj'lo-hyoideus  muscles.  It  then 
emerges  between  the  stylo-hyoideus  and  the  great  cornu  of  the  hyoid  bone,  passes 
upward  on  the  latter  parallel  with  the  posterior  border  of  the  lower  jaw,  and  termin- 
ates about  two  inches  (ca.  5  cm. )  below  the  temporo-maxillary  articulation  by  divid- 
ing into  superficial  temporal  and  internal  maxillary  branches.  It  is  crossed  deeply 
near  its  origin  by  the  superior  laryngeal  and  pharyngeal  branches  of  the  vagus 
nerve.  Just  before  its  emergence  its  superficial  face  is  crossed  by  the  hypoglossal 
nerve,  and  the  glosso-pharyngeal  nerve  passes  over  its  inner  surface  at  the  ventral 
border  of  the  great  cornu.  The  chief  collateral  branches  are  the  masseteric,  ex- 
ternal maxillary,  and  posterior  auricular.  It  also  furnishes  variable  branches  to 
the  submaxillary  and  parotid  glands,  the  guttural  pouch,  and  the  pharyngeal 
h'mph  glands,  as  well  as  twigs  to  some  adjacent  muscles. 

1.  The  inferior  masseteric  or  maxillo-muscular  artery  fA.  masset erica  inferior) 
is  given  off  from  the  external  carotid  at  its  emergence  from  beneath  the  stylo- 
hj'oideus.  It  passes  do'maward  and  slightly  forward  under  cover  of  the  parotid 
gland  and  over  the  tendon  of  insertion  of  the  sterno-cephalicus  to  the  posterior 
border  of  the  mandible  and  appears  on  the  masseter  muscle,  into  which  it  plunges 
after  a  short  course  on  its  surface.  It  gives  branches  also  to  the  internal  pterygoid 
and  stylo-maxillaris  muscles  and  the  ])arotid  gland. 

2.  The  external  maxillary,  facial,  or  submaxillary  artery  ( A.  maxillaris  externa)' 
arises  from  the  external  carotid  on  the  inner  surface  of  the  posterior  belh-  of  the  di- 
gastricus (Fig.  436).  It  runs  downward  and  forward  on  the  lateral  wall  of  the 
pharynx  across  the  deep  face  of  the  stylo-hyoideus  toward  the  great  cornu  of 
the  hyoid  bone,  accompanied  by  the  glosso-pharyngeal  nerve  in  front  and  the  hj-- 
poglossal  nerve  behind.  After  giving  off  the  lingual  artery  at  the  posterior  border 
of  the  great  cornu,  it  inclines  more  ventrally  on  the  inner  surface  of  the  internal 
pterygoid  muscle,  crosses  over  the  hyo-glossus  muscle,  the  hypoglossal  nerve,  the 
submaxillary  duct,  and  the  intermediate  tendon  of  the  digastricus,  and  turns  for- 
ward in  the  submaxillary  space.  Here  it  lies  on  the  lower  part  of  the  internal 
pterygoid  muscle,  and  is  related  internallj'  to  the  submaxillary  lymph  glands, 
above  to  the  anterior  belly  of  the  digastricus,  and  below  to  the  homonymous  vein. 
At  the  anterior  border  of  the  masseter  it  turns  around  the  lower  border  of  the  jaw 
and  runs  upward  on  the  face  in  front  of  that  muscle."  At  the  turn  the  artery  is 
in  front,  the  vein  in  the  middle,  and  the  parotid  duct  posterior.  The  artery  and 
vein  pass  upward  along  the  anterior  border  of  the  masseter,  under  cover  of  the 
facial  panniculus  and  the  zj'gomaticus,  and  are  crossed  superficially  by  branches 

'  By  some  authors  the  term  facial  is  applied  to  the  artery  only  after  it  turns  aroimd  the  lower 
border  of  the  jaw. 

-  The  artery  is  conveniently  placed  at  its  inflection  for  taking  the  pulse,  .since  it  is  super- 
ficial and  lies  directly  on  the  bone. 


548 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


of  the  facial  nerve  and  deeply  l)y  the  parotid  duct.  The  artery  terminates  over 
thelevtaorlabii  j'uperioris  proprius  by  dividing  into  the  dorsal  nasal  and  the  angu- 
lar artery  of  the  eye.     The  chief  branches  of  the  external  maxillary  are  as  follows: 

(1)  The  pharyngeal  artery  (A.  palatina  ascendens)  arises  usually  behind  the 
stylo-pharyngeus,  passes  between  that  muscle  and  the  great  cornu,  and  runs  for- 
ward on  the  lateral  wall  of  the  pharynx  under  the  elastic  pharyngeal  fascia.  It  is 
distributed  to  the  soft  i)alate,  pharynx,  and  tonsil. 

(2)  The  lingual  artery  (A.  lingualis)  is  a  large  branch  which  diverges  from  the 
parent  tnuik'at  an  acute  angle,  runs  along  the  ventral  border  of  the  great  cornu 
of  the  hyoid  bone,  and  dips  under  the  hyo-glossus  muscle.     It  then  passes  across 


Fig.  435. — Superficiai.  DissKmoN  of  Head  of  Horse.  Most  of  the  Panniculus  is  Removed. 
a.  Dilatator  naris  superior;  6,  levator  labii  superioris  proprius;  c,  levator  naso-labialis;  d,  dilatator  iiaris 
lateralis;  c,  buccinator;  /,  zygomaticus;  g,  depressor  labii  inferioris;  h,  stump  of  retractor  anguli  oris;  )',  nias- 
seter;  k,  k,  scutularis;  /,  scutulo-auriculares  superficiales;  m,  zygomatico-auricularis;  n,  parotido-auricularis;  o, 
stylo-maxillaris;  p,  sterno-cephalicus;  p' ,  tendon  of  p;  q,  omo-hyoideus;  r,  splenius;  s,  tendon  of  splenius  and 
trachelo-mastoideus;  /,  corrugator  supercilii;  u,  orbicularis  oris;  v,  parotid  gland;  w,  z.vgomatic  arch;  x,  scutiform 
cartilage;  l/,  upper  commissure  of  nostril;  1,  facial  nerve;  2,  superior  buccal  nerve;  rf,  inferior  buccal  nerve;  4, 
transverse  facial  nerve;  5,  cervical  branch  of  facial  nerve;  6,  posterior  auricular  branch  of  second  cervical  nerve; 
7,  cutaneous  cervical  branch  of  same;  S,  infratrochlear  nerve;  9,  frontal  nerve;  10,  lacrimal  nerve;  W,  end  of 
auriculo-pali)ebral  nerve;  Jl,  inferior  masseteric  artery  and  vein;  13,  transverse  facial  artery  and  vein;  13,  facial 
artery;  14,  inferior  labial  artery;  IS,  superior  labial  artery;  16,  lateral  nasal  artery;  17,  dorsal  nasal  artery;  IS, 
angvilar  artery  of  the  eye;  / 9,  posterior  auricular  artery;  ^0.  ;?/,  jugular  vein;  ;?.g,  external  ma.xillary  vein;  55, 
great  auricular  vein;  2.<.  parotid  duct;   24',  origin  of  same.     (After  Ellenberger-Baum,  Top.  Anat.  d.  Pferdes.) 


the  kerato-hyoideus,  turns  inward  under  tlie  intercornual  joint  of  the  h>oid  bone, 
and  runs  forward  in  the  tongue  between  the  hyo-glo.ssus  and  genio-glo.ssus.  This 
l)art  (A.  jirofunda  linguie)  is  flexuous  and  is  accompanied  by  branches  of  the  hypo- 
glossal and  lingual  nerves.  It  is  the  chief  artery  of  the  tongue,  and  anastomoses 
with  the  opposite  artery  aiul  the  sublingual. 

(3)  The  sublingual  artery  (A.  sublingualis)  is  a  smaller  vessel  w  Inch  arises  at 
the  anterior  extremity  of  the  submaxillary  gland  (Fig. 436).  It  passes  forward  on  the 
anterior  belly  of  the  digastricus  between  the  ramus  of  the  mandible  and  the  mylo- 
hyoideus,  perforates  the  latter,  runs  along  the  lower  border  of  the  sublingual  gland, 
and  ramifies  in  the  mucous  membrane  of  the  anterior  part  of  the  floor  of  the  mouth. 


THE  EXTERNAL  CAROTID  ARTERY 


549 


It  detaches  branches  to  the  muscles  and  skin  in  the  sulmiaxillary  space,  the  sub- 
maxillary 1}  inph  glands,  antl  the  sublingual  gland.  It  also  gives  off  the  small 
submental  artery,  which  runs  forward  superficially  toward  the  lower  lip,  supplying 
twigs  to  the  skin  and  the  mvlo-hvoideus. 


Fig.  436. — Parotid.  Masseteric,  and  Lingual  Regions  of  Horse:  Deep  Di.ssectiox.  Third  Layer. 
a,  Mylo-hyoideus,  anterior  part,  reflected:  6,  genio-hyoideus;  c,  genio-glossus:  d,  sublingual  gland;  c, 
ramus  of  mandible,  the  greater  part  of  which  is  removed:  e',  stump  of  masseter;  /,  maxillary  tuberosity;  7,  great 
cornu  of  hyoid  bone;  A.  wing  of  atlas;  (,  intermediate  tendon  of  digastrieus;  i"',  anterior  belly,  i",  posterior  belly 
of  digastricus;  k,  posterior  part  of  mylo-hyoideus;  /,  hyo-glossus;  m,  pterygoideus  internus  (cut);  n,  stylo-hyoideus; 
o,  stylo-maxillaris  (cut);  p,  crico-pharyngeus;  q,  obliquus  capitis  ant.;  r,  tendon  of  trachelo-raastoideus; 
8,  rectus  cap.  ant.  major;  t,  mastoido-humeralis  (cut);  u,  sterno-cephalicus  (cut);  r.  sterno-thyroideus 
(cut);u',  sterno-hyoideus  (cut);  x,  omo-hyoideus;  i/,  obliquus  cap.  post.;  z,  splenius  (cut);  l-J,,  upper  cheek  teeth;  4', 
last  cheek  tooth;  5,  stump  of  facial  nerve;  6,  stump  of  buccinator  nerve;  7,  lingual  ner\'e:  /'.superficial  branch.  7", 
deep  branch  of  lingual  nerve;  5,  stumps  of  inferior  alveolar  artery,  vein  and  ner\'e;  S,  mylo-hyoid  nerve  (cut);  10, 
glosso-pharyngeal  nerve;  //,  hypoglossal  nerve;  12,  superior  laryngeal  nerve:  i5,  ventral  branch  of  first  cervical 
nerve;  14,  vagus  and  sympathetic;  15,  dorsal  branch  of  spinal  accessory  nerve;  16,  ventral  branch  of  same;  17, 
inferior  cerebral  vein;  i5,  submaxillary  duct;  ^5,  common  carotid  artery;  ^0,  parotid  branch;  31,  thyro-laryngeal 
artery;  22,  pharyngeal  artery;  23,  laryngeal  artery;  24,  internal  carotid  artery;  25,  occipital  artery;  26,  external 
carotid  artery;  27-31,  external  maxillary  artery;  2S,  posterior  palatine  artery;  29,  lingual  artery:  30,  sub- 
lingual artery;  32,  internal  maxillary  artery;  S3,  internal  maxillary  vein  (origin):  34,  remnant  of  parotiri  gland; 
35,  thyroid  gland;  36,  jugular  vein;  37,  pharj-ngeal  lymph  glands,  (.\fter  Ellenberger-Baum,  Top.  Anat.  d. 
Pferdes.) 


In  some  cases  the  sublingual  artery  arises  from  the  lingual  and  the  submental  from  the 
external  maxillary.  Sometimes  the  subhngual  remains  on  the  external  face  of  tlie  mylo-hyoideus 
— thus  resembling  the  submental  of  man — and  the  sublingual  gland  is  supplied  by  a  special 
branch  of  the  Ungual. 

Not  uncommonly  a  considerable  branch,  given  off  in  the  submaxillary  space,  turns  round 
the  lower  border  of  the  jaw  and  enters  the  middle  of  the  lower  part  of  the  masseter  muscle.  In 
some  cases  this  artery  is  of  large  size  and  its  pulsation  can  be  felt.     It  is  accompanied  by  a  vein. 

(4)  The  inferior  labial  artery  (A.  labialis  inferior)  arises  from  the  facial  a  little 
before  it  reaches  the  depressor  labii  inferioris  (Fig.  435).  It  passes  forward,  dips 
under  the  depressor  muscle,  and  continues  to  the  lower  lip.  It  supplies  branches  to 
the  muscles  and  skin  in  this  region,  to  the  inferior  buccal  glands,  the  mucous  mem- 
brane of  the  cheek,  and  the  lower  lip,  anastomosing  with  the  mental  artery  and  the 
corresponding  vessels  of  the  oppo.site  side.  It  detaches  a  branch  (A.  anguli  oris) 
to  the  angle  of  the  mouth,  which  anastomoses  with  the  superior  labial. 


550  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

(5)  The  superior  labial  artery  (A.  laliialis  superior)  arises  from  the  facial  in 
front  of  the  facial  crest  (Fig.  435).  It  pa.sses  forward  under  the  dilatator  naris  lat- 
eralis and  levator  nasoIaljiaUs  to  the  upper  lij),  gives  twigs  to  the  upper  part  of  the 
cheek  and  the  lateral  nasal  region,  and  ramifies  in  the  upper  lip,  anastomosing  with 
the  opposite  artery  and  tlic  jialato-labial. 

(6)  The  lateral  nasal  artery  (A.  lateralis  nasi)  arises  usually  a  little  above  the 
preceding  one,  and  runs  forward  parallel  with  it  and  under  the  levator  nasolabialis 
to  the  nostril  (Fig.  435).  It  supplies  branches  to  the  lateral  nasal  region  and  the 
nostril. 

The  vessel  is  often  double.  It  may  arise  from  the  superior  lal)ial  at  the  point  of  hifuroation 
of  tlie  facial  or  with  the  dorsal  nasal  from  the  infraorbital  artery  (as  in  the  ox).  In  some  cases 
it  gives  olT  a  dorsal  nasal  l)ranch. 

(7)  The  dorsal  nasal  artery  (A.  dorsalis  nasi)  arises  on  the  levator  labii  superi- 
oris  proprius  and  passes  forwartl  under  the  levator  nasolabialis  to  the  tlorsum  nasi 
(Fig.  435). 

(8)  The  angular  artery  of  the  eye  (A.  angularis  oculi)  runs  toward  the  internal 
canthus  of  the  eye,  where  it  anastomoses  with  the  orbital  branch  (Ramus  malaris) 
of  the  infraorbital  artery  (Fig.  435) . 

In  adtlition  to  the  preceding,  unnamed  branches  are  supplied  to  the  submaxil- 
lary salivary  gland  and  the  submaxillary  lymph  glands. 

3.  The  posterior  auricular  artery  (A.  auricularis  posterior)  arises  at  an  acute 
angle  from  the  external  carotid  just  above  the  origin  of  the  masseteric.  It  passes 
upward  under  cover  of  the  parotid  gland,  to  which  it  gives  branches,  and  divides 
into  several  branches  which  supply  the  skin  and  muscles  of  the  external  ear  (Fig. 
435).  The  posterior  branch  passes  to  the  posterior  part  of  the  base  of  the  ear, 
where  it  divides  into  two  branches;  of  these,  one  (Ramus  intermedins)  passes  up  the 
convex  surface  of  the  extei^nal  ear  to  the  apex,  while  the  other  (Ramus  medialis) 
winds  around  to  the  anterior  (inner)  border,  and  forms  an  arch  with  the  inter- 
mediate branch.  The  external  branch  (Ramus  lateralis)  passes  up  the  posterior 
(external)  border  of  the  ear  and  forms  an  arch  with  the  intermediate  branch. 
The  deep  branch  (.\.  auricularis  profunda)  enters  the  interval  between  the  exter- 
nal auditory  canal  and  mastoid  process,  and  passes  through  an  opening  into  the 
interior  of  the  external  ear  and  ramifies  in  the  skin  which  lines  it.  It  gives  off  the 
stylomastoid  artery,  which  passes  through  the  stylomastoid  foramen  into  the  tym- 
panum, forms  an  arch  arouiul  the  membrana  tympani,  and  supplies  the  middle  ear 
and  its  muscles. 

THE  SUPERFICIAL  TEMPORAL  ARTERY 

This  artery  (A.  temporalis  superficialis)  is  much  the  smaller  of  the  two  terminal 
branches  of  the  external  carotid.  It  passes  upward  behind  the  posterior  bonier  of 
the  ramus  of  the  mandible  under  cover  of  the  parotid  glanil,  and  diviiles  below 
the  level  of  the  condyle  into  the  anterior  aiu'icular  and  transverse  facial  arteries. 
It  is  crossed  superficially  by  the  facial  nerve. 

The  anterior  auricular  artery  (A.  auricularis  anterior)  passes  upward  behind 
the  temp(jro-ni:uidil Hilar  articulation  under  cover  of  the  parotid  gland,  crosses  the 
zygomatic  arch,  and  reaches  the  temporalis  muscle.  It  is  crossed  deeply  at  its 
origin  by  the  superficial  temporal  nerve  and  is  accompanied  by  a  satellite  vein 
and  the  auriculo-i)alpebral  branch  of  the  facial  nerve.  It  is  distributed  to  the 
skin  and  the  temporal  and  anterior  auricular  muscles,  and  sends  a  liranch  through 
the  conchal  cartilage  to  the  skin  which  lines  it.  Collateral  twigs  are  detached  to 
the  jiarotid  gland,  and  an  anterior  branch  anastomoses  with  the  supraorbital 
artery.  A  branch  sometimes  passes  into  the  parieto-temporal  canal  ami  anasto- 
moses with  the  jiosterior  meningeal  (mastoid)  artery. 

The  transverse  facial  artery  (A.  transversa  faciei)  is  larger  than  the  preceding. 


THE    INTERNAL    MAXILLARY    ARTERY 


551 


It  turns  around  the  neck  below  the  condyle  of  the  nian(Uble  and  emerges  from  be- 
neath the  parotid  j»;land  (Fig.  435),  It  then  passes  forward  a  short  distance  on 
the  masset(*r  about  half  an  inch  below^  the  zygomatic  arch  and  plunges  into  the 
muscle,  in  which  it  commonly  divides  into  two  chief  branches.  It  is  accom- 
panied by  a  vein  and  a  branch  of  the  superficial  temporal  nerve.     It  supplies  the 


Fig.  437. — Deep  Dissection  of  Head  of  Horse. 
The  left  ramus  of  the  mandible  and  structures  connected  with  it  have  been  removed,  a,  a.  Stumps  of 
styloglossus;  b,  genio-glossus;  c,  genio-hyoideus;  d,  omo-hyoideus;  e,  kerato-hyoideus;  /,  thyro-hyoideus;  g,  thyro- 
pharyngeus;  h.  crico-thyroideus;  (,  sterno-thyroideus;  A:,  thyroid  gland;  m,  crico-pharyngeus;  n,  palatinus  and 
palato-pharyngeus;  t»,  pterygoideus  externus;  p,  tensor  palati;  g,  levator  palati;  r,  temporalis;  s,  rectus  cap.  ant. 
major;  (,  obliquus  cap.  ant.;  u,  guttural  pouch;  v,  great  cornu  of  hyoid  bone,  posterior  extremity  of  which  is 
removed  and  indicated  by  dotted  line;  U',  position  of  small  cornu,  dotted  line;  x,  thyroid  cornu;  y,  tongue;  z. 
anterior  pillar  of  soft  palate;  1 ,  superficial  temporal  nerve;  $,  chorda  tympani;  S,  stump  of  inferior  alveolar  ner\'e; 
4-  4,  Ungual  nerve,  intermediate  part  removed;  5,  deep  temporal  ner\'e;  6,  masseteric  nerve;  7,  buccinator  nerve; 
8,  great  palatine  nerve;  9,  infraorbital  nerve;  10,  sphenopalatine  and  posterior  nasal  ner\'es;  11,  spinal  accessory 
ner\*e;  12,  vagus;  13,  pharyngeal  branch  of  vagus;  14,  superior  laryngeal  ner\'e;  Id,  vago-sympathetic  trunk; 
16,  .sympathetic,  with  superior  cervical  ganglion  a  little  further  back;  17,  glosso-pharyngeal  nerve;  IS,  phar>'ngeal 
and  19,  lingual  branches  of  glosso-pharyngeal;  20,  hypoglossal  nerve;  SI ,  left  recurrent  ner\-e;  £2,  common  carotid 
arterj-;  23,  parotid  branch;  24,  thyro-laryngeal  artery;  24',  laryngeal  artery;  25,  occipital  artery;  26,  internal 
carotid  artery;  27,  external  carotid  artery;  2S-30,  external  maxillary  artery;  29,  pharyngeal  artery;  31,  lingual 
artery;  32,  internal  maxillary  artery;  33,  stump  of  inferior  alveolar  artery;  34,  middle  meningeal  artery;  35, 
deep  temporal  artery;  36,  buccinator  artery;  37,  palatine  artery;  38,  end  of  internal  maxillary  artery;  39, 
right  external  maxillary  artery;  40,  satellite  vein  of  39;  41,  right  parotid  duct;  42,  submaxillary  lymph  glands; 
43,  pharyngeal  lymph  glands;  44,  trachea;  45,  wing  of  atlas;  -jff,  dottetlhne  indicating  outline  of  submaxillary 
gland;    ^7,   lacrimal  gland.     (After  EIlenherger-Baum,  Top.  Anat.  d.  Pferdes.) 

masseter  and  the  skin  of  this  region,  and  anastomoses  with  the   external  maxil- 
lary and  posterior  deep  temporal  arteries. 

The  pulse  may  usually  be  felt  in  this  artery  as  it  passes  below  the  arti<'uIation  of  the  jaw. 


THE  INTERNAL  MAXILLARY  ARTERY  (Figs.  437,  438,  439) 
This  artery  (A.  maxillaris  interna)  is  much  the  larger  of  the  two  terminal 
branches  of  the  external  carotid.     It  begins  at  the  inner  side  of  the  posterior  border 


552 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


of  the  mandible  about  two  inches  (ca.  5  cm.)  below  the  articulation  of  the  jaw 
and  ends  in  the  anterior  part  of  the  pterygo-palatine  fossa.  On  account  of  its 
complex  course  and  the  large  number  of  branches  given  off  it  is  convenient  to  divide 
it  into  three  parts. 

The  first  part  is  much  the  longest,  forms  an  S-shaped  curve,  and  is  in  great 
part  in  contact  with  the  guttural  pouch.  It  passes  upward  and  forward  on  the 
inner  surface  of  the  mandible  a  distance  of  about  an  inch  (ca.  2  to  3  cm.)  and  is 
related  here  to  the  vein,  which  is  ventral.  It  then  turns  inward  below  the  external 
pterygoid  muscle  and  the  iiaferior  maxillary  nerve,  passes  between  that  muscle 

and  the  tensor  palati,  and  runs  forward 
to  enter  the  alar  (pterygoid)  foramen. 
This  part  gives  off  the  following  branches: 

1.  The  inferior  alveolar  or  dental 
artery  (A.  alveolaris  mandibulir  s.  in- 
ferior) passes  downward  and  forward 
with  the  homonymous  vein  and  nerve, 
being  at  first  between  the  external  and 
internal  pterygoid  muscles,  then  between 
the  latter  and  the  ramus  of  the  mandible. 
It  enters  the  mandibular  foramen,  passes 
downwartl  and  forward  in  the  mandibular 
canal,  and  terminates  at  the  mental  fora- 
men by  tlividing  into  mental  and  incisor 
branches.  The  mental  branch  (A.  nien- 
talis)  emerges  through  the  mental  fora- 
men and  anastomoses  in  the  lower  lip 
with  the  opposite  artery  and  the  inferior 
lal)ial.  The  incisor  branch  continues  for- 
ward in  the  bone,  supplies  twigs  to  the 
canine  and  incisor  teeth,  and  anastomoses 
with  its  fellow  of  the  opposite  side.  Col- 
lateral branches  are  detached  to  the  ptery- 
goid and  mylo-hyoid  muscles,  and  within 
the  bone  to  the  teeth,  alveolar  periosteum, 
the  gums,  and  the  spongy  substance  of  the 
mandible. 

2.  The  pterygoid  arteries,  two  or 
three  in  number,  are  distributed  to  the 
pterygoid  and  tensor  and  levator  palati 
muscles. 

3.  The  tympanic  artery  is  a  very 
small  vessel  which  passes  along  the 
Eustachian  tube  to  the  petro-tympanic 
fissure  (of  Glaser)  and  enters  the  middle 
ear. 

4.  The  middle  meningeal  artery  (A.  mcningea  media)  arises  beneath  the  buc- 
cinator nerve  where  the  internal  maxillary  turns  forward.  It  passes  backward 
across  the  temporal  wing  of  the  .sphenoid  to  the  antero-e.xternal  part  (foramen 
spinosum)  of  the  foramen  lacerum.  Entering  the  cranium,  it  divides  into  branches 
which  course  in  the  grooves  on  the  temporal  and  parietal  bones  and  supply  the 
dura  mater.     It  anastomoses  with  the  posterior  meningeal. 

The  .size  of  tliis  artery  is  variable,  and  is  in  inverse  ratio  to  that  of  the  posterior  meningeal. 

5.  The  posterior  deep   temporal   artery   (A.   temporalis  profunda  aboralis) 


Fig.  438. — Right  Eve  of  Horse. 
a.  Remnants  of  periorbita;  b,  levator  palpe- 
brse  superioris;  c,  obliquus  oculi  inferior;  d,  rectus 
oculi  inferior;  e,  rectus  oculi  externus;  /,  rectus 
oculi  superior;  g,  sclera;  {/.'  cornea;  h,  lacrimal 
gland;  /,  frontal  nerve;  k,  frontal  arterv;  I,  branch 
of  lacrimal  ner\'e  to  gland;  in,  lacrimal  artery;  n, 
zygomatic  nerve;  o,  branch  of  ophthalmic  artery; 
p,  branch  of  oculomotor  ner\'e  to  obliquus  oculi 
inferior;  (j,  maxillary  nerve;  r,  infraorbital  nerve; 
8,  posterior  nasal  nerve;  t,  great  palatine  nerve; 
«,  small  palatine  nerve;  r,  internal  maxillary  artery; 
w,  buccinator  artery  (cut);  x,  infraorbital  artery; 
j:',  malar  artery;  y,  sphenopalatine  artery;  s,  great 
palatine  artery;  /,  small  palatine  (or  staphyline) 
artery;  /,  posterior  deep  temporal  artery;  5,  S, 
stumps  of  orbital  margin;  .{.facial  crest;  5,  temporal 
fossa;  6.  foramen  lacerum  orbitale;  7,  anterior  end  of 
alar  canal;  S,  posterior  opening  of  same.  (After 
Ellenberger,  in  Leisering's  .\tlas.) 


THE    INTERNAL    MAXILLAKY    ARTERY  553 

arises  from  the  internal  maxillary  just  before  the  latter  enters  the  canal  of  the 
pterygoid  process.  It  passes  upward  and  backward  in  the  temporal  fossa  on  the 
deep  face  of  the  temporalis  muscle,  in  which  it  ramifies.  It  sends  a  branch  outward 
to  the  masseter,  and  ana.*tonioses  with  the  superficial  temporal  and  middle  men- 
ingeal arteries. 

In  some  cai?rs  the  tympanic  and  middle  meningeal  arise  from  this  artery. 

The  second  part  lies  in  the  alar  canal  and  is  about  an  inch  (ca.  2  to  3  cm.)  in 
length.     It  gives  off  two  liranches — the  anterior  deep  temporal  and  the  ophthalmic. 

1.  The  anterior  deep  temporal  artery  (A.  temporalis  profunda  oralis)  emerges 
from  the  canal  through  the  temporal  or  small  alar  foramen,  and  passes  upward  in 
the  anterior  part  of  the  temporal  fossa  on  the  deep  face  of  the  temporalis  muscle, 


Fir,,  439. — Left  Eye  of  Horse,  Deeper  Dissectiox. 
The  outer  plate  of  bone  has  been  removed  behind  the  pterygoid  crest  to  expose  the  vessels  and  nerves. 
a,  a.  Remnants  of  periorbita;  6,  stump  of  rectus  ocuh  superior;  c,  obliquus  oculi  inferior;  d,  rectus  oculi  inferior; 
e,  rectus  oculi  lateralis;  f',  retractor  oculi;  /,  rectus  oculi  internus;  g,  g,  obliquus  oculi  superior;  /(.  eyeball;  i, 
trochlear  ner\-e;  k.  ophthalmic  ner\'e;  k' ,  nasal  nerve;  k",  infratrochlear  nerve;  k'",  ethmoidal  nerve;  I,  optic 
ner\-e;  m.  frontal  nerve;  n,  lacrimal  ner\'e;  o,  zygomatic  ner\'e;  p.  nei^'e  to  obliquus  inferior  (from  oculomotor); 
q,  maxillary  nerve;  r,  infraorbital  nerve;  s,  sphenopalatine  nerve;  ^  great  palatine  nerve;  »,  small  palatine  nerve; 
V,  internal  maxillary  artery:  w,  buccinator  artery  (cut  off);  x,  infraorbital  artery;  a-',  malar  artery;  y,  spheno- 
palatine artery;  s,  great  palatine  artery;  z' ,  small  palatine  (or  staphyline)  artery;  1 ,  2,  stumps  of  zygomatic  arch; 
,:?,  stump  of  supraorbital  process;  4,  facial  crest;  5,  temporal  fossa;  6,  ophthalmic  artery;  7,  muscular  branch  of  5; 
,•?,  lacrimal  arter>'  (cut);  9,  frontal  artery;  10,  anterior  deep  temporal  artery;  11,  ethmoidal  artery,  (.\fter 
EUenberger-Baum,  Top.  .\nat.  d.  Pferdes  ) 

in  which  it  is  chiefly  distributed.  It  gives  twigs  to  the  orbital  fat  and  the  skin  of 
the  frontal  region, 

2.  The  ophthalmic  artery  (A.  ophthalmica  externa)  emerges  from  the  anterior 
opening  of  the  alar  canal,  and  enters  the  apex  of  the  periorbita  or  ocular  sheath. 
Within  this  it  forms  a  semicircular  bend  under  the  rectus  oculi  superior  and  is 
continued  b.y  the  ethmoidal  artery.     Its  branches  are  as  follows: 

(a)  The  supraorbital  or  frontal  artery  (A.  supraorbitalis)'  is  a  small  vessel 
which  often  arises  from  the  anterior  deep  temporal  or  the  internal  maxillarj-.  It 
passes  along  the  inner  wall  of  the  orbit  in  company  with  the  nerve  of  the  same 
name  to  the  supraorbital  foramen,  through  which  it  emerges.  It  is  distributed  to 
the  orbicularis  oculi,  the  corrugator  supercilii,  and  the  skin  of  the  supraorbital  region. 

(6)  The  lacrimal  artery  (A.  lacrimalis)  runs  upward  and  forward  within  the 
'  This  vessel  appears  to  represent  both  the  supraorbital  and  frontal  of  man. 


554 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


periorbita  along  the  outer  edge  of  the  loviitor  palpebrae  superioris  to  the  lacrimal 
gland,  in  which  it  is  chiofly  distrilDuted.     It  also  sends  twigs  to  the  upper  eyelid. 

(f)  Muscular  branches  (Rami  musculares)  supply  the  orbital  nuisdos,  the 
periorbita,  the  third  cyclitl,  and  the  conjunctiva. 

(f/)  Ciliary  branches  (Aa.  ciliares),  two  sets  of  very  slender  arteries,  arise 
from  the  ophthalmic  direct  and  from  the  muscular  branches.  The  anterior  ciliary 
arteries  (Aa.  ciliaries  anteriores)  pierce  the  sclera  in  front  of  the  equator  and  ramify 
chiefly  in  the  ciliary  body  and  the  iris.  The  posterior  ciliary  arteries  (Aa.  ciliares 
posteriores)  pierce  the  posterior  part  of  the  sclera;  most  of  them  ramify  in  the 
choroid  coat  as  the  short  ciliary  arteries,  but  two  of  larger  size,  the  long  ciliary 


Fig.  440.— S. 


Section  of  He 


Horse,  Cut  a  Littli 


Ri. 


Mediax  Plane. 


1,  Skin;  2,  nasal  bone;  3,  frontal  bone;  4,  parietal  bone;  4',  tentorium  osseum;  6,  occipital  bone;  6, 
sphenoid  bone:  7,  hard  palate;  5,  premaxilla;  5,  mandible;  iO,  hyoid  bone;  i/,  septum  between  frontal  sinuses; 
IS,  alar  cartilage;  13,  dilatator  naris  transversus;  14,  septum  nasi  with  venous  plexuses,  16,  palato-labial  artery 
JG,  16',  upper  and  lower  septal  branches  of  16;  17,  septal  branch  of  sphenopalatine  artery  and  satellite  vein 
IS,  septal  branch  of  ethmoidal  artery;  13,  sphenoidal  sinus;  30,  guttural  pouch;  21,  pharynx;  22,  pharyiigea! 
orifice  of  Eustachian  tube;  23,  posterior  naris;  24,  soft  palate;  26,  palatinus  muscle;  26,  pharyngeal  muscles 
27,  oesophagus;  2S,  dotted  line  indicating  position  of  posterior  pillar  of  soft  palate;  29,  lamina;  ^9',  arch  of  cricoid 
cartilage;  60,  arytenoideus  transversus  muscle;  SI,  ejjigiottis;  S2,  body  of  thyroid  cartilage;  SS,  vocal  process 
and  cord;  5.{,  arytenoid  cartilage;  55,  lateral  ventricle  of  larynx;  3G,  trachea;  rf7,  ventral  straight  muscles  of  head; 
38,  longus  colli;  39,  atlas;  40,  axis;  ^/,  lig.  nuchce;  42,  dorsal  spinal  muscles;  43,  muscles  of  external  ear;  44, 
omo- and  sterno-hyoideus;  ^5,  tongue;  .45,  mylo-hyoideus;  ^T*.  genio-hyoideus;  4'?.  genio-glossus;  45,  longitudinalis 
inferior;  60,  longitud.  superior;  61,  hyo-ei)iglotticus;  S2,  chin  and  mentalis  muscle;  63,  venous  plexus  of  hard 
palate;  64,  corpus  callosum;  66,  septum  pellucidum;  66,  fornix;  67,  thalamus;  6S,  pineal  body;  69,  corpora 
quadrigemina;  60,  cerebral  peduncle;  GI,  corpus  mammillare;  62,  pituitary  body;  63,  chiasma  opticum;  64.  inter- 
carotid  artery;  65,  medulla  oblongata;  66,  interventricular  foramen;  67,  infundibulum;  6S,  third  ventricle;  69, 
cerebral  aqueduct ;  70,  anterior  medullary  velum;  7/,  fourth  ventricle;  73,  posterior  medullary  velum;  7.J,  basilar 
artery;  74,  spinal  cord;  76,  ethmoitlal  nerve;  76,  septal  branch  of  posterior  nasal  nerve;  76',  branch  of  same  to 
organ  of  Jacobson;  77,  olf.actory  nerve  to  organ  of  Jacobson;  75,  nasal  branches  of  palatine  artery,  (.\fter  Ellen- 
berger,  in  Leisering's  .\tlas.) 


arteries,  run  forward,  one  on  each  side,  between  the  sclera  and  choroid  to  the 
perii)hery  of  the  iris.  Here  they  divide  into  branches  which  anastomose  and  form 
a  circle  (C'irculus  iridis  major).  From  this  secondary  branches  arc  detached  which 
form  a  .secoml  circle  around  the  ptij^il  (Circulus  iriilis  minor). 

(e)  The  central  artery  of  the  retina  (Arteria  centralis  retinae)  is  a  small  vessel 
which  arises  from  the  ojihthalmic  or  from  a  posterior  ciliary  artery.  It  pierces  the 
optic  nerve  a  short  distance  liehind  the  sclera  and  runs  in  its  center  to  the  lamina 
cribrosa,  where  it  breaks  up  in  thirty  to  forty  fine  branches.  These  appear  in 
the  fundus  of  the  eye  at  the  margin  of  the  optic  papilla  antl  radiate  in  the  posterior 
part  of  the  retina. 

(/)  The  ethmoidal  artery  (\.  ethmoidalis)  is  the  continuation  of  the  oph- 


THE    INTERNAL    MAXILLARY    ARTERY  555 

thalmic.  It  enters  the  cranial  cavity  through  the  ethmoidal  foramen,  passes 
inward  on  the  cril^riform  plate,  and  divides  into  meningeal  and  nasal  branches. 
The  former  ramify  in  the  anterior  part  of  the  dura  mater  and  anastomose  with 
branches  of  the  artery  of  the  corpus  callosum.  The  nasal  branch  passes  through 
the  cribriform  plate,  gives  branches  to  the  mucous  membrane  of  the  lateral  mass 
of  the  ethmoid  ami  the  adjacent  part  of  the  septum  nasi,  and  runs  forward  on  the 
superior  turbinal. 

The  third  part  passes  forward  in  the  pterygo-palatine  fossa,  accomi:)anied  by 
branches  of  the  maxillary  nerve.  On  reaching  the  posterior  palatine  foramen  it 
is  continued  by  the  palatine  artery.     Its  branches  are  as  follows: 

(1)  The  buccinator  artery  (A.  buccinatoria)  arises  from  the  lower  aspect  of  the 
internal  maxillary  shortly  after  its  emergence  (Fig.  437j.  It  turns  around  the  max- 
illary tuberosity,  accompanied  liy  the  buccinator  nerve,  and  under  the  masseter 
muscle,  enters  the  cheek,  and  runs  forward  in  it.  It  supplies  branches  to  the 
cheek,  the  superior  buccal  glands,  and  the  masseter  and  pterygoid  muscles.  Near 
its  origin  it  gives  off  a  branch  to  the  orbital  fat  behind  the  periorbita. 

'2)  The  infraorbital  or  superior  dental  artery  (A.  infraorbitalis)  arises  from 
the  upper  aspect  of  the  internal  maxillary  a  little  in  front  of  the  preceding  vessel. 
It  passes  upward  and  forward  to  the  maxillary  foramen,  runs  in  the  infraorbital 
canal  in  company  with  the  nerve  of  the  same  name,  and  is  continued  forward 
within  the  jaw  to  the  incisor  teeth.  It  gives  branches  to  the  teeth  and  gums,  and 
detaches  a  branch  through  the  infraorbital  foramen  which  anastomoses  with  the 
lateral  nasal  and  superior  labial.  About  midway  between  its  origin  and  the  maxil- 
lary foramen  it  gives  off  the  malar  or  orbital  branch  (Ramus  malaris),  which  passes 
along  the  floor  of  the  orbit  to  end  in  the  lower  lid  and  anastomose  with  the  angularis 
oculi.     It  gives  twigs  to  the  inferior  oblique  muscle  and  the  lacrimal  sac. 

The  infraorbital  artery  is  usually  small  at  its  emergence  upon  the  face,  but  in  some  cases  it 
is  rather  large  and  may  partially  replace  the  superior  labial  and  lateral  nasal  arteries. 

(3)  The  staphyline  or  small  palatine  artery  (A.  palatina  minor)  is  a  small 
vessel  which  passes  forward  in  the  groo\'e  at  the  inner  side  of  the  maxillary  tuber- 
ositj'  to  the  soft  palate.  In  the  groove  it  is  accompanied  by  the  nerve  of  the  same 
name  and  the  palatine  vein. 

(4)  The  sphenopalatine  artery  (A.  sphenopalatina)  arises  in  the  extreme 
anterior  part  of  the  iJterygo-palatine  fossa  and  passes  into  the  nasal  cavity,  where 
it  divides  into  internal  and  external  liranches.  The  internal  branch  is  distributed 
to  the  mucous  membrane  of  the  septum  nasi;  the  external  one  goes  to  the  inferior 
turbinal,  the  inferior  meatus,  the  posterior  nares,  and  the  maxillary  and  frontal 
sinuses.     It  may  arise  from  the  infraorljital. 

(5)  The  palatine  or  palato-labial  artery  (A.  palatina  major)  is  the  direct  con- 
tinuation of  the  internal  maxillary.  It  passes  through  the  palatine  canal  to  the 
roof  of  the  mouth,  accompanied  by  the  palatine  nerve,  and  rims  forward  in  the 
palatine  groove,  where  it  is  joined  l^j'  the  vein.  A  little  behind  the  plane  of  the 
corner  incisor  teeth  it  curves  inward  over  a  bar  of  cartilage  to  the  foramen  in- 
cisivum,  where  it  unites  with  its  fellow  of  the  opposite  side.  The  single  artery 
thus  formed  passes  up  through  the  foramen  and  divides  under  the  transverse 
dilator  of  the  nostril  into  two  branches.  These  ramify  in  the  upper  lip  and  anasto- 
mose with  the  lateral  nasal  and  superior  labial  arteries.  In  its  course  in  the  roof 
of  the  mouth  the  palatine  artery  gives  off  branches  to  the  hard  and  soft  palate  and 
the  gums,  and  others  which  pass  through  the  accessory  palatine  foramina  to  be 
distributed  in  the  mucous  membrane  of  the  lower  part  of  the  nasal  cavity.  Com- 
monly two  branches,  right  and  left,  are  detached  from  the  convexity  of  the  arch 
formed  by  the  union  of  the  two  arteries;  these  run  forward  in  the  anterior  part  of 
the  hard  palate. 


556  BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 

Arteries  of  the  Thoracic  Limb 

THE  brachial  ARTERY 

The  brachial  artery,  after  turning  around  the  lower  liorder  of  the  scalenus  at 
the  first  rib,  passes  backward  and  a  little  downward  across  the  origin  of  the  coraco- 
brachialis  and  the  insertion  of  the  subscapularis  muscle  at  the  inner  side  of  the 
shoulder  joint.  At  the  posterior  border  of  the  subscapularis  it  gives  off  the  sub- 
scapular arter}',  and  turns  downward  on  the  inner  surface  of  the  arm.  In  its  course 
in  the  arm  it  inclines  a  little  forward,  crosses  the  humerus  very  obliquely,  and 
divides  at  the  antero-internal  aspect  of  the  distal  third  of  the  shaft  of  the  bone  into 
the  anterior  and  posterior  radial  arteries.' 

It  is  related  internally  to  the  serratus  magnus  and  the  posterior  deep  pectoral 
muscles,  and  the  cut)ital  lymph  glands.  Externally  it  lies  on  the  subscapularis, 
the  brachialis,  the  insertion  of  the  teres  major  and  latissimus  dorsi,  and  the  inner 
head  of  the  triceps.  The  coraco-brachialis  muscle  lies  along  the  front  of  the  artery, 
which,  however,  overlaps  the  muscle  distally.  The  vein  crosses  the  inner  face  of 
the  artery  and  runs  down  behind  it,  accompanied  part  way  by  the  ulnar  and  radial 
nerves.  The  musculo-cutaneous  and  median  nerves  form  a  loop  around  the  artery 
close  to  its  origin,  and  the  latter  nerve  then  passes  down  in  front  of  the  artery. 
The  chief  branches  are  as  follows: 

1.  The  suprascapular  artery  (A.  thoracico-acromialis)  is  a  small  and  somewhat 
flexuous  ve-;-;?l,  which  arises  near  the  anterior  liorder  of  the  subscapularis,  runs 
upward,  and  dips  in  between  that  muscle  antl  the  supraspinatus.  It  gives  ])ranches 
to  these  muscles,  the  anterior  deep  pectoral,  and  the  mastoido-humeralis.  A 
branch  passes  in  front  of  the  coraco-brachialis  to  the  shoulder  joint  and  the  proximal 
end  of  the  humerus. 

This  vessel  may  be  double,  or  be  represented  by  one  or  more  branches  of  the  infeiior  cervical 
artery. 

2.  The  subscapular  artery  (A.  subscapularis)  is  a  very  large  vessel  which  arises 
at  the  posterior  border  of  the  subscapularis  muscle.  It  passes  upward  in  the  inter- 
stice between  that  muscle  and  the  teres  major  on  the  inner  surface  of  the  long  head 
of  the  triceps,  turns  aroimd  the  posterior  border  of  the  scapula  below  the  posterior 
angle,  and  ends  in  the  infraspinatus  and  deltoid.  Besides  collaterals  (Rami 
musculares)  to  the  subscapularis,  teres  major,  triceps,  and  tensor  fasciae  antibrachii 
it  gives  off  the  following  named  branches: 

(a)  The  thoracico-dorsal  (A.  thoracicodorsalis)  is  a  long  artery  which  is  usually 
given  off  about  an  inch  from  the  origin  of  the  subscapular,  crosses  the  inner  face 
of  the  teres  major,  and  runs  upward  and  backward  on  the  latissimus  dorsi.  It  gives 
branches  to  these  muscles,  the  abdominal  panniculus  and  the  axillary  lymph  glands. 

(b)  The  posterior  circumflex  artery  (A.  circumflexa  humeri  posterior)  arises 
a  little  above  the  preceding  v(>ssel  and  passes  outward  behind  the  shoulder  joint 
between  the  long  and  external  heads  of  the  triceps  with  the  axillary  (or  circumflex) 
nerve.  It  gives  branches  to  these  muscles,  the  joint  capsule,  and  the  muscles  and 
skin  of  the  outer  side  of  the  shoulder,  anastomosing  with  the  anterior  circumflex 
artery. 

(c)  The  circumflex  artery  of  the  scapula  (A.  circumflexa  scapula?)  arises  about 
two  or  three  inches  (ca.  .">  to  7..')  cm.)  above  the  shoulder  joint,  passes  forwaril  to 
the  posterior  bortler  of  the  scapula,  and  divides  into  two  liranches.  The  outer  one 
runs  forward  on  the  external  surface  of  the  scapula  below  the  spine  and  gives 
branches  to  the  supraspinatus,  infraspinatus,  and  teres  minor.  The  inner  branch 
passes  forward  in  a  similar  fashion  on  the  costal  surface  of  the  scapula  and  supjilies 
branches  to  the  subscapularis. 

'  The  term  axillary  is  often  applicj  to  the  artery  from  the  (irst  rib  to  the  point  of  origin  of 
the  subscapular  branch. 


THE    BRACHIAL    ARTERY 


557 


Posterior  deep  pecto- 
ral muscle 
Tendon  of  panniculus 
Neroe  to  biceps 
Anterior  circumflex 
artery 
Anterior  superficial 
pectoral  muscle 


Extensor  carpi  radiahs 

Radius 

Accessory  cephalic  letn 

Fig.  441. — Dissection  of  Shoulder    %         '•■:■•  Mi-       I  Sirimk. 

A,  Brachial  artery;  B,  .subscapular  artery;  C,  thoracico-dor.sai  artery;  D.  deep  brachial  artery;  E,  ulnar 
artery;  F,  anterior  radial  artery;  G,  posterior  radial  (or  median)  artery;  H,  brachial  vein;  /.  external  thoracic 
(or  ".spur")  vein;  J,  brachial  vein;  K,  K,  K,  posterior  radial  veins;  L.  cephalic  vein;  L\  contmunicating  vein; 
M,  brachialis  muscle;  -V,  internal  epicondyle  of  humerus;  O,  prescapular  lymph  glands;  F,  position  of  axillary 
lymph  glands:  0,  position  of  cubital  lymph  glands;  /,  suprascapular  nerve;  S.  subscapular  nerves;  3,  thoraco- 
dorsal ner\-e;  4.  musculo-cutaneous  nerve;  4'.  cutaneous  branch  of  musculo-cutaneous  nerve;  o.  median  iier\'e: 
tf,  a.xillary  nerve;  7.  ulnar  nerve;  5,  radial  nerve;  9,  thoracic  nerves.     (After  Schmaltz,  .\tlas  d.  .\nat.  d.  Pferdes.) 


558 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


3.  The  anterior  circumflex  (or  prehumeral)  artery  (A.  circumflexa  humeri 
anterior)  arises  usually  at  the  upper  border  of  the  teres  major.  It  passes  forward 
and  outward  between  the  two  parts  of  the  coraco-brachialis  or  between  the  latter 


I'l/tar  rurre 

Brachial  vessels 
Median  nerve 


Cephalic  vein 
Anastomotic  l)i-anch 

Ciitnncous  briinrli  of 

imilian  nerve 

Extensor  carpi  radialis 

Median  nerve 

Accessory  cephalic  vein 

Cephalic  vein 

Post,  radial  (or  median) 
artery 


Flexor  carpi  inlernus  (cut) 


Internal  lateral  ligament 

of  carpus 

Tendon  of  extensor 

carpi  obiiquus 

Metacarpal  tuberosity 


Dorsal  interosseous  artery 
and  nerve 


Fic.  •)42.- 
C-b..  Coraco-brat'hial 


t'Tiox  OF  Right  Forearm  and  Carpi's 

B.m.,  internal  epicondyle  of  humerus;    R,  ^ 
Schmaltz,  Atlas  d.  Anat.  d.  Pfcrile 


Long  licad  of  triceps 

Internal  head  of  triceps 

Ulnar  vessels 

Tensor fasciiF  antibrachii  {cut) 


Inar  head  of  flexor  carpi  medius 
Humeral  origin  of  flex,  carpi  med. 
Origin  of  flexor  carpi  inlernus 


Common  i7iterosseous  artery 
Superficial  flexor  of  digit 
Ulnar  head  of  deep  flexor 
Fascia,  cut  and  reflected 
Deep  flexor  of  digit 
Ulnar  vessels  and  nerve 


Outer  branch  \  of  median 
Inner  branch  j    nerve 

Tendon  of  flexor  carpi  internus 

Flexor  carpi  medius  (cut) 
E.tt.  volar  met.  artery 
E.H.  met.  nerve 
E.rt.  met.  vein 
Int.  met.  nerve 
Large  met.  artery 
Int.  volar  met.  artery 
Branch  to  deep  volar  arch 
Superficial  flexor  tendon 
Check  ligament 
Internal  metacarpal  vein 


Internal  Sirface. 
bcutaneous  surface  of  ratlins. 


antl  the  humerus.  It  givps  branches  to  the  coraco-bracliialis  and  deep  ])ectoral  and 
ends  in  the  upjier  part  of  the  biceps  and  in  the  mastoido-lunucralis.  It  anastomoses 
with  the  posterior  circumflex. 


THE    POSTERIOR    RADIAL    ARTERY  559 

Not  rarely  it  arises  below  the  middle  of  the  humerus  and  passes  upward  between  the  biceps 
and  coraco-brachialis.  In  those  cases  a  small  branch  for  the  coraco-brachialis  is  usually  given 
off  at  the  usual  point  of  origin  of  the  anterior  circumflex. 

4.  The  deep  brachial  artery  (A.  profunda  brachii)  is  a  large  hut  short  trunk 
which  arises  usually  about  the  niidiUe  of  the  humerus.  It  passes  backward  and 
divitles  into  several  branches  which  supply  the  triceps,  tensor  fasciae  antibrachii, 
anconeus,  and  l)rachialis.  A  liranch  runs  in  the  musculo-spiral  groove  with  the 
radial  nerve  to  the  front  of  the  elliow  joint  and  anastomoses  with  the  anterior 
ratlial.  A  slender  branch  passes  down  along  the  external  border  of  the  extensor 
carpi  and  supplies  cutaneous  twigs.  Anastomoses  occur  with  the  ulnar  and  recur- 
rent interosseous  arteries. 

The  point  of  origin  is  inconstant  and  it  is  not  uncommon  to  find  two  arteries  instead. 
Often  a  large  branch  for  tlie  posterior  deep  pectoral  muscle  is  detached  close  to  the  origin  or  arises 
from  the  brachial  directly. 

5.  Muscular  branches  (Rami  musculares)  are  distributed  to  the  teres  major, 
deep  pectoral,  coraco-brachialis,  and  biceps.  The  largest  and  least  variable  of 
these  supplies  the  lower  part  of  the  biceps. 

6.  The  ulnar  artery  (A.  collateralis  ulnaris  superior)  arises  a  little  below  the 
nutrient  foramt'u  of  the  humerus  and  passes  downward  and  backward  along  the 
lower  edge  of  the  internal  head  of  the  triceps  under  cover  of  the  brachial  vein  and 
the  ten.sor  fascia  antibrachii.  It  gives  branches  to  these  muscles,  the  posterior 
superficial  pectoral,  the  cubital  lymph  glands,  panniculus,  and  skin.  At  the  inter- 
nal epicondyle  of  tlie  humerus  it  is  joined  by  the  ulnar  nerve  and  turns  downward 
under  the  ulnar  head  of  the  flexor  carpi  medius.  It  continues  with  the  vein  and 
nerve  under  the  deep  fascia  of  the  forearm  lietween  the  ulnar  and  humeral  heads  of 
the  perforans,  and  in  the  distal  half  of  the  region  between  the  external  and  middle 
flexors  of  the  carpus.  It  unites  just  above  the  carpus  (under  cover  of  the  flexor 
carjji  externus)  with  a  Ijranch  of  the  radial  artery,  with  which  it  forms  the  supra- 
carpal  arch.  It  detaches  small  collaterals  to  the  muscles  along  which  it  passes 
and  terminal  twdgs  to  the  outer  surface  of  the  carpus. 

7.  The  nutrient  artery  of  the  humerus  (A.  nutritia  humeri)  is  a  short  vessel 
which  enters  tlie  nutrient  furanuMi  i)f  the  humerus.     It  often  arises  from  the  ulnar. 

8.  The  anterior  radial  artery  l.\.  collateralis  radialis  inferior)  passes  downward 
and  a  little  outwartl  on  the  anterior  face  of  the  humerus  under  cover  of  the  liiceps 
and  brachialis  to  the  front  of  the  elbow  joint,  where  it  is  joined  by  the  radial  nerve. 
It  then  descends  on  the  anterior  surface  of  the  radius  under  cover  of  the  anterior 
extensor  of  the  cUgit  to  the  carpus,  where  it  concurs  in  the  formation  of  the  rete 
carpi  dorsale,  anastomosing  with  the  posterior  radial  and  interosseous  arteries.  It 
supplies  branches  to  the  elbow  joint,  the  biceps,  brachialis,  and  the  extensors  of 
the  carpus  and  digit.  A  cutaneous  branch  emerges  between  the  distal  end  of  the 
biceps  and  the  brachialis. 

THE  POSTERIOR  RADIAL  ARTERY 

The  posterior  radial  or  median  artery  (A.  mediana)  is  the  direct  continuation 
of  the  brachial.  It  passes  downward  and  slightly  backward,  at  first  on  the  inner 
surface  of  the  humerus,  and  then  over  the  capsule  and  internal  lateral  ligament 
of  the  elliow  joint,  under  cover  of  the  posterior  superficial  pectoral  muscle.'  Below 
the  elbow  it  dips  under  the  flexor  carpi  internus  and  passes  down  the  inner  part  of 
the  posterior  surface  of  the  radius.  In  the  distal  part  of  the  forearm  it  inclines 
backward  and  is  separated  from  the  radius  by  the  reinforcing  band  (Caput  tendin- 
eum)  of  the  superficial  flexor  of  the  digit  and  is  continued  by  the  large  metacarpal 
artery. 

'  The  pulse  can  be  taken  where  the  artery  lies  on  the  lateral  ligament,  since  the  pectoral 
muscle  is  thin  here. 


560 


BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 


It  is  accompanied  by  the  median  nerve,  which  lies  in  front  of  the  artery  at  its 
origin,  then  crosses  over  it  obliquely  at  the  elbow  joint  and  becomes  posterior.  In 
the  arm  the  brachial  vein  lies  bchinil  and  partly  upon  the  artery;  lower  down  there 


Deltoid 

Maslniihi-huiiicrnli.t 
Exiininl  In, 1. 1  of 
tnapx  { 


Cutaneous  branch  of 

axillary  neri'c 

Anterior  radial  artery 

Anterior  extensor 

Brachialia 


Extensor  carpi  radialis 


Extensor  erir/ii  ohlifjiiiis 

Tendon  of  rxlensm-  earpi  radialis 

Ext.  liitir(d  liy.  of  carpns 

Rete  earpi  dorsalc 

Tendon  of  ant.  extensor 

Briincli  to  liiteral  extensor 


Tensor  fascia  antibrachii 
Lonij  head  of  triceps 

Branch  of  radial  tierre  to  exi.  and 
int.  heads  of  triceps  and  anconeus 
Deep  brachial  artery 

Raili(d  nerre 

Long  head  of  triceps 

Inlirnol  head  of  triceps 

Anconeii.'i 

External  head  of  triceps  {cut  off) 

Olecranon 

•  Ulnar  head  of  deep  flexor 

—  Cutaneous  branch  of  nlnnr  nerve 
— ■  External  lateral  lig.  of  elbow 

Flexor  carpi  extern  us 

(cut  and  reflected) 


Interosseous  artery 

Ulna 

Ulnar  head  of  anterior  extetisor 

—  Deep  flexor  of  digit 

—  Lateral  extensor  of  digit 

—  I'lnar  nerve  and  vein 

--  Flexor  carpi  extern  us 

—  Dors(d  interos.ieous  artery 

—  Superficied  Ijranch  of  nui:-r  nerre 

Cur  pal  .fheath  (opened) 
U liter  tendon  of  flex,  carpi  ext. 
Accessory  carpal  hone 
Accessorio-mitacarpid  ligaments 


Blind  friini  iieiissiiri/  carpal  to 
hilinil  ,.i:l,  i,^,,r  lendon 

Lateral  extensor  lendon 


Fic.  44.3. — Dissection  of  Left  Forearm  of  Uohse,  Kxtkrnal  Surfack.     (.\tter  Srhmaltz,  .\tlas  d.  .\nat.  d. 

Pferdes.) 


arc  usually  two  satellite  veins,  anterior  and  posterior.     The  chief  collateral  branches 
are  as  follows: 

1.  Articular  branches  for  the  elbow  joint. 


THK    PO.STEKIOU    RADIAL    ARTERY 


561 


2.  Muscular  branches  to  the  flexors  of  the  carpus  and  digit.     The  hirgcst  of 
these  arise  at  the  ]iroxiinal  third  of  the  forearm. 

3.  The  common  interosseous  artery  (A.  interossea  eommunis)  is  a  vessel  of 


Artery  of  rcte  carpi  mlnre 


Oblique  liganu  nt 


Internal  lateral  liq 
First  carpal  boiic 


Deep  volar  metacarpal  arlcrii 


Int.  metacarpal  bout 


Radius 


A  ccessorio-radial  lig. 
Accessorio-ulttar  lig. 

External  lateral  lig. 
Check  ligament 

A cccssorio-imlacarpal  lig. 
Deep  volar  arch 
Suspensory  ligament 
E.rt.  imtacarpal  bone 


Fig.  444. — Deep  Dissection  gp  Right  C-\rpus  of  Horse,  Po.«tkrior  ^'IEw. 
7,  Raiiial  carpal  bone;  2,  accessory  carpal  bone;  J,  second  carpal  bone.    (After  Schmaltz,  Atlas  d.  .\nat.  d.  Pferdes.) 

considerable  size  which  arises  at  the  level  of  the  interosseous  space,  through  which 
it  passes.  Before  entering  the  space  it  gives  off  a  small  Ijranch,  the  volar  interos- 
seous (A.  interossea  volaris),  which  descends  to  the  radial  head  of  the  perforans. 
In  the  space  it  supplies  the  nutrient  arteries  of  the  radius  and  ulna.     Emerging 


Cutaneous  branch  of  inw^cidn- 

cutanroiis  nu  i  r 

Tendon  of  exlensur  carpi  uhln/  m^ 


Lateral  liyaniLut 


Tendon  of  extensor  carpi  radialis 
Tendon  of  anterior  dig.  extensor 

Skin 

Lateral  ligament 

Tendon  of  lateral  dig.  extensor 


Tendon  of  deep  dig.  flexor 
Tendon  of  superficial  dig.  flexor 
Long  tendon  of  flex,  carpal  extcrnus 
—  Superficial  branch  of  ulnar  nerve. 


Tendon  of  flex,  carpi  intirnus 

Int.  metacarpal  vein 

Int.  volar  or  small  met.  arterii 

Common  dig.  or  large  met.  at  tin/ 

Posterior  annular  ligament 

Internal  metacarpal  ntric 

External  metacarpal  vein 

External  metacarpal  nerve 

External  volar  met.  artery 

Fig.  445. — Cross-sectio.n  of  Right  Carpus  of  Horse. 
The  soft  structure.s  are  cut  at  the  level  of  the  radio-carpal  articulation,  exposing  the  proximal  row  of  carpal 
bone-^.     Cr.  Radial  carpal  bone:  Ci,  intermediate  carpal  bone;  Cu,  ulnar  carpal  bone:   Ca,  accessory  carpal  bone. 
(.\ftei-  Schmaltz,  .\tlas  d.  .Anat.  d.  Pferdes.) 


from  the  space  it  gives  off  branches  to  the  flexor  carpi  extcrnus,  a  small  recurrent 
branch  (A.  interossea  recurrens)  which  passes  upward  on  the  outer  surface  of  the 
ulna  and  anastomoses  with  the  deep  brachial  and  ulnar  arteries,  and  is  continued 
36 


562 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


as  the  dorsal  interosseous  artery.  This  vessel  (A.  interossea  dorsalis)  passes  down 
hctwccii  the  anterior  and  hiteral  extensors  of  the  digit  and  concurs  with  the  anterior 
radial  in  forming  a  network  on  the  anterior  surface  of  the  carpus,  the  rate  carpi 
dorsale.  P'roni  the  latter  arise  two  small  vessels,  the  internal  and  external  dorsal 
metacarpal  arteries  (A.  metaearpea  dorsalis  medialis,  lateralis),  which  run  distally 
in  tlie  grooves  ix'tween  the  large  and  small  metacarpal  bones  and  anastomose 
with  the  volar  metacarpal  arteries. 

4.  The  artery  of  the  rete  carpi  volare  (A.  retis  carpi  volaris)  is  a  small  vessel 
which  arises  at  the  distal  third  of  the  forearm  and  passes  downward  to  the  posterior 
surface  of  the  carpus,  where  it  concurs  with  branches  of  the  volar  metacarpal 
arteries  in  forming  the  rete  carjji  volare. 

5.  The  external  volar  metacarpal  artery  (A.  metaearpea  volaris  lateralis)  is  a 
small  vessel  which  arises  just  above  the  carj^us  under  cover  of  the  flexor  carpi 
medius  and  anastomoses  with  the  ulnar  artery,  forming  the  supracarpal  arch. 
From  the  latter  a  branch  descends  with  the  outer  branch  of  the  median  nerve, 

inclines  outward  toward  the  posterior  bor- 
der of  the  accessory  carpal  bone,  and  arrives 
at  the  head  of  the  external  metacarpal  Ijone. 
Here  it  is  connected  with  the  internal  volar 
metacarpal  artery,  usuallj'  l)y  two  transverse 
branches,  thus  forming  the  deep  volar  or 
subcarpal  arch  (Arcus  volaris  profundus). 
Onv  of  these  l)ranehes  lies  between  the  sub- 
carpal  check  ligament  and  the  suspensory 
ligament;  the  other  (not  always  present) 
lies  beneath  the  latter  on  the  large  meta- 
carpal bone.  A  small  branch  descends  to 
the  fetlock  with  the  external  metacarpal 
nerve.  Below  the  arch  the  artery  pur- 
sues a  flexuous  course  downward  on  the 
posterior  face  of  the  large  metacarjaal  l^one 
alongside  of  the  external  small  metacarpal 
and  under  cover  of  the  suspensory  liga- 
ment. At  the  distal  third  of  the  meta- 
carpus it  commonl}'  unites  with  the  cor- 
responding vessel  of  the  inner  side  to  form 
a  short  trunk  which  passes  backward 
through  the  angle  of  divergence  of  the 
branches  of  tlie  suspensory  ligament  and 
joins  the  external  digital  or  the  common  digital  artery. 

6.  The  internal  volar  or  small  metacarpal  artery  (A.  metaearpea  \'olaris 
meilialis)  is  given  off  from  the  posterior  radial  at  an  acute  angle,  usually  a  little 
abo\-e  the  external  one  or  by  a  common  trunk  with  it.  It  passes  down  the  inner 
side  of  the  carpus  behind  the  tendon  of  the  flexor  carpi  internus  and  embedded  in 
the  i)osterior  annular  ligament.  Arriving  at  the  proximal  end  of  the  inner  meta- 
carpal bone  it  becomes  more  deeply  placed  and  is  connected  with  the  external  volar 
artery  by  one  or  two  transverse  branches  as  stated  above.  It  then  pursues  a 
flexuous  course  downward  alongside  of  the  inner  small  metacarpal  bone,  like  the 
corresponding  external  artery,  with  which  it  commonly  unites  as  described  above. 
It  is  larger  than  the  external  artery  and  suijplies  the  nutrient  artery  to  the  large 
metacarpal  bone. 


Fig.  446. — Cross-section  of  Middle  of  Right 
Met.\carpu8  of  Horse. 
a.  Common  digital  (or  large  metacarpal) 
artery;  b,  internal  metacarpal  vein;  c,  internal 
metacarpal  nerve;  d,  e-xternal  metacarpal  nerve; 
e,  branch  of  external  volar  metacarpal  artery; 
/,  external  metacarpal  vein;  g,  fj,  tl,  deep  volar 
or  interosseous  metacarpal  arteries;  h,  tendon  of 
anterior  extensor;  i,  tendon  of  lateral  extensor; 
k.  anastomotic  branch  connecting  metacarpal 
nerves;  /.  deej)  flexor  tendon;  m,  check  ligament; 
n,  superficial  flexor  tendon;  o,  suspensory  liga- 
ment; p,  large  metacarpal  bone;  (j,  q,  small 
metacarpal  bones;  r,  skin,  (.\fter  Ellenberger, 
in  Leisering's  .\tlas.) 


The  foregoing  account  describes  the  most  common  arrangement  of  the  dorsal  and  volar 
metacarpal  arteries.  Variations  in  their  origin  and  connections  are  common,  hut  have  no  great 
surgical  importance.     Collateral  brandies  are  omitted  for  the  same  reason.     In  some  cases  the 


THE    COMMON    DIGITAL    ARTERY 


563 


internal  volar  metacarpal  is  connected  with  the  common  digital  or  large  metacarpal  artery  a 
little  below  the  carpus  by  a  branch  passing  obliciuely  across  the  inner  border  of  the  deep  flexor 
tendon;  this  forms  a  superficial  volar  arch. 

THE  COMMON  DIGITAL  ARTERY 
The  common  digital  or  large  metacarpal  artery'  is  the  direct  continuation  of 
the  posterior   radial.     It    tlescentls  in   tlie   carpal   canal   along  the  inner  side  of 


Internal  lateral  ligament  of  carpus 

Tendon  of  cxtcnfior  carpi,  radialis 
Tendon  of  extensor  carpi  obliijuus 


Lateral  ligament  of  fetlock  joint 

Ant.  extensor  tendon 

Extensor  branch  of  suspensori/ 
ligament 

Dorsal  artery  of  first  phalanx 


Lateral  ligament  of  pastern  joint 


External  metacarpal  vein 
Internal  metacarpal  vein 

Piislirior  atinular  ligament  of 
carpus 


Sujierficial  flexor  tendon 
Internal  metacarpal  nerve 
Communicating  branch 
Large  metacarpal  artery 
Internal  metacarpal  vein 
Suspensory  ligament 
Lumbricalis  inuscle 
Anterior  digital  nerve 
Posterior  digital  nerve 
Digital  artery 
Digital  vein 
Ligament  of  ergot 
Deep  flexor  tendon 
Lateral  cartilage 
Coronary  plexus 


Coronary  matrix 
Laminar  matrix 


Fig.  447. — Dissection  of  Right  C.\rpus,  MHTACARprs,  and  Digit  of  Horse,  Inner  View,     (.\fter  Schmaltz, 
Atlas  d.  Anat.  d.  Pferdes.) 


the  flexor  tendons  in  company  with  the  inner  branch  of  the  median  nerve  and  a 
satellite  vein.  Continuing  down  the  limb  it  preserves  this  relation  to  the  tendons 
to  the  distal  third  of  the  metacarpus,  where  it  inclines  toward  the  middle  line  of  the 
limb  behind  the  suspensory  ligament,  and  divides  into  the  internal  and  external 
digital  arteries.  In  the  metacarpus  the  artery  is  related  to  the  vein  in  front  and 
the  artery  behind,  and  is  covered  by  the  fascia  and  skin.  It  furnishes  collateral 
branches  to  the  suspensory  ligament,  the  flexor  tendons,  and  the  skin. 

'  This  vessel  is  also  termed  the  A.  metacarpea  volaris  superficialis  or  the  palmar  metacarpal 
artery. 


564  BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 

THE  DIGITAL  ARTERIES 

The  internal  and  external  digital  arteries  (A.  digitalis  medialis,  lateralis)  are 
formed  by  the  bifurcution  of  the  foninioii  digital  at  the  distal  third  of  the  meta- 
carpus. They  diverge,  pass  down  over  the  outer  surface  of  the  corresponding 
sesamoid  at  the  fetlock,  and  descend  parallel  with  the  borders  of  the  deep  flexor 
tendon  to  the  volar  grooves  and  foramina  of  the  third  phalanx.  Entering  the 
latter  the  two  arteries  unite  in  the  semilunar  canal  and  form  the  terminal  arch 
(Arcus  terminalis),  from  which  numerous  branches  pass  through  the  bone  to  the 
wall  surface  and  ramify  in  the  matrix  of  the  wall  and  sole  of  the  hoof.  A  number  of 
})ranches  emerge  through  the  foramina  at  the  lower  border,  where  they  anastomo.'^e 
with  each  other  in  arciform  fashion.  These  branches  were  named  by  Spooner  the 
inferior  connnunicating  arteries,  and  the  anastomotic  arch  formed  by  them  is 
termetl  the  circmnfiex  artery  of  the  third  phalanx  (Chauveau)  or  the  artery  of  the 
lower  border  of  the  third  jihalanx  (Leisering). 

Each  artery  is  accomjianied  by  a  vein  and  by  the  digital  nerves.  Above  the 
fetlock  the  artery  is  most  ileeply  placed  and  is  covered  by  the  vein;  the  nerve  is 
behind  the  vein.  At  the  fetlock  the  artery  has  become  superficial  and  is  related 
to  the  vein  in  front  and  the  posterior  branch  of  the  nerve  behind.  The  anterior 
branch  of  the  nerve  crosses  over  the  artery  obliquely  to  the  lateral  aspect  of  the 
first  phalanx.  The  vessels  and  nerves  are  crossed  obliquely  b}^  a  small  tendinous 
band,  the  ligament  of  the  ergot,  which  begins  in  the  fibrous  basis  of  the  ergot  at 
the  back  of  the  fetlock  and  extends  downward  and  forward  to  end  in  the  fascia  at 
the  side  of  the  pastern  joint. 

In  addition  to  branches  to  the  joints,  tentlons  and  synovial  sheath,  ergot,  and 
skin,  the  digital  arteries  give  off: 

1.  The  artery  of  the  first  phalanx  or  perpendicular  artery  (A.  phalangis 
primae),  a  short  trunk  which  arises  at  a  right  angle  about  the  middle  of  the  first 
phalanx,  and  divides  into  dorsal  and  volar  Ijranches  (Rami  dorsalcs  et  volares). 
The  dorsal  (anterior)  branch  passes  between  the  first  phalanx  and  the  extensor 
tendon  and  ramifies  on  the  front  of  the  digit,  anastomosing  with  its  fellow.  The 
volar  (posterior)  branch  dips  in  between  the  flexor  tendons  and  the  inferior  sesa- 
moidean  ligaments  and  anastomoses  with  the  opposite  artery. 

2.  The  artery  of  the  plantar  cushion  (A.  toricae  phalangis  tertisp)  arises  at  the 
])roximal  border  of  tlie  lateral  cartilage  and  passes  backward  and  downward  to 
ramify  in  the  ])lantar  cushion  and  tlic  matrix  of  the  heels  and  frog. 

3.  The  dorsal  artery  of  the  second  phalanx  (Ramus  dorsalis  phalangis  secun(hr) 
arises  a  little  above  the  navicular  bone,  and  passes  forward  under  cover  of  the 
lateral  cartilage  and  the  extensor  tendon  to  the  front  of  the  second  jihalanx,  where 
it  anastomoses  with  the  opposite  vessel.  It  gives  branches  to  the  skin,  the  tendon, 
the  coffin  joint,  and  the  coronary  matrix  of  the  hoof. 

4.  The  volar  artery  of  the  second  phalanx  (Ramus  volaris  phalangis  secundae) 
is  smaller  than  tlie  preceding,  opposite  to  which  it  arises.  It  passes  above  the 
proximal  border  of  the  third  sesamoid  and  unites  with  the  opposite  artery-. 

The  arteries  of  the  second  phalanx  form  what  is  termed  by  Cliauveau  tlie  coronary 
circle.  The  dorsal  (anterior)  part  of  the  cirfle  g:i\'es  off  commonly  an  artery  (A.  coronalis 
phalangis  tertice)  near  either  side  of  the  extensor  tendon,  which  divides  into  two  branches.  The 
central  Inanch  unites  with  that  of  the  opposite  side,  while  the  other  joins  a  branch  of  the  artery 
of  the  plantar  cushion.  In  this  way  is  formed  the  circumflex  artery  of  the  coronary  cushion, 
an  anastomotic  arch  which  lies  on  the  extensor  tendon  at  the  coronet.  In  some  cases  de- 
scending branches  of  the  arteries  of  the  first  phalanx  concur  in  tlie  formation  of  the  arch. 

5.  The  dorsal  artery  of  the  third  phalanx  or  jireplantar  artery  (A.  dorsalis  phal- 
angis tertiie)  arises  at  the  dee])  face  of  the  wing  of  the  third  phalanx,  passes  outward 
through  the  notch  or  foramen  there,  and  rims  forward  in  the  groove  on  the  wall 
surface.     It  gives  off  ascending  and  descending  branches,  which  ramify  in  the  matrix 


BRAN'CHES    OF   THE    THORACIC    AORTA  565 

of  the  wall  of  the  hoof,  anastomosiiig  above  with  the  circumflex  artery  of  the  cor- 
onarj-  cushion  and  hclow  with  the  circumflex  artery  of  the  third  ])halanx.  Before 
jiassing  through  the  wing  it  detaches  a  retrograde  branch  to  Ihe  plantar  cushion, 
and  after  emerging  one  which  ramifies  on  the  outer  aspect  of  the  lateral  cartilage. 

The  terminal  part  of  tlie  ctigital  artery  after  giving  off  the  preceding  vessel  is  sometimes 
termed  the  plantar. 

BRANCHES  OF  THE  THORACIC  AORTA 
In  addition  to  the  coronary  arteries  and  the  common  brachiocephalic  trunk 
(which  have  been  described),  the  thoracic  part  of  the  aorta  gives  off  branches  to  the 
thoracic  walls  and  viscera  and  to  the  sjiinal  cord  and  its  membranes.  The  visceral 
branches  (Rami  viscerales)  are  the  bronchial  and  oesophageal,  which  arise  by  a 
broncho-tt'sophageal  trunk.  The  parietal  branches  (Rami  parietales)  are  the 
intercostal  and  phrenic  arteries. 

1.  The  broncho-oesophageal  (Truncus  broncho-oesophageus)  is  a  short,  usually 
liulboiis,  trunk  which  arises  at  the  sixth  thoracic  vertebra  from  the  aorta  or  in 
common  with  the  first  aortic  intercostal  arteries.  It  passes  (under  cover  of  the 
vena  azygos)  down  the  right  face  of  the  aorta  toward  the  bifurcation  of  the  tra- 
chea and  divides  into  bronchial  and  CESophageal  branches. 

(a)  The  bronchial  artery  (A.  bronchialis)  crosses  the  left  face  of  the  a-sophagus 
to  the  liifurcation  of  the  trachea,  where  it  divides  into  right  and  left  branches. 
Each  enters  the  hilus  of  the  corresjwntling  lung  al)ove  the  bronchus,  which  it 
accompanies  in  its  ramification.  It  supjilies  the  lung  tissue  and  also  detaches 
twigs  to  the  bronchial  lymph  glands  and  the  mediastinum. 

(6)  The  oesophageal  artery  (A.  cesophagea)  (Fig.  429)  is  a  small  vessel  which 
]3asses  backward  above  the  oesophagus  in  the  posterior  mediastinum  and  anasto- 
moses with  the  oesophageal  branch  of  the  gastric  artery.  It  detaches  twig.s  to  the 
oesophagus  and  the  mediastinal  lymph  glands  and  pleura,  and  also  gives  off  two 
branches  which  pass  between  the  layers  of  the  ligaments  of  the  lungs  and  ramify 
in  the  subpleural  tissue.  Very  commonly  there  is  another  artery  which  runs  back- 
ward ventral  to  the  oesophagus. 

In  some  cases  there  is  no  broncho-cesophageal  trunk,  the  bronchial  and  oesopliageal  arising 
separately.     In  other  cases  the  second  aortic  intercostal  arises  in  common  with  them  also. 

2.  The  intercostal  arteries  (Aa.  intercostales)  (Figs.  428,  429)  number  eighteen 
pairs.  The  first  arises  from  the  deep  cervical  artery,  the  next  three  from  the 
sulicostal  branch  of  the  dorsal  artery,  and  the  remainder  from  the  aorta.  The  aortic 
intercostals  arise  from  the  dorsal  face  of  the  aorta  in  pairs  close  together ;  the  fifth 
and  sixth  usually  spring  from  a  common  stem.  Each  passes  across  the  bodj'  of  a 
vertebra  to  the  corresponding  intercostal  space,  detaches  twigs  to  the  vertebra*  and 
the  pleura,  antl  divides  into  dorsal  and  ventral  branches.  The  dorsal  branch  (Ramus 
dorsalis)  gives  off  a  spinal  branch  (Ramus  spinalis)  which  passes  through  the  inter- 
vertebral foramen,  gives  twigs  to  the  memliranes  of  the  spinal  cord,  perforates  the 
dura,  and  reinforces  the  ventral  spinal  artery.  A  muscular  branch  passes  to  the 
muscles  and  skin  of  the  back.  The  ventral  branch  (Ramus  ventralis)  is  much  the 
larger.  It  passes  downward,  at  first  almost  in  the  middle  of  the  intercostal  space 
between  the  intercostal  muscles,  then  gains  the  jjosterior  border  of  the  rib  and  is 
subpleural.  Each  is  accompanied  by  a  vein  and  nerve,  the  artery  being  in  the 
middle  and  tliC  vein  in  front.  At  the  lower  part  of  the  space  it  unites  with  a  ventral 
intercostal  branch  of  the  internal  thoracic  or  the  asternal  artery.  It  supplies  the 
intercostal  muscles,  the  ribs  and  the  ])leura,  and  gives  off  perforating  branches 
which  pass  out  to  the  serratus  magnus,  the  abdominal  muscles,  and  the  skin. 

3.  Tlie  phrenic  arteries  (Aa.  phrenica?)  are  two  or  three  .small  vessels  which 
arise  at  the  hiatus  aorticus  from  the  ventral  aspect  of  the  aorta,  often  by  a  common 


5G6 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


trunk.     They  supply  the  crura  of  tlie  diaphragm. 
common  with  an  intercostal  artery. 


In  some  cases  thev  arise  in 


BRANCHES  OF  THE  ABDOMINAL  AORTA 
The  collateral  liranchcs  of  the  alxlominal  part  of  the  aorta  are  distributed 
chiefly  to  the  walls  and  contents  of  the  abdominal  cavity,  but  some  branches  are 
supplied  to  the  spinal  cord  and  its  membranes,  and  others  extend  into  the  pelvis 
anil  to  the  scrotum.  The  visceral  branches  are  the  cocliac,  anterior  mesenteric, 
renal,  posterior  mesenteric,  and  the  spermatic  or  utero-ovarian.  The  parietal 
branches  are  the  lumbar  arteries. 


■Plan  of  Branches  of  Celiac  .\rtkry  of  Horse. 
artery;  3,  hepatic  artery;    4,  splenic  artery;    6,  posterior  gastric  artery;   6,  an- 


FiG.  448 

/,  Cccliac  artery;   2,  gastri _... ,  _,  .„, , ,   ,,  ., ., .   .,  ^ 

tenor  gastric  artery;   7,  cesophageal  branch;  S,  gastro-duodenal  artery;   9.  pancreat 

gastro-epiploic  artery;   ;;,  pyloric  artery;   IS,  left  gastro-epiploic  artery;   IS,  short  gastric  branches  of  spier 


>-duodenal  artery;    W,  right 


I.  The  coeliac  artery  or  axis  (A.  coeliaca)  is  an  unpaired  vessel,  usually  half  an 
inch  or  less  (ca.  1  cm.)  in  length,  which  arises  from  the  ventral  aspect  of  the  aorta 
at  its  emergence  from  the  hiatus  aorticus.  It  divides  on  the  ilorsal  surface  of  the 
pancreas  into  three  l)ranches — the  gastric,  hepatic,  antl  splenic. 

1.  The  gastric  artery  (A.  gastrica  sinistra)  passes  downward  and  forwanl  in 
the  gastro-phrenic  ligament,  gives  off  cesophageal  and  pancreatic  branches,  and 
divides  above  and  behind  the  cardia  into  anterior  and  posterior  branches. 

(a)  The  anterior  branch  (Ramus  cranialis)  crosses  the  lesser  curvature  just  to 
the  right  of  the  cardia  and  ramifies  on  the  parietal  surface  of  the  stomach.  The 
i)ranclies  pursue  a  flexuous  course  toward  the  greater  curvature  and  anastomose 
with  the  short  gastric  arteries  and  the  gastric  branch  of  the  hepatic  artery. 

(h)  The  posterior  branch  (Ramus  caudalis)  is  distributed  in  a  similar  fashion 
on  the  visceral  surface. 


BRANCHES  OF  THE  ABDOMINAL  AORTA 


567 


(c)  The  oesophageal  branch  (Ramus  cesophageus)  passes  through  the  hiatus 
cpsophageus  into  the  tliorafic  cavity  above  the  cesophagus  and  anastomoses  with 
the  CESophageal  Ijraach  of  the  broncho-ccsophageal  artery. 


Fig.  449.— Pi.ax  of  Chief  Branches  of  .\xterior  Mesenteric  Artery  of  Horse. 
/    Stump  of  anterior  mesenteric  artery;   2,  stumps  of  arteries  of  small  intestine;    3,  e-vternal  ca-cal  artery; 
i,  internal  cxcal  arterj-;    5.  ileal  artery;    6,  ventral  colic  artery;    7,  dorsal  colic  artery:    8,  middle  coUc  or  first 
artery  of  small  colon. 

The  gastric  artery  often  arises  bv  a  common  trunk  with  the  splenic.  The  two  terminal 
branches  may  arise  separately,  or  the  anterior  from  tlie  splenic  and  the  posterior  from  the  hepatic. 
The  ccsophageal  branch  often  arises  from  the  splenic  or  the  posterior  gastric. 

2.  The  hepatic  artery  (A.  hepatica)  is  larger  than  the  gastric.  It  passes  for- 
ward to  the  right  and  ventrally  on  the  dorsal  surface  of  the  pancreas,  covered  by 


BLOOD-VASCTLAR    SYSTEM    OF   THE    HORSE 


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BRANCHES    OF   THE    ABDOMINAL    AORTA  569 

I  I  r  I  the    gastro-pancreatic    fold,    crossing    obliquely 

^  I  I S  under    the    vena   cava,    and   reaches   the    inner 

._=     "^s-s      >^!J^'-^|r  border  of  the  portal  vein.     It  divides  into  three 

=■  =      a.i  m     -      •--  i  .-  Qj.  £q^jj.  iji-jjiiches  which  enter  the  portal  fissure 

li  of  the  liver  anil  ramifj-  within  the  gland  with  the 

o  M  ])ortal  vein  and  the  hejDatic  duct.     It  gives  off  the 

I  i  g  Ife:"  £  i-  following  collateral  branches: 

(«)  Pancreatic  branches  (Aa.  ]  ancreatica?) 
are  given  off  as  the  artery  crosses  the  pancreas, 
in  which  it  is  partly  embedded. 

(6)  The  pyloric  artery  (A.  gastrica"  clextra) 
8  i  I  f-  =  J-"  1^-  i-  arises  above  the  first  curve  of  the  duodenum.     It 

descends  to  the  pylorus,  sending  branches  to  the 
first  part  of  the  duodenum  and  the  pjdorus,  and 
anastomoses  with  the  gastric  and  right  gastro- 
epiploic arteries.  It  may  arise  from  the  gastro- 
_ ._      ^      -  -.  duodenal. 

^^  I  «  5.    -^  ll  i^.ll  I  i  I  (c)  The  gastro-duodenal  artery  (A.  gastro- 

I  I  2  f    .|  ^.  1^  2  i-s  i  J  duodenalis)  passes  to   the  second    curve   of   the 

is  if      i"B 'i  >' s'^  g  1^  duodenum    and    divides    into    the    right    gastro- 

8'c3i^s|'^^  ejjiploic    and    the    pancreatico-duodenal.       The 

-»l9sii  ill  right  gastro-epiploic   artery   (A.   gastroepiploica 

§*«i=-°s°-t  dextra)  crosses  over  the  po.sterior  surface  of  the 

'■a  I  c^-7il— :'IZ  duodenum   and   enters   the   great   omentum,    in 

^«- i  t-^-|l  I  S  which    it    runs    to    the   left,    parallel    with    the 

z   il-^. ■«■     I  ■^- 1 1"  I  I  It  "  greater    curvature    of    the    stomach.      It    gives 

2^^'     lli'sli°eS  branches  to  the  latter  and  to  the  omentum  and 

forms  an  anastomotic  arch  with  the  left  gastro- 
epiploic artery.     The  pancreatico-duodenal  artery 
oJgHs     5J*-|3"  -3^  -^  (A.  pancreaticoduodenalis)  divides  into  pancreatic 

««1      a*7.  i^°--§  and  duodenal  branches.    The  former  (Ramus  pan- 

■2"  I     °^'  *  £  1  i-f'  i  J  I  creaticus)  supplies  the  middle  part  of  the  pancreas 

I.  ■^-    -S"  4  =  I  3  °  I J  :=  and  is  often  replaced  by  a  number  of  variable 

twigs.     The  duodenal  branch  (Ramus  duodenalis) 
passes  to  the  right  along  the  lesser  curvature  of 
_  the   duodenum   and  anastomoses  with  the  first 

|i=°|-3i^"'  branch  of  the  anterior  mesenteric  artery. 

I  S  «"  =  :^'  I  H  ^  i  3.  The    splenic    artery   (A.   lienalis)   is  the 

J  'I  ■-'!  "  i  .i  i  3  largest  branch  of  the  cccliac.     It  passes  to  the  left 

i*   alS-l      ||E|£2||z-=  (with  the  large  satellite  vein)  on  the  left  extremity 

of  the  pancreas  and  across  the  saccus  csecus  of  the 
stomach.     Entering   the  suspensory  ligament  of 
^  'I  I  u  I     d  E  I  X  1  "i  I  "3  I  the  spleen,  it  runs  in  the  hilus  of  the  spleen  to 

o-s"'-  ■S  =  2's3  =  '5oj1-  the  apex,  bevond  which  it  is  continued  as  the 
«""S'»  -S9fH3°H'"3-f  left  gastro-epiploic.  It  gives  off  the  following 
a  §  i  I     -:  I  r.  1 .1  I  ]^-  S  i  ^        branches : 

(fl)  Pancreatic  branches  (Rami  j-ancreatici) 
to  the  left  extremity  of  the  jjancreas. 

(b)  Splenic  branches  (Rami  lienalcs),  which 
plunge  into  the  sul)stance  of  the  spleen. 

(c)  Gastric  branches  (Aa.  gastricse  breves), 
which  pass  in  tlie  gastro-splenic  omentum  to  the 
greater  curvature  of  tlie  stomach,  where  they  bi- 
furcate and  anastomose  with  the  gastric  arteries. 


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570  BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 

(d)  The  left  gastro-epiploic  artery  (A.  gastroopiploica  siiiit<tra)  itr  the  continua- 
tion of  the  sph'iiic  artery.  It  passes  to  the  right  in  the  great  omentum,  parallel 
with  the  greater  curvature  of  the  stomach,  and  anastomoses  with  the  right  gastro- 
epiploic. It  gives  off  branches  to  the  greater  curvature  of  the  stomach,  and  twigs 
to  the  omentum. 

II.  The  anterior  or  great  mesenteric  artery  (A.  mcsenterica  cranialis)  arises 
from  the  ventral  face  of  tlie  aorta  at  the  first  lumbar  vertebra.  It  is  a  large  un- 
paired trunk,  about  an  inch  (ca.  2to3  cm.)  in  length,  which  passes  ventrally  between 
the  vena  cava  and  the  left  adrenal  into  the  root  of  the  great  mesentery,  when  it 
divides  into  three  liranchcs — left,  right,  and  anterior.' 

1.  The  left  branch  gives  off  at  once  about  fifteen  to  twenty  arteries  of  the 
small  intestine  (Aa.  intestinales).-  These  come  off  close  together  and  pass  in 
divergent  fashion  between  the  layers  of  the  great  mesentery,  each  dividing  into 
two  branches  which  anastomose  with  adjacent  branches  to  form  a  series  of  arches. 
In  the  anterior  part  of  the  series  secondary  arches  are  formeil  by  the  union  of 
branches  given  off  from  the  primary  set  of  arches.  From  the  convex  side  of  these 
arches  terminal  branches  pass  to  the  wall  of  the  small  intestine,  in  which  they 
ramify  and  form  a  vascular  network.  They  are  accompanied  by  satellite  veins  anil 
by  nerves  and  lymph-vessels.  The  first  artery  anastomoses  with  the  pancreatico- 
duodenal, and  the  last  with  the  ileal  branch  of  the  great  mesenteric  artery.  Branches 
are  supplied  to  the  mesenteric  lymph  glands. 

2.  The  right  branch  (A.  ileo-cseco-colica)  might  be  regarded  as  the  continuation 
of  the  trunk.  It  runs  downward  and  a  little  forward  and  to  the  right  and  gives 
off  the  ileal,  the  two  ciecal,  and  the  ventral  colic  arteries. 

(1)  The  ileal  or  ileo-caecal  art(>r}'  (A.  ilea)  passes  in  retrograde  fashion  along 
the  terminal  part  of  the  ileum  and  unites  with  the  last  branch  of  the  left  division. 

(2)  The  external  or  inferior  caecal  artery  (Ramus  csecalis  lateralis)  passes  be- 
tween the  CEecum  and  the  origin  of  the  colon  and  runs  on  the  external  muscular 
band  of  the  caecum  to  the  apex,  where  it  anastomoses  with  the  internal  artery. 
Besides  numerous  collaterals  to  the  csecum,  it  gives  off  the  arterj'  of  the  arch, 
which  passes  along  the  lesser  curvature  of  the  base  of  the  ciecum  and  runs  on  the 
outer  face  of  the  origin  of  the  great  colon. 

(3)  The  internal  or  superior  caecal  artery  (Ramus  ca'calis  medialis)  passes 
along  the  inner  band  to  the  apex  of  the  csecum,  where  it  anastomoses  with  the 
external  caecal  artery. 

(4)  The  ventral,  right,  (jr  direct  colic  artery  (A.  colica  ventralis)  runs  along  the 
opposed  surfaces  of  the  ventral  (first  and  second)  parts  of  the  great  colon  to  the 
pelvic  flexure,  where  it  unites  with  the  dorsal  colic  artery.  It  supplies  the  ventral 
parts  of  the  great  colon  and  sends  a  branch  to  the  base  of  the  caecum. 

3.  The  anterior  branch  divides  after  a  very  short  course  into  the  dorsal  and 
middle  colic  arteries. 

(1)  The  dorsal,  left,  or  retrograde  colic  artery  (A.  colica  dorsalis)  is  a  large  vessel 
which  passes  along  the  dorsal  (fourth  and  third)  parts  of  the  great  colon  to  the 
pelvic  flexure,  where  it  joins  the  ventral  colic  artery. 

(2)  The  middle  colic  artery  or  first  artery  of  the  small  colon  (A.  colica  media) 
is  a  much  smaller  vessel  which  jiasses  to  the  origin  of  th(>  small  colon,  enters  the 
colic  mesentery,  and  forms  an  arch  by  joining  the  first  branch  of  the  posterior 
mesenteric  artery  close  to  the  lesser  curvature  of  the  bowel.  It  sends  an  anasto- 
motic branch  to  the  dorsal  colic  artery. 

'  In  the  great  majority  of  subjects  this  vessel  and  some  of  its  branches  are  the  seat  of  more 
or  less  extensive  verminous  aneurysm,  produced  by  the  Selerostomum  armatum.  In  the  author's 
experience  an  entirely  normal  specimen  is  quite  exceptional  in  adult  horses. 

•  The  left  branch  is  a  descriptive  convention  rather  than  a  reality,  since  the  arteries  of  the 
small  intestines  spring  from  the  mesenteric  trunk  either  directly  or  by  short  common  stems 
with  an  adjacent  vessel. 


BRANCHES  OF  THE  ABDOMINAL  AORTA  571 

III.  The  renal  arteries  (Aa.  renalesl,  right  and  left,  are  relatively  large  vessels 
which  arise  from  the  aorta  near  the  anterior  mesenteric.  The  right  artery  is  the 
longer  of  the  two.  It  crosses  over  the  dorsal  surface  of  the  vena  cava  to  the  right 
and  somewhat  forward.  At  the  hilus  it  divides  into  several  (five  to  eight)  branches; 
some  of  these  enter  the  gland  at  the  hilus,  while  others  pass  to  the  ventral  surface 
and  enter  there.  The  left  artery  is  short  and  usually  arises  a  little  further  hack; 
it  passes  directly  outward  to  the  kidney  and  is  then  disposetl  like  the  right  one. 
Small  collateral  branches  are  supplied  to  the  ureters  and  the  adrenals.  The  latter 
also  receive  small  vessels  directly  from  the  aorta.  The  distribution  within  the 
kidney  has  been  described. 

Variations  in  the  renal  arteries  are  fre(iiient.  Two  or  more  arteries  may  occur  on  one  or 
both  sides.  Accessory  arteries  are  more  common  on  the  left  side  and  usually  enter  the  posterior 
pole  of  the  gland.     They  may  arise  from  the  aorta,  the  external  iliac,  or  the  circumflex  iliac  artery. 

IV.  The  posterior  or  small  mesenteric  artery  (A.  mesenterica  caudalis)  is  an 
unpaired  vessel  which  arises  from  the  ventral  face  of  the  aorta  at  the  fourth  lumbar 
vertebra,  i.  e.,  about  five  or  six  inches  (ca.  12  to  15  cm.)  behind  the  origin  of  the 
anterior  mesenteric  artery.  It  is  much  smaller  than  the  latter  and  supplies  the 
greater  part  of  the  small  colon  and  rectum.  It  descends  in  the  colic  mesentery 
and  divides  into  two  branches.  The  anterior  branch  (A.  colica  sinistra)  gives  off 
three  or  four  arteries  which  divide  and  form  anastomotic  arches  close  to  the  bowel. 
The  first  arch  is  formed  by  union  with  the  middle  colic  branch  of  the  anterior 
mesenteric.  The  posterior  branch  or  anterior  htemorrhoidal  artery  (A.  haemor- 
rhoidalis  cranialis)  passes  backward  in  the  upper  part  of  the  mesentery  and  the 
mesorectum  and  terminates  near  the  anus  by  anastomosing  with  the  internal 
pudic  artery.     Three  or  four  of  its  anterior  collateral  branches  form  arches. 

V.  The  spermatic  arteries  (Aa.  spermaticfe  interns),  right  and  left,  are  long 
slender  arteries  which  arise  from  the  aorta  near  the  posterior  mesenteric  and  supply 
the  testicle  and  epididymis.  Each  passes  backward  in  a  narrow  fold  of  peritoneum 
(Plica  vasculosa)  to  the  internal  inguinal  ring  and  descends  through  the  inguinal 
canal  to  the  scrotum.  In  the  canal  and  scrotum  it  pursues  a  very  flexuous  course 
in  the  anterior  border  of  the  spermatic  cord,  surrounded  by  the  pampiniform  plexus 
of  veins,  and  associated  closely  with  the  spermatic  nerves  and  lymphatics  and 
unstriped  muscle-fibers.  It  passes  between  the  epididymis  and  testicle,  runs  in 
flexuous  fashion  along  the  attached  border  of  the  latter,  turns  around  the  posterior 
pole,  and  runs  forward  on  the  free  border  to  the  anterior  pole.  The  largest  branches 
arise  from  its  ventral  part,  pass  tortuously  up  either  side  of  the  gland  embedded 
in  the  tunica  albuginea,  and  give  off  fine  branches  to  the  gland  substance.  Small 
collateral  branches  are  detached  to  the  ureter  and  the  spermatic  cord. 

The  utero-ovarian  arteries  in  the  female  correspond  to  the  preceding 
vessels,  but  are  much  shorter.  Each  is  placed  in  the  anterior  part  of  the  l)road 
ligament  of  the  uterus  and  divides  into  ovarian  and  uterine  branches.  The  ovarian 
branch  (A.  ovarica)  pursues  a  flexuous  cour.se  to  the  ovary,  which  it  supplies.  The 
uterine  branch  (A.  uterina  cranialis)  passes  to  the  concave  border  of  the  cornu  of 
the  uterus,  which  it  supplies,  anastomosing  with  the  uterine  artery. 

\T.  The  lumbar  arteries  (Aa.  lumbales)  are  in  series  with  the  intercostal 
arteries  and  have  a  similar  origin  and  distribution.  There  are  usually  six  pairs  of 
lumbar  arteries,  of  which  five  arise  from  the  aorta  and  the  sixth  from  the  internal 
iliac  or  the  lateral  sacral  at  the  junction  of  the  last  lumbar  vertebra  and  the  sacrum. 
Each  passes  across  the  body  of  a  lumbar  vertebra  to  the  intertransverse  space, 
gives  branches  to  the  sublumbar  muscles,  and  divides  into  dorsal  and  ventral 
branches.  The  dorsal  branch  (Ramus  dorsalis),  the  larger  of  the  two,  passes 
upward  to  ramify  in  the  extensor  muscles  of  the  spine  and  the  skin  of  the  loins; 
it  gives  off  a  spinal  branch  (Ramus  spinalis)  which  comports  itself  like  the  corre- 
sponding branch   of  an   aortic   intercostal   artery.     The  ventral  branch  (Ramus 


572 


BLOOD-VASCLLAR    SYSTEM    OF   THE    HORSE 


Internal  iliac  lymph  glands 

Circumflex  iliac  rf.s.fcii 

External  iliac  lymph  glands 

Inguinal  ligaments 

Posterior  branch  of  circum- 
flex iliac  artery 
External  cutaneous  nerve 

External  spermatic  nerre 
Tensor  fascia:  lata: 

Femoral  nerre  and  ante- 
rior femoral  vessels 
Femoral  artery 
Precrural  lymph  glan'ls 

Deep  inguinal  lymph 

glands 

Fascia  lata 


Saphenous  nerves 
Saphenous  vessels 


Jjilernal  patellar  ligament 
Middle  patellar  ligament 


Fic.  451. — DissEcnox  of  Pelvis.  Thigh,  and  Cpper  Part  of  Leg  of  Horse,  Internal  View. 

/-.Lumbar  vessels;  V'.c,  posterior  vena  cava;  --l,  aorta  (termination);  C,  sympathetic  trunk;  /,  internal  iliac 
arter>-*  3.  lateral  sacral  arterj-;  3,  mitidle  coccygeal  arter>-;  4.  lateral  coccygeal  arter>-;  $,  umbilical  artery  icut 
off);  0,  internal  pudic  arterj-;  5',  vesico-prostatic  artery;  7.  obturator  arter>-;  8,  a.  profunda  penis  (from  left 
obturator);  P,  posterior  gluteal  (or  ischiatic)  vessels;  iO.  external  iliac  artery;  //,//',  deep  femoral  artery;  13, 
prepubic  arter>-;  /3.  branch  of  deep  femoral  arter>';  /4,  great  sciatic  nerve;  ;5,  posterior  gluteal  ner^-e;  /ff  (above), 
internal  pudic  ner\*e;  16  (below  near  |>elvic  outlet),  suburethral  venous  plexas;  77,  sacro-coccygeus  inferior;  18, 
coccygeus;  /S,  recto-coccygeus;  50.  retractor  ani;  5/,  3/'.  two  headsof  obturator  intemiLs;  52,  symphysis  pelvis; 
8S,  prepubic  tendon;  24  suspensor>*  ligament  of  penis;  2.5,  retractor  penis  muscle;  SO,  bulbo-cavernosus  muscle; 
27,  urethra  (cross-section);  23,  cms  ijenis  (cross-section);  29.  suspenj*or>-  ligaments  of  anus  (=  upper  part  of 
retractor  penis  muscle) ;  3</,  anal  lymph  glands;  5/,  tibial  ner\-e.     (.\fter  Schmaltz,  .\tlasd.  .Anat.  d.  Pferdes.) 


THE    INTERXAL    ILIAC    ARTERY 


ventralis)  runs  outward  in  the  intertransverse  space,  passes  between  the  transversus 
and  obliquus  internus  abdominis,  gives  branches  to  these  muscles,  and  ends  in  the 
obUquus  externus,  the  panniculus,  and  the  skin  of  the  flank. 


THE  INTERNAL  ILIAC  ARTERY 
The  internal  iliac  or  h5rpogastric  arteries  (Aa.  hj-pogastricae)  result  from  the 
bifurcation  of  the  aorta  under  the  fifth  or  sixth  lumbar  vertebra.     They  diverge 
at  an  angle  of  about  60  degrees,  and  each  passes  backward  under  the  wing  of  the 


Sacro-coccygeus  inferior 
Recto-coccygeus 

Sphincter  ani  externus 

Retractor  ani 


Fig.  .152. — ^Dissectiox  of  PERixErM  of  Horse  {>L\i.e). 

1,  Bulbo-urethral  (Cowper's)  gland;  ;?,  transversus  perinei  muscle  (?):  5,  ischio-urethral  muscle:  .f,  retractor  penis 

muscle;   o,  bulbo<»vernosu3  muscle.     (.4fter  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


sacrum,  then  inclines  downward  on  the  pelvic  surface  of  the  shaft  of  the  ilium,  and 
divides  a  little  above  the  psoas  tubercle  into  iliaco-femoral  and  obturator  arteries. 
The  chief  branches  are  as  follows : 

1.  The  last  pair  of  lumbar  arteries  jiass  up  through  the  foramina  at  the 
junction  of  the  last  lumbar  vertebra  and  the  sacrum. 

2.  The  internal  pudic  artery  (A.  pudentla  interna)  arises  near  the  origin  of  the 
internal  iliac.  It  passes  backward  and  somewhat  do^\-nward,  at  first  along  the 
iliac  head  of  the  obturator  internus.  then  above  the  superior  ischiatic  spine  on  the 
inner  surface  of  the  sacro-sciatic  ligament,  perforates  the  latter  and  runs  for  a 
variable  distance  in  its  substance  or  on  its  e.Nternal  face.  It  then  re-enters  the 
peh-ic  cavity,  passes  backward  on  the  retractor  ani  to  the  ischial  arch,  and  divides 


574 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


into  the  perineal  and  the  artery  of  the  Inilb  in  the  male,  perineal  and  artery  of  the 
clitoris  in  the  female.  It  is  accompanied  by  the  internal  pudic  nerve.  Its  chief 
branches  are  as  follows: 

(1)  The  umbilical  artery  is  given  off  from  the  internal  pudic  aliout  an  inch 
(ca.  2  to  3  cm.)  from  the  origin  of  that  vessel.  It  is  a  very  large  artery  in  the 
foetus,  in  which  it  curves  downward  and  forward  at  the  side  of  the  bladder  in  the 
edge  of  the  umbilical  fold  of  peritoneum,  passes  through  the  umbilical  opening, 
becomes  a  component  of  the  umbilical  cord  and  ramifies  in  the  fa'tal  placenta. 
After  birth  it  extends  only  to  the  vertex  of  the  bladder  and  is  much  reduced.  Its 
lumen  is  almost  obliterated  and  its  wall  is  very  thick,  giving  the  vessel  a  cord-like 
character,  hence  it  is  commonly  termed  the  round  ligament  of  the  bladder.'     It 


Coccygcus  jnuscle 
Anal  lymph  glands 
Branch  of  posterior  gluteal 
artery 

Posterior  hcEmorrhoidal 
nerve 

\  uliar  branch  of 
pudic  nirvc 
li  I  rnal  pudic 
t  'J 
J      I  ch  of  pu- 
I     I  cm-  to 
I  t  ris 


Obluralor  arltry 


Fig.  453  — Dissection 


Mare 


:IXEUM 

/,  Sacro-coccygeus  superior;  3,  sacro-coccygeua  lateralis;  3,  intertransversales;  4.  sacro-coccygeus  inferior; 
5.  recto-coccygeus;  6,  sphincter  ani  externus;  S',  branch  connecting  sphincter  ani  with  constrictor  vulva-;  ?■ 
vestibular  bulb;  S,  tuber  ischii;   9.  sacro-scL-itic  lig.inent.      (After  Schmiiltz,  .\tlas  d.  .\nat.  d.  Pferdes.) 


gives  off  small  vesical  branches  (Aa.  vesicales  craniales)  to  the  blaildcr,  and  twigs 
to  the  prostate  and  vasa  deferens  in  the  male.  In  the  mare  a  small  brancli  runs 
forward  along  the  ureter  into  the  broad  ligament  of  the  uterus. 

(2)  The  middle  haemorrhoidal  or  vesico-prostatic  artery  (A.  haniiorrhoidalis 
media)  in  the  male  arises  usually  near  the  jjrostate  and  runs  backward  lateral  to 
the  n>ctum.  It  svij)])lies  liranches  to  the  rectum,  l)ladder,  urethra,  and  accessory 
genital  glands.  In  the  female  the  homologous  vessel  is  much  larger  and  gives  off 
the  posterior  uterine  artery  (A.  uterina  caudalis).  This  runs  forward  on  the  side 
of  the  vagina,  to  which  it  gives  branches,  and  ramifies  on  the  body  of  the  uterus, 
anastomosing  with  the  anterior  and  middle  uterine  arteries.  (In  some  cases  this 
artery  arises  from  the  internal  iliac  or  the  umbilical.) 

(3)  The  perineal  artery  (A.  perinei)  is  relatively  small  in  the  male.     It  i)asses 

'  Tlic  obliteration  in  the  adult  extends  a  variable  distance  from  the  vesical  end  toward  the 
origin,  but  usually  involves  only  a  small  part. 


THE    INTERNAL    ILIAC    ARTERY 


575 


upward  at  the  side  of  the  anus,  which  it  supplies,  and  gives  twigs  to  the  bulho- 
cavernosus  muscle  and  the  skin  of  the  perineum.  In  the  female  it  is  large  and  is 
distributed  to  the  anus  and  vulva,  and  gives  a  large  branch  to  the  vestibular  bulb. 

(4)  The  artery  of  the  bulb  (A.  bulbi  urethrae)  may  be  regarded  as  the  direct 
continuation  of  the  internal  putlic  in  the  male.  It  lies  at  the  side  of  the  urethra 
above  the  ischial  arch,  dijis  uniler  the  bulbo-cavernosus  muscle,  and  ramifies  in 
the  corpus  spongiosum.  Before  doing  so  it  gives  off  a  small  branch  which  turns 
around  the  ischial  arch  to  reach  the  dorsum  penis,  and  anastomoses  with  the  deep 
branch  of  the  obturator. 

(4a)  The  artery  of  the  clitoris  (.\.  clitoridis)  is  the  homologue  in  the  female 
of  the  preceding  vessel,  but  is  much  smaller.  It  passes  to  the  ventral  surface  of 
the  vulva  with  the  internal  pudic  nerve,  supplies  the  clitoris,  and  gives  twigs  to  the 
vulva. 

3.  The  lateral  sacral  artery  (A.  sacralis  lateralis)  arises  at  the  hunbo-sacral 


Fig.  454. — Cross-section  of  Tail  of  Horse. 
1,  Dorso-Iateral  coccygeal  vessels  ami  nerve;    2,  ventrolateral    coccygeal    artery  and  nerve;    S,  middle 
coccygeal  artery;    4.  sacro-coccygeus  superior;    J,',  sacro-coccygeus  lateralis;    S.  6'.  inteitransversales;    6.  saero- 
coccygeus  inferior;  7,  recto-coccygeus;  S.  coccygeal  fascia;    9,  fibro-cartilage  between  fourth  and  fifth  coccjgeal 
vertebrae.     The  veins  are  black. 


articulation  (Fig.  451).  It  passes  backward  under  the  wing  of  the  sacrum,  then 
along  the  pelvic  surface  of  the  bone  below-  the  inferior  sacral  foramina  and  the 
nerves  emerging  from  them,  and  is  continued  by  the  lateral  coccygeal  artery. 
The  branches  are  as  follows: 

(1 )  Spinal  branches  (Rami  spinales)  enter  the  vertebral  canal  through  the  for- 
amen between  the  last  lumbar  vertebra  and  the  sacrum  and  through  the  ventral 
sacral  foramina.  They  give  off  liranches  to  the  spinal  cord  and  its  membranes 
which  reinforce  the  ventral  spinal  artery,  and  others  which  emerge  through  the 
dorsal  sacral  foramina  and  sujijily  the  muscles  and  skin  of  the  croup. 

(2)  The  middle  coccygeal  artery  (A.  coccygea)  is  an  unpaired  vessel  which 
arises  from  the  right  or  left  lateral  sacral  or  from  a  lateral  coccygeal  artery.  It 
passes  backward  on  the  pelvic  surface  of  the  sacrum  to  the  median  line  and  con- 
tinues in  that  position  along  the  tail  between  the  depressor  muscles,  supplying 
these  and  the  skin. 

(.3)  The  posterior  gluteal  or  ischiatic  artery   (A.  glutea  caudalis)  emerges 


576 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


Internal  nrcum- 

JICX    VCSKlh 

Pironenl  nerve 

Tibial  nerre 
Posterior  femoral 

artery 
N .  cutaneus 

sura; 
Popliteal  lymph 

glands 
Gastroenemius 
Reevrrenl  tarsal 

vessels 


Tc.rscl  or  acces- 
ticry  tendon  of 
biceps  femcris 

Deep  flexor  of 
diffit 

Gastrocnemius 
tendon 

Superficial  flextr 
tendon 

c  .      ,  ,  <^^_.  ^_  >^_ «.    M    i         Tuber  calcis 

Superficial  peroneal  nciit 

Dcep  peroneal  neru 
Proximal  annular  lujnn 

Middle  annular  ligament 
External  lateral  ligament 

Distal  annular  lir/nment  ■ 

Fio.  455. — DissKCTioN  OK  Pelvis,  Thigh,  and  Le<:  of  Hohm  .  1  xtti:\m.  Vikw. 
1,  Dorsal  branches  of  last  intercostal  and  first  three  lumbar  nerves;  ii,  (.ulaneous  branch  of  fourth  lumbar 
nerve;  d.  ventral  branches  of  last  intercostal  nerve;  4.  branches  of  ilio-hyijogastric  nerve;  6,  superficial  branch  of 
ilio-inguinal  nerve;  6,  great  sciatic  nerve;  7,  8,  nerves  to  biceps  femoris  (from  posteiior  gluteal  nerve);  9,  nerve  to 
semitendinosus  (from  same);  10,  posterior  cutaneous  nerve  of  thigh;  II,  internal  pudic  nerve;  IS,  anterior  gluteal 
vessels  and  nerves;  IS,  posterior  gluteal  (or  ischiatic)  vessels;  14,  branches  of  obturator  vessels;  IB,  proximal 
muscular  branches  of  great  sciatic  nerve  to  biceps  femoris.  semitendinosus,  and  semimelTibranosus;  16,  nerve  to 
tensor  fascia-  latx  (from  anterior  gluteal  nerve);  /~,  gluteus  profundus;  ;S,  stump  of  gluteus  medius;  i9.  gemellus; 
M,  trochanter  major;  21,  stump  of  biceps  femoris;  SS.  sacro-coccygeus  superior;  SS",  sacro-coccygeus  lateralis; 
£f,  coccygeus;  24,  sacro-coccygeus  inferior;  $5,  line  of  fusion  of  aponeuroses  of  internal  and  external  oblique 
muscles  of  abdomen;  25'.  aponeurosis  of  external  oblitjue  muscle  (lamina  iliaca);  S6,  branches  of  iliaco-femoral 
vessels;  27.  ilio-lumbar  vessels;  SS,  ilio-ltimbar  lif  rii:tnt  or  deep  layer  of  lumbo-dorsal  fascia;  29,  external  angle 
of  ilium;  SO,  internal  angle  of  ilium;  S;,  lateial  sacio-iliac  ligament;  as,  sacro-sciatic  ligament.  (After  Schmahz, 
Atlas  <l.  Anaf.  d.  Pferdes.) 


THE    INTERNAL    ILIAC    ARTERY  577 

through  the  upper  part  of  the  sacro-sciatic  hgament  and  runs  backward  and  down- 
ward on  the  latter  under  cover  of  the  biceps  femoris  (Fig.  455).  It  gives 
branches  to  that  muscle  and  to  the  semitendinosus  and  semiinemliranosus,  and 
anastomoses  with  the  oliturator,  deep  femoral,  and  posterior  femoral  arteries. 

(4)  The  lateral  coccygeal  artery  (A.  caudalis  lateralis  ventralis)  continues  the 
direction  of  the  lateral  sacral,  but  is  much  smaller  than  the  preceding  vessel.  It 
passes  back  between  the  depressor  and  intertransversales  muscles  of  the  tail  and 
tlivides  into  two  branches  which  supply  twigs  to  the  muscles  and  skin. 

4.  The  ilio-lxunbar  artery  (A.  iliolumbalis)  arises  at  a  right  angle  from  the 
internal  iliac  antl  runs  outward  behind  the  sacro-iliac  joint,  crossing  the  ventral 
surface  of  the  ilium  under  cover  of  the  iliacus  muscle.  It  gives  branches  to  the  ilio- 
psoas and  longissimus,  and  terminates  by  turning  around  the  external  border  of  the 


Internal  iliac  art'Ttj 
External  iliac  artery 
Circumjtex  iliac  artery 
External  angle  of  ilium 


Inguinal  ligament 

Sartorius 

Femoral  neree 


Fcmoriil  iissds 


Internal  circumflt 
vess?h 
Trochanter  tertius 


Obturator  vessels 


Biceps  femoris 
Semitendinosus 
Sentimembranosus 


Fig.  456. — Deep  Dissection  of  Ventral  Wall  of  Pelvis  of  Horse  (Male). 
J,  External  pudic  arter>'  and  small  satellite  vein;    2,  anastomosis  between  external  pudic  and  internal  cir- 
cumflex veins;   5,  accessor>' ligament:   4.  round  ligament;   5,  transverse  ligament;   ff,  head  of  femur;   7,  obturator 
externus  (stumps);  5,  inner  margin  of  obturator  foramen;   9,  origin  of  gracilis;   /O.  origin  of  adductor;    11,  hulho- 
cavernosus;   13,  retractor  penis;    13,  suspensory  ligament  of  penis,     (-\fter  Schmaltz,  .\tlas  d.  .\naf .  d.  Pferdes.) 


ilium  a  little  behind  the  external  angle,  giving  branches  to  the  gluteus  medius 
and  tensor  fasciae  latse  (Fig.  45.5). 

5.  The  anterior  gluteal  artery  (A.  glutea  cranialis)  is  the  largest  branch  of  the 
internal  iliac.  It  arises  usually  opposite  to  the  preceding  vessel  and  passes  outward 
through  the  great  sacro-sciatic  foramen,  dividing  into  several  branches  as  it 
emerges;   these  enter  the  gluteal  muscles  (Fig.  455). 

6.  The  iliaco-femoral  or  external  circumflex  artery  (A.  circumflexa  femoris 
lateralis)  passes  downward  and  outward  across  and  beneath  the  shaft  of  the  ilium, 
under  cover  of  the  iliacus  muscle,  and  dips  in  between  the  rectus  femoris  anil 
vastus  externus.  It  is  accompanied  by  two  satellite  veins.  It  gives  collateral 
branches  to  the  iliopsoas,  the  glutei,  and  the  tensor  fasciae  latae,  supplies  the 
nutrient  artery  of  the  ilium,  and  terminates  in  the  quadriceps  femoris   (Fig.  455). 

7.  The  obturator  artery  (A.  obturatoria),  the  inner  terminal  branch  of  the 
internal  iliac,  passes  downward  and  backward  on  the  pelvic  surface  of  the  shaft  of 

37 


578  BLOOD-VASCVLAR    SYSTEM    OK   THE    HORSE 

the  ilium  along  the  ventral  border  of  the  iliac  head  of  the  obturator  internus,  ac- 
companied by  the  satellite  vein  and  nerve,  which  lie  in  front  of  the  artery 
(Fig.  451).  On  reaching  the  anterior  border  of  the  obturator  foramen  it  dips 
under  the  obturator  internus  and  passes  obliciuely  through  the  foramen.  In  this 
part  of  its  course  it  gives  off  a  vesical  branch  and  twigs  to  the  obturator 
internus  and  the  hijvjoint.  After  its  emergence  from  the  pelvic  cavity  it  runs 
b.ickward  on  the  ventral  face  of  the  ischium,  passes  through  the  semimemliranosus 
and,  ill  the  male,  enters  the  crus  penis,  forming  the  arteria  profunda  ])cnis.  It 
anastomoses  with  the  internal  pudic,  and  usually  with  the  external  jiudic  liy  a 
branch  which  runs  forward  on  the  dorsum  penis.  Large  collateral  liranches  are 
detached  to  the  adductors  of  the  thigh,  the  biceps  femoris  and  semit(>ndinosus, 
forming  anastomoses  with  the  deej)  femoral  and  jiosterior  femoral  arteries.  In 
the  female  the  terminal  part  is  small  and  enters  the  root  of  the  clitoris. 


ARTERIES  OF  THE  PELVIC  LIMB 
The  main  arterial  trunk  of  each  pelvic  limb  descends  as  far  as  the  lower  border 
of  the  popliteus  muscle,  where  it  divides  into  the  anterior  and  posterior  tibial 
arteries.  The  different  parts  of  the  trunk  receive  special  names  which  correspond 
to  the  several  regions  through  which  it  passes.  In  the  abdomen  it  is  termed  the 
external  iliac  artery,  in  the  proximal  two-thirds  of  the  thigh  it  is  called  the  femoral 
artery,  while  below  this  it  is  termed  the  popliteal  artery. 


The  External  Iliac  Artery  Figs.  450,  451) 
The  external  iliac  artery  (A.  iliaca  externa)  arises  from  the  aorta  under  the 
fifth  lumbar  vertelira,  usually  just  in  front  of  the  origin  of  the  internal  iliac.  It 
descends  at  the  side  of  the  pelvic  inlet  along  the  tendon  of  the  psoas  minor,  crosses 
the  insertion  of  that  muscle,  and  reaches  the  level  of  the  anterior  border  of 
the  pubis,  where  it  becomes  the  femoral  artery.  It  is  covered  by  the  perito- 
neum and  fascia,  and  is  related  behind  to  the  corresponding  vein.  Its  branches 
are  as  follows: 

1.  The  circxmiflex  iliac  artery  (A.  circumfiexa  ilium  profunda)  arises  from  the 
external  iliac  at  its  origin  or  from  the  aorta  directly.  It  passes  across  the  iliac 
fascia  toward  the  external  angle  of  the  ilium,  near  which  it  divides  into  two  branches. 
The  artery  lies  between  the  fascia  and  the  peritoneum  and  is  accom])anied  by  two 
veins  and  the  external  cutaneous  nerve  of  the  thigh.  The  anterior  branch  gives 
twigs  to  the  iliacus  and  psoas  muscles,  and  passes  downward  and  forward  in  the 
flank  between  the  obliquus  internus  and  transversus  abdominis,  in  which  it  ramifies. 
The  posterior  branch  perforates  the  abdominal  wall  and  runs  downward  on  the 
inner  face  of  the  tensor  fascise  latae  to  the  fold  of  the  flank,  supplying  branches  to 
that  muscle,  the  jianniculus,  the  precrural  lymph-glands,  and  the  skin. 

2.  The  cremasteric  artery  (A.  spermatica  externa)  is  a  very  small  vessel 
which  arises  in  a  variable  manner.  It  sjirings  most  often  from  the  external  iliac 
near  its  origin,  but  may  come  from  the  circumflex  iliac,  the  aorta  between  the 
external  and  internal  iliac,  or  the  latter  vessel.  It  accompanies  the  cremaster 
jnuscle  to  the  inguinal  canal,  supplies  twigs  to  that  muscle,  the  tunica  vaginalis,  and 
other  constituents  of  the  sjiermatic  cord  (Fig.  450l. 

2a.  The  middle  uterine  artery  (A.  uterina  media)  of  the  female  is  regarded 
as  the  homologue  of  the  preceding  vessel.  It  has  a  similar  origin,  but  is  a  much 
larger  artery,  which  passes  between  the  layers  of  the  broad  ligament  and  reaches 
the  horn  of  the  uterus  close  to  its  junction  with  the  body.  It  is  distributed  to 
both,  and  anastomoses  with  the  anterior  and  posterior  uterine  arteries. 


THE    FEMORAL    ARTERY 


579 


The  Femoral  Artery  Figs.  450,  45  d 
The  femoral  artery  is  the  main  arterial  trunk  of  the  thigh.  It  begins  at  the 
level  of  the  anterior  border  of  the  pubis,  from  which  it  is  se]Ku-iite(l  by  the  femoral 
vein.  It  descends  almost  vertically  in  the  femoral  canal  behind  the  sartorius 
muscle,  covered  at  first  by  the  internal  femoral  fascia  and  lower  down  by  the 
gracilis.  After  passing  over  the  insertion  of  the  pectineus,  it  perforates  the 
adductor  muscle,  crosses  in  the  vascular  groove  of  the  posterior  surface  of  the  femur, 
and  is  continued  between  the  two  heads  of  the  gastrocnemius  as  the  popliteal  artery. 


Fig.  457. — Disskction  of  iNorixAL  Regiox  .4nd  Inner  SrRFACE  op  Thigh  of  Horse. 
1  External  pudic  arter>';  2,  anterior  branches  of  /;  S,  posterior  branches  of  1;  4,  transverse  anastomosis 
between  external  pudic  veins;  4'  venous  plexus  of  dorsum  penis:  5,  femoral  arterj"  6,  saphenous  ner^'e:  7.  an- 
terior border  of  external  inguinal  ring;  S.  obliquus  abdominis  inlernus;  9,  posterior  border  of  external  inguinal 
ring;  W,  tunica  vaginalis;  II.  vas  deferens:  IJ,  cremaster  muscle;  13.  prepuce;  14>  glans  penis;  13.  external 
urethral  orifice:  16,  posterior  branches  of  circumflex  iliac  vessels;  17.  saphenous  vessels;  IS.  fold  of  flank;  /5, 
penis  (cut);  A,  superficial  inguinal  lymph  glands;  B,  precrural  lymph  glands;  C,  ileep  inguinal  lymph  glands. 
(After  Schmaltz,  .Atlas  d.  .Anat.  d.  Pferdas.) 


It  is  related  at  its  origin  to  the  sartorius  in  front,  the  femoral  vein  beliiiul  (which 
separates  it  from  the  pectineus),  and  the  iliacus  externally.  Lower  down  it  is 
related  superficially  to  the  deep  inguinal  lymph  glands,  and  deeph'  to  the  vastus 
internus,  while  the  saphenous  nerve  is  in  front  of  it,  and  the  vein  passes  to  its 
external  face.     The  chief  branches  are  as  follows: 

1.  The  prepubic  artery  (Truncus  pudendo-epigastricus)  arist  s  from  the  femoral 
artery  at  its  origin,  usually  Ijy  a  common  trunk  with  the  deep  femoral.  It  passes 
forward  and  a  little  inward  and  downward  across  the  edge  of  the  inguinal  ligament, 
and  then  runs  on  the  abdominal  .surface  of  the  ligament  to  the  inner  part  of  the 
internal  inguinal  ring,  where  it  divides  over  the  upper  border  of  the  internal  olilique 
muscle  into  the  posterior  at>dnminal  and  external  pudic  arteries. 

(1)  The  posterior  abdominal  artery  (A.  epigastrica  caudalis)  passes  along  the 


580  BLOOD-VASCULAR   SYSTEM    OF   THE    HORSE 

external  border  of  the  rectus  abdominis  and  anastomoses  in  the  umbilical  region 
with  the  anterior  alKloiiiiual  artery  (Figs.  272).  It  supplies  branches  to  the  rectus 
and  ol)liquus  interiius  muscles. 

(2)  The  external  pudic  artery  (A.  pudenda  externa)  descends  on  the  inguinal 
ligament  through  the  inner  part  of  the  inguinal  canal  and  emerges  at  the  inner 
angle  of  the  external  ring.  In  the  male  it  divides  into  the  subcutaneous  abdominal 
artery  and  the  dorsal  artery  of  the  penis.  The  former  runs  forward  a  short  distance 
from  the  linea  alba,  and  gives  liranclies  to  the  superficial  inguinal  Ij-mph  glands, 
the  sheath,  and  the  scrotum.  The  latter  passes  to  the  dorsum  penis  and  ends  at 
the  glans  as  the  arteria  glandis.  It  gives  off  collateral  branches  (Rami  profundi 
penis)  to  the  corpus  cavernosum,  one  of  which  usually  passes  backward  and  anasto- 
moses with  a  branch  of  the  obturator  artery.  Branches  are  also  supplied  to  the 
superficial  inguinal  lymph  glands,  the  prepuce,  and  the  scrotum.  In  the  female  the 
mammary  artery  takes  the  place  of  the  dorsal  artery  of  the  penis;  it  plunges  into 
the  Ijase  of  tlie  mammary  gland. 

2.  The  deep  femoral  artery  (A.  profunda  femoris)  arises  either  by  a  common 
trunk  with  the  preinibic  or  a  little  distal  to  it  (Fig.  451).  It  passes  backward  and 
downward  across  the  inner  face  of  the  femoral  vein,  then  below  the  puliis  in  the 
space  between  the  hip  joint  and  the  pectineus  muscle.  On  reaching  the  obtura- 
tor externus  it  inclines  more  ventrally  and  outward,  passes  out  between  the  inter- 
nal border  of  the  femur  and  the  quadratus  femoris,  and  ramifies  in  the  biceps 
femoris  and  semitendinosus.  It  supplies  large  collateral  branches  to  the  adduc- 
tor muscles  and  twigs  to  tlie  deeji  inguinal  lymi)h  glands  and  the  hip  joint. 

3.  The  anterior  femoral  artery  (A.  femoralis  cranialis)  arises  a  little  distal  to 
the  preceding  vessel  from  the  opposite  side  of  the  femoral  trunk.  It  passes  forward, 
outward,  and  a  little  downward  across  the  doe\)  face  of  the  sartorius,  and  dips  in 
between  the  rectus  femoris  and  vastus  internus  (Fig.  451).  It  is  related  extern- 
ally to  the  ilio-psoas  and  the  femoral  nerve. 

In  some  cases  this  artery  is  replaced  by  a  large  branch  of  the  external  circumflex,  which 
passes  between  the  ilio-psoas  and  rectus  femoris  and  enters  the  interstice  between  the  latter 
muscle  and  the  vastus  internus. 

4.  Innominate  muscular  branches  (Rami  musculares)  of  variable  size  and 
arrangement  are  given  off  to  the  muscles  of  this  vicinity. 

5.  The  saphenous  artery  (A.  saphena)  is  a  small  vessel  which  arises  from  the 
femoral  about  its  middle  or  from  a  muscular  branch,  and  emerges  Ijetween  the 
sartorius  and  gracilis  or  through  the  latter  to  the  inner  surface  of  the  thigh  (Fig. 
457).  It  is  joined  by  the  large  saphenous  vein  and  the  saphenous  nerve  and 
passes  down  superficially  on  the  fore  part  of  the  gracilis,  continues  on  the  deep 
fascia  of  the  leg,  and  ilivides  above  the  hock  into  two  branches,  which  accom- 
pany the  radicles  of  the  vein.  It  gives  off  cutaneous  twigs  and  anastomoses  with 
the  recurrent  tibial  artery. 

In  some  cases  this  anastomosis  does  not  occur.  The  artery  may  be  larger  and  directly 
continuous  with  the  internal  tarsal  artery. 

6.  The  articular  branch  (A.  genu  suprema)  is  a  slender  artery  which  arises 
from  the  femoral  just  before  it  passes  through  the  adductor.  It  descends  along  the 
posterior  border  of  the  vastus  internus  to  the  inner  surface  of  the  stifle  joint,  where 
it  ramifies. 

7.  The  nutrient  artery  of  the  femur  (A.  nutritia  femoris)  is  given  off  at  the 
middle  of  the  femur  and  enters  the  nutrient  foramen. 

8.  The  posterior  femoral  or  femoro-popliteal  artery  (A.  femoris  caudalis)  is  a 
large  vessel  which  arises  from  the  posterior  face  of  the  femoral  just  before  the  trunk 
passes  between  the  two  heads  of  the  gastrocnemius  (Fig.  455).  It  is  very  short 
and  divides  into  two  branches.    The  ascending  branch  passes  upward  and  outward 


THE    POPLITEAL    ARTERY — POSTERIOR    TIBIAL    ARTERY  581 

between  the  adductor  (in  front)  and  the  semimembranosus  (behind),  and  enters 
the  biceps  femoris,  in  which  it  ramifies.  The  descending  branch  passes  downward 
and  backward  on  the  external  head  of  the  gastrocnemius,  then  curves  upward  be- 
tween the  biceps  femoris  and  semitendinosus  (crossed  externally  by  the  tibial 
nerve)  and  divides  into  branches  to  these  muscles.  A  branch  is  detached  from 
the  convexity  of  the  curve  which  passes  down  between  the  heads  of  the  gas- 
trocnemius, gives  branches  to  that  muscle  and  the  flexor  perforans,  and  is  con- 
tinued by  a  slender  artery  which  accompanies  the  tibial  nerve  and  unites  with 
the  recurrent  tibial  arterj-.  A  branch  ascends  alongside  of  the  sciatic  nerve  be- 
tween the  biceps  and  semitendinosus  and  anastomoses  with  a  descending  branch 
of  the  obturator. 

The  Popliteal  Artery 
This  artery  (A.  poplitea)  is  the  direct  continuation  of  the  femoral.  It  lies 
between  the  two  heads  of  the  gastrocnemius,  at  first  on  the  posterior  face  of  the 
femur,  then  on  the  femoro-tibial  joint  capsule.  It  then  passes  down  through  the 
popliteal  notch  under  cover  of  the  popliteus,  inclines  outward,  and  divides  near  the 
upper  part  of  the  interosseous  space  into  anterior  and  posterior  tibial  arteries. 
The  satellite  vein  lies  along  its  inner  side.  Collateral  branches  are  supplied  to  the 
stifle  joint  and  the  gastrocnemius  and  popliteus. 


posterior  tibial  artery 
The  posterior  tibial  artery  (A.  tibialis  posterior)  is  much  the  smaller  of  the  two 
terminals  of  the  popliteal.  It  lies  at  first  between  the  tibia  and  the  popliteus, 
then  between  that  muscle  and  the  deep  and  inner  heads  of  the  deep  flexor.  Lower 
down  it  descends  along  the  tendon  of  the  inner  head,  becomes  superficial  in  the 
distal  third  of  the  leg,  and  passes  behind  the  tendon.  At  the  level  of  the  tuber 
calcis  it  forms  an  C/D-shaped  curve,  runs  downward  along  the  deep  flexor  tendon 
accompanied  by  the  plantar  nerves,  and  divides  at  the  lower  part  of  the  hock  into 
internal  and  external  plantar  arteries.     The  collateral  branches  are  as  follows: 

1 .  The  nutrient  artery  of  the  tibia  (A.  nutritia  tibise). 

2.  Muscular  branches  (Rami  musculares)  to  the  popliteus  and  deep  flexor. 

3.  The  external  tarsal  artery  (A.  tarsea  lateralis)  arises  at  the  distal  end  of  the 
leg  and  is  distributed  to  the  outer  surface  of  the  hock.  It  gives  off  a  small  recur- 
rent branch  which  ascends  along  the  external  border  of  the  gastrocnemius  tendon 
and  anastomoses  with  a  branch  of  the  posterior  femoral  artery. 

4.  The  recurrent  tibial  artery  (A.  tibialis  recurrens)  is  given  off  from  the  second 
part  of  the  curve,  ascends  in  relation  to  the  tibial  nerve,  and  anastomoses  with  the 
descending  branch  of  the  posterior  femoral  and  with  the  saphenous  artery. 

5.  Small  branches  (internal  calcaneal)  to  the  inner  aspect  of  the  hock. 

6.  The  plantar  arteries,  internal  and  external  (A.  plantaris  medialis,  lateralis), 
are  the  small  terminals  of  the  posterior  tibial.  They  descend  along  the  sides  of 
the  tarsal  sheath  of  the  deep  flexor  with  the  plantar  nerves  to  the  proximal  part  of 
the  metatarsus,  where  they  unite  with  the  perforating  tarsal  artery  to  form  the 
plantar  arch  (Arcus  plantaris).  Four  plantar  metatarsal  arteries  proceed  from  this 
arch.  The  two  slender  superficial  plantar  metatarsal  arteries  (A.  inetatarsea  plan- 
taris superficialis  medialis,  lateralis)  descend  on  cither  side  of  the  deep  flexor  tendon 
with  the  plantar  nerves  and  unite  with  the  great  metatarsal  or  with  the  corre- 
sponding digital  artery.  The  two  deep  or  interosseous  plantar  metatarsal 
arteries  (A.  metatarsea  plantaris  profundus  medialis,  lateralis)  descend  between 
the  suspensory  ligament  and  the  corresponding  small  metatarsal  bone  and  unite 
near  the  fetlock  with  the  great  metatarsal.     The  inner  artery  is  the  larger  of  the 


582 


BLOOD-VASCULAU    SYSTEM    OF   THE    HORSE 


two  and  usually  appears  to  be  the  continuation  of    the  perforating  tarsal.     It 
supplies  the  nutrient  artery  of  the  large  metatarsal    bone.     In   other   cases   it  is 


Tibial  iiiserlion  of  srnii-    \ 
tfn(liii(isi(!< 

Saphenous  vein 

Poplileus 

Flexor  dig.  longus 
(s.  acceissoriuli) 


Posterior  tibial  vesach 
Anterior  extensor 


Internal  lateral  tii/dimnl  of  tinck 

Pi-roncus  terlius  ■ — 


Inner  {citncon)  tendon  of 
libialis  (inlirior 


Outline  of  bursa 


Great  nielalarsal 


Ftg.  458. — DissF.rTiON-  oi-  Lr.r,  and  H 


Tendon  of  semiten- 
dinosus 
Gaslrncnemiux 
{internal  head) 


Tendon  of  (jaalroc- 


Teiidon  ofsujierlicidl 

fliror 

Tiirsal  bndaii  of 

s,llllh,nllln,.<u>:' 

Tibial  ,„nr 

I'leurrent  libiiU 
I'ssels 

Deep  flexor  tendon 
Internal  tarsal 
iirlerij 


Tendon  of  flexor  dig.  lon- 
gus (s.  aecessorius) 
■r E.rl(  mid  plantar  rein 

lull  nidi  plantar  arleru 


—  I  nil  mat  plantar  nerre 
Del  p  flexor  tendon 


Internid  planiiir  meta- 
tarsal ressels 


(.\fl,T  Si-hnialtz,  Atlas  il.  Anat.  ,1.  Tfcides.) 


the   direct  continuation  of  the  infernal   plantar  artcrj',  the  external  artery  only 
uniting  with  the  perforating  tarsal. 


ANTERIOR   TIBIAL    ARTERY 


583 


ANTERIOR  TIBIAL  ARTERY 

The  anterior  tibial  artery  (A.  tibialis  anterior)  is  much  the  larger  of  the  two 
terminal  branches  of  the  iiopliteal.     It  passes  forward  through  the  upper  part  of 


Vaslus  r.c/r/-/,».s- 

Gaslrocncmiiis,  (xlrnml 


Superficial  flexor 


Articular  rcsscl. 

Joint  capsule 

External  condyle  of  femur 

Popliteuf! 
Joint  capsule,  opened 

External  lateral  ligament 

Recurrent  tibial  vessels 


Salens 
Tibialis  posterior 


Lateral  extensor  tendon 
Recurrent  tarsal  vein 
External  plantar  vein 

External  tarsal  rein 
External  tarsal  artery 


Trochlea  of  tibial  tarsal  bone      ji  J —  \B 
External  lateral  ligament  _JL,A 

Fibular  tarsal  ban 


Femoral  ressels 
Posterior  femoral  artery 
Popliteal  artery 

Adductor 
dastrocnemius,  internal  head 
Tibial  nerve 


Flexor  dig.  longus  s.  accessor- 

ius 

Flexor  hallucis  longus 


Recurrent  tibial  artery 


External  tarsal  artery 
Internal  tarsal  artery 
Upper  end  of  tarsal  sheath 
Deep  flexor  tendon 
Long  flexor  tendon 
Plantar  nerves 
Plantar  arteries 
Joint  capsule,  opened 


Fic.  459. — Deep  Dissection-  of  Right  Stifle,  Leg,  and  Hock  of  Horse,  Posterior  View. 
The  hock  is  flexed  at  a  right  angle,  and  the  tulier  calcis  is  sawn  off.     The  tibial  nerve  is  drawn  inward  to 
show  its  musQular  branches.     Branches  of  tibial  nerve:    /,  Z.  to  gastrocnemius;    d.  4.  to  superficial  flexor;    S,  to 
popliteus;  6,  to  flexor  longus  or  accessorius;  7,  to  deep  flexor.     (After  Schmaltz,  Atlas  d.  Anat.  d.  Pferdes.) 


584 


BLOOD-VASCULAR    SYSTEM    OF   THE    HORSE 


the  interosseous  space  and  descends  with  two  satellite  veins  on  the  outer  part  of 
the  front  of  the  tibia,  under  cover  of  the  tibialis  anterior.     At  the  lower  part  of  the 


PahU 

Tendon  of  liiceps  fcniDri-t 

External  patellar  ligament 
Gastrocnemius 

External  condyle  of  tibia 

External  lateral  ligament 

Peroneal  nerve 


Superficial  peroneal  nerve 

Lateral  extensor 

Anterior  extensor 


Peroneus  tertius 


Loop  of  outer  tendon  of 
peroneus  tertius 

Perforating  tarsal  artery 
Slump  of  extensor  breiris 
Great  metatarsal  artery 
Lateral  extensor  tendon 
Anterior  extensor  tendon 


1  astiis  internus 

.  1  rcessory  cartilage  of  patella 

Gracilis 

Sartorius 

Trochlea  of  femur 

Jiil<rnal  patellar  ligament 

-j  Middle  patellar  ligament 

Internal  tuberosity  of  tibia 
Inlirnal  lateral  ligament 

Gastrocnemius 

Crest  of  tibia 

Tibial  tendon  of  semiten- 
dinosus 

Tibialis  anterior 
Suplienous  vein 
Deep  fascia  (reflected) 


Straight  tendon  of  j)cro- 
neus  tertius 

Inner  (cunean)  tendon  of 
tibialis  anterior 


Distal  annular  ligament 
Great  metatarsal  vein 
Deep  peroneal  nerve 


Fig.  460.— Sui'kr 


.  DisRKCTioN-  OF  RiGHT  SriFLF,  I, EC,  .\ND  HocK  OF  HoRSE,  Fro.st  Vif.w.     (After  Schmaltz, 
Alla.<  il.  Anat.  d.  I'feriles.) 


leg  it  deviates  to  the  outer  border  of  the  tendon  of  this  muscle,  passes  on  to  the 
capsule  of  the  hock  joint,  gives  off  the  perforating  tarsal  artery,  and  is  continued  as 


THE   VEINS  585 

the  great  metatarsal  artery.  It  gives  off  muscular  branches  to  the  dorso-latcral 
group  of  muscles  of  the  leg  and  articular  branches  to  the  hock.  The  peroneal 
branch  (A.  peronea)  is  a  variable  vessel  which  descends  along  the  fibula  under  the 
lateral  extensor:  it  gives  off  muscular  liranches  and  one  which  perforates  the  fascia 
and  divides  into  ascending  and  descending  cutaneous  twigs. 

The  perforating  tarsal  artery  (A.  tarsea  jjerforans)  is  given  off  under  cover  of 
the  outer  tendon  of  the  ])eroneus  tertius.  It  passes  backward  through  the  vascular 
canal  of  the  tarsus  with  a  satellite  vein  and  unites  on  the  upper  part  of  the  sus- 
pensory ligament  with  the  plantar  arteries  (or  only  with  the  e.xternal  plantar)  to 
form  the  plantar  arch. 

In  well-injected  specimens  it  is  seen  that  there  is  a  fine  arterial  network  (Rete 
tarsi  dorsale)  on  the  flexor  surface  of  the  hock,  which  is  formed  by  twigs  from  the 
anterior  tiliial  and  lateral  tarsal  arteries.  From  it  proceed  two  very  slender  dorsal 
metatarsal  arteries.  The  inner  one  descends  in  the  furrow  between  the  inner  small 
and  large  metatarsal  bones,  and  anastomoses  usually  in  the  proximal  part  of  the 
metatarsus  with  the  internal  superficial  plantar  metatarsal,  uniting  sometimes  with 
the  deep  plantar  metatarsal.  The  external  vessel  passes  down  under  the  periosteum 
on  the  anterior  face  of  the  large  metatarsal  bone  and  becomes  lost  or  joins  the  large 
metatarsal  artery. 

Sometimes  the  anterior  tibial  artery  passes  undi\-ided  through  the  tarsus,  gives  off  the 
internal  deep  plantar  metatarsal,  and  is  continued  as  a  very  large  internal  superficial  plantar 
metatarsal  along  the  deep  flexor  tendon,  thus  resembUng  the  arrangement  in  the  fore  limb. 

In  a  few  cases  the  perforating  tarsal  is  a  large  vessel,  directly  continuing  the  anterior  tibial, 
and  is  continued  by  a  large  internal  deep  plantar  metatarsal.  The  great  metatarsal  is  then 
small.     Other  variations  are  common. 

THE  GREAT  METATARSAL  ARTERY 

This  artery  (A.  metatarsea  dorsalis  lateralis)  is  the  direct  continuation  of  the 
anterior  tibial.  It  passes  downward  and  outward  under  the  extensor  brevis  and 
the  tendon  of  the  lateral  extensor,  at  first  on  the  joint  capsule  and  then  in  the  oblique 
vascular  groove  on  the  upper  part  of  the  large  metatarsal  bone.  It  then  descends 
in  the  groove  formed  by  the  appositioii  of  the  large  and  external  small  metatarsals, 
inclines  inward  between  the  two,  and  divides  on  the  lower  part  of  the  posterior 
face  of  the  large  metatarsal  bone  into  the  internal  and  external  digital  arteries.  It 
is  not  usually  accompanied  by  a  vein.  Beyond  this  the  arterial  arrangement  is 
the  same  as  in  the  thoracic  limb. 


THE  VEINS' 
PULMONARY  VEINS 
The  terminal  pulmonary  veins  (\'v.  pulmonales),  usually  seven  or  eight  in 
number,  return  the  aerated  blood  from  the  lungs  and  open  into  the  left  atrium  of 
the  heart.  They  are  destitute  of  valves.  Their  tributaries  arise  in  the  capillary 
jilexuses  in  the  lobules  of  the  lungs,  and  unite  to  form  larger  and  larger  trunks 
which  accompany  the  branches  of  the  bronchi  and  pulmonary  arteries.  A  very 
large  vein  is  formed  by  the  union  at  an  acute  angle  of  a  trunk  from  each  lung,  where 
the  latter  are  adherent  to  each  other. 

SYSTEHIC  VEINS 
The  Veins  of  the  Heart   Fig3.426. 427^ 
The  coronary  sinus  (.~>inus  coronarius)  is  a  very  short  bulbous  trunk  which 
receives  most  of  the    blood    from    the   wall    of   the   heart.     It   is   situated  just 

'  Most  of  the  veins  are  depicted  in  the  illustrations  of  the  section  on  the  arteries,  to  which 
reference  is  to  be  made. 


586  THE    VEINS 

below  the  termiiuitioii  of  the  po.sterior  vena  cava  and  is  eoviTed  in  part  l)y  a 
thin  \a\vr  of  ventricular  niusclc-fihcrs.  It  opens  into  the  right  atrium  just  l.elow 
the  posterior  vena  cava.  It  is  formed  by  the  union  of  two  tributaries.  The  great 
cardiac  or  left  coronary  vein  (\.  cordis  magna)  begins  at  the  left  side  of  the  apex 
of  the  heart,  ascends  in  the  left  longitudinal  groove  and  turns  backward  in  the 
coronary  groove,  in  which  it  winds  around  the  posterior  border  of  the  heart  to  the 
right  side  and  joins  the  coronary  sinus.  The  middle  cardiac  or  right  coronary  vein 
(\'.  cordis  media)  begins  on  the  right  side  of  the  apex,  ascends  in  the  right  longitu- 
dinal groove  and  joins  the  coronary  sinus,  or  opens  separately  into  the  atrium  just 
in  front  of  the  orifice  of  the  left  vein,  so  that  a  common  trunk  (coronary  sinus) 
does  not  then  exist. 

The  small  cardiac  veins  (^'v.  cordis  minores),  three  to  five  in  number,  are 
small  vessels  which  return  some  blood  from  the  riglit  ventricle  and  atrium;  they 
open  into  the  latter  near  the  coronary  groove^  in  sjiaces  between  the  musculi 
pectinati. 

THE  ANTERIOR  VENA  CAVA  (Fig.  429) 
The  anterior  vena  cava  (V.  cava  cranialis)  returns  to  the  heart  the  })lood  from 
the  head,  neck,  thoracic  limbs,  and  the  greater  part  of  the  thoracic  wall.  It  is 
formed  at  the  ventral  part  of  the  thoracic  inlet  by  the  confluence  of  the  two  jugu- 
lar and  two  brachial  veins.  Its  origin  is  attached  to  the  first  pair  of  ribs.  It 
passes  l)ackward  in  the  anterior  mediastinum,  at  first  median  and  ventral  to  the 
common  carotid  trunk,  then  deviates  to  the  right  of  the  anterior  aorta,  and  opens 
into  the  right  atrium  opposite  to  the  third  rib.  The  demarcation  l^etween  vein  and 
atrium  is  not  very  distinct.  It  contains  no  valves  except  at  the  mouths  of  its 
radicles.  Its  length  is  about  five  to  six  inches  (ca.  12  to  15  cm.)  and  its  caliber  about 
two  inches  (ca.  5  cm.)  in  a  subject  of  medium  size.  Its  right  face  is  crossed  by 
the  right  phrenic  nerve,  and  on  the  left  it  is  related  to  the  anterior  aorta  and  brachio- 
cephalic artery.  It  receives,  in  addition  to  small  pericardial  and  mediastinal 
veins,  the  following  tributaries: 

1.  The  internal  thoracic  vein  (V.  thoracica  interna)  is  a  satellite  of  the  artery 
of  that  name.     It  opens  into  the  anterior  vena  cava  at  the  first  rib. 

2.  The  vertebral  vein  (V.  vertebralis)  corresponds  to  the  homonymous  artery. 
On  the  right  side  it  terminates  either  in  front  of  the  deep  cervical  vein  or  by  a  short 
common  trunk  with  it.  On  the  left  side  it  almost  always  unites  with  the  deep 
cervical  and  vertebral  vein  to  form  a  common  trunk. 

3.  The  deep  or  superior  cervical  vein  (V.  cervicalis  profunda)  corresponds  to 
the  artery.  On  the  right  side  it  leaves  the  artery  at  the  first  intercostal  space, 
crosses  the  right  face  of  the  trachea  and  opens  into  the  vena  cava;  it  may  form  a 
common  trunk  with  the  dorsal  or  vertebral.  On  the  left  side  there  is  nearlj'  always 
a  conmion  trunk  for  all  three. 

4.  The  dorsal  vein  (Y.  costo-cervicalis)  corresponds  to  the  artery.  On  the 
right  side  it  leaves  the  artery  on  entering  the  thorax,  crosses  the  right  face  of  the 
trachea,  and  opens  into  the  vena  cava  in  front  of  the  deep  cervical  or  by  a  common 
trunk  with  it.  On  the  left  side  it  almost  always  joins  the  deep  cervical  and  verte- 
bral to  form  a  short  common  trunk  which  crosses  the  left  face  of  the  intrathoracic 
part  of  the  brachial  artery  opposite  the  second  rib  and  opens  into  the  anterior  vena 
cava. 

The  Vena  Azygos 

The  vena  azygos  (Fig.  429)  is  an  unpaired  vessel  which  arises  at  the  level  of 

the  first  lumbar  vertebra  by  radicles  coming  from  the  psoas  and  the  crura  of  the 

diaphragm;    it  is  connected  with  the  first  lumbar  vein.     It  passes  forward  along 

the  right  side  of  the  bodies  of  the  thoracic  vertebrae,  in  contact  usually  with  the 


VEINS    OF   THE    HEAD    AND    NECK  587 

thoracic  duct,  which  separates  the  vein  from  the  aorta.  At  the  seventh  vertehra 
it  leaves  the  spine,  curves  downward  and  forward  over  the  right  side  of  the  tiioracic 
duct,  trachea,  and  oesophagus,  and  opens  into  the  right  atrium  opposite  the  third 
intercostal  space.     Its  tributaries  are: 

1.  The  last  fourteen  intercostal  veins  (Vv.  intercostalcs)  of  the  right  side. 
On  the  left  side  the  last  four  to  seven  intercostal  veins  usually  empty  into  the  vena 
hemiazygos.  This  vessel  runs  on  the  left  side  of  the  aorta  from  the  fourteenth 
to  the  eleventh  thoracic  vertebra,  passes  between  the  aorta  and  the  spine,  and  joins 
the  vena  azygos.     In  its  absence  its  tributaries  join  the  vena  azygos. 

2.  The  oesophageal  vein  (V.  oesophagea),  satellite  of  the  oesophageal  artery, 
joins  the  vena  azygos  as  it  inclines  downward. 

3.  The  bronchial  vein  (\'ena  bronchialis)  unites  with  the  jireceding  to  form  a 
short  common  trunk  (Ellenlierger-Baum),  or  empties  into  the  great  coronary  vein 
(Chauveau).' 

VEINS  OF  THE   HEAD  AND  NECK 
Jugular  Veins 

The  jugular  veins  (Vv.  jugulares),  right  and  left  (Fig.  431),  arise  behind  the 
posterior  border  of  the  lower  jaw  about  two  and  a  half  inches  (ca.  6  to  7  cm.)  below 
the  teinporo-maxillary  articulation  by  the  union  of  the  superficial  temporal  and 
internal  maxillary  veins.  Each  passes  downward  and  backward,  at  first  embedded 
more  or  less  in  the  parotid  gland,  and  continues  in  the  jugular  furrow  to  the  thoracic 
inlet,  where  it  unites  with  its  fellow  and  the  two  brachial  veins  to  form  the  anterior 
vena  cava.  In  the  neck  it  is  covered  by  the  skin,  fascia,  and  panniculus,  and  is 
superficial  to  the  carotid  artery,  from  which  it  is  separated  in  the  anterior  two- 
thirds  of  the  region  by  the  omo-hyoideus  muscle."  It  contains  valves  at  the  mouths 
of  its  tributaries  and  has  several  pairs  of  semilunar  valves  variably  disposed  along 
its  course.     Its  tributaries  are  as  follows: 

1.  The  internal  maxillary  vein  (V.  maxillaris  interna)  is  larger  than  the 
external  maxillarj'.  It  may  he  considered  to  begin  as  the  continuation  backward 
of  the  buccinator  vein  where  the  vessel  crosses  the  alveolar  border  of  the  mandible 
(about  two  inches  (ca.  5  cm.)  behind  the  last  molar  tooth).  It  runs  backward  on 
the  inner  surface  of  the  ramus  below  the  external  pterygoid  and  covered  by  the 
internal  pter^'goid  muscle  for  a  distance  of  about  three  inches  (ca.  7  to  8  cm.), 
then  inclines  a  little  downward  and  runs  ventral  to  the  artery  for  about  an  inch 
(ca.  2  to  3  cm.).  It  crosses  the  external  face  of  the  artery  at  the  posterior  border 
of  the  jaw,  and  is  joined  by  the  superficial  temporal  vein  to  form  the  jugular.  Its 
principal  radicles  are: 

(1)  The  dorsal  lingual  vein  {V.  dorsalis  lingute),  which  is  a  satellite  of  the 
lingual  nerve. 

(2)  The  inferior  alveolar  or  dental  vein  (V.  alveolaris  mandibulae),  a  satellite 
of  the  corresponding  artery.     It  often  unites  with  the  jireceding. 

(3)  Pterygoid  veins  (Rami  pterygoidei). 

(4)  The  deep  temporal  vein  (V.  temporalis  profunda)  is  a  large  vessel  which 
receives  tributaries  from  the  temporalis  muscle  and  emissaries  from  the  parieto- 
temporal canal.     It  is  connected  with  the  anterior  cerebral  vein  and  usually  with 

'  Chauveau  says  "the  bronchial  veins,  which  ramifj'  on  the  bronchi  lil^e  the  arteries  of  which 
they  are  satellites,  open  into  tlie  great  coronary  vein  very  near  its  moutli,  after  liaving  uuitcil  to 
form  a  single  vessel,  which  sometimes  opens  directly  into  the  atrium."  Ellenberger  and  Haum 
state  that  the  bronchial  and  a'sophageal  veins  open  into  the  vena  azygos  separately  or  l)y  a  com- 
mon trunk.  Martin  describes  a  short  broncho-ocsophageal  trunk,  but  the  vein  which  lie  figures 
as  the  bronchial  does  not  come  from  the  lungs,  but  is  a  small  mediastinal  vessel.  The  author 
finds  such  a  vessel  entering  the  terminal  part  of  the  oesophageal  vein.  Iiut  no  distinct  bronchial 
vein  in  the  horse. 

■  M'Fadyean  records  a  case  in  which  the  vein  lay  on  the  deep  face  of  the  omo-hyoideus  with 
the  carotid  artery. 


588 


THE    VEINS 


the  meningeal  veins  by  its  frontal  branch.     The  latter  drains  chiefly  the  lacrimal 
gland  and  passes  behind  the  supraorbital  process. 

2.  The  superficial  temporal  vein  (V.  temporalis  superficialis)  is  a  satellite  of 
the  corresponding  artery.  It  is  formed  by  the  confluence  of  the  anterior  auricular 
and  transverse  facial  veins.  The  former  receives  the  superior  cerebral  vein  (\'. 
cereliralis  dorsalis),  whicli  is  the  emissary  of  the  transverse  sinus  of  the  dura  mater; 
it  emerges  from  tlie  parieto-temporal  canal  behind  the  postglenoid  process.  The 
transverse  facial  vein  (^'.  transversa  faciei)  runs  at  first  above  the  artery  of  like 
name,  then  plunges  deeply  into  the  masseter  and  unites  in  front  with  the  facial 
vein.     It  is  connected  with  the  vena  reflexa. 

3.  The  inferior  masseteric  or  maxillo-muscular  vein  (^^  masseterica)  joins  the 
jugular  at  the  upper  border  of  the  sterno-ceiihalicus  tendon.  It  is  a  short  trunk 
formed  by  the  confluence  at  the  posterior  border  of  the  jaw  of  masseteric  and 


Fig.  401. — .Superficial  Vessels  and  Nerves  of  Head  axd  .Interior  Part  of  Neck  of  Horse. 
a,  Masseter;  6.  parotid  gland;  c,  parotido-auricularis;  i,  masseteric  artery;  5,  parotid  branch;  ^.transverse 
facial  artery;  .4.  facial  artery;  5.  5.  inferior  labial  artery;  7,  superior  labial  artery;  5.  lateral  nasal  artery;  5,  in- 
fraorbital artery;  iO  dorsal  nasal  artery;  7i,  angular  artery  of  eye;  /.?, /3,  jugular  vein;  i .4.  great  auricular  vein; 
16,  masseteric  vein;  16,  superficial  temporal  vein«  17,  transverse  facial  vein;  17',  deep  temporal  vein;  IS,  external 
maxillary  vein;  i5;  facial  vein;  .50.  labial  vein;  j?7,  dorsal  nasal  vein;  22,  lateral  nasal  vein;  33,  angular  vein  of 
e.ve;  34,  25,  facia\  nerve;  55',  5.5",  superior  and  inferior  buccal  nerves;  26,  transverse  facial  ner\'e;  27,  auriculo- 
palpebral  nerve;  55,  anterior  auricular  nerve;  29,  cervical  branch  of  facial  nerve;  30,  ventral  branch  of  second 
cervical  nerve;  30',  30",  S&",  auricular  and  cutaneous  branches  of  30:  31 ,  branches  of  dorsal  division  of  first  and 
.second  cervical  nerves;  33,  dor.sal  branch  of  spinal  accessory  nerve,      (.\fter  l.eisering's  .\tlas.1 


pterygoid  veins.     The  former  is  usually  connected  by  a  large  branch  with  the  l)uc- 
cinator  vein. 

4.  The  great  auricular  vein  (\.  auricularis  magna)  is  a  satellite  of  the  posterior 
auricular  artery  above,  but  joins  the  jugular  a  variable  distance  below  and  liehind 
the  point  of  origin  of  the  artery. 

5.  The  inferior  cerebral  vein  (V.  cereliralis  ventralis)  is  an  emissary  of  the 
cavernous  sinus  of  the  dura.  It  is  a  satellite  of  the  internal  carotid  arterj',  receives 
the  condyloid  vein,  and  joins  the  jugular  near  the  occipital  vein  or  by  a  common 
trunk  with  it. 

(i.  The  occipital  vein  {\ .  occipitalis)  arises  in  the  fossa  atlantis  by  the  union  of 
muscular  and  cerebrosjiinal  branches.  The  former  comes  from  the  muscles  of  the 
poll  and  passes  through  the  foramen  transversarium.  The  latter  is  connected  with 
the  occipital  sinus  of  the  dura  mater  and  emerges  from  the  spinal  canal  by  the 
intervertebral  foramen . 

7.  The  external  maxillary  or  facial  vein  {\.  maxillaris  externa)  arises  by  radicles 
which  correspond  in  general  to  the  branches  of  the  arterj'  of  like  name.     It  passes 


JUGULAR    VEINS 


589 


do^^^l  over  the  cheek  along  the  anterior  border  of  the  masseter  muscle  behind  the 
arterj',  crossing  over  the  parotid  (hict.  which  lies  behind  the  vein  lower  down.  Thus 
on  the  ramus  and  as  they  turn  around  its  lower  border  the  artery  is  in  front,  the  vein 
in  the  middle,  and  the  duct  posterior.  In  the  submaxillary  space  the  vein  is  ventral 
to  the  artery  for  some  distance,  then  parts  company  with  the  artery,  runs  straight 
liackward  along  the  lo\\ei'  border  of  the  parotid  gland,  and  opens  into  the  jugular 
vein  at  the  posterior  angle  of  the 
gland.'  The  chief  differences  in  the 
tributaries  of  the  vein  as  compared 
with  the  branches  of  the  corrts]iond- 
ing  artery  are  as  follows: 

The  labial  veins  (\'v.  labiales) 
form  a  plexus  in  the  submucous  tissue 
of  the  cheek  from  which  two  veins 
emerge.  The  upper  one  i)asses  back 
and  joins  the  buccinator  vein.  The 
lower  one  (V.  labialis  communis) 
joins  the  external  maxillary  vein. 

Three  veins  connect  with  the  ex- 
ternal maxillary  at  the  anterior  border 
of  the  masseter. 

The  upper  one  is  the  transverse 
facial,  which  unites  close  to  the  enil 
of  the  facial  crest. 

A  little  lower  is  the  large  valve- 
less  vena  reflexa  or  alveolar  vein. 
This  passes  liack  under  the  upjier 
part  of  the  masseter  on  the  maxilla, 
turns  around  the  tuber  maxillare,  j^er- 
forates  the  periorbita,  and  joins  the 
ophthalmic  vein.  It  is  relatively 
small  at  each  end,  but  presents  one 
or  two  large  fusiform  dilatations.  It 
receives  the  following  tributaries:  («) 
The  palatine  vein  (V.  palatina  major), 
which  separates  from  the  palatine 
artery  at  the  anterior  palatine  fora- 
men and  passes  in  the  groove  lietween 
the  tuber  maxillare  and  the  palate 
bone.  The  palatine  veins  form  a 
very  rich  plexus  of  valveless  vessels 
in  the  submucosa  of  the  hard  palate, 
which  consists  of  several  layers  an- 
teriorly, (b)  The  sphenopalatine 
vein  (V.  spheno-palatina)  forms  a 
rich  plexus  of  valveless  vessels  on 
the  turbinal  bones  and  the  septum 

nasi.     It  is  usually  joined  by  the  infraorbital  vein  (V.  infraorbitalis)  to  form  a  short 
common  trunk. 

The  venous  plexuses  are  remarkably  developed  in  certain  parts  of  the  nasal  mucosa.  On 
the  septum  a  httle  below  its  middle  and  on  the  turbinals  the  veins  are  in  several  lavers.  The 
olfactory  region  does  not  share  in  this  arrangement  and  the  veins  here  are  small  and  join  the  eth- 
moidal vein. 

'  The  venous  angle  formed  by  this  junction  indicates  the  position  of  the  thyroid  gland. 


Fio.    462. — Dissection    of 

Adjacent  P.\rt  c 

a,  Ramus  of  mandibl 

c,  c' ,  onio-hyoidei  and  sterE 

right  side):   d,  hyoid  bone: 


SrBMAXILLAHY     SpACE     AND 

Neck  of  Horse. 

b,  sterno-cephalicus  muscle; 
-hyoidei  (portion  removed  on 
anterior  belly  of  digastriciis; 
/.  g,  raylo-hyoideus:  h.  submaxillary  lymph  gland.s  (por- 
tion removed  on  right  side):  i.  parotid  gland:  A;,  submaxil- 
lary gland:  ;.  chin:  m.  stylo-maxillaris;  /.  parotid  duct: 
3,  facial  vein:  S,  facial  artery:  4.  external  maxillary  vein: 
5,  sublingual  vein;  6,  sublingual  artery:  7.  ventral  branch 
of  first  cervical  ner\e:  S.  mylo-hyoid  nerve.  (.After 
Ellenberger,  in  Leisering's  -Atlas.) 


590 


THE    VEINS 


(c)  The  ophthalmic  vein  (\.  oiilitlialmica)  is  a  short  trunk,  connected  in  front 
with  the  vena  refit'xa  and  behind  with  the  cavernous  sinus  through  the  foramen 
hicerum  orbitale.     It  receives  veins  which  correspond  to  the  arterial  branches. 

The  buccinator  vein  {\.  buccinatoriu)  extends  backward  from  tlie  external 
maxiUary  along  the  lower  border  of  the  depressor  labii  inferioris  and  buccinator 
under  cover  of  the  masseter,  passes  between  the  ramus  of  the  mandible  and  the 
tuber  maxillaro  and  is  continued  as  the  internal  maxillary  vein.  It  has  a  large 
fusiform  dilatation  and  is  valveless.  It  receives  a  large  common  labial  vein  from 
the  laliial  jjlexus,  and  is  usually  connected  with  the  masseteric  vein. 


Fin.  463. — Deeper  V 


AND  Nerves  of  Head  of  Horse. 


The  parotid  f;lancl,  most  of  the  masseter  muscle,  and  a  portion  of  the  ramus  of  the  tnaiidible  are  remove.!. 
a.  Remnant  of  nias-seter  muscle;  6,  internal  pterygoid  muscle:  c,  stylo-mandibularis;  d,  d\  levator  labii  superioris 
proprius  (portion  removed);  e,  periorbita;  i,  ma.sseteric  artery;  /',  parotid  branch;  ;?,  trunk  for  anterior  (.:*)  and 
posterior  {4)  auricular  arteries;  5,  5',  superficial  temporal  artery;  6" ,  transverse  facial  artery;  6,  inferior  alveolar 
(or  dental)  artery;  6' ,  mental  continuation  of  6;  7,  buccinator  artery;  6'.  infraorbital  artery;  9,  II,  jugular  vein; 
10,  external  maxillary  vein;  12,  inferior  cerebral  vein;  IS,  facial  vein;  t/,,  angular  vein  of  eye;  16,  dorsal  nasal 
vein;  16,  lateral  nasal  vein;  17,  superior  labial  vein;  IS,  19,  inferior  labial  veins;  20,  labial  jjlexus;  21,  22,  emer- 
gent veins  of  plexus;  23,  vena  reHexa;  2^,  trunk  of  sphenopalatine  and  infraorbital  veins;  2S,  palatine  vein; 
3G,  great  auricular  vein;  27,  28,  superficial  temporal  vein;  29,  transverse  facial  vein;  SO,  buccinator  vein;  31, 
dorsal  lingual  vein;  5.?,  inferior  alveolar  or  dental  vein;  5.^,  pterygoid  vein;  54.  deep  temporal  vein;  55.  superior 
cerebral  vein;  SG,  external  nasal  nerve;  S7,  anterior  nasal  nerve;  38,  superior  labial  ner\-e;  .•i9,  ma.sseteric  nerve; 
39' ,  end  branches  of  39;  40,  buccinator  nerve;  4h  pterygoid  ner\'e;  4/a,  inferior  alveolar  or  dental  nerve;  4tb, 
mylo-hyoid  nerve;  42,  posterior  auricular  nerve;  43,  auricular  branch  of  vagus;  44,  internal  auricular  nerve;  46, 
auriculo-palpebral  nerve  (cut);   4e,  digastric  nerve,     (.\fter  Leisering's  .\tlas.) 


The  lingual  vein  (V.  lingualis)  is  not  a  satellite  of  the  artery.  It  is  formed  at 
the  side  of  the  lintjual  process  of  the  hyoid  bone  by  the  confluence  of  several  veins 
which  come  from  the  substance  of  the  tongue.  One  or  two  considerable  vessels 
run  jiartly  in  the  sub.stance  of  the  hyo-glossus,  and  another  in  the  genio-hyoideus. 
The  vein  is  at  first  covered  by  the  mylo-hyoideus,  perforates  that  muscle,  runs 
back  along  the  omo-hyoideus  in  relation  to  the  submaxillary  lymjih  glands,  and 
joins  the  external  maxillary  near  the  posterior  liorder  of  the  jaw.  Near  its  termina- 
tion it  receives  the  sublingual  vein,  or  the  hitter  may  open  into  the  external  maxil- 
lary directly. 

8.  The  thyroid  vein  {\.  thyreoitlea)  is  a  large  vessel  which  joins  the  jugular 
near  the  external  maxillary  vein.  It  receives  anterior  thyroid,  laryngeal,  and 
pharyngeal  radicles,  and  sometimes  a  posterior  thyroid  vein. 


THE    SINUSES    OF   THE    DURA    MATER  591 

9.  Muscular,  tracheal,  and  oesophageal  veins. 

10.  Tho  cephalic  vein  (Vena  cephalica)  enters  the  jugular  near  its  termination. 
It  will  l)e  (l(>srril)e(|  with  the  veins  of  the  thoracic  limb. 

1 1 .  The  inferior  cervical  vein  (V.  ccrvicalis  ascendens)  accompanies  the  artery. 
It  may  open  into  the  brachial  vein. 

The  Sinuses  of  the  Dura  Mater 

These  (Sinus  durae  matris)  are  blood-spaces  between  the  meningeal  an<! 
]K'riosteal  layers  of  the  dura  mater  and  are  lined  with  endothelium.  In  many 
l)laces  the  lumen  is  crossed  by  fibrous  strands.  They  receive  the  veins  of  the  brain, 
communicate  with  the  meningeal  and  diploic  veins,  and  with  veins  outside  of  tlie 
cranium;  their  connections  with  the  latter  are  by  means  of  small  emissary  veins 
(Emissaria).  They  convey  the  blood  directly  or  indirectly  to  the  jugular  veins. 
Some  are  paireil,  others  unjiaired.  They  may  be  divided  into  dorsal  and  basilar 
systems.     The  dorsal  system  comprises  the  following: 

The  superior  longitudinal  or  sagittal  sinus  (S.  sagittalis  superior)  is  situated 
in  the  u])per  border  of  the  falx  cerebri  along  the  internal  sagittal  crest.  It  begins 
at  the  crista  galli  and  ends  at  the  tentorium  osseum  l)y  dividing  into  two  transverse 
sinuses.     It  receives  the  superior  cerebral  veins.     Along  each  side  are  small  pouches 


Fig.  464. — Median  Section  of  Head  of  Horse,  Upper  Part  with  Septum  Nasi  Removed. 
a,  Lateral  mass  of  ethmoid  bone;  b,  superior  turbinal;  c,  inferior  turbinal;  rf,  d',  turbinal  folds;  e,  frontal 
sinus;  /,  falx  cerebri;  g,  tentorium  cerebelli;  h,  medial  surface  of  hemisphere;  /,  cerebellum;  k,  occipital  bone; 
k' ,  occipital  condyle;  fr",  paramastoid  process;  /.  external  auditory  meatus;  m,  temporal  condyle;  n,  parieto- 
temporal canal;  /,  branches  of  ethmoidal  artery;  2,  2' ,  branches  of  sphenopalatine  artery;  S,  S' ,  branches  of  spheno- 
palatine vein;  4<  branches  of  ethmoidal  nerve;  5,  5' ,  branches  of  sphenopalatine  nerve;  6,  artery  of  corpus  callo- 
sum;  7,  superior  sagittal  sinus;  S,  straight  sinus;  9,  vena  magna  cerebri;  10,  inferior  sagittal  sinus;  11,  11', 
transverse  sinuses:  12,  superior  petrosal  sinus;  IS,  superior  occipital  .sinus;  14,  superior  cerebral  vein;  15,  corpus 
callosum;    16,  fornix,      (.\fter  Eilenberger,  in  Leisering's  .\tlas.) 

(Lacunae  laterales)  into  which  the  veins  open.  The  lumen  of  the  sinus  is  traversed 
by  fibrous  bands  and  is  partially  divided  by  a  longitudinal  septum. 

The  transverse  sinuses  (S.  transversi),  right  and  left,  pass  outward  in  the 
transverse  grooves  of  the  parietal  bones,  enter  the  parieto-temporal  canals,  and 
are  continued  by  the  superior  cerebral  veins  to  the  superficial  temporal  veins. 
The  two  sinuses  are  connected  by  the  sinus  communicans. 

The  inferior  longitudinal  or  sagittal  sinus  (S.  sagittalis  inferior)  runs  backward 
on  the  upper  surface  of  the  corpus  callosum  along  the  concave  edge  of  the  fal.x 
cerebri  and  joins  the  great  cerebral  vein  (of  Galen)  to  form  the  straight  sinus. 

The  straight  sinus  (S.  rectus)  passes  upward  and  backward  between  the  cere- 
bral hemispheres  and  in  the  tentorium  cerebelli  and  joins  the  superior  sagittal  sinus. 
The  point  of  meeting  is  the  confluence  of  the  sinuses  (Confluens  sinuum). 

The  occipital  sinuses  (S.  occipitales)  lie  on  either  side  of  the  vermis  cerebelli. 
They  empty  anteriorly  into  the  sinus  communicans  and  communicate  behind  with 
the  spinal  veins. 

The  superior  petrosal  sinuses  (S.  petrosi  superiores)  pass  in  the  tentorium 
cerebelli  to  end  in  the  transverse  sinuses. 


592  THE    VEINS 

The  basilar  system  consists  of  the  following: 

The  cavernous  sinuses  (S.  cavernosi)  lie  in  the  inner  grooves  of  the  root  of  the 
temporal  wings  of  the  sphenoid  bone  at  either  side  of  the  sella  turcica.  The  two 
are  connected  l)y  a  wide  traverse  branch  (Sinus  intercavernosus)  behind  and 
below  the  posterior  part  of  the  pituitary  body.  Each  is  continuous  in  front  with 
the  ophthalmic  vein  and  below  with  the  inferior  petrosal  sinus.  The  third,  sixth, 
and  the  ophthalmic  and  maxillary  thvisions  of  the  fifth  nerve  lie  along  the  outer 
wall  of  the  sinus.  The  internal  carotid  artery  traverses  the  sinus  and  is  connected 
with  its  fellow  by  a  transverse  branch  which  lies  in  the  corresponding  part  of  the 
sinus.  An  oval  opening  in  the  floor  communicates  with  the  inferior  jjetrosal  sinus 
and  transmits  the  internal  carotid  artery. 

The  sinus  is  not  subdivided  by  strands  of  fibrous  tissue  as  in  man,  but  a  few  delicate  bands 
attach  the  artery  to  its  wall. 

The  inferior  petrosal  sinuses  (S.  petrosi  inferiores)'  lie  along  the  borders  of 
the  l)asilar  part  of  the  occipital  bone,  inclosed  in  the  thick  dura  which  closes  the 
foramen  lacerum.  The  anterior  part  extends  about  half  an  inch  (ca.  12  mm.) 
under  the  temporal  wing  of  the  sphenoid.  Here  communications  exist  with  veins 
in  the  pterygo-palatine  fossa.  The  posterior  end  is  bulbous  and  lies  in  the  condy- 
loid fossa;  it  communicates  with  the  condyloid  vein  issuing  from  the  hypoglossal 
foramen  and  is  drained  by  tlie  inferior  cerebral  vein;  it  also  receives  an  emissary 
vein  from  the  jjarieto-temporal  canal.  The  roof  of  the  sinus  is  perforated  by  an 
oval  opening  at  the  carotid  notch  which  opens  into  the  cavernous  sinus  and  trans- 
mits the  internal  carotid  artery;  the  latter  forms  the  first  bend  of  its  S-shaped 
curve  in  the  jietrosal  and  the  second  in  the  cavernous  sinus. 

The  basilar  plexus  (Plexus  liasilaris)  is  a  venous  plexus  situated  on  the  u]iiiit 
surface  of  the  l)asihir  part  of  the  occipital  bone.  It  is  connected  through  the  hypo- 
glossal foramen  with  the  inferior  petrosal  sinus  and  communicates  behind  with  the 
spinal  veins. 

The  Veins  of  the  Cranium 

The  veins  of  the  brain  (Ven;e  cerebri)  do  not  hi  general  accompany  the  cerebral 
arteries.  Th(\v  have  very  thin  walls,  no  muscular  coat,  and  no  valves.  They  are 
arranged  in  two  sets,  superficial  or  cortical  and  deep  or  central.  The  superficial 
veins  are  more  numerous  and  larger  than  the  arteries.  They  lie  on  the  surface  of 
the  brain  in  the  pia  mater  and  the  subarachnoid  space. 

The  superior  cerebral  veins  tlrain  the  upper  and  outer  part  of  the  cerebral 
cortex.  They  receive  veins  from  the  medial  surfaces  of  the  hemispheres  and  open 
into  the  superior  sagittal  sinus.  Their  terminal  parts  are  bulbous  and  their  open- 
ings are  directed  obliquely  forward,  i.  e.,  contrary  to  the  direction  of  the  blood- 
stream in  the  sinus. 

The  inferior  cerebral  veins  lie  on  the  inferior  and  external  aspect  of  the  hemi- 
spheres. They  ojien  into  the  inferior  system  of  sinuses.  The  middle  cerebral 
vein  runs  in  the  lateral  fissure  (of  Sylvius)  and  opens  into  the  cavernous  sinus. 

The  deep  cerebral  veins  issue  from  the  central  or  ganglionic  parts  of  the  brain 
at  the  transverse  fissure.  They  converge  to  form  the  great  cerebral  vein  (of  Galen) 
(V.  magna  cerebri).  This  passes  upward  and  backward  liehind  the  splenium  of 
the  corpus  callosum  and  is  continued  as  the  straight  sinus  to  join  the  sagittal  sinus. 

The  superior  cerebellar  veins  ramify  on  the  upper  surface  of  the  cerebellum. 
They  open  into  the  superior  system  of  sinuses  and  the  great  cerebral  vein.  The 
inferior  cerebellar  veins  are  larger  and  go  chiefly  to  the  basilar  plexus.  The  veins 
of  the  medulla  and  ])ons  end  in  the  inferior  system  of  sinuses. 

The  meningeal  veins  (Yens  meningeip)  arise  in  capillary  plexuses  in  the  super- 
ficial and  dee])  faces  of  the  dura  mater.  Some  end  in  the  sinuses  of  the  dura, 
others  accompany  the  meningeal  arteries. 

'  These  arc  termed  by  Chauveau  and  M'Fadycan  the  subsphenoidal  confluents. 


VEINS    OF   THE    THORACIC    LIMB 


593 


The  diploic  veins  (\'cnae  diploicse)  are  anastomosing  channels  in  the  sjjongy 
substance  of  the  cranial  bones.  Their  walls  are  thin,  consisting  in  many  places 
only  of  the  endothelium,  and  they  have  no  valves.  Some  open  inwaril  into 
venous  sinuses,  others  into  extracranial  veins. 


Spinai.  Veins 
Two  longitudinal  spinal  veins  or  sinuses  (Sinus  columnse  vertebralis)  extend 
along  the  floor  of  the  vcrtci)ral  canal,  one  on  either  side  of  the  superior  common 
ligament.  They  are  continuous  in  front  with  the  basilar  plexus.  Thej'  lie  in  the 
grooves  on  the  bodies  of  the  vcrtel.irie  and  are  connected  by  a  series  of  transverse 
anastomoses  which  pass  between  the  central  jDart  of  the  iDodies  of  the  vertebrje 
and  the  superior  common  ligament  or  in  channels  in  the  bone.  They  receive  veins 
from  the  spinal  cord,  the  dura  mater,  and  the  bodies  of  the  vertebra'  (X'ense  basis 
vertebrae).  Through  the  intervertebral  foramina 
efferent  vessels  connect  with  the  vertebral,  inter- 
costal, lumbar,  and  lateral  sacral  veins. 


V^^ 


VEINS  OF  THE  THORACIC  LIMB 

The  brachial  vein  (V.  brachialis)  is  a  satellite 
of  the  extrathoracic  part  of  the  brachial  artery. 
It  arises  at  the  inner  side  of  the  distal  end  of  the 
shaft  of  the  humerus  and  passes  upward  in  the 
arm  behind  the  artery  under  cover  of  a  layer  of 
fascia  and  the  posterior  superficial  pectoral  mus- 
cle. At  the  shoulder  it  is  ventral  to  the  artery, 
crosses  the  anterior  border  of  the  first  rib,  and 
concurs  with  its  fellow  and  the  two  jugulars  in 
the  formation  of  the  anterior  vena  cava.  The 
roots  of  the  vein  are  somewhat  variable,  but  most 
often  four  radial  veins  in  addition  to  a  large  ob- 
liriue  branch  from  the  cephalic  unite  in  its  forma- 
tion. Its  tributaries  correspond  in  general  to  the 
branches  of  the  artery,  but  a  few  differences  are 
worthy  of  notice.  The  thoracico-dorsal  vein 
joins  the  brachial  directly  or  opens  into  the  deep 
brachial.  The  external  thoracic  or  "spur"  vein 
(V.  thoracica  externa)  is  a  large  vessel  which 
arises  in  the  ventral  wall  of  the  abdomen,  passes 
forward  (embedded  more  or  less  in  the  panniculus) 

along  the  outer  border  of  the  posterior  deep  pectoral  muscle,  and  joins  the  brachial 
vein  near  the  first  rib.     It  often  communicates  with  the  subscapular  vein. 

The  cephalic  vein  (V.  cephalica)  arises  at  the  inner  side  of  the  carpus  as  the 
continuation  of  the  internal  superficial  metacarpal  vein.  It  runs  upward  on  the 
deep  fascia  of  the  forearm  at  first  in  the  furrow  between  the  flexor  carpi  internus 
and  the  radius.  Toward  the  middle  of  the  forearm  it  inclines  gradually  forward 
on  the  inner  surface  of  the  radius,  accompanied  by  a  cutaneous  branch  of  the  median 
nerve,  and  arrives  at  the  insertion  of  the  biceps.  Here  it  detaches  a  large  branch 
(Ramus  communicans)  which  passes  upward  and  backward  over  the  inner  insertion 
of  the  biceps,  the  posterior  radial  artery,  and  the  median  nerve,  and  joins  the  lira- 
chial  vein.  The  vein  to  this  point  is  often  termed  the  internal  subcutaneous  vein  of 
the  forearm  (V.  cephalica  antebrachii).  It  is  continued  (as  the  V.  cephalica 
humeri)  in  the  furrow  between  the  mastoido-humeralis  and  the  anterior  superficial 
pectoral  with  a  branch  of  the  inferior  cervical  artery,  crosses  the  deep  face  of  the 
38 


Fig.  465. — .Spinal  Vessels  of  Horse. 
The  vertebral  canal  has  been  oj>ene(l 
by  sawing  off  the  arches.  The  ner\'e- 
roots  are  cut  on  one  side  and  the  spinal 
cord  turned  over  to  right.  7,  Ventral 
or  middle  spina!  artery;  2.  reinforcing 
branches  from  vertebral,  intercostal,  or 
lumbar  arteries  (according  to  region):  ^, 
longitudinal  vertebral  sinuses;  a.  ventral 
surface  of  spinal  cord;  6,  dura  mater  (cut); 
f.  nerve-roots;  d.  superior  common  liga- 
ment. (.\fter  Ellenberge--,  in  Leisering's 
.\tlas.) 


594 


THE    VEINS 


corvical  panniculus,  and  opens  into  the  terminal  part  of  the  jugular  or  the  brachial 
vein.  It  receives  an  accessory  cephalic  vein  (^^  cephalica  accessoria),  which  arises 
from  the  carpal  network,  runs  upward  along  the  inner  border  of  the  extensor  carpi, 


Fifi.    460  — l)lS.Sl.f  TiON    OF    PliCTORAL    ReGION    AND    ANTtRIOR    TaRT    OF    AUUOMINAL    WaI.L    OF    lloRSE. 

1,  Jugular  vein;  S,  loose  connective  tissue  of  axillary  space;  S,  ascending  branch  of  inferior  cervical  artery; 
4,  descendiuK  branch  of  same;  6.  cephalic  vein;  6.  median  nerve;  7.  ulnar  nerve;  8,  brachial  artery;  0,  brachial 
vein;  10,  external  thoracic  or  "spur"  vein;  11,  anterior  abdominal  artery  and  vein;  IS,  branches  of  sixth  cervical 
nerve;  IS,  cutaneous  branch  of  axillary  nerve;  14,  cutaneous  branch  of  musculo-cutaneous  nerve;  IB,  cervical 
panniculus;  W.  sterno-cephalicus;  17,  scalenus;  IS,  mastoido-humeralis;  19,  anterior  superficial  pectoral;  SO, 
posterior  superficial  pectoral:  2/,  anterior  deep  pectoral;  23.  posterior  deep  pectoral;  .85,  abdominal  panniculus; 
94,  obliquus  abdominis  externus;  5.5,  rectus  abdominis:  SB,  coraco-brachialis;  27,  tensor  fascise  antibrachii; 
a,  preacapular  lymph  glands;  b,  prepectoral  lymph  glands;  r.  axillary  lymph  glands;  d,  cubital  lymph  glanda; 
ex.,  xiphoid  carlilage.     (.\fter  Schmaltz,  .Vtlas  d.  .\nat.  d.  Pferdes.) 


turns  along  the  lower  border  of  ttie  l)rachialis,  passes  under  the  superficial  tendon 
of  the  biceps  and  joins  the  cephalic. 


THE    POSTERIOR    VENA    CAVA  595 

The  deep  veins  of  the  fore;inn  are  variable.  Commonly  two  posterior  radial 
veins  (^'enae  medianoradiales)  accompan.y  the  artery  of  like  name,  one  in  front 
and  one  behind.  A  thirtl  vein  arises  by  ratlicles  emerging  from  the  proximal  part 
of  the  deep  flexor;  it  joins  the  posterior  satellite  of  the  posterior  radial  artery 
or  forms  one  of  the  roots  of  the  bracliial  vein.  The  conunon  interosseous  vein 
joins  the  posterior  satellite.  The  anterior  radial  vein  (\'.  coUateralis  radialis)  is 
a  satellite  of  the  artery.  The  ulnar  vein  is  usually  double  at  its  proximal  part, 
and  communicates  with  the  deep  l>rachial  vein. 

There  are  three  chief  metacarpal  veins.  The  internal  metacarpal  vein  {\. 
metacarpea  volaris  superficialis  nicdialis)  arises  from  the  volar  ^•(■nous  arch  above 
the  fetlock.  It  is  the  largest  vein  of  the  region  and  lies  in  front  of  the  large  meta- 
carpal artery.  It  separates  from  the  artery  at  the  proximal  end  of  the  metacarpus, 
passes  upward  on  the  inner  part  of  the  posterior  surface  of  the  carpus,  under  cover 
of  the  superficial  layer  of  the  posterior  annular  ligament,  and  is  continued  as  the 
cephalic  vein.  It  communicates  at  its  proximal  part  with  the  origin  of  the  posterior 
radial  veins  by  a  short  but  relatively  large  branch.  The  external  metacarpal  vein 
(V.  metacarpea  volaris  superficialis  lateralis)  arises  from  the  venous  arch  alcove  the 
fetlock  and  passes  upward  behind  the  external  border  of  the  suspensory  ligament 
in  front  of  the  external  branch  of  the  median  ner^■e  and  accompanied  by  a  small 
artery.  At  the  proximal  end  of  the  metacarpus  it  is  connected  with  the  deej)  meta- 
carpal vein  by  two  transverse  anastomoses  which  pass  across  the  suspensory  liga- 
ment. It  then  passes  upward  as  a  satellite  of  the  external  volar  metacarjaal  artery 
and  concurs  in  the  origin  of  the  ulnar  and  posterior  radial  veins.  The  deep  meta- 
carpal vein  (V.  metacarpea  volaris  profunda  medialis)  arises  from  the  venous  arch, 
passes  forward  between  the  two  branches  of  the  suspensory  ligauient,  and  ascends 
on  the  posterior  surface  of  the  large  metacarpal  bone.  At  the  proximal  end  of  the 
latter  it  communicates  with  the  other  metacarpal  veins,  ascends  with  the  small 
metacarpal  artery,  and  concurs  in  forming  the  radial  veins. 

The  venous  arch  (Arcus  venosus  volaris) ,  from  which  the  metacarpal  veins  arise, 
is  situated  above  the  sesamoids  of  the  fetlock  between  the  susjiensorj-  ligament 
and  the  deep  flexor  tendon.     It  is  formed  by  the  junction  of  the  two  digital  veins. 

The  digital  veins,  internal  and  external  (V.  digitalis  medialis,  lateralis), 
drain  the  venous  plexuses  of  the  foot.  They  arise  at  the  upper  edge  of  the  lateral 
cartilages  and  ascend  in  front  of  the  corresponding  arteries. 

It  is  convenient  to  recognize  the  following  venous  plexuses  of  the  foot,  which, 
however,  communicate  very  freely: 

1.  The  coronary  plexus  encircles  the  upper  part  of  the  foot.  It  is  attached 
to  the  terminal  ])art  of  the  extensor  tendon,  the  lateral  cartilages,  and  the  bulbs 
of  the  plantar  cushion. 

2.  The  dorsal  (or  laminal)  plexus  covers  the  dorsal  or  wall  surface  of  the  third 
phalanx  in  the  deep  layer  of  the  matrix  of  the  wall  of  the  hoof.  It  forms  the  cir- 
cumflex vein  of  the  third  phalanx  or  vein  of  the  distal  border  of  the  third  jihalanx, 
which  corresponds  to  the  artery  of  like  name. 

3.  The  volar  plexus  is  in  the  deep  layer  of  the  matrix  of  the  sole  of  the  hoof 
and  on  the  deep  surface  of  the  lateral  cartilages.  It  communicates  around  the 
inferior  border  of  the  third  phalanx  with  the  dorsal  plexus  and  through  the  lateral 
cartilages  with  the  coronary  plexus. 

The  deep  vein  of  the  third  phalanx  accompanies  the  terminal  part  of  the  digital 
artery.     It  drains  the  intraosseous  plexus. 

THE  POSTERIOR  VENA  CAVA  (Figs.  270.  450) 
The  posterior  vena  cava  (V.  cava  caudalis)  returns  almost  all  of  the  blood  from 
the  abdomen,  pelvis,  and  pelvic  limbs.     It  is  formed  by  the  confluence  of  the  right 


596  THE    VEINS 

anil  left  fonmiou  iliac  veins  at  the  fifth  lumbar  vertebra,  above  the  terminal  part 
of  the  aorta  and  ehiefiy  to  the  right  of  the  median  plane. 

The  moJe  of  origin  is  variable.  In  some  cases  there  is  a  common  trunk  formed  hy  the 
union  of  the  two  internal  iliac  veins  so  that  the  arrangement  resembles  the  termination  of  the 
aorta.     In  other  cases  the  internal  iliac  vein  does  not  exist. 

It  passes  forward  on  the  ventral  face  of  the  psoas  minor  to  the  right  of  the 
abdominal  aorta.  At  the  last  thoracic  vertebra  it  separates  from  the  aorta  and 
runs  forward  between  the  right  crus  of  the  diaiihragm  and  the  pancreas  till  it 
reaches  the  liver.  Here  it  inclines  downward  along  the  inner  border  of  the  right 
lobe  antl  the  parietal  surface  of  the  liver,  largely  emliedded  in  the  gland  substance, 
and  passes  through  the  foramen  veme  cavtt  of  the  diaphragm.  It  then  runs  for- 
ward and  somewhat  downward  between  the  mediastinal  lobe  and  the  main  mass 
of  the  right  lung  at  the  upper  margin  of  a  special  fold  of  the  right  pleura,  accom- 
panied by  the  right  phrenic  nerve,  and  opens  into  the  posterior  part  of  the  right 
atriinn.     It  receives  the  following  tributaries: 

1.  The  lumbar  veins  (Vv.  lumbales)  correspond  to  the  arteries.  Five  pairs 
usually  empty  into  the  vena  cava.  Sometimes  the  corresponding  veins  of  opposite 
sides  unite  to  form  a  commoii  trunk.     The  first  communicate  with  the  vena  azygos. 

2.  The  spermatic  veins  (Vv.  spermatica?  internee)  (Fig.  450)  accompany  the 
arteries  of  like  name.  In  the  spermatic  cord  they  form  the  pampiniform  plexus 
about  the  artery  and  nerves.  Their  termination  is  variable.  The  right  one  com- 
monly joins  the  vena  cava  near  the  renal  vein,  often  by  a  common  trunk  with  the 
left  one.  Frequently  the  left  vein  joins  the  left  renal,  and  sometimes  the  right 
one  ends  similarly. 

2«.  The  utero-ovarian  veins  are  much  larger  than  the  jjreceding  and  are 
satellites  of  the  arteries  in  the  broad  ligaments.  The  ovarian  branch  is  plexiform 
near  the  ovary.  The  uterine  branches  form  a  rich  plexus  in  the  wall  of  the  uterus. 
The  trunk  is  very  short. 

3.  The  renal  veins  (Vv.  renales),  satellites  of  the  arteries,  are  of  large  calilier 
and  thin-walled.  The  right  veiii  passes  inward  and  backward  on  the  ventral  face 
of  the  kidney  between  the  artery  in  front  and  the  ureter  behind.  It  joins  the  vena 
cava  above  the  right  adrenal.  The  left  vein  is  somewhat  longer.  It  passes  inward 
at  first  like  the  right  one,  then  bends  around  the  posterior  end  of  the  adrenal,  crosses 
the  origin  of  the  renal  artery  and  opens  into  the  vena  cava  a  little  further  back  than 
the  right  one.  They  receive  veins  from  the  adrenals,  but  some  adrenal  veins  open 
directly  into  the  vena  cava. 

4.  The  hepatic  veins  (Vv.  hepaticae)  return  the  blood  from  the  liver,  and  open 
into  the  vena  cava  as  it  lies  in  the  groove  in  the  liver.  Three  or  four  large  vessels 
open  into  the  vena  cava  just  before  it  leaves  the  liver,  and  numerous  small  ones 
discharge  into  its  embedded  part. 

5.  The  phrenic  veins  (Vv.  phrenicse),  two  or  three  in  number,  return  the  blood 
from  the  diaphragm.  They  are  very  large  in  comparison  with  the  arteries,  and 
join  the  vena  cava  as  it  lies  in  the  caval  opening. 

In  some  cases  there  is  a  small  middle  sacral  vein  (V.  sacralis  mejiia),  a  satellite  of  the  artery. 
It  opens  into  the  angle  of  junction  of  the  common  iliac  veins  or  into  One  of  the  latter. 

THE  PORTAL  VEIN 
The  portal  vein  (V.  portse)  is  a  large  tnmk  which  returns  the  blood  carried  to 
the  viscera  by  the  gastric,  splenic,  and  mesenteric  arteries.  Its  peripheral  tribu- 
taries correspond  closely  with  the  branches  of  the  arteries,  but  the  terminal  trunks 
do  not.  The  vein  is  formed  Ijehind  the  ixuicreas  and  below  the  posterior  vena  cava 
by  the  confluence  of  the  anterior  and  posterior  mesenteric  and  splenic  veins.  It 
passes  forward,  traverses  the  iiosterior  part  of  the  pancreas  very  obliquely,  inclines 


THE    COMMON    ILIAC    VEINS — THE    VEINS    OF   THE    PELVIC    LIMB  597 

ventrally  and  a  little  to  the  right,  and  reaches  the  portal  fissure  of  the  liver.  Here  it 
divides  into  three  branches  which  enter  the  liver  and  ramify  in  the  substance  of 
the  gland  like  an  artery,  terminating  in  the  lobular  capillaries.  From  the  lobules 
the  blooil  passes  into  the  hepatic  veins  and  through  these  to  the  posterior  vena 
cava.  Thus  the  blood  which  is  distributed  to  the  stomach,  nearly  the  entire  in- 
testinal tract,  the  pancreas,  and  the  spleen,  passes  through  two  sets  of  capillaries 
prior  to  its  return  to  the  heart,  viz.,  the  capillaries  of  these  viscera  and  of  the  liver. 

1.  The  anterior  mesenteric  vein  (V.  mesent erica  cranialis)  is  the  largest  of 
the  portal  radicles.  It  is  situated  to  the  right  of  the  artery  of  like  name,  and  its 
tributaries  correspond  in  general  to  the  branches  of  the  artery.  Usuallj'  a  single 
colic  vein  corresponds  to  the  two  arteries  of  the  right  portions  of  the  colon. 

2.  The  posterior  mesenteric  vein  (V.  mesentcrica  caudalis)  is  the  smallest  of 
the  radicles  of  the  portal.  It  accompanies  the  artery  in  the  colic  mesentery  and  its 
rectal  branches  anastomose  with  those  of  the  internal  pudic  vein. 

3.  The  splenic  vein  (\'.  lienalis)  is  the  very  large  satellite  of  the  splenic  arterj'. 
It  is  formed  by  the  union  of  two  radicles  at  the  base  of  the  spleen.  On  leaving  the 
hilus  of  the  spleen  it  passes  inward  between  the  anterior  pole  of  the  left  kidney  and 
the  saccus  ciBcus  of  the  stomach  and  above  the  left  end  of  the  pancreas,  receives 
commonly  the  posterior  gastric  vein  (^'.  gastrica  caudalis),  and  unites  with  the 
anterior  mesenteric  at  the  posterior  border  of  the  pancreas. 

The  collateral  tributaries  of  the  portal  veins  are  as  follows: 

(1)  Pancreatic  veins  (Rami  pancreatici). 

(2)  Tiie  gastro-duodenal  vein  (^'.  gastroduodenalis)  corresponds  mainly  to  the 
extrahepatic  Ijranchcs  of  the  hepatic  artery. 

(3)  The  anterior  gastric  vein  (\'.  gastrica  cranialis)  joins  the  portal  at  the 
portal  fissure. 

THE  COMMON  ILIAC  VEINS  (Fig.  456) 
These  (V.  iliacse  communes)   are  two  very  large  but  short  trunlcs  which  result 
from  the  union  of  the  internal  and  external  iliac  v-eins  of  each  side  at  the  sacro- 
iliac articulation.     The  left  one  is  the  longer  and  crosses  obliquely  over  the  terminal 
part  of  the  aorta.     The  chief  tributaries  of  each  are  as  follows: 

1.  The  last  lumbar  vein. 

2.  The  circumflex  iliac  veins  (A'v.  circumflexEe  ilium  profundae)  are  the  two 
satellites  of  each  corresponding  artery,  on  either  side  of  which  they  are  placed. 
They  may  open  directly  into  the  posterior  vena  cava  or  into  the  external  iliac  vein. 

3.  The  ilio-lumbar  vein  (^^  iliolumbalis)  may  open  into  the  common  iliac, 
the  external  iliac,  or  the  internal  iliac  vein. 

THE  INTERNAL  ILIAC  VEINS 
The  internal  iliac  or  hypogastric  veins  (\\\  h\-pogastricie),  right  and  left,  are 
usually  formed  by  the  confluence  of  lateral  sacral,  gluteal,  and  internal  pudic 
veins.  The  obturator  vein  may  open  into  them  also.  They  are  short  trunks  and 
are  smaller  than  the  external  iliac  veins.  The  tributaries  correspond  in  general  to 
the  branches  of  the  three  arteries  of  like  names.  The  interna!  pudic  veins  receive 
affluents  from  the  venous  plexuses  of  the  prepuce  and  penis  in  the  male;  of  the 
mammarj'  gland,  vulva,  vagina,  and  vestibular  bulb  in  the  female. 

THE  VEINS  OF  THE  PELVIC  LIMB 
The  external  iliac  vein  (V.  iliaca  ex-terna)  (Figs.  4.50.  4.51)  lies  behind  the  cor- 
responding artery  at  the  brim  of  the  pelvis.     It  is  the  upward  continuation  of  the 
femoral  vein,  and  unites  at  the  sacro-iliac  joint  with  the  internal  iliac  to  form  the 
common  iliac  vein.     Its  tributaries  are  as  follows: 


598  THE    VEINS 

1.  The  obturator  vein  (V.  obturatoria)  is  a  satellite  of  the  artery  and  usually 
opens  into  the  external  iliae  at  the  insertion  of  the  psoas  minor.  Its  radicles 
anastomose  with  those  of  tlie  internal  and  external  pudie  veins  (Figs.  451,  455). 

2.  The  iliaco-femoral  or  external  circumflex  veins  {\v.  circumflexse  femoris 
laterales)  are  the  two  satellites  of  the  homonymous  artery.  They  open  a  little 
higher  than  the  obturator. 

The  femoral  vein  (Figs.  450,  451)  lies  behind  the  artery  in  the  upper  part  of 
the  thigh,  external  to  it  lower  down.     Its  chief  tributaries  are: 

1.  A  very  large  but  short  trunk  formed  by  the  union  of  the  deep  femoral  and 
the  external  pudic  vein.  The  deep  femoral  vein  (V.  profunda  femoris)  corresponds 
otherwise  to  the  artery.  The  external  pudic  vein  (V.  pudenda  externa)  arises 
chiefly  from  a  rich  plexus  of  large  veins  situated  above  and  along  the  sides  of  the 
penis  and  prepuce  in  the  male,  the  mammary  glands  in  the  female.  It  passes 
through  a  foramen  in  the  anterior  part  of  the  tendon  of  origin  of  the  gracilis  and 
runs  outward  in  the  suljpubic  groove  behind  the  pectineus  to  unite  with  the  deep 
femoral  vein.  The  right  and  left  veins  are  connected  M'  a  large  transverse  anasto- 
mosis and  each  has  a  large  connection  with  the  obturator  vein.  Each  receives 
the  posterior  abdominal  vein  {V.  e]iigastrica  caudalis)  which  accompanies  the  artery 
of  like  name.  The  subcutaneous  abdominal  vein  (V.  abdominalis  subcutanea) 
arises  in  the  skin  and  panniculus  of  the  ventral  abdominal  w-all,  anastomoses  with 
the  internal  and  external  thoracic  and  deep  abdominal  veins,  and  joins  the  external 
pudic  or  posterior  al)dominal  vein. 

A  small  vein  accom])anies  the  external  pudic  artery  in  the  inguinal  canal. 

2.  The  anterior  femoral  vein  (V.  femoris  cranialis)  accompanies  the  artery. 

3.  The  saphenous  vein  (V.  saphena)  (Figs.  451,  458,  400)  arises  at  the  inner 
side  of  the  flexion  surface  of  the  tarsus  as  the  upward  continuation  of  the  internal 
metatarsal  vein.  Its  course  is  distinctly  visible.  It  ascends  on  the  subcutaneous 
surface  of  the  tibia  and  the  popliteus  muscle,  inclosed  between  layers  of  the  deep 
fascia,  inclines  a  little  backward  to  the  proximal  part  of  the  leg,  then  deviates 
slightly  forward,  runs  upward  on  the  gracilis,  passes  betw'een  that  muscle  and  the 
sartorius,  and  joins  the  femoral  or  the  external  pudic  vein.'  On  the  upper  part  of 
the  capsule  of  the  hock  joint  it  forms  an  arch  with  the  anterior  tibial  vein.  The 
vein  has  numerous  valves.  The  satellite  artery  is  relatively  small  and  lies  in 
front  of  the  vein  as  far  as  the  junction  with  tlu^  recurrent  tibial  vein,  which  it  ac- 
companies on  the  leg.  It  receives  the  recurrent  tibial  vein  {V.  recurrens  tibialis)- 
at  the  proximal  fourth  of  the  leg.  This  vessel  arises  at  the  inner  surface  of  the 
tarsus  and  forms  an  arch  with  the  posterior  tibial  vein  at  the  level  of  the  tuber 
calcis.  It  ascends  in  the  furrow  in  front  of  the  gastrocnemius  tendon,  inclines  for- 
ward at  the  proximal  third  of  the  leg,  and  joins  the  saphenous  vein  at  an  acute 
angle.  It  has  numerous  valves.  A  smaller  vein  from  the  anterior  face  of  the 
metatarsus  joins  the  saphenous  at  the  hock. 

4.  Muscular  branches  which  correspond  to  the  arteries. 

5.  The  posterior  femoral  or  femoro-popliteal  vein  (V.  femoris  caudalis)  is  a 
satellite  of  the  artery.  It  receives  the  recurrent  tarsal  or  external  saphenous  vein 
(V.  tarsea  recurrens),  which  arises  at  the  outer  side  of  the  lioek,  ascends  on  the 
deep  fascia  of  the  external  surface  of  the  leg  in  front  of  the  tentlo  Achillis,  passes 
between  the  biceps  femoris  and  semitendinosus,  and  joins  the  posterior  femoral 
vein.  It  is  connected  with  the  recurrent  tibial  vein  bj^  a  large  anastomotic  branch 
which  crosses  in  front  of  the  tuber  calcis.  I'sually  a  branch  from  it  ascends  along 
the  great  sciatic  nerve  and  anastomoses  with  the  obturator  vein. 

'The  placo  and  mode  of  termination  is  quite  variable.  It  may  disappear  from  the  surface 
of  Ihe  thisli  at  any  point  above  the  distal  third.  In  some  cases  it'pa-sscs  through  the  anterior 
pari  of  the  gracilis  instead  of  dipping  in  between  that  muscle  and  the  sartorius. 

•  This  often  joins  the  posterior  femoral  or  the  popliteal  vein. 


THE    LYMPHATIC    SYSTEM  599 

The  popliteal  vein  (\'.  poplitea)  lies  along  the  inner  side  of.  the  artery  (Fig. 
459).     It  is  fornu'd  liy  the  confluence  of  anterior  and  posterior  tibial  veins. 

Two  anterior  tibial  veins  (\'v.  tibiales  anteriores)  usually  accompany  the  artery 
of  like  name;  tlie  outer  vein  is  much  the  larger.  In  other  cases  there  is  a  single 
large  vein  in  the  proximal  part  of  the  leg,  two  lower  down.  They  arise  from  a 
number  of  anastomosing  radicles  on  the  front  of  the  capsule  of  the  hock  joint, 
chiefly  as  the  continuation  of  the  perforating  tarsal  vein.  The  origin  of  the  chief 
vein  is  connected  with  the  saphenous  by  a  large  anastomotic  branch. 

The  posterior  tibial  vein  (V.  tibialis  posterior)  is  commonly  double  (Fig.  458). 
It  arises  at  the  level  of  the  tuber  calcis,  where  it  has  a  communication  with  the 
recurrent  titiial  vein.     It  is  a  satellite  of  the  artery 

The  internal  or  great  metatarsal  vein  {\.  metatarsea  dorsalis  medialis)  (Figs. 
458,  460)  arises  from  the  venous  arch  above  the  sesamoids  at  the  fetlock,  but  is 
practically  the  upward  continuation  of  the  internal  digital  vein.  It  ascends  along 
the  inner  border  of  the  deep  flexor  tendon,  then  in  the  groove  on  the  inner  aspect 
of  the  proximal  part  of  the  large  metatarsal  bone  to  the  capsule  of  the  hock  joint, 
and  is  continued  by  the  saphenous  vein. 

The  external  metatarsal  vein  (V.  metatarsea  plantaris  lateralis)  arises  from 
the  venous  arch  aliove  the  fetlock,  but  appears  to  be  the  upward  continuation  of 
the  external  digital  vein.  It  ascends  along  the  outer  border  of  the  deep  flexor 
tendon  in  front  of  the  jilantar  nerve,  and  is  connected  with  the  deep  metatarsal 
vein  at  the  proximal  part  of  the  metatarsus  by  a  transverse  branch.  It  then  passes 
upward  along  the  deep  flexor  tendon  in  relation  to  the  plantar  nerves  and  the  inner 
tarsal  artery  and  is  continued  by  the  recurrent  tibial  vein. 

The  deep  metatarsal  vein  (V.  metatarsea  plantaris  medialis)  arises  from  the 
plantar  venous  arch,  passes  forward  between  the  branches  of  the  suspensory  liga- 
ment, and  ascends  on  the  posterior  face  of  the  large  metatarsal  bone.  At  the  proxi- 
mal end  of  the  metatarsus  it  is  connected  with  the  external  metatarsal  vein  b}^  a 
transverse  branch.  It  then  passes  (as  the  perforating  tarsal  vein)  through  the 
vascular  canal  of  the  tarsus  and  forms  the  chief  radicle  of  the  anterior  tibial  vein. 

The  plantar  venous  arch  (Arcus  venosus  plantaris)  and  the  digital  veins  are 
arranged  like  those  of  the  thoracic  limb. 


The  Lymphatic  System 

The  lymphatic  system  (Systema  Ij-mphaticum)  is  subsidiary  to  the  venous 
part  of  the  circulatory  system,  from  which  it  arises  in  the  embryo.  It  consists  of 
the  lymph  vessels  and  glands. 

The  lymph  vessels  (Vasa  lymphatica)  contain  a  colorless  fluid,  the  l.ymph, 
which  contains  numerous  lymphocytes.'  The}'  resemble  the  veins  in  structure 
but  have  thinner  walls  and  are  provided  with  more  numerous  valves.  The  vessels 
are  sacculated  opposite  the  segments  of  the  valves  and  have  a  characteristic  beaded 
appearance  when  distended.  The  collecting  IjTiiph  vessels  do  not  usually  form  rich 
plexuses,  as'veins  often  do,  their  branching  is  more  limited  and  less  tree-like  than 
that  of  the  blood-vessels,  and  their  caliber  therefore  increases  less  from  the  periphery 
toward  their  termination.  All  of  the  lymph  is  ultimately  carried  into  the  venous 
system  by  two  trunks,  the  thoracic  duct  and  the  right  lymphatic  duct.  Almost  all 
of  the  lymph  passes  through  at  least  one  group  of  lymph  glands  before  entering  the 
blood-vascular  system. 

The  lymph  glands  or  nodes  (Lymphoglandulse)  are  intercalated  in  the  course 
of  the  lymph'  vessels.     They  vary  widely  in  size,  some  being  microscopic,  others 

'  The  term  chyle  is  often  applied  to  the  lymph  carried  by  the  efferent  vessels  of  the  intestine 
when  it  contains  products  of  digestion,  and  these  vessels  may  be  designated  as  lacteals  or  chyle 


600  THE    ^'EINS 

several  inclics  in  length.  In  form  tliey  may  bo  globular,  ovoid  and  flattened, 
elongated,  or  irregular.  In  certain  situations  they  are  aggregated  into  groups,  and 
a  knowledge  of  the  position  of  these  and  the  territory  drained  into  them  is  im- 
portant. It  is  convenient,  when  possible,  to  indicate  their  position  with  regard  to 
arteries  on  the  course  of  which  they  are  placed.  In  color  they  are  usually  gra>-  or 
yellowish-brown  in  the  dead  subject,  pink  or  reddish-brown  during  life,  but  this 
varies  according  to  their  position  and  functional  state.  The  bronchial  glands 
arc  often  blackened  by  infiltration  with  carbon.  The  mesenteric  glands  are  creamy 
or  white  while  the  chyle  is  passing  through,  but  pink  at  other  times.  Vessels 
which  carry  lymph  to  a  gland  are  called  afferent;  the  efferent  vessels  which  convey 
it  away  are  larger  and  fe\\er.  Each  gland  has  a  depression,  the  hilus,  at  which  the 
blood-vessels  enter  and  the  cfTerent  lymph  vessels  emerge. 

Lymph  nodules  or  follicles  (Noduli  lymphatici)  are  minute  masses  of  lymphoid 
tissue  which  occur  in  certain  mucous  membranes.  They  may  be  solitary,  as  in  the 
solitary  glands  of  the  intestine,  or  aggregated  into  masses  or  patches,  as  in  the  tonsils 
and  the  so-called  Peyer's  patches. 

The  lymph  nodule  or  follicle  is  thp  unit  of  structure  of  the  lymph  gland.  It  consists 
essentially  of  an  artery  surrounded  by  a  reticulum  of  connective  tissue,  the  meshes  of  which 
contain  numerous  lymphocytes.  Smroiuiding  this  i.s  a  rich  plexus  of  lymph  vessels,  forming  the 
so-called  sinus,  iiicldsr.l  in  soiiio  cases  by  a  fibrous  capsule.  The  gland  consists  of  a  mass  of 
follicles,  inclosed  in  a  lihrous  capsule,  from  which  trabeculae  pass  in  and  unite  the  follicles.  Be- 
neath the  capsule  i>  llir  peripheral  sinus,  wliich  consists  of  a  very  rich  plexus  of  lymph  vessels; 
to  this  the  afferent  vessels  pa.ss  at  various  points  of  the  surface.  In  the  cortical  substance  the 
cells  are  in  rounded  masses,  the  cortical  nodules,  while  in  the  medullary  substance  they  lie 
around  the  arteries,  forming  the  so-called  medullary  cords.  The  medulla  is  redder  than  the  cor- 
tex, since  it  is  more  vascular;  it  contains  the  central  lymph  sinuses,  which  have  a  similar  structure 
to  the  peripheral  sinu.s. 

The  haemolymph  glands  dift'cr  from  the  lymjah  glands  in  color  and  structure. 
They  are  of  a  deep  red  color,  which  is  due  to  the  high  vascularity  of  the  cortical 
substance.  The  peripheral  sinuses  especially  are  greatly  developed  and  contain 
numerous  red  blood-cells.  There  is  no  clear  division  into  cortical  and  medullary 
substance,  and  the  trabeculae  contain  smooth  muscle-cells.  Some  have  afferent 
and  efferent  lymph  vessels  and  others  do  not.  They  resemble  the  spleen  in  some 
respects,  but  their  significance  is  not  yet  clear.  They  are  numerous  in  the  ox  and 
sheep,  nmch  fewer  in  the  dog,  and  apparently  are  alisent  in  the  horse.  The^^  occur 
along  the  course  of  the  aorta,  in  the  perineal  fat,  at  the  portal  fissure,  and  with 
the  gastric  anil  mesenteric  lymph  glands.  In  the  ox  they  are  also  found  under  the 
trapezius  muscle,  under  the  skin  of  the  ujjpcr  part  of  the  flank,  and  in  other  places 
less  constantly. 

The  tissue  or  lymph  spaces  are  interstices  of  varying  size  between  cells  or 
in  the  meshes  of  connective  tissue.  They  contain  a  fluid  derived  from  the  blood- 
plasma,  which  is  usually  called  lymph.  They  are  drained  bj'  the  veins  and  lyiniih 
vessels.     The  large  serous  sacs  are  often  included  in  this  category-. 

The  exact  relationship  be  tween  the  lymphatic  capillaries  and  the  tissue  spaces  is  still  a  matter 
of  controversy.  It  is  held  by  some  that  the  lymph-ves.sels  are  in  direct  communication  with  the 
tissue  spaces,  while  others  maintain  that  the  lymphatics  are  complete  closed  tubes.  Communi- 
cation between  I  he  s|i:n  is  and  \  csscls  is  in  general  very  free.  Mall  has  shown  that  granules  in- 
jected into  till-  liipaii.'  .iitiiv  ill-.'  Kiurned  by  the  lymphatics  as  well  as  by  the  veins,  and  intra- 
muscular injeetiuiis  will  enter  I  he  lymph-vessels  of  the  tendon  in  spite  of  the  absence  of  lymphatics 
in  muscle. 


Lymphatic  System  of  the  Horse 

THE  THORACIC  DUCT    (Figs.  428,  429) 
The  thoracic  duct(Ductus  tlioracicus)is  the  chief  collecting  trunk  of  the  lymi)h- 
atic  .s.ystem.     It  l>egins  as  an  elongated  irregular  dilatation,  the  cistema  or  recepta- 
culumchyli,  which  is  situated  between  the  right  side  of  the  aorta  ami  the  right  itus 


THE  LYMPH  GLANDS  AND  VESSELS  OF  THE  HEAD  AND  NECK        GOl 

of  the  diaphragm  at  the  first  and  second  huiil)ar  vcitihne.  The  ihict  enters  the 
thorax  through  the  hiatus  aorticus  and  runs  forward  on  the  riglit  of  the  median 
plane  between  the  vena  azygos  and  the  aorta,  covered  by  the  pleura.  At  the  sixth 
or  seventh  thoracic  vertebra  it  inclines  somewhat  ventrally,  crosses  obliciucly  over 
the  left  face  of  the  esophagus,  and  passes  forward  on  the  left  side  of  the  trachea 
to  the  inlet  of  the  thorax.  The  extrathoracic  terminal  part  passes  downward  and 
forward  a  variable  ilistance  (3  to  4  cm.)  on  the  deep  face  of  the  left  scalenus  muscle, 
bends  inward  and  backward  under  the  bicarotid  trunk,  and  opens  into  the  ujijier 
part  of  the  origin  of  the  anterior  vena  cava  just  liehind  the  angle  of  junction  of  the 
jugular  veins.  The  terminal  bend  is  ampuUate  and  sometimes  divides  into  two 
very  short  branches  which  open  close  together. 

Since  the  duct  develops  from  a  plexus  of  ducts  in  the  embryo,  considerable  variation  from 
the  more  usual  course  occurs.  There  is  often  a  left  duct  which  arises  at  tfie  cisterna  or  at  a 
varialile  point  from  the  right  duct,  runs  across  the  left  intercostal  arteries  parallel  to  tlie  latter, 
and  unites  with  it  over  the  base  of  the  heart  or  further  forward.  The  two  are  connected  bj 
cross-branches.  In  some  cases  the  left  duct  is  the  larger,  and  there  may  indeed  be  none  on  the 
right  side.     Other  variations  are  common. 

The  chief  tributaries  of  the  thoracic  duct  are  as  follows: 

1.  The  two  lumbar  trunks  (Trunci  lumbales)  are  formed  liy  the  confluence 
of  the  efferent  ducts  of  the  lumbar  glands,  and  commonly  unite  with  each  other 
and  with  the  posterior  intestinal  trunk  before  opening  into  the  cistern. 

2.  The  intestinal  trunks  (Trunci  intestinales),  two  or  three  in  number,  receive 
the  efferents  of  the  Ij'mph  glands  of  the  intestine,  stomach,  liver,  and  spleen.' 

In  its  course  through  the  thorax  the  thoracic  duct  receives  efferents  from  the 
intercostal,  mediastinal,  and  bronchial  glands.  At  the  thoracic  inlet  it  is  joined  bj- 
ducts  from  the  prepectoral  and  right  axillarj'  glands,  and  by  the  left  tracheal  duct. 
The  duct  is  provided  v/ith  several  pairs  of  valves;  the  best  developed  are  at  its 
termination. 

THE  RIGHT  LYMPHATIC  DUCT 
This  vessel  (Ductus  lymphaticus  dexter) — when  present — collects  the  lymi)h 
from  the  right  side  of  the  head,  neck,  and  thorax,  and  from  the  right  thoracic  limb. 
It  is  most  frequently  absent,  being  represented  by  a  number  of  short  ducts  which 
terminate  in  the  thoracic  duct,  the  right  jugulo-brachial  junction,  or  the  origin  of 
the  anterior  vena  cava.  When  present  in  its  typical  form,  it  results  from  the 
confluence  of  efferent  ducts  from  the  right  axillary  and  prepectoral  lymph  glands 
with  the  right  tracheal  duct.  It  lies  on  the  deep  face  of  the  scalenus  muscle  above 
the  terminal  part  of  the  right  jugular  vein.  It  is  more  or  less  ampullate  and  usually 
opens  into  the  anterior  vena  cava  to  the  right  of  the  thoracic  duct.  It  may  be 
connected  with  the  latter  by  considerable  anastomoses  and  may  join  it. 

The  duct  is  very  variable  in  form  and  in  regard  to  its  aiTerents.  Often  it  is  a  very  short, 
irregular,  and  bulbous  trunk;  in  some  cases  it  is  about  an  inch  and  a  half  (ca.  3  to  4  cm.)  in  length 
and  receives  the  tracheal  duct  at  its  terminal  bend.  The  lymphatico-venous  connections  here 
need  fiu-ther  study. 


THE  LYMPH  GLANDS  AND  VESSELS  OF  THE  HEAD  AND  NECK 
1.  The  submaxillary  lymph  glands  (Lg.  submaxillares)  (Figs.  437,  462)  are 
arranged  in  two  elongated  groups  in  the  submaxillary  space  along  each  side  of  the 
omo-hyoid  muscles.  The  two  groups  are  in  apposition  in  front  of  the  insertion 
of  these  muscles  and  diverge  posteriorly  in  the  form  of  a  V,  extending  Ijackward 
about  four  or  five  inches  (ca.  10  to  12  cm.).     They  are  covered  by  the  skin  and  a 

'  The  lymph  vessels  of  these  organs  appear  to  vary  considerably  in  their  mode  of  termina- 
tion, and  the  arrangement  needs  further  study.  Some  ducts  from  the  stomach,  liver,  and  spleen 
open  directly  into  the  cistern. 


602  THE    VEINS 

thin  layer  of  fascia  and  panniculus.  and  arc  therefore  palpable.  Anteriorly  they 
are  firmly  attached  to  the  niylo-hyoidci,  but  otherwise  they  are  rather  movable 
in  the  normal  state.  Each  group  is  related  externally  to  the  external  maxillary 
artery  and  the  anterior  belly  of  the  digastricus,  below  to  the  external  maxillary 
vein,  and  above  to  the  lingual  and  sublingual  veins. 

They  receive  afferent  vessels  from  the  lips,  nostrils,  nasal  region,  cheeks,  the 
anterior  part  of  the  tongue,  the  jaws,  the  floor  of  the  mouth,  and  the  greater  part 
of  the  hard  palate  and  nasal  cavity.  The  efferent  vessels  pass  to  the  anterior 
cervical  and  pharyngeal  glands. 

The  superficial  lymph  vessels  of  the  face  converge  to  twelve  to  fifteen  trunks  which  turn 
around  the  lower  liorder  of  the  jaw  with  the  facial  vessels.  Those  of  the  lips  form  plexuses  at 
the  commissures.  The  nasal  mucous  membrane  is  richly  supplied  with  lymph  vessels  which 
accompany  the  veins;  posteriorly  they  communicate  w^th  the  subdural  and  subarachnoid  spaces 
and  send  efferents  to  the  pharyngeal  anti  anterior  cervical  glands. 

2.  The  phaiyngeal  lymph  glands  (Figs.  4.36,  437,  569)  may  consist  of  two 
groups.  One  lies  on  the  lateral  surface  of  the  pharynx  along  the  course  of  the  ex- 
ternal carotid  artery.  These  glands  are  related  externally  to  the  stylo-maxillaris 
and  digastricus  ancl  often  to  the  submaxillary  gland  also,  above  to  the  guttural 
pouch.  Other  glands  (Lg.  retropharyngeales)  are  commonly  found  on  the  guttural 
pouch  along  the  course  of  the  internal  carotid  artery.  They  lie  below  the  artery 
and  are  covered  by  the  aponeurosis  of  the  mastoido-humeralis  and  the  cervical 
end  of  the  submaxillary  gland. 

They  receive  afferent  vessels  from  the  cranium,  the  posterior  part  of  the  tongue, 
the  soft  palate,  pharynx,  guttural  pouch,  larynx,  posterior  part  of  the  nasal  cavity, 
and  efferents  from  the  sulimaxillary  glands. 

3.  The  anterior  cervical  lymph  glands  (Lg.  cervicales  craniales)  are  situated 
chiefly  along  the  course  of  the  common  carotid  artery  in  the  vicinity  of  the  thyroid 
gland,  under  cover  of  the  cervical  angle  of  the  ])arotid  gland.  Some  occur  between 
the  thyroid  and  the  submaxillary  salivary  gland,  others  above  and  partly  upon 
the  thyroid.  They  are  related  deeply  to  the  posterior  part  of  the  larynx,  the 
trachea,  the  thyroid  gland,  and  the  cesophagus;  below  to  the  external  maxillary 
vein  and  the  outer  border  of  the  omo-hyoideus.' 

These  glands  are  variable.  Often  there  are  none  in  front  of  the  thyroid  and  the  group  may 
extend  back  a  considerable  distance  along  the  course  of  the  carotid  artery. 

Their  afferents  are  deep  lymph  vessels  from  the  head,  the  pharynx,  larynx, 
guttural  pouch,  and  thyroid  gland,  and  efferents  from  the  submaxillary  and  pharyn- 
geal glands.     Their  efferent  vessels  go  to  the  middle  and  posterior  cervical  glands. 

4.  The  middle  cervical  lymph  glands  (Lg.  cervicales  mediae)  form  an  inconstant 
group  situated  a  little  in  front  of  the  middle  of  the  neck  on  the  trachea  below  the 
carotid  artery.  The  group  is  usually  small  and  in  some  cases  is  absent,  being 
replaced  by  a  number  of  glands  occurring  at  intervals  along  the  course  of  the  carotid 
artery.  In  other  subjects  the  group  consists  of  several  glands  of  considerable  size. 
They  are  intercalated  in  the  course  of  the  tracheal  lymph  ducts. 

5.  The  posterior  cervical  or  prepectoral  lymph  glands  (Lg.  cervicales  caudales) 
form  a  large  group  below  the  trachea  at  tlie  entrance  to  the  thorax  (Fig.  466). 
They  occupy  the  interstices  between  the  vessels  and  muscles  and  extend  forward  a 
variable  distance  on  the  ventral  aspect  of  the  trachea.  They  are  covered  by  the 
panniculus  and  sterno-cephalicus.  Their  afferent  vessels  come  from  the  head, 
neck,  thorax,  and  thoracic  limb.  They  receive  efferent  ducts  of  the  anterior  and 
middle  cervical,  prescapular,  and  axillary  glands.  Their  efferents  go  to  the  thoracic 
duct  on  the  left,  to  the  right  lymjihatic  duct  on  the  right,  or  open  directly  into  the 
vena  cava. 

6.  The    prescapular    or    superficial    cervical    lymph  glands    (Lg.    cervicales 
'  Abscess  here  can  be  reached  readily  by  an  incision  between  the  vein  and  the  omo-hyoideus. 


THE    LYMPH    GLANDS    AND    VESSELS    OF   THE    THORAX  603 

supcrficiales)  lie  on  the  anterior  border  of  the  anterior  deep  pectoral  muscle,  in 
relation  to  the  omo-hyoideus  internally  and  the  mastoido-humcralis  externally 
(Figs.  431,  441,  46(3).  They  are  on  the  course  of  the  ascending  branch  of  the  in- 
ferior cervical  artery.  They  receive  afferents  from  the  neck,  breast,  shoulder,  and 
arm.     Their  efferents  pass  to  the  prepectoral  glands. 

The  tracheal  ducts,  right  and  left  (Ductus  trachealis  dexter,  sinister),  are  col- 
lecting trunks  for  tlie  lymph  of  the  head  and  neck.  Thej'  lie  on  the  trachea  in 
relation  to  the  carotid  arteries.  The  right  one  goes  to  the  prepectoral  glands  or 
to  the  right  lymphatic  duct,  the  left  one  to  the  terminal  part  of  the  thoracic  duct. 


THE  LYIVIPH  GLANDS  AND  VESSELS  OF  THE  THORAX 

1.  The  intercostal  lymph  glands  (Lg.  intercostales)  are  small  and  are  situated 
at  the  sides  of  the  bodies  of  the  thoracic  vertebrae,  in  series  corresponding  to  the 
intercostal  spaces.  They  receive  afferents  from  the  vertebral  canal,  the  spinal 
muscles,  the  diaphragm,  intercostal  muscles,  and  pleura.  The  efferent  vessels  go 
to  the  thoracic  duct. 

In  the  young  subject  these  glands  are  more  numerous  than  in  the  adult,  and  tliere  are  also 
glands  along  the  dorsal  face  of  the  thoracic  aorta  which  seem  to  disappear  later. 

2.  The  anterior  mediastinal  lymph  glands  (Lg.  mediastinales  craniales)  (Fig. 
428)  are  numerous.  Some  are  situated  on  the  course  of  the  brachial  arteries  and 
their  branches;  on  the  right  side  they  are  related  deeply  to  the  trachea,  on  the  left 
to  the  oesophagus  also.  They  are  variable  in  size  and  disposition  and  are  continuous 
in  front  with  the  prepectoral  glands.  Other  glands  lie  along  the  ventral  face  of 
the  trachea  on  the  anterior  vena  cava  and  the  right  atrium  of  the  heart ;  these  are 
continuous  behind  with  the  bronchial  glands.  A  few  glands  usually  occur  along  the 
dorsal  surface  of  the  trachea,  and  there  is  often  one  at  the  angle  of  divergence  of 
the  brachiocephalic  trunk.  The  afferent  vessels  come  chiefly  from  the  pleura, 
the  pericardium,  the  heart,  the  thj'mus  or  its  remains,  the  trachea,  and  the  oesopha- 
gus.    Their  efferent  vessels  pass  to  the  prepectoral  glands  and  the  thoracic  duct. 

The  glands  along  the  ventral  face  of  the  trachea  are  frequently  enlarged  and  usually  pig- 
mented in  dissecting-room  subjects.  The  left  recurrent  ner\e  hes  above  them  on  the  ventral 
face  of  the  trachea. 

3.  The  bronchial  Ijrmph  glands  (Lg.  bronchiales)  are  grouped  around  the 
terminal  part  of  the  trachea  and  the  bronchi.  One  group  lies  on  the  upper  surface 
of  the  bifurcation  of  the  trachea  and  is  continued  a  short  distance  backward  under 
the  oesophagus  (Fig.  428).  Others  lie  below  the  trachea  and  bronchi  and  also 
occupy  the  angle  between  the  aortic  arch  and  the  pulmonary  artery,  concealing 
the  left  recurrent  nerve  and  often  covering  the  vagus  in  this  part  of  its  course. 
Small  glands  occur  along  the  chief  bronchi  in  the  substance  of  the  lungs  (Lg.  pul- 
monales).  They  receive  the  deep  and  most  of  the  superficial  lymph  vessels  of  the 
lungs,  and  the  efferents  from  the  posterior  mediastinal  glands.  Their  efferent 
ves.sels  go  to  the  thoracic  duct  and  the  anterior  mediastinal  glands.  The  deep 
lymph  vessels  of  the  lung  arise  in  plexuses  which  surround  the  terminal  bronchi 
and  accompany  the  bronchi  to  the  root  of  the  lung.  The  superficial  vessels  form 
a  rich  network  under  the  pleura;  most  of  them  pass  to  the  bronchial  glands. 

The  bronchial  glands  are  commonly  pigmented  except  in  young  subjects  and  are  often 
enlarged  and  inilurated. 

4.  The  posterior  mediastinal  lymph  glands  (Lg.  mediastinales  caudales)  are 
usually  small  and  are  scattered  along  the  posterior  mediastinum  above  the  oesopha- 
gus. They  receive  afferent  vessels  from  the  oesophagus,  mediastinum,  diaphragm, 
and  liver.  The  efferents  go  to  the  bronchial  and  anterior  mediastinal  lymph  glands, 
partly  to  the  thoracic  duct  directly. 


604  THE    VEINS 

Sometimes  one  or  two  small  glands  are  situated  in  the  aeute  angle  between  the 
posterior  vena  cava  and  the  diaphragm. 

THE  LYMPH  GLANDS  AND  VESSELS  OF  THE  ABDOMEN  AND  PELVIS 
The  lymph  glands  of  the  abdomen  consist  of  two  nutin  grouiis,  ])arietal  antl 
visceral.  The  parietal  glands  lie  in  the  subperitoneal  or  subcutaneous  tissue; 
they  receive  the  lymph  \essels  from  the  abdominal  and  pelvic  walls,  from  parts  of 
the  viscera,  and  from  the  proximal  lymph  glands  of  the  pelvic  limbs.  The  visceral 
glands  lie  on  the  walls  of  the  viscera  or  in  the  peritoneal  folds  which  connect  the 
organs  with  the  wall  or  with  atljacent  viscera.  They  receive  all  or  most  of  the 
lymph  vessels  from  the  organs  with  which  they  are  connected. 
The  parietal  glands  comprise  the  following: 

1.  The  limibar  lymph  glands  (Lg.  lumbales)  lie  along  the  course  of  the  abdom- 
inal aorta  and  ]iosterior  vena  cava  (Fig.  450).  Some  are  placed  along  the  lower 
surface  and  sides  of  the  vessels,  others  above.  A  few  small  glands  may  be  found 
above  the  sublumbar  muscles.  The  small  nodes  which  are  situated  at  the  hilus 
of  the  kidneys  are  often  termed  the  renal  lymph  glands.  They  receive  afferent 
vessels  from  the  lumbar  wall  of  the  abdomen  and  the  paired  viscera  (kidneys, 
adrenals,  genital  organs),  also  the  inguinal  vessels  and  the  efferents  of  the  iliac 
glands.  Their  efferents  go  to  the  thoracic  duct,  constituting  the  Imnbar  trunks 
of  origin  of  that  vessel. 

2.  The  internal  iliac  lymph  glands  (Lg.  iliacae  internffi)  are  grouped  about  the 
terminal  part  of  the  aorta  and  tlie  origins  of  the  iliac  arteries  (Fig.  450).  Their 
afferent  vessels  come  chiefly  from  the  pelvis,  pelvic  viscera,  and  tail,  and  they  receive 
efferent  vessels  of  the  external  iliac  and  deep  inguinal  glands. 

3.  The  external  iliac  lymph  glands  (Lg.  iliacie  externa')  form  a  group  on  either 
side  on  the  iliac  fascia  at  the  i)ifurcation  of  the  circumflex  iliac  artery  (Fig.  450). 
Their  afferent  vessels  come  from  the  flank  and  abdominal  floor,  the  outer  surface 
of  the  thigh,  and  the  precrural  glands.  The  efferent  vessels  go  to  the  lumbar  and 
internal  iliac  glands. 

4.  The  sacral  lymph  glands  (I^g.  sacrales)  are  small  nodes  situated  along  the 
border's  of  the  sacrum  and  on  its  pelvic  surface.  They  receive  afferents  from  the 
roof  of  the  pelvis  and  from  the  tail,  and  their  efferent  vessels  pass  to  the  internal 
iliac  glands. 

5.  The  superficial  inguinal  lymph  glands  (Lg.  inguinales  superficiales)  lie  on 
the  abdominal  tunic  in  front  of  the  external  inguinal  ring  (Fig.  457).  They  form 
an  elongated  group  along  the  course  of  the  subcutaneous  abdominal  artery,  on 
either  side  of  the  penis  in  the  male,  above  the  mammary  glands  in  the  female; 
in  the  latter  they  are  often  termed  mammary.  Their  afferents  come  from  the  inner 
surface  of  the  thigh,  the  abdominal  floor,  the  sheath  and  scrotum  in  the  male,  and 
the  mannnary  glands  in  the  female.  The  efferent  vessels  ascend  through  the 
inguinal  canal  and  go  to  the  deep  inguinal  and  lumbar  glands. 

G.  The  ischiatic  Ijrmph  gland  (Lg.  ischiadica)  is  a  small  node  which  may  be 
found  at  the  lesser  sciatic  notch.  It  receives  lymph  from  the  adjacent  parts 
and  from  the  popliteal  glands,  and  sends  efferents  to  the  sacral  and  internal  iliac 
glands. 

The  visceral  glands  include  the  following: 

1.  The  gastric  lymph  glands  (Lg.  gastricije)  are  situated  along  the  course  of 
the  gastric  arteries.  Several  occur  along  the  attachment  of  the  gastro-phrenic 
ligament.  A  group  lies  at  the  lesser  curvature  a  short  distance  below  the  cardia. 
There  is  another  small  group  on  the  visceral  surface  where  the  posterior  gastric 
artery  divides  into  its  primary  branches.  Two  or  three  small  nodes  are  usually 
found  on  the  ventral  aspect  of  the  pylorus.     Other  small  glands  are  scattered 


THE    LYMPH    GLANDS    AND    VESSELS    OF   THE    THORACIC    LLMB  GOo 

along  the  course  of  the  gastro-epiploic  and  short  gastric  arteries  in  the  great  and 
gastro-splenic  omenta.  The  efferent  vessels  pass  largely  to  the  coeliac  radicle  of 
the  thoracic  duct,  hut  along  the  left  part  of  the  great  curvature  they  go  to  the 
splenic  glands. 

2.  The  hepatic  lymph  glands  (Lg.  hepaticae)  lie  along  the  portal  vein  and  hepa- 
tic artery  and  in  the  lesser  omentum.  Their  efferent  vessels  go  to  the  cceliac 
radicle  of  the  cisterna  chyli. 

Many  of  the  lymph  vessels  from  the  parietal  surface  of  the  liver  pass  in  the  falciform  and 
lateral  ligaments  to  the  diaphragm  and  anastomose  with  its  lymphatics.  Some  pass  through  the 
diaphragm  with  the  vena  cava  and  go  to  the  mediastinal  glands. 

The  pancreatic  lymph  vessels  follow  the  course  of  the  blood-vessels  whic-h 
supply  the  gland:   most  of  them  go  to  the  splenic  and  hepatic  glands. 

3.  The  splenic  lymph  glands  (Lg.  lienales)  lie  along  the  course  of  the  splenic 
blood-vessels.  Their  afferent  vessels  come  from  the  subscapular  network  of 
the  spleen,  from  the  greater  curvature  of  the  stomach,  and  from  the  left  part  of 
the  pancreas.     The  eiTerents  jiass  to  the  cceliac  radicle  of  the  thoracic  duct. 

4.  The  mesenteric  lymph  glands  (Lg.  mesentericse)  are  situated  in  the  great 
mesentery  near  its  root.  They  are  numerous  and  hence  lie  close  together.  They 
receive  a  very  large  number  of  afferent  vessels  (400  to  .500)  from  the  small  intestine. 
They  have  several  considerable  efferents  which  concur  in  the  formation  of  the  in- 
testinal radicles  of  the  cisterna  chyli. 

The  lymph  vessels  of  the  intestine  form  three  sets  of  capillary  plexuses,  ^^z.,  in  the  subserosa, 
submucosa,  and  mucosa.  The  lymph  follicles,  solitar}-  and  aggregate,  lie  in  the  zone  of  the  plexus 
of  the  mucosa.     The  collecting  vessels  arise  from  the  subserous  plexus. 

.5.  The  lymph  glands  of  the  caecum  are  numerous  and  arc  distributed  along  the 
course  of  the  ctecal  blood-vessels.  Their  efferents  enter  into  the  formation  of  an 
intestinal  radicle  of  tlie  cisterna  chyli. 

G.  The  lymph  glands  of  the  great  colon  are  extremely  numerous  and  are  placed 
close  together  along  the  colic  Ijlood-vessels.  Their  efferent  vessels  are  large  and 
numerous.  They  converge  to  two  large  trunks  which  concur  with  those  of  the 
ctecum  and  small  intestine  to  form  an  intestinal  radicle  of  the  cisterna  chyli. 

The  intestinal  radicles  of  the  cisterna  chyli  are  formed  by  the  confluence  of  efferents  from 
the  intestinal  lymph  glands.  The  anterior  trunk  lies  on  the  left  side  of  the  anterior  mesenteric 
artery,  pa-sses  between  that  vessel  and  the  coeliac  artery,  turns  sharply  backward  across  the  right 
renal  vessels  and  opens  into  the  cisterna.  It  is  formed  by  the  union  of  the  coeliac  trunk  with 
efferents  from  the  glands  of  the  small  intestine,  caecum  and  colon.  It  is  about  four  inches  (ca. 
10  cm.)  in  length  and  is  ampullate.  The  posterior  trunk  receives  vessels  from  the  small  intestine 
and  small  colon.  It  usually  opens  into  a  trunk  formed  by  the  union  of  the  right  and  left  lumbar 
ducts.  It  is  usually  ampullate  at  its  termination  ( Franck).  The  arrangement  of  these  collecting 
trunks  is,  however,  very  variable. 

7.  The  lymph  glands  of  the  small  colon  are  situated  in  part  on  the  wall  of  the 
bowel  along  the  attaclunent  of  the  mesentery,  in  part  between  the  layers  of  the 
latter  along  the  course  of  the  l)lood-vessels.  The  efferent  vessels  go  to  the  lumbar 
glands  and  to  the  posterior  intestinal  radicle  of  the  thoracic  duct. 

The  lymph  vessels  of  the  rectum  pass  chiefly  to  the  lumbar  and  internal  ihac 
glands. 

5.  The  anal  lymph  glands  (Lg.  anales)  form  a  small  group  on  either  side  of  the 
sphincter  ani  externus  (Figs.  451,  453).  They  receive  aflerents  from  the  anus, 
perineum,  and  tail.     Their  efferents  go  to  the  internal  iliac  glands. 


THE  LYIVIPH  GLANDS  AND  VESSELS  OF  THE  THORACIC  LIMB 
1.  The  axillary  lymph  glands  (Lg.  axillares),  some  ten  to  twelve  in  number,  are 
grouped  on  the  iimer  face  of  the  distal  part  of  the  teres  major  and  the  tendon  of 
the  latissimus  dorsi  at  the  angle  of  junction  of  the  external  thoracic  and  subscapular 


GOG  THE    VEINS 

veins  with  the  brachial  (Fig.  466).  Their  effercnts  include  most  of  the  lymph 
vessels  of  the  limb,  which  come  directly  or  as  efferents  from  the  cubital  glands. 
They  receive  also  lymph  vessels  from  the  thoracic  wall.  The  efferents  accompany 
the  brachial  blood-vessels  and  end  in  the  prepectoral  glands  and  the  thoracic  and 
right  lymphatic  ducts. 

2.  The  cubital  lymph  glands  (Lg.  cubitales),  usually  eight  to  ten  in  number, 
form  a  discoid  oval  group  at  the  inner  side  of  the  distal  part  of  the  shaft  of  the 
humerus  (Figs.  441,  446).  They  lie  behind  the  biceps  muscle  on  the  brachial 
vessels  and  median  nerve  and  are  cov(>red  by  the  deep  fascia  and  the  posterior 
superficial  pectoral  muscle.  They  receive  as  affercnts  most  of  the  vessels  from  the 
limb  below  this  point.  Their  efferents  pass  chiefly  to  the  axillary  glanrls,  but  in 
part  to  the  prescapular  glands  also. 

A  number  of  superficial  lymph  vessels  ascend  with  or  near  the  suljcutaneous 
veins  (cephalic  and  accessorj'  cephalic)  and  join  the  prescapular  and  prepectoral 
glands.  Superficial  vessels  from  the  chest-wall  and  shoulder  run  across  the  latter 
to  the  prescapular  glands.  The  superficial  lymphatics  of  the  pectoral  region  form 
a  j^lexus  which  drains  into  the  prepectoral  and  prescapular  glands  by  a  number  of 
vessels  which  accompany  the  cephalic  vein.  The  deep  lymph  vessels  of  the  pec- 
toral region  run  with  the  external  thoracic  vein  to  the  axillary  glands. 


THE  LYMPH  GLANDS  AND  VESSELS  OF  THE  PELVIC  LIMB 
i.  The  precrural  or  subiliac  lymph  glands  (Lg.  sul)iliaca?)  are  situated  in  tlie 
fold  of  the  groin  on  the  anterior  liorder  of  the  tensor  fasciae  lattB,  about  midway 
between  the  point  of  the  hip  and  the  patella  (Figs.  450,  451,  457).  They  lie  on 
the  course  of  the  posterior  branch  of  the  circumflex  iliac  artery,  and  number  usually 
about  a  dozen.  They  receive  superficial  lymj^h  vessels  from  the  hip,  thigh,  and 
flank.  Their  efferent  vessels  ascend  with  the  posterior  circumflex  iliac  vein,  enter 
the  abdomen  near  the  external  angle  of  the  ilium,  and  join  the  external  iliac  l.ymph 
glands. 

2.  The  deep  inguinal  lymph  glands  (Lg.  inguinales  profunda)  form  a  large 
group  situated  in  the  upjx-r  part  of  the  femoral  canal  between  the  pectineus  and 
sartorius  muscles  (Figs.  451,  457).  They  cover  the  femoral  vessels  and  are  related 
superficially  to  the  inguinal  ligament.  They  receive  nearly  all  of  the  lymph  vessels 
of  the  limb  below  them.     Tlieir  efferent  vessels  ascend  to  the  internal  iliac  glands. 

3.  The  popliteal  lymph  glands  (Lg.  poplitese),  usually  four  to  six  in  number, 
lie  behind  the  origin  of  the  gastrocnemius  and  between  the  biceps  femoris  and  semi- 
tendinosus  at  the  division  of  the  posterior  femoral  artery  into  its  primary  Ijranches 
(Fig.  455).  They  receive  the  deep  lymph  vessels  of  the  distal  part  of  the  limb. 
Their  efferent  vessels  chiefly  follow  the  course  of  the  femoral  vessels  to  the  deep 
inguinal  glands,  but  one  or  two  ascend  in  company  with  a  vein  along  the  great  sciatic 
nerve  and  may  enter  a  gland  at  the  lesser  sciatic  notch.  From  this  a  vessel  ac- 
companies the  internal  pudic  vein  and  joins  the  internal  iliac  glands. 

Several  superficial  lymph  vessels  ascend  with  or  near  the  internal  metatarsal  and  saphenous 
veins,  enter  the  femoral  canal,  and  end  in  the  deep  inguinal  glands. 


The  Fcetal  Circulation 

The  blood  of  the  fa>tus  is  oxygenated,  receives  nutrient  matter,  and  gives  off 
waste  matter  by  close  contiguity  with  the  maternal  blood  in  the  placenta.  The 
chief  differences  in  the  blood-vascular  system  as  compared  with  that  which  obtains 
after  birth  are  correlated  with  this  interchange. 

The  umbilical  arteries,  right  and  left,  are  large  vessels  which  arise  from  the 


THE    FCETAL    CIRCULATION  607 

internul  iliac  arteries  and  pass  downward  and  forwartl  in  the  uml)ilical  folds  of  peri- 
toneum on  either  sitle  of  the  bladder  to  the  umbilicus.  Here  they  are  incorporated 
with  the  umbilical  vein  and  the  urachus  in  the  umbilical  cord,  ramify  in  the  allan- 
tois,  and  end  as  the  capillaries  of  the  fcctal  placenta.  They  conduct  the  impure 
blood  to  the  placenta.  After  birth  these  vessels  retract  with  the  l)ladder  to  the 
pelvic  cavity;  their  lumen  becomes  greatly  reduced  and  the  wall  thickened  so 
that  they  arc  cord-like  and  are  termed  the  round  ligaments  of  the  bladder. 

The  umbilical  vein  receives  the  oxygenatetl  blood  from  the  placenta.  Its 
radicles  converge  to  form  in  the  horse  a  single  large  trunk  which  separates  from  the 
other  constituents  of  the  umbilical  cortl  on  entering  the  abdomen  and  passes  for- 
ward along  the  abdominal  floor  in  the  free  border  of  the  falciform  ligament  of  the 
liver.  It  enters  the  latter  at  the  umbilical  fissure  and  joins  the  portal  vein,  so 
that  the  blood  conveyed  by  it  passes  through  the  capillaries  of  the  liver  before 
entering  the  posterior  vena  cava. 

In  the  ox  and  dog  some  of  the  blood  in  the  imibilical  vein  is  conveyed  directlj- 
to  the  vena  cava  by  the  ductus  venosus  (Arantii).  This  vessel  is  given  off'  within 
the  liver  from  a  venous  sinus  formed  by  the  confluence  of  the  portal  and  umbilical 
veins  and  passes  directly  to  the  posterior  vena  cava. 

The  foramen  ovale  is  an  opening  in  the  septum  l)etween  the  atria,  by  wliich  the 
latter  communicate  with  each  other.  It  is  guarded  by  a  valve  (Valvula  foraminis 
ovalis)  which  prevents  the  Ijlood  from  passing  from  the  left  atrium  to  the  right. 
After  birth  the  foramen  soon  closes,  but  this  part  of  the  septum  remains  membran- 
ous, and  there  is  a  deep  fossa  ovalis  in  the  right  atrium  which  indicates  the  posi- 
tion of  the  former  opening.  In  some  cases  the  foramen  persists  to  a  variable 
extent  in  the  adult  without  apparent  disturbance  of  the  circulation. 

The  pulmonary  circulation  is  very  1  mited  in  the  foetus,  and  most  of  the  blood 
which  enters  the  pulmonary  artery  passes  through  the  ductus  arteriosus  to  the 
aorta.  This  vessel  is  larger  than  the  divisions  of  the  pulmonary  which  go  to  the 
lungs  and  joins  the  left  side  of  the  aortic  arch.  After  birth  the  pulmonary  circula- 
tion undergoes  promptly  an  enormous  increase  and  the  ductus  is  rapidly  trans- 
formed into  a  fibrous  cord — the  ligamentum  arteriosum. 

The  only  arterial  blood  in  the  fictus  is  that  carried  by  the  umbilical  vein. 
This  blood  is  mixed  in  the  liver  with  the  venous  blood  of  the  portal  vein,  and  after 
passing  through  the  capillaries  of  the  liver  is  carried  by  the  hepatic  veins  to  the 
posterior  vena  cava.  The  latter  receives  also  the  venous  blood  from  the  posterior 
part  of  the  trunk  and  the  pelvic  limbs.  It  is  generally  believed  that  the  blood  car- 
ried into  the  right  atrium  by  the  posterior  vena  cava  passes  largely,  if  not  entirely, 
through  the  foranaen  ovale  into  the  left  atrium,  while  the  blood  flowing  into  it 
through  the  anterior  vena  cava  passes  into  the  right  ventricle.  On  this  basis  the 
blood  received  by  the  left  atrium  consists  chiefly  of  mixed  blood  from  the  posterior 
vena  cava,  since  the  small  amount  of  blood  conveyed  by  the  pulmonary  veins  is 
venous.  This  mixed  lilood  passes  into  the  left  ventricle  ami  is  forced  into  the 
systemic  arteries.  The  venous  blood  from  the  anterior  part  of  the  body  and  the 
thoracic  limbs  is  conveyed  by  the  anterior  vena  cava  to  the  right  atrium,  passes 
into  the  right  ventricle,  and  is  forced  into  the  pulmonary  artery.  A  small  amount 
is  carried  to  the  lungs,  but  the  bulk  of  it  passes  by  the  ductus  arteriosus  into  the 
aorta  behind  the  point  of  origin  of  the  brachiocephalic  trunk  (anterior  aorta), 
and  is  carried  to  the  posterior  part  of  the  body,  a  large  part  passing  by  the  umbilical 
arteries  to  the  placenta. 


608 


THE    BLOOD-VASCULAR   SYSTEM    OF   THE    OX 


THE  BLOOD-VASCULAR  SYSTEM  OF  THE  OX 
The  Pericardium  and  Heart 

The  pericardium  is  attached  by  two  fibrous  bands  (Ligamenta  sterno-peri- 
('ar(Haca)  to  the  .sternum  opposite  the  facets  for  the  sixth  costal  cartilages;  these 
Hganients,  right  and  loft,  are  embedded  in  the  mass  of  fat  which  separates  the  apex 
of  the  pericardium  from  the  floor  of  the  thorax. 


Ai(liru}r  nrm 
cava 


Brachiocr  plialtL 
trunk 

Riijhl  auricle 
I'ubnonary  arUrij 


Lignmrnlum  arkriosum 

Left  branch  of  pulmonary  artery 
Pulmonary  rcht.t 
/  \\         Po^hrior  rcna  cava 


Vena  hiiniazyyos 
I.( ft  auricle 


Right  ventricle 
Left  coronary  art(  rt/ 


Poxtrrior  branch  of  left 
cnriiiiiirii  artery  in 
ill/,  mil iliiile  rp-oove 
Left  nnlricle 


Tlie  heart  of  the  a(hdt  ox  has  an  average  weight  of  about  .'')}  2  to  fi  pounds  (ca. 
2.5  to  2.7  kg.),  or  about  0.4  to  0.5  per  cent,  of  the  body-weight.  Its  length  from 
base  to  apex  is  relatively  longer  than  that  of  the  horse  and  the  base  is  smaller  in 
both  its  (liameters. 

A  shallow  intermediate  groove  (Sulcus  intermediiis)  extends  from  the  coronary 
groove  down  the  left  side  of  the  po.sterior  border,  but  tloes  not  reach  the  apex.  The 
amovmt  of  fat  in  and  near  the  grooves  is  much  greater  than  in  the  horse. 

The  heart  is  situated  more  to  the  left  of  the  median  plane  than  in  the  horse  and 
is  opposite  to  the  third,  fourth,  and  fifth  ribs  when  it  is  contracted.     It  has  exten- 


THE    ARTERIES  (509 

sive  contact  with  the  lateral  wall  of  the  thorax  on  the  left  side,  but  none  on  the  right 
side,  where  a  consideraMo  thickness  of  lung  covers  the  pericardium.' 

Two  bones,  the  ossa  cordis,  (h>velo])  in  the  aortic  fibrous  ring.  The  right  one 
is  in  apposition  witli  tlie  atrio-ventricular  rings  and  is  irregularly  triangular  in 
form.  Its  left  face  is  concave  anil  gives  attachment  to  the  right  posterior  cusp  of 
the  aortic  valve.  The  right  surface  is  convex  from  before  backward.  The  base 
is  superior.  The  posterior  border  bears  two  projections  separatetl  by  a  notch.  It 
is  usually  a  little  more  than  an  inch  (ca.  4  cm.)  in  length.  The  left  bone  is  smaller 
and  is  inconstant.  Its  concave  right  border  gives  attachment  to  the  left  posterior 
cusp  of  the  aortic  valve.  There  is  a  large  fleshy  moderator  band  in  the  right 
ventricle. 

The  Arteries = 

The  great  arterial  trunks  in  the  thorax  resemble  those  of  the  horse  in  general 
disposition. 

The  left  coronary  artery  is  much  larger  than  the  right  one ;  it  gives  off  a  branch 
wliich  descends  in  the  intermediate  groove,  and  terminates  l>y  running  downward 
in  the  right  longitudinal  groove.  The  right  artery,  after  emerging  from  the  interval 
between  the  right  auricle  and  the  pulmonary  artery,  divides  into  liranches  which  are 
distributed  to  the  wall  of  the  right  ventricle. 

The  brachiocephalic  trunk  (anterior  aorta)  is  usually  four  or  five  inches  (ca. 
10  to  12  cm.)  in  lengtli. 

The  brachial  arteries  give  off  in  tlie  thorax  the  following  branches: 

1.  A  common  trunk  for  the  suljcostal,  dorsal,  superior  or  deep  cervical, 
and  vertebral  arteries. 

(1)  The  subcostal  artery  commonly  arises  separately,  but  may  1  c  given  off  as 
in  the  liorse.     It  sui)iilics  the  first  three  intercostal  arteries. 

(2)  The  dorsal  artery  is  relatively  small.  It  usually  ascends  in  front  of  the 
first  costo-vertehral  joint  and  is  distributed  as  in  the  horse. 

(3)  The  superior  or  deep  cervical  artery  may  arise  from  a  common  stem 
(Truncus  vertebro-cervicalis)  with  the  vertebral,  or  may  constitute  a  branch  of  that 
artery.  It  passes  up  between  the  first  thoracic  and  last  cervical  vertebra  or  be- 
tween the  sixth  and  seventh  cervical  and  is  distributed  as  in  the  horse. 

(-4)  The  vertebral  artery  i)asses  along  the  neck  as  in  the  horse  to  the  inter- 
vertebral foramen  between  the  second  and  third  cervical  vertebra;,  gives  off  a 
muscular  branch,  and  enters  the  vertebral  canal  (Fig.  469).  It  runs  forward  on 
the  floor  of  the  canal— connected  with  its  fellow  by  two  or  three  transverse  anas- 
tomoses—and divides  in  the  atlas  into  two  branches.  The  smaller  internal  division 
(cerebrospinal  artery)  passes  forwartl  to  the  floor  of  the  cranium  and  concurs  with 
the  condyloid  artery  and  branches  of  the  internal  maxillary  in  the  formation  of  a 
large  rete  mirabile.  The  large  external  branch  emerges  through  the  intervcrteljral 
foramen  of  the  atlas  and  ramifies  in  the  muscles  of  the  neck  in  that  region,  com- 
pensating for  the  smallness  of  the  branches  of  the  occipital  artery.  It  also  sends  a 
branch  to  the  rete  mirabile.  The  collateral  branches  detached  to  the  cervical  mus- 
cles are  large  and  compensate  for  the  small  size  of  the  deep  cervical  artery.  The 
collateral  spinal  branches  of  the  vertebrals  pass  through  the  intervertebral  for- 
amina, divide  into  anterior  and  posterior  branches,  and  form  two  longitudinal 
trunks  which  are  connected  by  cross-branches  so  as  to  form  irregular  polygonal 
figures. 

2.  The  internal  thoracic  artery. 

'  It  is,  of  course,  only  the  pcricanliuin  wliich  comes  in  contact  with  the  wall,  but  it  is  cus- 
tomary as  a  matter  of  convenience  to  speak  of  the  relation  of  the  heart  as  tlioUKh  it  were  direct. 

-  Only  the  most  important  differential  features  of  the  arrangement  of  the  vessels  as  compared 
with  those  of  the  horse  will  be  considered. 
39 


610  THE    BLOOD-VASCULAR    SYSTEM    OF   THE    OX 

3.  The  inferior  cervical  artery  corresponds  usually  to  the  ascending  branch  of 
that  vessel  in  tlic  horse. 

4.  The  external  thoracic  artery  is  large  and  usually  gives  off  a  branch  which  is 
equivalent  to  the  desceniling  branch  of  the  inferior  cervical  artery  of  the  horse. 


THE  COMMON  CAROTID  ARTERY 
The  carotid  arteries  usually  arise  from  a  common  trunlc  about  two  inches  (ca. 
5  cm.)  in  length,  but  in  exceptional  cases  are  given  off  separately  from  the  brachio- 


FiG.  46S.— Schema  of  Chief  Arteries  op  Head  of  Cow. 
1,  Common  carotid  artery;  S,  thyro-laryngeal;  S,  thyroid;  4,  laryngeal;  6,  pharyngeal;  6.  occipital;  7, 
condyloid;  S,  middle  meningeal;  9,  pharyngeal;  /O.  external  maxillary;  I/,  Ungual;  J2,  sublingual;  /d.  superior 
labial;  H,  internal  maxillary;  IS.  masseteric;  16,  inferior  alveolar;  17,  buccinator;  IS.  great  palatine;  19. 
sphenopalatine:  20,  posterior  auricular;  «/,  superficial  temporal;  2^.  posterior  meningeal;  23,  anterior  auricular; 
S.^,  artery  to  matrix  of  horn;  35,  deep  temporal;  SS,  arteries  to  rete  mirabile;  a?,  frontal;  aS,  malar;  2S',  dorsal 
na.sal  continuation  of  malar;   39,  infraorbital;   39' ,  lateral  nasal  continuation  of  29. 

cephalic.  Each  jiursues  a  course  similar  to  that  of  the  horse  and  is  accompanied 
by  the  small  internal  jugular  vein,  but  is  separated  from  the  external  jugular  vein 
by  the  omo-hyoid  and  sterno-mastoid  muscles.  It  divides  at  the  digastricus  into 
occipital,  external  maxillary,  and  external  carotid  arteries.  In  addition  to  tracheal, 
(rso])liageal,  :md  muscular  branches,  it  gives  off  the  thyroid  and  laryngeal  arteries. 
The  thyroid  artery  (A.  thyreoidea  cranialis)  bends  around  the  anterior  end  of  the 
thyroid  giantl,  in  which  it  ramifies.  The  accessory  tliyroid  artery  is  usually 
absent.     The  laryngeal  artery  may  arise  with  the  thyroiil. 


THE    COMMON    CAROTID    ARTERY 


611 


1.  The  occipital  artery  is  relatively  small.     It  gives  off: 

(1)  The  pharyngeal  artery,  which,  however,  may  arise  from  the  external 
carotid. 

(2)  Several  l)ranehes  to  the  muscles  (chiefly  the  flexors)  and  to  the  atlanto- 
occipital  joint. 

(3)  The  condyloid  artery  jiasses  into  the  cranium  through  the  anterior  foramen 
in  the  condyloid  fossa,  and  joins  the  vertebral  in  the  formation  of  the  rete  mirabile 
about  the  pituitary  gland.  Before  entering  the  cranium  it  gives  off  a  branch  to 
the  pharyngeal  lymph  glands,  and  the  middle  meningeal  artery;  the  latter  i)asscs 
through  the  foramen  lacerum.  Another  branch  enters  the  temporal  canal  and  gives 
twigs  to  the  temporalis  muscle  and  the  mucous  membrane  of  the  frontal  sinus.  A 
muscular  branch  emerges  from  the  intervertebral  foramen  of  the  atlas.  A  diploic 
branch  goes  into  the  occipital  condyle  and  squama,  and  emits  twigs  to  the  occipital 
muscles. 

2.  The  external  maxillary  artery  is  smaller  than  that  of  the  horse,  but  pursues 


Fig.  469. — Floor  of  Cranium  and  .\nterior  Part  of  Vertebral  Canal  of  Ox. 
1,  Vertebral  artery;  2,  muscular  branches  of  /;  3,  branches  of  /  to  the  rete  mirabile,  4;  5,  branches  of  in- 
ternal maxillary  artery  to  rete;  6.  branch  of  internal  maxillary  artery  entering  cranium  through  foramen  ovale; 
7,  condyloid  artery;  S,  emergent  artery  from  rete,  distributed  like  internal  carotid  artery  of  horse;  9.  9' ,  longitu- 
dinal vertebral  sinuses;  a,  cribriform  plate;  6,  optic  foramina;  c,  for.  lacerum  orbitale  +  rotundum;  d,  foramen 
ovale;  e,  occipital  condyle;  /,  g,  h,  first,  second,  and  third  cervical  vertebrae.     (After  Leisering's  Atlas.) 


a  similar  course.  The  lingual  artery  is  large,  and  often  arises  separately  from  the 
common  carotid;  it  gives  ofl"  a  branch  to  the  submaxillary  gland,  and  the  sublingual 
artery.  After  turning  around  the  jaw  the  facial  gives  off  the  two  labial  arteries. 
The  superior  labial  is  latge;  it  usually  gives  off  a  branch  which  runs  forward 
almost  parallel  with  the  lateral  na-sal.  The  angular  artery  is  absent  or  rudinientary, 
and  the  lateral  and  dorsal  nasal  arteries  spring  from  branches  of  the  internal 
maxillary. 

.3.  The  external  carotid  artery  passes  upward  between  the  stylo-hyoideus 
and  the  great  cornu  of  the  hyoid  bone,  turns  forward  across  the  external  face  of  the 
latter,  and  divides  into  superficial  temporal  and  internal  maxillary  arteries.  It 
gives  off  the  following  collateral  branches: 

(1)  Branches  to  the  parotid  and  submaxillary  glands. 

(2)  The  pharyngeal  artery,  which,  however,  often  arises  from  the  occipital. 

(3)  The  posterior  auricular,  which  resembles  that  of  the  horse  and  sends  a 
stylo-mastoid  branch  into  the  tympanum.  It  may  arise  from  the  superficial 
temporal. 


G12  THE    BLOOD-VASCULAR   SYSTEM    OF   THE    OX 

(4)  The  masseteric  artery  rcsombles  that  of  the  horse,  but  is  smaller. 

The  superficial  temporal  artery  is  large  and  presents  the  following  special 
features:  (1)  Its  transverse  facial  branch  passes  into  the  central  part  of  the  masse- 
ter.  (2)  It  gives  off  a  Ijranch  which  corresponds  to  the  posterior  meningeal  artery 
of  the  horse,  enters  the  temporal  canal,  and  ramifies  in  the  dura  mater,  giving  oft" 
twigs  to  the  external  ear,  the  temporal  muscle,  and  the  frontal  sinus.  (3)  It 
usually  gives  off  the  anterior  auricular  artery.  (4)  Branches  are  supplied  to  the 
frontalis  umscle  and  the  eyelids.  (5)  A  large  branch  passes  around  the  outer  side 
of  the  ba.se  of  the  horn-core,  supplies  the  matrix  of  the  horn,  and  anastomoses 
across  the  back  of  the  frontal  emincnice  with  the  artery  of  the  opposite  side. 

The  internal  maxillary  artery  is  less  curved  than  in  the  horse  and  is  entirely 
extraosseous,  since  the  alar  canal  is  absent.  The  principal  differential  features  in 
its  branching  are  as  follows: 

(1)  The  ophthalmic  artery  forms  a  rete  mirabile  within  the  periorbita.  Its 
frontal  branch  enters  the  supraorbital  canal  and  ramifies  chiefly  in  the  frontal  sinus. 

(2)  Several  branches  take  the  place  of  the  internal  carotid  artery.  One  of 
these  enters  the  cranial  cavity  through  the  foramen  ovale  and  several  small  ones 
pass  through  the  foramen  which  represents  the  foramen  rotundum  and  foramen 
lacerum  orbitale  of  the  horse.  They  concur  with  the  vertebral  and  condyloid 
arteries  in  the  formation  of  an  extensive  rete  mirabile  on  the  cranial  floor  around 
the  sella  turcica.  From  each  side  of  the  rete  an  artery  arises  which  is  distributed  in 
general  like  the  internal  carotid  of  the  horse. 

(3)  The  malar  artery  is  large;  it  arises  by  a  comnion  triuik  with  the  infra- 
orbital and  gives  ofi  the  dorsal  nasal  and  the  angular  artery  of  the  eye. 

(4)  The  infraorbital  artery  is  large  and  emerges  from  the  infraorbital  foramen 
to  form  tlie  lateral  nasal  artery. 

(5)  The  palatine  artery  is  smaller  than  in  the  horse  and  usually  arises  by  a 
common  trunk  with  the  sphenopalatine.  It  passes  through  the  palatine  canal 
and  along  the  palatine  groove,  enters  the  nasal  cavity  through  the  incisive  fissure, 
and  does  not  go  to  the  upper  lip.  It  forms  a  rete  mirabile  about  the  nasopalatine 
canal  and  terminates  in  the  mucous  membrane  of  the  anterior  part  of  the  nasal 
cavity. 

ARTERIES  OF  THE  THORACIC  LIMB 
Tiie  brachial  artery  pursues  the  same  course  in  the  arm  as  that  of  the  horse. 
At  the  elbow  it  becomes  the  median.'     The  chief  differential  features  in  its  branches 
are  as  follows: 

1.  Tli(>  subscapular  artery  is  almost  as  large  as  the  continuation  of  the  brachial. 
The  posterior  circumflex  artery  sends  branches  backward  and  downward  into  the 
triceps,  taking  the  place  in  part  of  the  deep  brachial  artery.  The  thoracico-dorsal 
artery  supjilies  branches  to  the  pectoral  muscles  and  the  triceps  as  well  as  the  teres 
major  and  latissimus  dorsi:   it  may  arise  directly  from  the  brachial. 

2.  The  deep  brachial  artery  is  small. 

3.  Tlie  superior  collateral  ulnar  artery  is  often  doulilc,  and  does  not  extend  to 
the  carjius. 

The  median  artery  (jjosterior  railial  artery)  descends  along  the  inner  part  of 
the  posterior  surface  of  the  radius  and  divides  near  the  middle  of  the  forearm  into 
the  radial  and  ulnar  arteries.  It  gives  off  at  the  upper  third  of  the  forearm  the 
common  interosseous  artery,  a  large  vessel  which  anastomoses  with  the  deep  bra- 
ciiial,  passes  through  the  ])roxinuil  interosseous  space,  and  descends  (as  the  dorsal 
interosseous)  in  the  groove  between  the  radius  and  ulna,  and  concurs  in  the  forma- 
tion of  the  rete  carpi  dorsale.     At  the  distal  end  of  the  forearm  it  sends  a  branch 

'  The  homologie.s  of  tlie  vessels  of  the  lower  parts  of  the  limbs  are  still  unoortain.  The  account 
given  here  is  mainly  based  on  the  views  of  Sussdorf  and  Baum. 


ARTERIES   OF   THE   THORACIC    LIMB 


613 


tlirough  the  distal  interosseous  space,  which  passes  downward,  assists  in  forming 
the  rete  carpi  volare,  and  is  continued  in  the  metacarpus  as  the  external  deep  volar 
metacarpal  artery.  This  is  a  small  vessel  which  passes  down  under  the  outer 
border  of  the  suspensory  ligament  and  assists  in  forming  the  deep  volar  arch  near 
the  fetlock. 

The  radial  artery  is  smaller  than  the  ulnar.  It  descends  on  the  flexor  carpi 
internus.  passes  over  the  postero-internal  surface  of  the  carpus,  and  is  continued  as 
the  internal  deep  volar  metacarpal.  At  the  distal  end  of  the  forearm  and  at  the 
carpus  it  furnishes  branches  to  the  retia  carpi.     Another  branch  (A.  met.  perforans 


Fig.  470. — Artfhiks  of  Di6t.\i-  Part  of  Right  Fore 
Limb  of  Ox,  -\.NTtRioB  Vikw. 
a.  Interosseous  arter>';  b,  dorsal  branch  of 
radial  arter>"  c,  rete  carpi  dorsale;  rf,  dorsal  meta- 
carpal arterj-;  e,  dorsal  common  digital  arterj-;  /,  /, 
dorsal  proper  digital  arteries. 


Fig-  471.' — .\rteries  of  Distal  Part  of  Right  Fore 
Limb  of  Ox.  Posterior  View. 
ff,  L'lnar  artery;  h,  radial  arterj-;  i,  volar  branch 
of  common  interosseous  arterj';  k,  /.  m,  deep  volar 
metacarpal  arteries:  .4. r.,  volar  arches;  n,  volar  com- 
mon digital  arterj-;  o,  o',  p,  volar  proper  digital  arteries. 


proximalis)  runs  outward  between  the  suspensory  ligament  and  the  large  meta- 
carpal bone,  passes  through  the  proximal  foramen  of  the  bone,  and  unites  with  the 
interosseous  artery;  before  passing  through  the  foramen  it  detaches  the  middle 
deep  volar  metacarpal  artery  (A.  met.  volaris  prof.  III.),  which  descends  on  the 
posterior  face  of  the  metacarpal  bone,  receives  an  anastomotic  branch  from  the 
internal  deep  arterv,  and  concurs  in  the  formation  of  the  deep  volar  arch  above  the 
fetlock. 

The  ulnar  artery,  the  larger  of  the  two  divisions  of  the  median,  descends  under 


614  THE    BLOOD-VASCULAR   SYSTEM    OF   THE    OX 

cover  of  the  flexor  carpi  internus  without  giving  ofi"  any  large  branches  in  the  fore- 
arm. It  passes  through  the  carpal  canal  and  continues  along  the  inner  side  of  the 
deep  flexor  tendon  as  the  volar  common  digital  artery.  At  the  distal  third  of  the 
metacarpus  this  vessel  is  joined  by  a  iirancli  from  the  internal  deep  volar  meta- 
cari)al  artery,  forming  the  superficial  volar  arch.  Near  this  another  branch  of  the 
common  digital  (or  of  the  internal  digital)  passes  around  the  outer  border  of  the 
flexor  tendons  to  the  posterior  face  of  the  metacarpal  bone  and  concurs  with  the 
deep  volar  metacarpal  arteries  in  the  formation  of  the  deep  volar  arch.  A  l)ranch 
from  the  arch  pa.sses  forward  through  the  inferior  foramen  of  the  metacarpal  bone 
and  joins  the  dorsal  metacarjjal  artery  which  descends  from  the  rete  carpi 
dorsale  in  the  anterior  metacarpal  groove. 

The  volar  common  digital  artery  (A.  metacarpea  volaris  su])(rficialis  III.) 
passes  into  tlie  interdigital  space  and  divides  into  two  volar  proper  digital  arteries, 
which  descend  along  the  interdigital  surfaces  of  the  chief  digits  and  pass  through 
the  foramina  at  the  upper  part  of  the  interdigital  surfaces  of  the  third  phalanges, 
enter  the  cavities  in  these  bones,  and  ramify  in  a  manner  similar  to  the  correspond- 
ing vessels  in  the  horse.  The  volar  common  digital  detaches  a  branch  (A.  inter- 
digitalis  perforans)  which  passes  forward  through  the  upper  part  of  the  interdigital 
space  and  anastomoses  with  the  dorsal  metacarpal  artery. 

The  volar  proper  digital  arteries  (or  the  eommon  digital)  give  off,  in  addition  to  other 
collaterals,  branches  which  correspond  to  the  arteries  of  the  plantar  cushion  of  the  horse.  These 
pass  to  the  bulbs  of  the  claws  and  anastomose  with  each  other  and  with  the  inner  and  outer 
chgital  artorios,  forming  an  arch  from  which  numerous  branches  are  distributed  to  the  matrix 
of  the  hoofs. 

The  dorsal  metacarpal  artery  (A.  met.  dorsalis  III.)  is  a  small  vessel  which 
arises  from  the  rctc  car])i  ilorsale,  descends  in  the  groove  on  the  anterior  face  of  the 
metacarpal  lione,  and  is  joined  l)y  the  inferior  perforating  metacarpal  artery  from 
the  deep  volar  arch  to  constitute  the  dorsal  common  digital  artery.  This  vessel 
(A.  digitalis  commimis  dorsalis  III.)  divides  into  two  dorsal  proper  digital  arteries. 

The  internal  digital  artery  (A.  digiti  III.  medialis)  is  the  continuation  of  the 
internal  dec])  volar  metacarpal  artery.  It  descends  on  the  inner  side  of  the  inner 
digit  and  terminates  at  the  bulb  of  the  claw  by  anastomosing  with  the  corresponding 
volar  proper  digital  artery.  It  gives  off  a  branch  to  the  rudimentary  digit  and 
forms  a  transverse  anastomosis  behind  the  first  phalanx  with  the  volar  common 
digital  or  its  inner  division. 

The  external  digital  artery  (A.  digiti  IV.  lateralis)  arises  from  the  deep  volar 
arch,  passes  down  on  the  outer  side  of  the  external  digit  and  is  distributed  like  the 
inner  one. 

BRANCHES  OF  THE  THORACIC  AORTA 
The  bronchial  and  oesophageal  arteries  often  arise  separately. 
Ten  pairs  of  intercostal  arteries  usually  arise  from  the  aorta.     The  other  three 

come  from  the  sulx'ostal  artery. 

The  two  phrenic  arteries  are  very  variable  in  origin.     They  may  come  from 

the  aorta,  the  co'liac,  left  ruminal,  or  an  intercostal  or  lumbar  artery. 


BRANCHES  OF  THE  ABDOMINAL  AORTA 
The  cceliac  artery  is  aljout  four  to  five  inches  (ca.  10  to  12  cm.)  in  length.     It 

passes  downward  and  curves  forward  between  the  rumen  and  pancreas  on  the  left 

and  the  right  crus  of  the  diaphragm  and  th(>  posterior  vena  cava  on  the  right.     It 

gives  off  five  chief  liranches. 

1.  The  hepatic  artery  arises  from  the  convex  side  of  the  curve  of  the  ca-liac 

artery  as  it  crosses  the  jjosterior  vena  cava.     It  passes  downward,  forward,  and  to 


BRANCHES  OF  THE  ABDOMINAL  AORTA  015 

the  right  above  the  portal  vein  to  the  portal  fissure,  and  gives  off  the  following 
branches: 

(1)  Pancreatic  branches. 

(2)  Dorsal  and  ventral  branches  to  the  liver.  The  ventral  branch  is  the  larger; 
it  gives  off  the  right  gastric  arter_y,  which  runs  in  the  lesser  omentum  to  supply  the 
origin  of  the  duodenum  and  the  pylorus,  anastomosing  with  the  dorsal  branch  of 
the  omaso-abomasal  artery. 

(.'■!)  The  cystic  artery  supplies  the  gall-bladder. 

(4)  The  gastro-duodenal  artery  divides  into  right  gastro-epiploic  and  pan- 
creatico-duodenal  branches.  The  right  gastro-epiploic  artery  anastomoses  with 
the  left  gastro-epiploic.  The  pancreatico-duodenal  artery  anastomoses  with  the 
first  intestinal  branch  of  the  anterior  mesenteric  artery. 

2.  The  right  ruminal  artery  (A.  ruminalis  dextra)  is  the  largest  branch,  and 
usually  arises  by  a  short  common  trunk  with  the  splenic.  It  runs  downward  and 
backward  on  the  right  face  of  the  dorsal  sac  of  the  rumen  to  the  posterior  transverse 
fissure,  in  which  it  turns  around  to  the  left  and  anastomoses  with  branches  of  the 
left  ruminal  artery.  It  gives  off  a  pancreatic  branch,  dorsal  and  ventral  coronary 
arteries,  branches  to  the  great  omentum,  and  ramifies  on  both  surfaces  of  the  rumen. 

3.  The  left  ruminal  artery  (A.  ruminalis  sinistra)  runs  downward  on  the  anterior 
part  of  the  right  face  of  the  rumen,  enters  the  anterior  furrow,  in  which  it  runs  from 
right  to  left,  and  continues  backward  in  the  left  longitudinal  groove,  anastomosing 
with  branches  of  the  right  artery.  It  supplies  chiefly  the  left  face  of  the  rum(>n. 
but  not  its  posterior  part.  It  usually  gives  off  near  its  origin  the  reticular  artery 
(A.  reticularis);  this  rather  small  vessel  passes  forward  on  the  dorsal  curvature  of 
the  rumen  and  turns  downward  in  the  rumino-reticular  groove,  in  the  Ijottom  of 
which  it  runs  around  ventrally  to  the  right  side.  It  gives  off  a  branch  which  passes 
to  the  left  of  the  cardia  and  along  the  lesser  curvature  of  the  reticulum  to  the  neck 
of  the  omasum.  The  reticular  branches  anastomose  with  the  omaso-abomasal  and 
left  ruminal  arteries. 

4.  The  omaso-abomasal  artery  (A.  gastrica  sinistra)  appears  as  the  continua- 
tion of  the  ca?liac.  It  passes  forward  and  downward  to  the  greater  curvature  of 
the  omasum  and  divides  after  a  course  of  four  or  five  inches  into  two  branches. 
The  dorsal  branch  curves  sharply  backward  on  the  dorsal  surface  of  the  omasum, 
continues  along  the  lesser  curvature  of  the  abomasum,  and  anastomoses  with  the 
hepatic  artery.  It  supplies  branches  to  the  omasum  and  to  the  lesser  curvature 
and  pyloric  part  of  the  abomasum.  The  ventral  branch  (A.  gastro-epiploica 
sinistra)  runs  forward  and  downward  over  the  anterior  extremity  of  the  omasum, 
passes  backward  in  the  great  omentum  close  to  the  ventral  curvature  of  the  aboma- 
sum, and  anastomoses  with  the  right  gastro-epiploic.  A  considerable  branch  from  it 
curves  around  in  front  of  the  neck  of  the  omasum  to  communicate  with  the  reticular 
artery.  Another  Ijranch  runs  back  across  the  left  side  of  the  omaso-abomasal 
junction,  and  a  third  goes  to  the  lesser  (ventral)  curvature  of  the  omasum. 

5.  The  splenic  artery  usually  arises  by  a  common  trunk  with  the  right  ruminal 
artery.  It  passes  forward  and  to  the  left  across  the  dorsal  curvature  of  the  rumen 
and  enters  the  hilus  of  the  spleen. 

The  anterior  mesenteric  artery  arises  from  the  aorta  just  behind  the  coeliac, 
and  has  about  the  same  caliber  as  the  latter.  It  passes  downward  and  a  little  to 
the  right,  and  crosses  the  colon  as  it  emerges  from  the  spiral  to  run  backward. 
After  detaching  twigs  to  the  pancreas  it  gives  off  in  succession  the  following 
branches : 

1.  A  branch  (A.  colica  media)  passes  to  the  colon  as  it  emerges  from  the  spiral 
arrangement.  This  artery  is  comparable  to  the  middle  colic  or  artery  of  the 
small  colon  of  the  horse;  it  runs  backward  along  the  terminal  part  of  the  colon, 
which  it  supplies. 


616 


THE    BLOOD-VASCULAR    SYSTEM    OF   THE    OX 


Fig.  472. — Gastric  Ahteries  of  Ox,  Right  View   (Partly  Schematic). 

1,  Coeliac  artery;   S,  right  ruminal  ;  S,  splenic;    4.  reticular;    5,  left  ruminal;   6,  omaso-abomasal;   7,  dorsal 

branch  of  6:   S,  ventral  branch  oi  6  (=  left  gastro-epiploic);    A,  dorsal  sac  of  rumen;   B,  ventral  sac  of  rumen; 

C,  C,  posterior  blind  sacs;    D,  a?sophagus;  E,  reticulum;    F.  omasum;    G,  abomasum;  H,  duodenum;    /,  right 

loogitudinal  furrow  of  rumen.    By  an  oversight  the  reticular  artery  is  shown  as  arising  from  the  omaso-abomasal. 


Fig.  473. — Gastric  Ar 
/.  Left  ruminal  artery;    S,  continual 
nimino-reticular  groove;   .1,  dorsal  sac  of  rumen;   a.  ventral  sac  ot  rumen;   f.  (.  .  po 
gus;  £,  reticulum;  F,  rumino-reticular  groove;  G,  left  longitudinal  furrow  of  rumen 


ii:s  OF  Ox,  Left  Virw   (Partly  Schematic). 

of  right  ruminal  artery;   3,  reticular  artery,  which  disappe 


rumen;   C,  T.  posterior  blind  sacs;  />,  ccsopha- 


BRANCHES  OF  THE  ABDOMINAL  AORTA 


617 


2.  The  ileo-cseco-colic  artery  ramifies  on  the  right  face  of  the  spiral  part  of  the 
colon.     It  gives  off  the  iieo-cjeeai  artery,  which  divides  into  ileal  and  caecal  arteries. 

3.  An  artery  (Ramus  collateralis)  runs  in  the  mesentery  in  a  curve  along  the 
ventral  border  of  the  coils  of  the  colon.     (This  vessel  is  absent  in  the  sheep.) 

4.  An  artery  which  constitutes  the  direct  continuation  of  the  anterior  mesen- 
teric pursues  a  course  in  the  mesentery  corresponding  to  the  series  of  mesenteric 
lymph  glands. 

The  two  preceding  vessels  are  essentially  the  arteries  of  the  small  intestine, 


Small 


Fig.  474. — Plan  of  Br.\nches  of  A.nterior  Mesexteric  .\rtert  of  Ox. 
/,  .\nterior  mesenteric  arterj"    ^.  middle  colic  arter>-;    3,  ileo-cseco-colic  artery;    4,  ramus  collateralis;    6, 
continuation  of  anterior  mesenteric  artery,  giving  off  branches  to  small  intestine;   6,  csecal  artery;   7,  colic  branch 
of  posterior  mesenteric  arterj-;  .4.  termination  of  duodenum. 


which  they  supply  with  the  exception  of  its  initial  and  terminal  parts.  The  first 
gives  off  no  considerable  branches  in  its  course  along  the  ventral  border  of  the  coils 
of  the  colon,  but  on  curving  upward  along  the  latter  it  anastomoses  with  the  second 
artery  and  detaches  numerous  branches  to  the  small  intestine  which  form  series  of 
superposed  anastomotic  arches.  It  supplies,  roughly  speaking,  about  one-third  of 
the  small  intestine  and  terminates  by  joining  the  ileal  artery.  The  second  artery 
gives  off  numerous  branches  which  also  form  arches  and  supply  about  the  first 
two-thirds  of  the  small  intestine,  exclusive  of  the  small  part  supplied  by  branches 
of  the  coeliac  artery.     Both  arteries  give  branches  to  the  lymph  glands.' 

'  It  is  difficult  to  make  the  arrangement  of  these  vessels  clear  in  a  brief  textual  description, 
but  a  reference  to  the  schematic  figure  will  explain  the  main  facts. 


618 


THE    BLOOD-VASCULAR    SYSTEM    OF   THE    OX 


The  posterior  mesenteric  artery  arises  from  the  aorta  near  its  termination.  It 
is  small  and  su])i)ii('s  branches  to  the  terminal  part  of  the  colon  and  to  the  rectum. 

The  renal  arteries  arise  from  the  aorta  close  together.  The  right  one  passes 
outward  and  forward  across  the  dorsal  face  of  the  posterior  vena  cava  to  the  hilus 
of  the  kidney.  The  left  one  runs  liackward.  but  necessarily  varies  in  direction  in 
conformity  with  the  position  of  the  kidney  {q.  i'.). 

The  spermatic  arteries  resemble  those  of  the  horse. 

The  utero-ovarian  arteries  are  small. 

The  five  ]Kurs  of  lumbar  arteries  derived  from  the  aorta  are  distributed  much 
as  in  the  horse.     Tlie  sixth  usually  comes  from  the  internal  iliac  artery. 

The  middle  sacral  artery  is  a  vessel  about  3  mm.  in  diameter  which  continues 


Fig.  475. — Pelvic  Arteries  of  Cow. 
Part  of  the  right  wall  of  the  uterus  and  vagina  is  removeti  and  the  cervix  uteri  is  shown  in  sagittal  section, 
a,  .\orta;  6,  utero-ovarian  artery;  6',  ovarian,  and  t",  uterine  branch  of  6;  c.  external  iliac  artery;  rf,  right  internal 
iliac  artery;  e,  conunon  trunk  of  umbilical  artery  (c')  and  middle  uterine  artery  (/);  g,  ilio-lumbar  artery;  h, 
anterior  gluteal  arteries:  /,  middle  ha-morrhoidal  artery; /:,  posterior  uterine  artery;  /,  perineal  artery;  7h,  posterior 
gluteal  artery;  n,  obturator  arteries;  o,  artery  of  clitoris;  p,  posterior  mesenteric  arterj-;  r.  anterior  ha-mor- 
rhoidal  artery;  «,  middle  sacral  artery;  i,  ovary;  5,  apparent  body  of  uterus,  really  apposed  horns;  2',  cornu; 
3,  vagina:  4,  cervix  uteri;  4' ,  vaginal  part  of  uterus  Cos  uteri);  5,  6' ,  broad  ligaments,  large  part  of  right  one  re- 
moved; 6,  urinary  bladder;  7,  rectum;  5,  sacrum;  p,  symphysis  pelvis,     (.\fter  Zieger.) 


the  aorta.  It  arises  from  the  dorsal  face  of  the  aorta  at  the  angle  of  divergence  of 
the  internal  iliacs,  runs  backward  on  the  pelvic  surface  of  the  sacrum  a  little  to  the 
left  of  the  median  line,  and  is  continued  as  the  middle  coccygeal  artery.  It  gives 
off  small  collateral  branches  to  the  spinal  cord  and  the  muscles  of  the  tail  and  the 
lateral  coccygeal  arteries.  The  latter  may  have  a  common  trunk  of  origin,  and 
each  divides  into  dorsal  and  ventral  branches.  The  middle  coccygeal  artery  runs 
through  the  ventral  (htemal)  arches  of  the  coccygeal  vertebra;.  The  coccygeal 
arteries  are  connected  at  pretty  regular  intervals  by  segmental  anastomoses. 

The  internal  iliac  arteries  are  much  longer  than  in  the  horse.  Each  passes 
backward  on  the  sacro-sciatic  ligament  and  divides  about  the  middle  of  the  pelvic 
wall  into  posterior  gluteal  and  internal  pudic  branches.  The  chief  differences  in 
its  distribution  are  :    (1)    A  large  trunk  gives  origin  to  the  umbilical  and  middle 


ARTERIES    OF   THE    PELVIC    LIMB  619 

uterine  arteries.  The  umbilical  artery  is  usually  largely  obliterated  and  its  terminal 
branches  receive  their  blood  through  anastomoses  with  the  internal  pudic.  It 
gives  off  near  its  origin  two  small  vessels,  the  ureteral  artery  (A.  urcterica)  and  the 
deferential  artery  (A.  defcrentialis),  which  accompany  the  ureter  and  the  vas 
deferens  respectively.  The  middle  uterine  artery  (A.  uterina  media)  is  very  large. 
It  is  distributed  chiefly  to  the  cornu  of  the  uterus,  and  compensates  for  the 
small  size  of  the  utero-ovanan  artery.  (2)  The  ilio-limibar  artery  is  relatively 
small  and  is  distributetl  chiefly  to  the  subluml)ar  muscles.  It  is  sometimes 
rejilaced  tiy  branches  of  the  circumflex  iliac  and  gluteal  arteries.  (3)  The 
anterior  gluteal  artery  is  commonly  re])resented  by  several  vessels.  (4)  The 
obturator  artery  is  represented  by  several  small  branches  which  supply  the 
obturator  and  adductor  muscles.  (5)  The  iliaco-femoral  anil  lateral  sacral 
arteries  are  alisent.  The  absence  of  the  latter  is  compensated  by  the  middle  sacral 
and  gluteal  arteries.  (6)  The  posterior  gluteal  (or  ischiatic)  artery  is  large.  It 
emerges  through  the  lesser  sciatic  notcli  ami  ramifies  in  the  biceps  femoris  and 
adjacent  muscles.  (7)  The  internal  pudic  artery  (A.  urethro-genitalis)  is  the  direct 
continuation  of  the  internal  iliac.  It  gives  off  liranches  to  the  rectum,  bladder, 
urethra,  and  genital  organs.  In  the  male  it  supplies  the  accessory  genital  glands 
and  divides  into  dorsal  and  deep  arteries  of  the  ]3enis;  the  a.  dorsalis  penis  runs 
along  the  dorsum  penis  to  the  glans  and  gives  twigs  to  the  j^repuce;  the  a.  profunda 
penis  gives  off  a  perineal  branch  and  enters  the  corpus  cavcrnosum  penis.  In  the 
female  it  gives  off  a  large  posterior  uterine  artery,  which  supplies  tlie  posterior 
part  of  the  uterus  and  gives  branches  to  the  vagina  and  bladder.  It  ends  as  the  a. 
clitoridis,  which  supplies  the  clitoris  and  adjacent  parts. 


ARTERIES  OF  THE  PELVIC  LIMB 

The  external  iliac  artery  has  the  same  course  as  in  the  horse.  The  circumflex 
iliac  artery  is  large.  A  branch  from  it  emerges  between  the  abdominal  and  lumbar 
muscles  near  the  external  angle  of  the  ilium  and  ramifies  like  the  terminals  of  the 
ilio-lumbar  artery  of  the  horse. 

The  femoral  and  popliteal  arteries  pursue  a  similar  course  to  those  of  the  horse. 
The  chief  differences  in  their  branches  are  as  follows: 

1.  The  external  pudic  artery  is  distributed  chiefly  to  the  scrotum  in  the  male. 
In  the  cow  it  is  usually  termed  the  mammary  and  is  very  large,  especially  during 
lactation.  Each  divides  at  the  Ijase  of  the  mammarj'  gland  into  two  branches 
which  are  distributed  to  the  anterior  and  posterior  parts  ("quarters")  of  the  gland. 
A  small  branch  accompanies  the  subcutaneous  abdominal  vein  to  the  xiphoid  region. 

2.  The  deep  femoral  artery  gives  off  an  obturator  branch  which  passes  up 
through  the  obturator  foramen  to  sujjply  the  oljturator  internus  and  compensates 
otherwise  for  the  at).sence  of  the  obturator  artery. 

.3.  The  anterior  femoral  artery  is  large.  It  often  gives  off  the  external  cir- 
cumflex artery  of  the  thigh,  which  perforates  the  proximal  end  of  the  ciuadriceps, 
gives  branches  to  that  muscle,  tlie  iliacus,  glutei,  and  tensor  fasciie  lata'. 

4.  The  saphenous  artery  is  large.  It  descends  in  front  of  the  homonymous 
vein  to  the  postcro-internal  surface  of  the  hock,  where  it  divides  into  two  plantar 
branches.  The  internal  plantar  artery  (A.  plantaris  medialis)  is  the  direct  continua- 
tion of  the  saphenous.  It  descends  at  first  along  the  inner  border  of  the  superficial 
flexor  tendon  and  is  continued  as  the  internal  superficial  plantar  metatarsal  artery 
along  the  inner  side  of  the  deep  flexor  tendon  with  the  internal  plantar  nerve. 
It  anastomoses  at  the  proximal  end  of  the  metatarsus  witli  the  perforating  meta- 
tarsal artery,  assisting  in  the  formation  of  the  proximal  plantar  arch.  Near  the 
fetlock  it  concurs  with  the  perforating  branch  of  the  dorsal  metatarsal  artery  in 
the  formation  of  the  distal  plantar  arch.     Below  this  it  is  continued  as  the  internal 


620 


THE    BLOOD-VASCULAR   SYSTEM    OF   THE    OX 


digital  artery.  Tlie  external  plantar  artery  (A.  plantaris  lateralis)  is  small.  It 
descends  along  the  outer  Iwrder  of  the  deep  flexor  tendon  with  the  external  plantar 
nerve,  concurs  with  the  perforating  tarsal  and  the  internal  plantar  arteries  in  the 
formation  of  the  proximal  plantar  arch,  and  gives  branches  to  the  rete  tarsi 
dorsale.     Continuing  downward  along  the  deep    flexor  tendon  as   the   external 


-$" 


Fit;.  476. — AnTKRiFs  of  Distal  Part  of  Right 
Hind  Limb  of  Ox,  Anterior  View. 
a,  Anterior  tibial  artery;  b,  proximal  perforating 
metatarsal  artery;  c,  dorsal  metatarsal  artery;  d, 
dorsal  common  digital  artery;  e,  e',  dorsal  proper 
digital  arteries. 


Fig.    477. — Arteries    of    Distal    Part    of    Right 
Hind  Limb  of  Ox,  Posterior  View. 

f.  Saphenous  artery;  /,/',  internal  and  external 
plantar  arteries;  g,  g' ,  internal  and  external  superficial 
plantar  metatarsal  arteries;  h,  deep  plantar  metatarsal 
artery;  i,  j,  internal  and  external  plantar  digital 
arteries;  k,  plantar  common  digital  artery;  /,  /',  internal 
and  external  plantar  digital  arteries. 


superficial  plantar  metatarsal  artery,  it  assists  in  forininii;  the  distal  plantar  arch 
and  heconies  the  external  digital  artery. 

The  posterior  tibial  artery  is  relatively  small  and  is  distributed  chiefly  to  the 
muscles  on  tlie  posterior  surface  of  the  tibia.  Lower  down  it  is  replaced  by  the 
saphenous  artery  as  descrilxMl  above. 

The  anterior  tibial  artery  has  the  same  course  as  in  the  horse.  It  is  continued 
down  the  groove  on  the  front  of  the  metatarsal  bone  as  the  dorsal  metatarsal 
artery.  This  is  the  chief  artery  of  the  region  and  is  accompanied  by  two  veins. 
It  detaches  the  proximal  perforating  metatarsal  artery,  which  passes  thr(nigh  the 
proximal  foramen  of  the  metatarsal  bone  and  concurs  with  the  superficial  plantar 


THE    VEINS  G21 

arteries  in  forming  the  proximal  plantar  arch.  Near  the  distal  end  of  the  metatarsal 
bone  it  gives  off  the  distal  perforating  metatarsal  artery  vvhirh  passes  hack  through 
the  distal  metatarsal  foramen  and  assists  in  forming  the  distal  i)lautar  arch.  The 
two  arches  are  connected  by  the  small  deep  plantar  metatarsal  artery  which  lies 
in  the  groove  on  the  jiosterior  face  of  the  large  metatarsal  bone. 

The  dorsal  common  digital  artery  is  the  direct  continuation  of  the  dorsal 
metatarsal.  It  divides  into  two  branches  which  unite  in  the  interdigital  space  with 
the  corresponding  branches  of  the  plantar  common  digital  to  form  the  proper 
digital  arteries. 

The  plantar  common  digital  artery  descends  from  the  distal  plantar  arch, 
anastomoses  in  the  interdigital  space  with  the  internal  and  external  digitals,  and 
divides  into  two  branches  which  join  those  of  the  dorsal  common  digital  arterj^  as 
before  mentioned. 

The  foregoing  is  a  brief  statement  of  the  more  common  arrangement  of  the 
vessels  in  the  distal  part  of  the  limb,  but  minor  variations  are  very  common. 


The  Veins  ' 

The  vena  hemiazygos  usually  takes  the  jjlace  of  the  vena  azygos.  It  lies 
along  the  left  side  of  the  aorta  and  the  bodies  of  the  thoracic  vertebrae,  turns  down 
across  the  left  face  of  the  aorta  and  left  pidmonary  artery,  runs  liack  over  the  left 
auricle  and  opens  into  the  great  coronarj*  vein  or  the  right  atrium.  It  receives 
the  intercostal  veins. 

Two  jugular  veins  occur  on  either  side.  The  internal  jugular  vein  (V.  jugu- 
laris  interna)  is  a  relatively  small  vessel  which  accompanies  the  carotid  artery.  It 
arises  by  occipital,  laryngeal,  and  thyroid  radicles,  receives  tracheal,  a'sophageal, 
and  muscular  branches,  and  joins  the  external  jugular  near  its  termination.  It  is 
sometimes  absent,  but  in  some  cases  it  appears,  on  the  other  hand,  to  be  large 
enough  to  interfere  with  venesection  practised  on  the  external  jugular.  The 
external  jugular  vein  (V.  jugularis  externa)  is  very  large  and  corresponds  to  the 
single  jugular  of  the  horse.  It  is  separated  from  the  carotid  artery  in  the  greater 
part  of  its  course  by  the  sternocephalicus  and  omo-hj-oideus  muscles. 

The  inferior  cerebral  vein  usually  does  not  unite  with  the  occipital;  the  latter 
is  continued  by  the  internal  jugular  vein. 

The  orbital  veins  form  a  network  between  the  periorbita  and  the  muscles  of 
the  eyeball.  This  plexus  communicates  with  the  cavernous  sinus  and  with  the 
superior  cereliral  vein.  It  is  also  drained  bj-  the  frontal  vein  which  runs  in  the 
supraorbital  canal  and  groove  and  joins  the  angular  vein  of  the  eye. 

The  dorsal  nasal  vein  is  usually  double. 

The  superior  labial  vein  usually  joins  the  infraorbital. 

The  vena  reflexa  is  absent  and  the  radicles  which  are  received  by  it  in  the  horse 
go  to  the  internal  maxillary  vein. 

The  sublingual  vein  is  very  large. 

The  veins  of  the  thoracic  limb  differ  chiefly  in  the  distal  part;  the  special 
features  are  as  follows: 

The  dorsal  digital  veins  ascend  on  the  front  of  the  digits  and  are  connected 
with  the  other  di.u;ital  veins  by  transverse  branches.  They  unite  near  the  fetlock 
to  form  the  dorsal  metacarpal  vein.  This  runs  upward  on  the  anterior  face  of  the 
metacarpus  and  carpus,  inclines  to  the  inner  surface  of  the  radius,  and  joins  the 
accessory  cephalic  or  the  cephalic  vein. 

The  volar  digital  veins  are  larger  than  the  dorsal.     They  lie  on  the  interdigital 

'  Most  of  the  differences  in  the  veins  of  the  ox  are  correlated  with  thc-ie  of  the  arteries  of 
which  they  are  satellites  and  will  not  be  described.  The  account  here  given  consists  chiefly  of 
those  differential  features  which  could  not  be  deduced  from  a  knowledge  of  the  arteries. 


622  THE    BLOOD-VASCULAR   SYSTEM    OF   THE    OX 

surfaces  of  the  digits  and  unite  in  the  interdigital  space  to  form  a  trunk  which  is  a 
satellite  of  the  volar  common  digital  artery. 

The  internal  and  external  digital  veins  lie  in  front  of  the  corresponding  arteries. 
They  are  connected  with  the  volar  digital  vein  by  a  large  branch  which  passes 
between  the  flexor  tendons  and  the  first  phalanx.  At  the  distal  end  of  the  meta- 
carpus each  inclines  forward  and  anastomoses  with  the  volar  common  digital  vein 
to  form  the  volar  venous  arch.  The  inner  vein  is  continued  as  the  internal  volar 
metacarpal  vein  along  the  inner  border  of  the  suspensory  ligament,  and  becomes  a 
satellite  of  the  radial  artery  in  the  forearm,  while  the  outer  one  is  continued  on  the 
posterior  face  of  the  metacarpal  bone  by  two  irregular  veins,  the  external  and 
middle  volar  metacarpals.  The  latter  anastomose  freely  with  each  other  and 
with  the  inner  vein.  They  unite  below  the  carpus  or  join  the  volar  common 
digital  vein. 

The  accessory  cephalic  vein  is  the  upward  continuation  of  the  dorsal  meta- 
carpal vein  and  is  much  larger  than  in  the  horse. 

The  posterior  vena  cava  is  partially  embedded  in  the  medial  border  of  the 
liver.  Its  abdominal  part  has  a  thicker  wall  than  in  the  horse.  Its  affluents 
correspond  to  the  arteries  of  which  they  are  satellites.  The  renal  veins  are  large 
and  thick-walled;  they  run  obliquely  forward  and  join  the  vena  cava  at  an  acute 
angle.     The  left  one  is  much  the  longer. 

Two  middle  sacral  veins  usually  accompany  the  artery. 

The  veins  of  the  mammary  glands  tleserve  special  notice.  They  converge  to 
a  venous  circle  at  tlie  base  of  the  udder,  which  is  drained  chiefly  l)v  two  pairs  of 
veins.  The  subcutaneous  abdominal  vein  (anterior  mammary  or  "milk"  vein) 
is  very  large  in  animals  of  the  dairy  lireeds  and  its  course  along  the  ventral  wall  of 
the  abdomen  is  easily  followed.  It  is  usually  flexuous.  It  emerges  at  the  anterior 
border  of  the  udder  about  two  or  three  inches  (ca.  5  to  8  cm.)  from  the  linea  alba, 
runs  forward  (deviating  a  little  outward),  dips  under  the  panniculus,  passes  through 
a  foramen  in  the  abdominal  wall  about  a  handbreadth  from  the  median  plane,  and 
joins  the  internal  thoracic  vein.  The  external  pudic  vein  (middle  manmiary  vein) 
is  also  of  considerable  size.  It  ascends  in  the  inguinal  canal  as  a  satellite  of  the 
artery  and  joins  the  external  iliac  vein.  The  right  and  left  veins  are  connected  at 
the  posterior  Iiorder  of  the  base  of  the  udder  by  a  large  transverse  branch.  From 
the  latter  arises  the  perineal  vein  (posterior  mammary  vein),  which  runs  medially 
upward  anil  backward  to  the  perineum,  turns  around  the  ischial  arch,  and  joins 
the  internal  pudic  vein.     In  the  male  these  veins  are  relatively  small. 

The  deep  veins  of  the  thigh  and  leg  resemble  those  of  the  horse,  but  there  is  no 
recurrent  tibial  vein. 

The  saphenous  vein  is  much  smaller  than  in  the  horse. 

The  recurrent  tarsal  vein  (external  saphenous)  is  large.  It  is  the  u])ward 
continuation  of  the  external  plantar  metatarsal  vein  and  anastomoses  with  the 
anterior  tibial  and  saphenous  veins.  It  arises  on  the  outer  face  of  the  hock, 
ascends  at  first  in  front  of  the  tendo  Achillis,  then  crosses  the  latter  externally, 
passes  up  between  the  biceps  femoris  and  semitendinosus,  and  joins  the  posterior 
femoral  vein. 

There  are  three  chief  metatarsal  veins.  The  great  dorsal  metatarsal  vein 
arises  at  the  distal  part  of  the  metatarsus  by  the  union  of  the  dorsal  digital  vein 
and  a  large  Ijranch  from  the  venous  arch  above  the  sesamoids.  It  ascends  super- 
ficially between  the  long  and  lateral  extensor  tendons  and  becomes  the  chief  radicle 
of  .the  anterior  tibial  vein.  The  internal  plantar  metatarsal  vein  arises  from  the 
venous  arch  above  the  fetlock,  ascends  along  the  inner  liorder  of  the  suspensory 
ligament,  passes  through  the  vascular  canal  of  the  metatarsus  and  centro-tarsal  (as 
the  perforating  tarsal)  and  joins  the  anterior  tibial  vein.     The  external  plantar 


THE    LYMPH    VESSELS   AND    GLANDS  623 

metatarsal  vein  is  larger  than  the  preceding.     It   passes  superficially  over   the 
outer  face  oi  the  hock  and  is  continued  by  the  recurrent  tarsal  vein. 

The  digital  veins  differ  from  those  of  the  fore  limb  chiefly  in  that  the  dorsal 
vein  is  large  and  the  plantar  absent  or  small. 

The  portal  vein  is  formed  usually  by  the  confluence  of  two  radicles,  gastric 
and  mesenteric.  It  receives  the  right  gastro-epiploic  vein  and  veins  of  the  pancreas. 
The  gastric  vein  is  the  largest  affluent.  It  is  formed  by  the  junction  of  three  veins, 
the  left  of  which  receives  the  splenic  vein.  The  anterior  mesenteric  vein  is  also 
formetl  by  the  confluence  of  three  radicles;  it  usually  receives  the  small  posterior 
mesenteric  vein.  The  portal  tributaries  are  in  general  satellites  of  the  correspond- 
ing arteries. 

The  Lyhph  Vessels  and  Glands 

The  thoracic  duct  arises  from  a  small  cisterna  cliyli  and  is  very  variable.  It  is 
exceptional  to  find  a  single  trunk  throughout,  as  is  often  the  case  in  the  horse.  The 
duct  is  largely  covered  by  fat  and  small  Ij'mph  glands.  There  are  often  two  ducts, 
one  on  either  side  of  the  aorta,  which  may  join  at  a  variable  point  or  terminate  close 
together  at  the  junctions  of  the  jugular  and  brachial  veins.  In  other  cases  the  duct 
is  single  for  a  variable  distance,  then  l)ifurcates  or  divides  into  three  or  four  branches, 
which  are  often  connected  by  plexiforna  anastomoses. 

The  efferent  vessels  from  the  intestine  converge  to  a  large  trunk  which  ac- 
comjianies  the  anterior  mesenteric  artery  and  vein.  It  passes  below  the  pancreas 
and  receives  usually  a  large  duct  which  is  formed  by  efferent  vessels  from  the  stom- 
ach, liver,  and  spleen;  this  duct  sometimes  opens  directly  into  the  cisterna.  The 
gastro-intestinal  trunk  receives  the  collecting  duct  (truncus  lumbalis)  of  the  lumbar 
lymph  vessels,  forms  a  bend  around  the  right  renal  vessels,  and  joins  the  cisterna. 

The  lymph  glands  in  the  ox  are  in  general  less  numerous  but  larger  than  those 
of  the  horse,  and  in  some  situations  a  single  large  gland  occurs  instead  of  a  group  of 
smaller  ones,  as  found  in  the  latter  animal. 

The  submaxillary  lymph  glands  are  usually  two  in  number,  right  and  left; 
each  is  situated  under  the  external  maxillary  vein  between  the  submaxillary  sali- 
vary gland  and  the  sterno-cephalicus  muscle.  Usually  one  or  two  hremol.vmph 
glands  are  near  it.  There  is  generally  a  small  gland  on  the  deep  face  of  the 
anterior  part  of  the  submaxillary  salivary  gland,  and  small  nodes  may  be  found 
further  forward  in  the  submaxillary  space. 

A  large  subparotid  lymph  gland  lies  on  the  postero-superior  part  of  the 
masseter  muscle,  partly  under  cover  of  the  upper  end  of  the  parotid  gland. 
Several  hsemolymph  glands  lie  on  its  deep  face. 

The  pharyngeal  lymph  glands  number  two  or  three  on  each  side.  Of  these,  two 
large  suprapharyngeal  glands  (Lg.  retropharj-ngeales)  are  situated  about  an  inch 
apart  between  the  dorsal  wall  of  the  pharynx  and  the  ventral  straight  muscles 
(Figs.  281,  365).  These  are  two  to  three  inches  long.  Enlargement  of  them  is 
likely  to  cause  difficulty  in  swallowing  and  in  respiration.  Behind  these  are 
se\-eral  hifimolymph  glands.  An  atlantal  gland  is  situated  below  the  wing  of  the 
atlas  on  the  spinal  accessory  nerve.  It  is  iliscoid,  oval  in  outline,  and  may  be 
an  inch  and  a  half  or  more  in  length.  It  is  partly  covered  by  the  upper  end 
of  the  submaxillary  salivary  gland. 

A  smaller  lymph  gland  (parapharyngeal)  is  usually  found  along  the  lower 
border  of  the  carotid  artery  (('.  e.,  ventral  to  the  atlantal  gland)  on  the  lateral 
wall  of  the  pharynx  and  under  cover  of  the  submaxillary  salivary  gland  or  at 
its  posterior  border. 

Two  or  three  small  anterior  cervical  lymph  glands  commonly  lie  along  the 
carotid  artery  a  little  further  back. 


624 


THE    BLOOD-VASCULAR   SYSTEM    OF   THE    OX 


The  middle  cervical  lymph  glands  comprise  a  series  of  small  nodes  along  the 
dorsal  face  of  the  trachea. 

In  the  sheep  and  goat  there  is  a  lymph  gland  at  the  middle  of  the  neck,  in  the  angle  between 
the  spinalis  and  complexus.  covered  by  the  splenius.  It  receives  vessels  from  the  atlantal  gland 
and  sends  effeicnts  lo  tlie  prescapular  gland. 

The  prescapular  or  superficial  cervical  lymph  gland  i.s  situated  at  the  anterior 
border  of  the  sujiraspinatus  under  cover  of  the  niastoido-humeralis  and  omo-trans- 
versarius.  It  is  elongated  and  may  be  an  inch  or  more  in  width  and  four  or  five 
inches  long.     Two  occur  in  exceptional  cases. 

\  chain  of  ha'molymph  glands  lies  along  the  front  of  the  shoulder,  covered  above  by  the 
trapezius.  Others  are  frequently  found  (in  the  calf  especially!  on  the  surface  of  the  omo-trans- 
versarius  at  the  point  whore  it  passe.-;  under  the  niastoido-huiucralis  (Forgeot). 

The  posterior  cervical  or  prepectoral  lymph  glands  number  commonly  three 
or  four  on  each  side.     One  or  two  are  placed  on  the  brachial  vessels,  one  below  the 


Fig.  478. — Superficial  Lymph  Gi,.^n-i)S  of  Cow  Projected  on  SrRF.\CE  of  Body. 

i.  Submaxillary:   3,  subparotid:   d,  atlantal:    4,  parapharyngeal:   S,  anterior  cervical:   6,  midiUe  cer%-ical:   7,  pre- 

scai>ular;  S,  precrural.     (With  u.se  of  tig.  in  EUenberger-Baum,  .\nat.  f.  KUnstler.) 

brachial  vein  at  the  first  ril),  and  one  at  tlic  junction  of  the  common  trunk  of  tlie 
external  and  subcutaneous  thoracic  veins  with  the  brachial. 

The  intercostal  lymph  glands  are  situated,  as  in  the  horse,  at  the  uj^jjcr  iJurts 
of  the  intercostal  sjiaces.     Associated  with  them  are  hsemolymph  glands. 

The  sternal  lymph  glands  are  situated  along  the  course  of  the  internal  thoracic 
artcrj'  at  the  lower  part  of  the  intercostal  spaces.  The  largest  is  close  to  the 
thoracic  inlet.     Several  glands  occur  in  the  fat  about  the  apex  of  the  pericardium. 


4.  Several  anterior  mediastinal  lymph  glands  are  placed  along  the  oesophagus 
and  the  trachea."     Hiemolyni|ili  glands  occur  here  also. 

Usually  three  large  bronchial  lymph  glands  are  present  (Fig.  289).  One  is 
situated  at  the  origin  of  each  chit'f  l)r(inclius  anil  the  third  is  under  the  trachea  at 
the  origin  of  the  special  bronchus  of  the  ajsical  lolie  of  the  right  lung.     Another 

'  The  upper  series  is  continuous  with  the  posterior  mediastinal  ((esophageal)  glands  and  the 
lower  or  tracheal  glands  with  the  bronchial.  Hence  we  might  well  designate  the  mediastinal 
glands  as  ccsophageal  (anterior  and  posterior)  and  tracheo-bronchial. 


THE    LYMPH    VESSELS    AND    GLANDS 


625 


may  lie  between  the  aorta  and  the  left  branch  of  the  pulmonary  artery.  These 
glands  are  often  pigmented.  Other  small  nodes  are  situated  on  the  bronchi  within 
the  lungs. 

The  posterior  mediastinal  lymph  glands  comprise  two  or  three  of  large  size 
placed  along  the  dorsal  wall  of  the  cesophagus.  There  may  be  a  single  gland 
about  eight  inches  (ca.  20  cm.)  long,  the  anterior  half  of  which  lies  on  the  (rsoph- 
agus  (Fig.  289).'  A  small  gland  is  situated  in  the  acute  angle  formed  by  the 
posterior  vena  cava  and  the  diaphragm. 

A  single  axillary  lymph  gland  is  situated  on  the  distal  part  of  the  teres  major 
on  the  course  of  the  vein  from  the  latissimus  dorsi. 

The  lumbar  l3Tnph  glands  form  an  irregular  series  scattered  along  the  abdom- 
inal aorta  and  posterior  vena.  A  bean-shaped  renal  lymph  gland  occurs  at  the 
hilus  of  each  kidney.     Hiemolymph  glands  occur  along  the  course  of  the  aorta. 


Fig.  479. — Ixtestine  of  Ox,  Sprea 
Ca,  Ciecum;  C,  colon;    D,  duodenum:    //,  ileum;   J ,  jejunum;     R,  rectu 


nteric  Ij-mph  glands.     (.A.fter 


The  internal  iliac  lymph  glands  comj^rise  a  group  of  five  or  six  at  the  termi- 
nation of  the  aorta  and  the  origin  of  the  vena  cava.  A  discoid  gland,  two  inches 
or  more  in  diameter,  occurs  near  the  side  of  the  pelvic  inlet  at  the  angle  of  diver- 
gence of  the  circumflex  iliac  artery  from  the  external  iliac.  A  small  gland  is 
sometimes  found  at  the  origin  of  the  prepubic  artery. 

The  external  iliac  lymph  glands  number  commonly  two  on  either  side,  and  are 
situated  near  the  point  of  the  hip  in  front  of  the  anterior  branch  of  the  circumflex 
iliac  artery. 

The  superficial  inguinal  lymph  glands  are  situated  centrally  below  the  prepubic 
tendon  and  in  the  narrow  space  l)etween  the  origins  of  the  graciles.  In  the  male 
there  are  usually  two  or  three  on  either  side  of  the  penis  behind  the  sigmoid  flexure. 
In  the  cow  they  are  supramammary,  i.  e.,  are  situated  above  the  posterior  margin 

'  When  enlarged,  as  is  often  the  case  in  tuberculosis,  tliis  gland  frequently  causes  difficulty 
in  swallowing  and  in  rumination  and  produces  chronic  or  recurrent  bloating. 
40 


626  CIRCULATORY    SYSTEM    OF   THE    PIG 

of  tlie  base  of  the  udder;  two  large  glands  which  are  in  apposition  with  each  other 
medially  are  constant,  and  above  these  there  are  often  two  smaller  glands. 

An  ischiatic  lymph  gland,  which  is  discoid  and  usually  about  an  inch  in  diam- 
eter, is  situatcil  on  the  lower  jiart  of  the  sacro-sciatic  ligament  near  the  lesser  sciatic 
notch  under  cover  of  the  bicejis  femoris. 

An  anal  lymph  gland  is  situated  on  the  retractor  ani  on  either  side. 

The  gastric  lymph  glands  are  numerous  and  comprise:  (1)  a  chain  along  the 
course  of  the  right  runiinal  artery  and  two  or  three  in  the  left  groove  of  the  rumen; 
(2)  several  on  the  reticulum  above  and  below  the  junction  with  the  omasum;  (3) 
a  series  along  the  course  of  the  superior  omasal  vessels  and  the  lesser  curvature  of 
the  abomasum;  (4)  an  extensive  chain  along  the  ventral  face  of  the  omasum  and 
the  great  curvature  of  the  aliomasum  at  the  attachment  of  the  great  omentum. 

Two  or  three  large  hepatic  or  portal  lymph  glands  are  found  at  the  upper  part 
of  the  ])ortal  fissure  of  the  liver. 

No  lymph  glands  occur  at  the  hilus  of  the  spleen.  The  efferent  vessels  from 
the  spleen  appear  to  go  to  glands  along  the  course  of  the  coeliac  artery. 

A  large  discoid  cceliaclymph  gland  lies  on  the  pancreas  and  the  coeliac  artery, 
covering  the  latter  as  it  gives  olt"  its  primary  branches. 

The  mesenteric  lymph  glands  are  large  and  numerous.  Thej'  form  a  chain  in 
the  lower  part  of  the  mesentery  along  the  course  of  the  great  mesenteric  artery. 
They  are  chiefly  elongated  and  narrow,  and  some  have  a  length  of  six  to  eight  inches 
(15  to  20  cm.)  or  more.  Sometimes  several  unite  and  form  a  narrow  band  about 
two  feet  in  length.  A  large  gland  occurs  at  the  origin  of  the  spiral  part  of  the  colon, 
a  group  is  found  near  the  anterior  mesenteric  trunk,  and  others  are  scattered  along 
the  coils  of  the  colon,  which  are  best  seen  on  the  right  side.  A  chain  of  small 
lymph  glands  extends  along  the  terminal  part  of  the  colon  and  the  dorsal  face  of  the 
rectum. 

The  precrural  lymph  gland  is  situated  on  the  aponeurosis  of  the  external  oblique 
at  the  anterior  border  of  the  tensor  fasciae  latae  a  short  distance  above  the  stifle. 
It  is  elongated  like  the  prescapular  gland  and  may  be  six  inches  (ca.  15  cm.)  long. 
Several  subcutaneous  hiemolym])h  glands  occur  in  this  vicinity;  others  are  situated 
further  forward  on  the  flank  not  far  from  the  last  rib.  There  is  usually  a  round, 
flattened  lymph  gland  about  an  inch  in  diameter  on  the  upper  part  of  the  quadriceps 
femoris  under  cover  of  the  tensor  fascise  latae,  and  one  or  more  small  ones  occur  on 
the  surface  of  the  latter  nuisrle. 

No  deep  inguinal  lymph  glands  are  present. 

A  single  popliteal  lymph  gland  an  inch  or  more  in  length  is  situated  somewhat 
lower  down  on  the  gastrocnemius  than  in  the  horse,  behind  the  tibial  and  peroneal 
nerves. 


CIRCULATORY  SYSTEM  OF  THE  PIG 
THE  HEART 

The  pericardium  is  attached  to  the  sternum  from  a  point  oiijiosite  to  the  third 
rib  as  far  as  the  xijihoid  cartilage,  and  also  to  the  sternal  part  of  the  diaphragm. 

The  heart  is  small  in  i)roportion  to  the  body-weight,  especially  in  fat  animals. 
It  is  relatively  short  and  wide.  The  apex  is  blunt  and  is  marked  by  a  notch  (In- 
cisura  apicis).  Its  long  axis  is  more  oblique,  but  it  is  less  asynunetrical  with  regard 
to  the  median  plane,  than  in  the  horse  or  ox.  The  lower  border  of  the  left  auricle 
(appendix)  is  marked  by  several  notches  and  is  situated  at  a  lower  level  than  the 


THE    ARTERIES  627 

right  one.     The  right  longitudinal  groove  is  placed  far  back  and  there  is  no  pos- 
terior sulcus. 

The  Arteries 

The  pulmonary  vessels  present  no  remarkable  features. 

The  aorta  resembles  that  of  the  horse  and  ox  in  its  course  and  relations,  but  the 
arch  is  more  strongly  curved.  There  is  no  common  brachiocephalic  trunk  (anterior 
aorta). 

The  brachiocephalic  artery  arises  first  from  the  aortic  arch  and  ])asscs  forward 
below  the  trachea  to  the  first  rib.  Here  it  gives  off  the  common  carotid  arteries, 
and  is  continued  around  the  first  rib  as  the  right  brachial. 

The  superior  cervical,  vertebral,  and  dorsal  arteries  usually  arise  liy  a 
common  trunk. 

The  inferior  cervical  artery  is  large;  its  ascending  branch  gives  off  the  posterior 
thyroid  artery  and  parotid  branches. 

The  internal  and  external  thoracic  arteries  give  branches  to  the  pectoral 
mammary  glands;   the  external  may  be  absent. 

The  left  brachial  artery  arises  from  the  aortic  arch  just  above  the  brachio- 
cephalic. It  curves  forward  and  downward  and  turns  around  the  anterior  border 
of  the  first  rib.  Its  superior  cervical,  vertebral,  and  dorsal  branches  usually  arise 
separately. 

The  carotid  arteries  arise  from  the  brachiocephalic  close  together  or  by  a  very 
short  common  trunk.  Thej'  terminate  in  occipital  and  internal  and  external  carotid 
divisions. 

The  occipital  artery  resembles  that  of  the  horse. 

The  internal  carotid  artery  usually  arises  by  a  common  trunk  with  the  occipital. 
After  giving  off  a  large  meningeal  branch  it  passes  through  the  foramen  lacerum 
and  forms  with  the  opposite  artery  a  rete  mirabile  which  resembles  that  of  the  ox, 
but  is  smaller  and  is  not  connected  with  the  vertebral  and  condyloid  arteries. 

The  external  carotid  artery  has  the  same  course  and  termination  as  in  the  horse. 
Its  branches  present  the  following  special  features:  (1)  The  lingual  artery  is 
relatively  large  and  supphes  the  pharyngeal  artery,  the  sublingual,  muscular 
branches,  and  branches  to  the  soft  palate,  submaxillary  gland,  and  larynx.  (2)  The 
external  maxillary  artery  is  small  and  is  distributed  chiefly  to  the  submaxillary 
gland,  the  pharj-ngeal  lymph  glands,  the  masseter  and  the  panniculus.  It  does 
not  extend  upon  the  lateral  surface  of  the  face.  (3)  The  posterior  auricular 
artery  is  long  and  relatively  large;  it  gives  off  the  posterior  meningeal. 

The  internal  maxillary  artery  jiursues  a  flexuous  course  between  the  ramus  of 
the  mandible  and  the  jitiTygoid  nniscles.  Its  branches  offer  the  following  special 
features:  (1)  The  inferior  alveolar  (or  dental)  is  large;  branches  from  it  emerge 
through  four  or  five  mental  foramina  and  take  the  place  of  the  inferior  labial. 
(2)  The  buccinator  artery  is  also  large  and  extends  to  the  lips.  (3)  The  uifra- 
orbital  artery  extends  to  the  snout  and  replaces  the  superior  labial  largely  and  the 
lateral  nasal  in  part.  The  malar  branch  compensates  largely  for  the  absence  of 
the  lateral  and  dorsal  nasal.     (4)    The  palatine  artery  is  small. 

The  intercostal  arteries  number  fourteen  to  sixteen  in  either  side;  of  these 
ten  to  twelve  arise  from  the  aorta,  usually  by  short  common  trunks.  Frequently 
an  intercostal  artery  is  given  off  from  that  of  an  adjacent  space. 

The  bronchial  and  (Esophageal  arteries  usually  arise  separately. 

The  coeliac  artery  is  half  an  inch  to  an  inch  long.  It  supplies  a  branch  to  the 
left  crus  of  the  diaphragm  and  divides  into  two  primary  l)ranches,  gastro-hepatic 
and  splenic.  The  gastro-hepatic  artery  is  the  larger.  It  gives  off  pancreatic 
branches,  the  anterior  gastric  artery,  branches  to  the  lesser  curvature  of  the 
stomach,  pyloric   and  gastro-duodenal  arteries.     The  latter  divides  into  pancre- 


628 


CIRCULATORY    SYSTEM    OF    THE    PIG 


atico-duodonal  ami  right  gastro-epiploic.  The  anterior  gastric  usually  supplies  the 
cesopluiKcal  artery.  The  continuing  trunk  (A.  hepatica  propria)  gives  off  a  cystic 
})ranch  and  divides  in  the  portal  fissure  into  four  branches  which  supply  the  liver. 
The  splenic  artery  gives  off  the  ])osterior  gastric  (usually),  branches  to  the  stomach 
above  the  cardia,  twigs  to  the  pancreas,  short  gastric  arteries  to  the  left  part  of 
the  great  curvatur(>,  and  sjilenic  liranches,  and  is  continued  as  the  left  gastro- 
epiploic artery. 

The  postorior  gastric  may  uri.sc  from  tlie  gastro-liepatic  or  in  tlic  angle  of  divergence  of  the 
two  primary  divisions  of  the  cochac.     The  a?sophageal  l>ranch  may  come  from  the  splenic. 


J""ii;,  4,S0. — Artehiks  of  DmTAL  Part  ok  Kic-.ht  Fore        Fig.  4S1. — Arteries  of  Dis 


,  Part  of  Kk:ht  Fore 


Limb  ok  Pig,  A.vterior  Vii:w. 
a.  Terminal  part  of  volar  interosseous  artery; 
b.   ilorsal  interosseous   artery;     c,   rete  carpi   tlorsale: 
f/.  dorsal  metacarpal  arteries;    e,  dorsal  coniinoii  dig- 
ital arteries;   /,  dorsal  projjer  iligital  arterie.s. 


Limb  of  Pig,  Posterior  View. 
0,  Ulnar  artery;  h,  superficial  branch  of  radial 
artery;  /,  collateral  ulnar  artery;  j,  volar  interosseous 
arterj-;  h,  deep  branch  of  radial  artery;  k\  deep  volar 
metacarpal  arteries:  /,  superficial  volar  metacarpal 
arteries;  iii,  volar  common  digital  artery;  n,  volar 
proper  digital  arteries. 


The  anterior  mesenteric  artery  is  long  like  that  of  the  ox.  It  gives  twigs  to 
the  i)ancreas,  the  ilio-ca'cal  and  two  colic  arteries,  and  is  continued  in  the  mesentery 
as  the  artery  of  the  small  intestine.  This  gives  off  numerous  branches  which  form 
a  series  of  arches  along  the  mesenteric  lymph  glands.  From  these  is  formed  a  rich 
network  which  gives  off  innumerable  fine  liranches  placed  close  together.  The 
colic  arteries  enter  the  axis  of  the  spiral  coil  of  the  colon  and  anastomose  at  its 
apex.     Their  branches  also  form  rich  networks. 

.\  phrenico-abdominal  artery  arises  on  either  side  a  little  in  front  of  the  renals. 
It  divides  into  braiiclics  which  go  to  the  costal  part  of  the  dia])liragm  and  the  abdom- 
inal muscles. 

The  renal  and  spermatic  arteries  present  no  special  characters. 


THE    ARTERIES 


629 


The  posterior  mesenteric  artery  arises  near  the  termination  of  the  aorta.  It 
is  small  and  is  clistrilnUcd  like  that  of  the  ox. 

Six  pairs  of  lumbar  arteries  arise  from  the  aorta.  The  .seventh  comes  from 
the  middle  sacral. 

The  terminal  branches  of  the  aorta  resemble  those  of  the  ox. 

The  arteries  of  the  shoulder,  arm,  and  forearm  resemble  in  general  those  of 
the  ox. 

The  main  facts  as  to  the  metacarpal  and  digital  arteries  are  as  follows:  The 
rete  carpi  dorsale  is  formed  essentially  by  the  terminals  of  the  interosseous  artery 
of  the  forearm.     It  gives  rise  to  three  dorsal  metacarpal  arteries  which  descend  in 


Fig.  482. — .\rteries  of  Dist.\l  Part  of  Right  Hind 
Limb  of  Pig,  .\nterior  View. 
a,  .\nterior  tibial  artery,  continued  on  tarsus 
as  the  dorsalis  pedis;  b,  perforating  tarsal  arterj"; 
c,  dorsal  metatarsal  arteries;  d,  common  digital  ar- 
teries;   e,  proper  digital  arteries. 


Fig.  483. — -Arteries  of  Dist.il  Part  of  Right  Hind 
Limb  of  Pig,  Posterior  View. 
/.  Saphenous  artery,  continued  as  internal 
tarsal  artery;  g,  external  tarsal  artery;  h,  internal 
plantar  artery;  h' ,  external  plantar  artery;  i,  per- 
forating tarsal  artery;  j,  deep  plantar  metatarsal 
arteries;  k,  common  digital  arter\-;  /,  proper  digital 
arteries. 


the  corresponding  interosseous  spaces  and  unite  with  branches  of  the  volar  meta- 
carpals to  form  three  common  digital  arteries.  Each  of  these  divides  into  two 
proper  digital  arteries,  which  descend  along  the  interdigital  surfaces  of  the  digits. 
On  tlie  volar  surface  are  two  volar  arches,  superficial  and  deep,  from  which  three 
superficial  and  three  deep  volar  metacarpal  arteries  arise.  The  deep  arteries 
unite  near  the  distal  end  of  the  space  between  the  principal  metacarpal  bones  to 
form  a  stem  which  unites  with  the  middle  (third)  superficial  artery.  The  superficial 
arteries  unite  to  form  an  arch  from  which  proper  digital  arteries  are  given  off  to  the 
axial  aspect  of  the  small  digits,  and  a  common  digital  which  supplies  two  volar 
proper  digital  arteries  to  each  of  the  chief  digits. 


630  CIRCULATORY    SYSTEM    OF   THE    PIG 

The  arteries  of  the  hip,  thigh,  and  leg  are  arranged  much  as  in  the  ox.  A  few 
special  features  may  be  noted. 

The  ilio-lumbar  artery  gives  off  a  branch  to  the  quadriceps  femoris.  It  may 
also  supply  the  jjostcrior  abdominal  artery,  which  otherwise  arises  from  the  deep 
femoral. 

The  deep  femoral  artery  is  given  off  above  the  level  of  the  pubis.  The  pos- 
terior abdominal  and  external  pudic  arteries  may  arise  from  it  by  a  short  common 
trunk  or  separately.  The  external  pudic  gives  branches  to  the  i)reinice  but  not 
to  the  penis.     Tiie  popliteal  artery  gives  off  the  peroneal. 

The  femoral  artery  gives  off  a  short  trunk  which  divides  into  anterior  femoral 
and  external  circuniflex  arteries,  the  latter  being  much  the  larger. 

The  saphenous  artery  is  large.  It  descends  on  the  inner  surface  of  the  leg  and 
hock  and  concurs  \\  ith  the  perforating  tarsal  arterj-  in  forming  the  proximal  plantar 
arch. 

The  posterior  tibial  artery  is  small,  being  replaced  distally  by  the  saphenous. 
It  gives  branches  to  the  nuiscles  on  the  posterior  face  of  the  tibia  and  supplies  the 
nutrient  artery  of  that  bone. 

The  anterior  tibial  artery  is  continued  as  the  dorsalis  jiedis  on  the  flexion  sur- 
face of  the  tarsus.  This  gives  off  the  perforating  tarsal  artery,  which  passes  back 
through  the  vascular  canal  of  the  tarsus  and  unites  with  the  terminal  branches  of 
the  saphenous  to  form  the  proximal  jilantar  arch. 

The  metatarsal  and  digital  arteries  resemble  in  arrangement  the  corresponding 
vessels  of  the  fore  limb. 

The  Veins 

The  veins  resemble  in  general  those  of  the  ox.  Thus  there  is  a  hemiazygos 
vein  and  two  jugular  veins,  the  internal  one  being  relatively  larger  than  in  the  ox. 
A  few  differential  features  may  be  noted. 

The  buccinator  vein  resembles  that  of  the  horse,  and  unites  with  the  vena 
reflexa  to  form  a  short  common  trunk  which  joins  the  facial. 

The  facial  vein  resembles  in  general  that  of  the  horse.  The  dorsal  nasal  vein 
is  large,  receives  the  veins  from  the  snout,  runs  backward  in  the  groove  of  the  nasal 
bone  and  joins  the  frontal  vein;  it  is  connected  with  its  fellow  by  a  transverse 
branch,  and  anastomoses  freely  with  the  malar  and  facial. 

The  veins  of  the  distal  parts  of  the  limbs  naturally  present  differences  which 
are  correlated  with  those  of  the  arteries. 


The  Lymph  Vessels  and  Glands 

The  thoracic  duct  often  divides  near  its  termination  into  two  branches  which 
unite  to  form  an  ami)ulla.  The  latter  suddenly  contracts  and  opens  into  the  termi- 
nal ])art  of  the  left  jugular  vein. 

The  submaxillary  lymph  glands  are  situated  in  the  space  between  the  omo- 
hyoid and  internal  pterygoid  muscles  in  relation  to  the  lower  part  of  the  anterior 
border  of  the  suliniaxillary  salivary  gland.  There  are  commonly  two  on  each 
side,  one  large,  the  other  small. 

The  parotid  lymph  glands  (Fig.  309)  are  reddish-brown  in  color.  There  are 
usually  four  of  considerable  size  on  either  side.  One  is  situated  at  the  upper  part  of 
the  pos^^erior  border  of  the  masseter,  partly  covered  by  the  parotid  gland.  Another 
large  subparotid  gland  lies  below  the  liase  of  the  ear.  Ventral  to  this  are  two 
smaller  glands,  one  above  and  one  below  the  external  jugular  vein. 

The  pharyngeal  (or  retropharyngeal)  lymph  glands  (Fig.  310)  are  situated  on 
the  dorsal  wall  of  the  i)liarynx  aliove  the  external  carotid  artery  and  below  and 


THE    LYMPH    VESSELS    AND    GLANDS 


631 


behind  the  paramastoitl  process.  There  are  usually  two  of  considerable  size  on 
either  side. 

The  middle  cervical  lymph  glands  form  a  group  on  the  mastoido-humeralis 
on  the  course  of  the  external  ju^uhir  vein. 

The  prescapular  lymph  glands  are  situated  at  the  anterior  border  of  the 
anterior  deep  pectoral  muscle  under  cover  of  the  trapezius  and  omo-transversarius. 

The  prepectoral  lymph  glands  are  reddish  in  color  and  usually  three  in  number. 
The  largest  is  placed  centrally  under  tlie  trachea;  the  others  are  situated  on  the 
brachial  vessels  as  they  turn  around  the  first  rib. 

Tlie  axillary  lymph  glands  are  usually  absent,  but  very  small  nodes  may  l)e 
found  near  the  insertion  of  the  latissimus  dorsi.     Cubital  glands  are  not  present. 


Fig.  484. — Stomach  and  Part  ok  Lvtestixe  of  P:g,  Spread  Out. 
a,  Pyloric  portion  of  stomach;    6,  duodenum;    c,  jejunum;   d,  caecum;   e, /,  colon;    ff,  pancreas;    A,  epiploi 
foramen  {ol  Winslow);    i,  portal  vein;    t,  hepatic  lymph  glands;    /,  gastric  lymph  glands;    m,  oesophagus.     (Afte 
Edelmann.) 


The  thoracic  lymph  glands  comprise:  (1)  a  gland  of  considerable  size  on  the 
first  segment  of  the  sternum;  (2)  about  half  a  dozen  reddish  glands  along  the  upper 
face  of  the  thoracic  aorta;  (3)  several  glands  along  the  lower  face  of  the  trachea; 
(4)  the  bronchial  lymph  glands ;  one  of  these  lies  on  the  bifurcation  of  the  trachea 
and  another  at  the  apical  bronchus  of  the  right  lung  (Fig.  371). 

The  Iimibar  lymph  glands  are  scattered  along  the  abdominal  aorta  and  the  vena 
cava.     Those  placed  near  the  hilus  of  the  kidney  are  often  designated  renal. 

The  internal  iliac  lymph  glands  are  rounded  and  relatively  large.  They 
comprise:  (1)  three  or  four  glands  situated  on  and  between  the  origin  of  the  cir- 
cumflex iliac  and  the  external  and  internal  iliac  arteries;  (2)  a  gland  in  the  angle 
of  divergence  of  the  internal  iliac  arteries. 


632  CIRCULATORY    SYSTEM    OF    THE    DOG 

The  external  iliac  lymph  glands  are  small,  two  or  three  in  number,  and  lie  in 
front  of  the  cirruniflcx  iliac  vessels  near  the  point  of  the  hip. 
The  visceral  lyiniili  glands  of  the  abdomen  comprise: 

1.  Gastric  lymph  glands  on  the  lesser  curvature  of  the  stomach. 

2.  Several  small  hepatic  lymph  glands  along  the  portal  vein. 

3.  An  elongated  splenic  lymph  gland  ou  the  splenic  vessels  near  the  dorsal  end 
of  the  spleen. 

4.  A  series  of  mesenteric  lymph  glands  situated  along  the  anastomotic  arches 
formed  by  the  vessels  of  the  small  intestine. 

5.  Several  caecal  lymph  glands  situated  along  the  first  part  of  the  csecal  vessels. 

6.  Two  series  of  colic  lymph  glands  which  accompany  the  arteries  of  the 
spiral  part  of  the  colon,  and  are  exposed  by  separating  the  coils  of  the  bowel. 
Small  glands  are  placed  in  the  colic  mesentery  and  above  the  rectum. 

7.  The  anal  lymph  glands  are  situated  on  either  side  on  the  retractor  ani. 

A  small  ischiatic  lymph  gland  is  found  on  the  sacro-sciatic  ligament  near  the 
lesser  sciatic  notch. 

The  precrural  lymph  glands  are  situated  on  the  aponeurosis  of  the  external 
oblique  below  the  external  angle  (if  the  ilium. 

The  superficial  inguinal  lymph  glands  are  situated  behind  the  external  ingui- 
nal ring.     No  deeji  inguinal  lymph  glands  are  present. 

The  popliteal  lymph  glands  are  small  normallj-  and  may  escape  notice. 

A  few  nodules  occur  in  front  of  the  chstal  part  of  the  tendo  Achillis. 


CIRCULATORY  SYSTEM  OF  THE  DOG 
The  Pericardium  and  Heart 

The  pericardium  is  attached  to  the  sternal  part  of  the  diaphragm  by  a  fibrous 
band,  and  is  connected  with  the  sternum  only  by  the  mediastinal  pleura. 

The  heart  is  almost  globular  in  form,  the  ape.x  being  much  blunter  than  in  the 
other  animals,  and  marked  by  a  notch.  Its  long  axis  is  almost  parallel  with  the 
sternum  and  the  apex  (covered  by  the  pericardium)  is  directed  against  the  sternal 
part  of  the  diaphragm.  Its  weight  averages  about  0.8  to  1  per  cent,  of  the  body- 
weight.' 

The  base  extends  forward  to  a  transverse  plane  through  the  lower  ends  of  the  third  pair  of 
ribs.  The  apex  lies  opposite  the  sixth  costal  cartilage  in  expiration.  On  the  right  side  the  peri- 
cardium is  in  direct  contact  with  the  chest-wall  over  a  narrow  triangular  area  (l)ase  anterior) 
from  the  fourth  to  the  sixth  intercostal  space  inclusive.  On  the  left  side  the  area  of  contact  is 
smaller  and  is  at  the  fourth,  fifth,  and  sixth  cartilages. 

The  two  coronary  arteries  may  arise  by  a  common  tnmk.  Each  divides  into 
circumflex  and  descending  branches.  The  left  artery  is  twice  as  large  as  the  right 
one. 

The  great  coronary  vein  ascends  in  the  left  longitudinal  groove  to  the  cor- 
onary groove,  in  which  it  winds  around  the  posterior  face  of  the  heart  to  the 
right  side  and  opens  into  the  right  atrium  below  the  posterior  vena  cava.  Near  its 
termination  it  receives  one  or  two  veins  which  ascend  along  the  right  longitudinal 
furrow.  Several  small  veins  from  the  wall  of  the  right  ventricle  open  into  the 
right  atrium  separately  or  by  a  common  trunk. 

'  The  relative  weight  is  subject  to  wide  variation.  It  is  large  in  hunting  dogs  and  such  as 
are  trained  for  speed  or  worked. 


THE    ARTERIES 


633 


The  Arteries 

There  is  no  common  brachiocephalic  trunk  (anterior  aorta).  Two  hirgc  ves- 
sels arise  from  the  convexity  of  the  aortic  arch;  these  are  the  brachiocephalic  and 
left  brachial  arteries.  The  brachiocephalic  gives  oE  the  two  carotid  arteries,  no 
common  trunk  being  present.  It  freciuently  also  sup]5lies  the  posterior  tliyroid 
artery.     The  intrathoracic  branches  of  the  lirachial  arteries  are  as  follows: 

A  common  trunk  gives  off  the  dorsal,  subcostal,  and  superior  cervical  arteries. 
The  dorsal  artery  passes  out  in  front  of  the  first  ril),  and  the  superior  cervical 
through  the  first  intercostal  space.     The  latter  is  relatively  small. 

The  vertebral  artery  may  arise  either  in  front  of  or  behind  the  trunk  above 
mentioned;  in  the  latter  case  it  crosses  the  inner  face  of  the  trunk.     It  passes  along 


Fig.  485. — .\rteries  of  Thoracic  Cavity  and  Part  of  Neck  of  Dog. 
a.  Aortic  arch;  a',  thoracic  aorta;  b.  bracliiocephaUc  arterj';  c,  left  brachial  artery;  rf.  rf,  common  carotid 
arteries;  e,  vertebral  artery;  /.  dorsal  artery;  tj,  deep  or  superior  cervical  artery  (usually  given  off  from  a  com- 
mon trunk  with  /':  h.  extrathoracic  part  of  /;  i,  subcostal  artery;  k,  inferior  cer\ucal  artery;  I.  descending 
branch  of  k:  m.  ascending  branch  of  k:  n,  internal  scapular;  o,  acromial;  p,  superficial  cer\'ical;  q.  s.  extrathoracic 
part  of  left  brachial;  r.  external  thoracic;  t,  internal  thoracic;  t' ,  asternal;  (".  anterior  abdominal;  u,  perforating 
branch  of  (;  r,  anterior  mediastinal  (thymic);  u',  ventral  intercostals;  x.  bronchial;  t/,  oesophageal;  2/.  dorsal 
intercostals;  z,  descending  branch  of  left  coronary  artery;  z*.  circumiiex  branch  of  same;  1,  cesophagus;  2, 
trachea;  3^,  bronchi;  3,  first  rib  (sawn  off);  4.  right  ventricle;  5,  left  ventricle;  -5'.  left  auricle;  5",  pulmonary 
artery  (cut  off);  (?,  diaphragm;  7,  S,  9,  last  three  cervical  vertebrae;  10,  thymus.  (.\fter  EUenberger,  in 
Leisenng's  Atlas.) 


the  neck  in  typical  fashion  to  the  third  cervical  vertebra  and  divides  into  three 
branches.  The  largest  of  these  supplies  the  muscles  in  this  region,  compensating 
for  the  absence  of  branches  of  the  superior  cervical  artery.  The  second  passes 
between  the  second  and  third  cervical  vertebra^  into  the  vertebral  canal  and  unites 
with  the  opposite  artery  and  a  branch  of  the  occipital  arterj-  to  form  the  basilar. 
The  third  branch  is  the  small  continuation  of  the  parent  trunk;  it  passes  to  the 
wing  of  the  atlas  and  anastomoses  with  the  occipital. 

The  inferior  cervical  artery  gives  off  the  superficial  cervical  which  ascends  in 
front  of  the  supraspinatus. 

The  internal  thoracic  artery  is  large  and  sends  perforating  branches  to  the 
pectoral  mammary  glands. 


634 


CIRCULATORY   SYSTEM    OF   THE    DOG 


The  external  thoracic  artery  arises  outside  of  the  thorax  and  sends  Ijranches 
to  the  mammary  ghinds. 

The  common  carotid  arteries,  left  and  right,  arise  in  that  order  from  the 
brachiocephalic.  In  the  neck  the  right  one  lies  on  the  trachea,  the  left  on  the 
oesophagus.  Collateral  branches  arc  the  posterior  thjToid  (which  may,  however, 
arise  from  the  right  or  left  brachial  or  the  inferior  cervical),  pharyngeal,  thryo- 
laryngeal,  muscular,  tracheal,  and  glandular  (to  the  submaxillary  gland).  Each 
carotid  divides  under  the  wing  of  the  atlas  into  occipital  and  internal  and  ex- 
ternal carotid  branches. 

The  occipital  artery  is  small.  It  gives  off  condyloid  and  posterior  meningeal 
branches,  jjasscs  up  through  the  notch  on  the  anterior  margin  of  the  wing  of  the 
atlas,  and  is  tlistributed  to  the  muscles  of  this  region.     Its  cerebrospinal  branch 


Fir,.  486.— SuPERFicuL  Vkssels  of  Head  of  Dog. 
/,  Facial  artery;  S.  inferior  labial  artery;  3,  artery  of  angle  of  mouth;  4.  superior  labial  artery;  6,  lateral 
nasal  artery;  e,  dorsal  na.sal  artery;  ?•,  superficial  temporal  artery;  S,  transverse  facial  artery;  S,  anterior  auricular 
artery;  10,  zygomatico-orbital  artery;  /;,  satellite  vein  of  10;  12.  ant.  auricular  vein;  IS,  superficial  temporal 
vein;  H,  internal  ma.\illary  vein;  Id,  post,  auricular  vein;  16.  17,  external  jugular  vein;  18,  external  maxillary 
vein;  i9,  J?ij,  facial  vein;  «0,  inf.  labial  vein;  «/,  buccinator  vein;  2^,  vena  refiexa;  2.<,  superior  labial  vein;  25, 
vena  angularis  oculi;  ^ff,  dorsal  nasal  vein;  a,  concha;  6,  parotid  gland;  c  submaxillary  gland;  (/.submaxillary 
lymph  glands;  <•.  mylo-hyoideus;  /,  digastricus;  i;,  masseter;  h.  zygomaticus;  i.  scutularis;  A-.  tejnporalis;  /,  or- 
bicularis oculi;  m,  zygnmatic  arch;  n,  retractor  angnli  oris;  o.  buccinator.     (EUeiiberger-Baum,  .\nat.  d.  Ihmdes.) 


passes  through  the  intervertebral  foramen,  and  unites  in  the  vertebral  canal  with 
its  fellow  and  a  branch  from  the  vertebral  artery  to  form  the  basilar.  A  retrograde 
branch  anastomoses  with  the  vertebral  as  in  the  horse. 

The  internal  carotid  artery,  also  small,  passes  to  the  foramen  lacerum  [)osterius, 
enters  the  carotid  canal  and  forms  a  bend  before  entering  the  cranium  through  the 
carotid  foramen.  It  forms  a  plexus  which  is  connectetl  by  liranches  with  the  middle 
meningeal  and  ophthalmic  arteries.  It  then  perforates  the  dura  mater  and  enters 
into  the  formation  of  the  arterial  circle  (of  Willis). 

The  external  carotid  artery  is  tiie  ihrect  continuation  of  the  common  carotid. 
It  passes  along  the  lateral  wall  of  the  pharynx,  emerges  from  beneath  the  digastricus. 
and  divides  into  suiierficial  temijoral  and  internal  maxillary  arteries.  It  gives  off 
the  large  fiexuous  lingual  artery  which  has  a  course  similar  to  that  of  the  horse. 


THE    ARTERIES  635 

The  external  maxillary,  smaller  than  the  lingual,  passes  along  the  upper  border  of 
the  digastrieus,  gives  off  the  sul)lingual,  gains  the  anterior  border  of  the  masseter, 
and  divides  into  superior  and  inferior  labial  and  the  angularis  oris.  The  last-named 
vessel  passes  forward  on  the  cheek  between  the  labials  to  the  angle  of  the  mouth. 
The  sublingual  artery  passes  at  first  along  the  upper  border  of  the  digastrieus 
and  continues  between  the  mylo-hyoideus  and  the  ramus  of  the  mandible.  The 
posterior  auricular  artery  arises  at  the  anterior  border  of  the  digastrieus,  gives 
branches  to  the  salivary  glands  and  the  adjacent  muscles,  and  ascends  on  the  convex 
face  of  the  concha.  It  divitles  into  two  branches  which  return  along  the  borders 
of  the  external  ear. 

The  superficial  temporal  artery,  after  giving  off  the  anterior  auricular  artery  and 
a  small  transverse  facial  artery,  turns  forward  under  the  tenijioral  fascia  toward  the 
eye,  and  dividt'S  into  upper  and  lower  branches  which  supply  the  frontal  region  and 
the  eyelids.  It  also  supplies  branches  to  the  parotid  gland  and  the  masseter  and 
temporalis  muscles. 

The  internal  maxillary  artery  pursues  a  course  similar  to  that  of  the  horse. 
The  mental  branches  of  the  inferior  alveolar  (or  dental)  artery  are  of  considerable 
size  and  are  distributed  in  the  lower  lip  and  gums.  Two  or  three  deep  temporal 
arteries  are  present.  The  anterior  one  may  arise  from  the  buccinator;  it  gi\'cs  off 
the  middle  meningeal,  which  sends  a  branch  to  the  carotid  ple.xus.  The  ophthalmic 
artery  gives  off  a  branch  which  enters  the  cranium  through  the  foramen  lacerum 
orbitale  and  connects  with  the  internal  carotid;  this  is  termed  the  internal  ophthal- 
mic and  gives  off  the  artcria  centralis  retinae.  The  superficial  branches  of  the 
infraorbital  artery  replace  the  dorsal  and  lateral  nasal  arteries,  and  compensate  for 
the  small  size  of  the  superior  labial. 

The  brachial  artery  in  its  course  in  the  arm  presents  no  special  features.  At 
the  elbow  it  passes  between  the  biceps  and  the  pronator  teres,  descends  (as  the 
median)  under  the  flexor  carpi  radialis  about  a  third  of  the  way  down  the  forearm, 
and  divides  into  railial  and  ulnar  arteries.  Among  its  collateral  branches  are: 
(1)  The  subscapular  artery,  which  passes  up  between  the  subscapularis  and  teres 
major,  turns  around  the  posterior  angle  of  the  scapula  and  terminates  in  the  supra- 
spinatus,  deltoid,  trapezius,  and  mastoido-humeralis.  In  about  half  the  cases  it 
gives  off  the  anterior  circumflex,  Avhich  often  arises  with  the  posterior  circumflex. 
Its  other  branches  resemble  those  of  the  horse.  (2)  The  anterior  circumflex  artery 
(in  about  half  the  cases).  (3)  The  deep  brachial  arises  aliout  a  third  of  the  way 
clown  the  arm.  (4)  The  bicipital  artery  (for  the  liiceps)  is  given  off  at  the  lower  part 
of  the  arm.  (.j)  The  proximal  collateral  radial  artery  (not  present  in  the  horse) 
arises  at  the  lower  fourth  of  the  arm,  crosses  over  the  terminal  part  of  the  biceps, 
descends  on  the  extensor  carpi  radialis,  and  concurs  with  a  branch  of  the  volar 
interosseous  in  forming  the  rete  carpi  dorsale.  It  often  supplies  the  bicipital 
artery.  (6)  The  anterior  radial  artery  (A.  collateralis  radialis  distalis)  is  very 
small.  (7)  The  common  interosseous  artery  is  given  off  a  little  below  the  elbow. 
It  supplies  branches  to  tlie  flexor  muscles  and  the  dorsal  interosseous  artery, 
which  passes  through  the  interosseous  .space,  gives  branches  to  the  extensor  muscles, 
and  by  its  terminal  twigs  concurs  in  the  formation  of  the  rete  carpi  dorsale.  The 
direct  continuation  of  the  trunk  is  the  volar  interosseous  artery,  which  descends 
under  cover  of  the  pronator  f|uadratus,  gives  off  a  branch  to  the  rete  carpi  dorsale 
and  the  fifth  volar  metacarpal  artery,  antl  terminates  by  joining  the  volar  liranch 
of  the  radial  artery  to  form  the  deep  volar  arch.  (8)  The  volar  antibrachial  artery 
(Ramus  volaris  antibrachii)  arises  below  the  interosseous  and  descends  at  first 
under  the  flexor  carpi  radialis,  then  between  the  heads  of  the  deep  flexor,  and  divides 
into  ascending  and  descending  branches. 

The  radial  artery,  the  smaller  terminal  of  the  brachial,  descends  along  the  inner 
border  of  the  radius,  and  divides  near  the  carpus  into  dorsal  and  volar  branches. 


636 


CIRCULATORY    SYSTEM    OF   THE    DOG 


The  dorsal  branch  assists  in  forming  the  rete  carpi  dorsale.  The  larger  volar 
branch  descends  l)ehind  the  inner  border  of  the  carpus  and  joins  the  end  of  the  volar 
interosseous  in  forming  the  deep  volar  arch.     From  this  areh  three  deep  volar 


Fig.  487. — Vessels  and  Nerves  of  Inner  Surface 
OF  Shoulder  and  Arm  of  Dog. 
a,  b.  Brachial  artery;  c,  subscapular  ves.sels;  d, 
thoracico-dorbal  vessels;  e,  deep  brachial  vessels;  /,  sup- 
erior collateral  ulnar  vessels;  g,  brachial  vein;  h,  h", 
cephalic  vein;  h',  mediano-radial  vein;  (,  anterior 
thoracic  nerves;  k,  musculo-cutaneous  nerve;  /,  median 
nerve;  m,  ulnar  ner\'e;  «,  radial  nerve;  o,  thoracico- 
dorsal  nerve;  1,  subscapularis  muscle;  2.  supraspinatus 
muscle;  S,  teres  major,  4,  latissimus  dorsi;  5,  deep 
pectoral  muscle;  6,  biceps  brachii;  7,  lonfi  head  of  tri- 
ceps; S,  tensor  fascitp  antibrarhii;  9,  internal  head  of 
triceps;  10,  pronator  teres.  (Ellenberger-Baum,  .\nat. 
d.  Hunde**.) 


Fig.  4S8. — Arteries  of  Forearm  of  Dog,  Inner 
View. 
a,  Brachial;  a',  median;  c,  common  interos- 
seous; d,  volar  antibrachial;  e,  radial;  *•',  e",  dorsal 
and  volar  branches  of  e;  f,f',  cutaneous  branches 
of  e;  (7,  ulnar;  /,  biceps  brachii;  2.  extensor  carpi 
radialis;  3,  pronator  teres;  4.  deep  digital  flexor; 
6,  radius;  6,  superficial  digital  flexor;  7,  flexor 
carpi  radialis;  S.  flexor  carpi  medius;  9,  humerus. 
(Ellenberger-Baum,  Anat.  d.  Hundes.) 


metacarpal  arteries  descend  in  the  second,  third,  and  fourth  intermetacarpal 
spaces  and  concur  with  the  corresponding  superficial  volar  and  the  dorsal  arteries 
to  form  the  common  digitals. 


THE    ARTEKIES 


637 


The  ulnar  artery  descends  on  the  deep  flexor  of  the  digit,  and  sends  a  connecting 
branch  to  the  radial  ahove  the  carpus.  Near  the  middle  of  the  metacarpus  it  gives 
off  the  first  volar  metacarpal  artery  and  divides  into  the  second,  third,  and  fourth 
superficial  volar  metacarpal  arteries.  The  first  volar  artery  unites  with  the  cor- 
responding dorsal  artery  to  form  the  first  common  digital  artery,  which  supplies 
proper  digital  arteries  for  the  opposed  surfaces  of  the  first  and  second  digits.  The 
superficial  volar  arteries  descend  in  the  spaces  between  the  other  metacarpal  bones, 
unite  near  the  metacarpo-phalangeal  joints  with  the  corresponding  deep  volar  and 
dorsal  metacarpal  arteries  to  form  three  common  digital  arteries.     Each  of  the  latter 


Fig.  489. — .\rteries  of  Distal  Part  of  Right  Fore 
Limb  of  Dog,  .Interior  View. 
a,  Branch  of  volar  interosseous  artery:  b, 
proximal  collateral  radial  arter>'  (external  branch); 
c,  radial  artery  (dorsal  branch);  d,  rete  carpi  dorsale; 
e,  deep  dorsal  metacarpal  arteries;  /.  superficial  dorsal 
metacarpal  arteries;  g,  common  digital  arteries;  k, 
proper  digital  arteries. 


Fig.  490. 
i.  Radial  artery;  ;.  ulnar  artery;  k.  volar  in- 
terosseous arterj-;  /.deep  volar  arch;  m.  external  (fifth) 
volar  metacarpal  artery;  n.  deep  volar  metacarpal 
arteries;  p,  superficial  volar  metacarpal  arteries:  o, 
q,   common   digital  arteries;    r,  proper  digital  arteries. 


divides  after  a  short  course  into  two  proper  digital  arteries,  which  run  along  the 
opposed  surfaces  of  the  second  to  the  fifth  digits.  The  external  digital  artery  of 
the  fifth  digit  comes  from  the  superficial  volar  arch  formed  by  the  union  of 
a  branch  of  the  volar  interosseous  with  the  fourth  superficial  volar  metacarpal 
artery. 

The  rete  carpi  dorsale  gives  off  four  dorsal  metacarpal  arteries  which  descend 
in  the  intermetacarpal  spaces  and  unite  near  the  metacarpo-phalangeal  joints  with 
the  volar  arteries  to  form  the  common  digitals. 

The  thoracic  aorta  supplies  the  last  nine  or  ten  pairs  of  intercostal  arteries, 
but  no  anterior  phrenic  arteries.     It  gives  off  two  or  more  oesophageal  branches,  in 


638 


CIRCULATORY    SYSTEM    OF   THE    DOG 


addition  to  the  broncho-oesophageal,  which  arises  close  to  or  with  the  sixth  inter- 
costal and  ramifies  in  the  usual  manner. 

The  abdominal  aorta,  after  giving  off  the  external  iliac  arteries,  continues 
about  half  an  inch  tu  an  inch  (ca.  1  to  3  cm.)  under  the  last  lumbar  vertebrsB,  gives 
off  the  internal  iliacs,  and  is  continued  by  the  middle  sacral  artery.  This  small 
vessel  runs  backward  under  the  sacrum  and  coccygeal  vertebrae  and  gives  off 
branches  in  segmental  fashion. 

The  coeliac  artery  gives  off  the  hepatic  artery  and  forms  a  short  gastro-splenic 
trunk.  The  hepatic  artery  gives  off  several  hepatic  branches,  and  the  pyloric  or 
right  gastric  artery,  which  passes  along  the  lesser  curvature  of  the  stomach,  anasto- 
moses with  the  (left)  gastric  artery,  and  is  continued  by  the  gastro-duodenal.     This 


Fig.  491. — End  Branches  of  Aorta  and  Radiclp;!?  of  rosTERioR  Vena  Cava  or  Dog. 
o,  .\bdominal  aorta;  6,  posterior  mesenteric  artery;  c,  lumbar  arteries;  d,  circumflex  iliac  artery;  e,  ex- 
ternal iliac  artery;  /,  deep  femoral  artery;  g,  posterior  abdominal  artery;  h,  external  pudic  artery;  a,  femoral 
artery;  i,  i,  internal  iliac  arteries;  t,  visceral  branch  of  iV  /,  parietal  branch  of  iV  m,  iUo-lumbar  artery;  n,  anterior 
gluteal  artery;  o,  lateral  coccygeal  artery;  p,  posterior  gluteal  artery;  q,  umbilical  artery;  r,  middle  h:i-mor- 
rhoidal  artery;  3,  posterior  hajmorrhoidal  artery;  s,  perineal  artery;  (,  art.  profunda  penis;  n,  art.  bulhi 
urethra;  i",  art.  dorsalis  penis;  u),  middle  sacral  artery,  a',  posterior  vena  cava;  other  veins  are  satellites  of 
arteries  and  correspondingly  named;  i,  ilio-psoas  muscle;  5,  tendon  of  psoas  minor;  3,  abdominal  mu.icles;  i, 
sartorius;  5,  rectus  femoris;  B' ,  vastus  internus;  6,  pectineus;  S',  adductor;  7,  gracilis;  8,  symphysi-s  pelvis;  9, 
ilium;  ;0,  pyriformis;  //.gluteus  superficialis;  12.  obturator  internus;  /rf,  penis;  H,  lumbar  vertebr.T.  (After 
Ellenberger,  in  Leisering's  .\tla3.) 


divides  near  the  jiylorus  into  right  gastro-epiploic  and  pancreatico-duodenal. 
The  (left)  gastric  artery  passes  to  the  lesser  curvature  of  the  stomach  and  ramifies 
chiefly  on  the  left  part  of  the  stomach,  giving  off  a  branch  which  anastomoses  with 
the  pyloric  liranch  of  the  hepatic.  The  splenic  artery  gives  off  pancreatic  branches, 
and  reaches  the  lower  part  of  the  spleen.  It  gives  off  the  left  gastro-epiploic,  and 
a  branch  which  passes  to  the  dorsal  end  of  the  spleen,  which  it  supplies,  besides 
giving  off  twigs  to  the  left  extremity  of  the  stomach. 

Th"^  anterior  mesenteric  artery  arises  close  behind  the  coeliac.  It  gives  off  a 
connnon  trunk  for  two  colic  arteries  and  the  ileo-c?eco-colic.  The  former  supply 
the  transverse  and  the  anterior  part  of  the  left  or  descending  colon,  while  the  latter 
divides  into  liranches  for  the  ileum,  caecum,  and  first  part  of  the  colon.  The  trunk 
is  continued  as  the  artery  of  the  small  intestine,  giving  off  fourteen  to  sixteen 


THE    AHTEKIES 


639 


branches  (Aa.  jpjiinales),  which  form  a 
series  of  anastomotic  arches  in  the 
mesentery  near  tlic  howcl. 

Two  phrenico-abdominal  arteries 
(Aa.  phreniciE  caudales)  come  off  from 
the  aorta  behind  the  anterior  mesenteric, 
and  divide  into  phrenic  and  abdominal 
branches.  Each  phrenic  artery  diverges 
from  its  fellow  in  descending  on  the  ab- 
dominal surface  of  the  corresponding  crus 
of  the  diaj^hragm  to  the  sternal  part.  The 
inner  branches  anastomose  with  those  of 
the  opposite  artery,  the  outer  branches 
with  intercostal  arteries  chiefly.  The  ab- 
dominal arteries  give  branches  to  the  lum- 
bar muscles,  the  renal  fat  and  capsules, 
and  ramify  in  the  oblicjue  abdominal 
muscles. 

The  renal  and  spermatic  arteries 
offer  no  special  featui'cs. 

The  utero-ovarian  artery  divides 
near  the  ovary  into  three  or  four 
branches  which  supplj'  the  ovary  and 
uterus,  anastomosing  with  the  uterine 
artery. 

The  posterior  mesenteric  artery  is 
small.  It  divides  into  two  branches 
which  supply  the  terminal  part  of  the 
colon  and  the  anterior  part  of  the 
rectum. 

The  circumflex  iliac  artery  usually 
arises  from  the  terminal  part  of  the 
aorta. 

The  external  iliac  artery  usually 
gives  off  no  collateral  branches. 

The  femoral  artery  has  the  usual 
course.  The  deep  femoral  gives  off  the 
posterior  abdominal  and  external  pudic 
arteries  by  a  very  short  common  trunk 
or  separately.  In  the  female  the  ex- 
ternal pudic  divides  into  anterior  and 
posterior  branches;  the  former  runs  for- 
ward, supplies  branches  to  the  inguinal 
lym]:)h  glands,  the  mammary-  glands  and 
skin,  and  anastomoses  with  the  mam- 
mary Ijranch  of  the  internal  thoracic 
artery;  the  posterior  branch  pursues  a 
flexuous  course  between  the  thighs  to 
the  vulva,  where  its  terminal  branches 
anastomose  with  the  internal  pudic 
artery.  The  anterior  femoral  may  arise 
by  a  short  common  trunk  with  the 
external  circumflex.  The  former,  ac- 
companied by  the  anterior  branch  of  the 


Dternal 


Fig.  492. — Arteries  of  Pelvic 
Li.MB  Of  Dog,  Internal  View. 
a.  Abdominal  aorta;  b,  fe- 
moral: c,  c',  deep  femoral;  d,  pos- 
terior abdominal;  e,  external  pudic;  /, 
cuniflex;  (/,  anterior  femoral  (accompanied  by 
terior  branch  of  femoral  nerve);  h,  external 
flex;  /,  k,  muscular  branches;  /,  articular  blanch; 
7/(,  saphenous;  n,  o,  plantar  and  dorsal  branches  of 
sai>henous;  q,  saphenous  nerve;  r,  obturator  nerve; 
/.ilio-psoas;  .2,  ilium;  5,  gracilis;  4<  semitendinosus; 
5,  adductor  raagnus;  G,  adductor  longus;  7,  quadri- 
ceps femoris;  8,  sartorius;  9,  semimembranosus;  10, 
gastrocnemius;  1 1 ,  tibialis  anterior;  IS,  tibia.  (EUen- 
berger-Baum,  Anat.  d.  Hundes.) 


640 


CIRCULATORY  SYSTEM  OF  THE  DOG 


femoral  nerve,  dips  in  between  the  rectus  femoris  and  vastus  inteinus.  The  ex- 
ternal circumflex  arterj^  passes  forward  between  the  sartorius  internally  and  the 
rectus  femoris  and  tensor  fasciae  lata;  externally  and  supplies  branches  to  these 
•muscles  and  the  glutei.  In  addition  to  muscular  branches  of  considerable  size, 
an  articular  branch  (A.  genu  suprema)  arises  a  little  below  the  middle  of  the  thigh 
and  runs  downward  and  forward  to  the  inner  face  of  the  stifle  joint.  The  saphenous 
artery  is  large.  It  arises  from  the  inner  surface  of  the  femoral  a  little  below  the 
middle  of  the  femur,  descends  superficially  to  the  upper  part  of  the  leg  and  divides 
into  two  branches.     The  smaller  anterior  branch  (Ramus  dorsalis)  passes  oiiliquely 


Fig.  493. — .\rterie8  of  Distal  Part  of  Right  Hind 
Limb  of  Dog,  Anterior  View. 
a,  E.xternal  branch  of  anterior  tibial  artery; 
b,  anterior  tibial  artery;  c,  saphenous  artery  (anterior 
branch):  d,  perforating  metatarsal  artery;  e,  dorsal 
metatarsal  arteri&s:  /.  deep  dorsal  metatarsal  arteries: 
(7,  superficial  dorsal  metatarsal  arteries:  h,  anasto 
between  dorsal  and  plantar  arteries; 
digital  arteries:  j.  proper  digital  arteries. 


Fig.  494. — .\rtehies  of  Distal  Part  of  Right  Hixn 
Limb  of  Dog,  Posterior  View. 
k,  Saphenous  artery  (posterior  branch);  I,  V, 
internal  and  external  plantar  arteries;  in,  perforating 
metatarsal  artery;  n,  deep  plantar  metatarsal  arterie;': 
o,  superficial  plantar  metatarsal  arteries;  p,  common 
digital  artery;    q,  proper  digital  arteries. 


downward  and  forward  across  the  inner  surface  of  the  tibia  to  the  flexion  surface  of 
the  hock  and  terminates  in  three  superficial  dorsal  metatarsal  arteries.  The  poste- 
rior branch  (Ramus  plantaris)  passes  down  on  the  inner  face  of  the  gastrocnemius 
and  the  long  digital  flexor.  It  gives  off  a  branch  (A.  tarsea  lateralis)  which  descends 
obliquely  to  the  external  surface  of  the  tarsus,  and  at  the  posterior  face  of  the  tarsus 
detaches  the  internal  and  external  plantar  arteries;  these  descend  on  either  side 
of  the  deej)  flexor  tendon  and  unite  with  the  perforating  metatarsal  artery  to  form 
the  proximal  i)laiitar  arch.  The  artery  continues  down  the  middle  of  the  plantar 
surface  of  the  metatarsus  and  divides  near  the  metacarpo-phalangeal  joints  into 


THE    VEINS  641 

three  superficial  plantar  metatarsal  arteries.  These  vessels  unite  with  throe  deep 
plantar  metatarsal  arteries  which  ilescend  from  the  proximal  ])lantar  arch  and  witii 
Ijranehes  from  the  dorsal  metatarsal  arteries.  From  these  anastomoses  four  digital 
arteries  result:   of  these,  the  central  two  have  a  common  digital  trunk. 

The  popliteal  and  posterior  femoral  arteries  present  nothing  of  special  interest. 

The  posterior  tibial  artery  is  small,  being  replaced  largely  bj-  the  saphenous. 
It  supplies  twigs  to  the  tlext)r  nmsdes  at  the  upper  part  of  the  leg. 

The  anterior  tibial  artery  descends  on  the  anterior  face  of  the  tibia  and  tarsus 
and  is  continued  as  the  perforating  metatarsal  artery,  which  passes  through  the 
u]i]ier  part  of  the  space  between  the  second  and  third  metatarsal  bones  and  concurs 
with  the  plantar  branches  of  the  saphenous  in  the  formation  of  the  plantar  arch. 
Besides  muscular  and  articular  branches,  the  anterior  tiliial  supplies  the  external 
or  fifth  dorsal  metatarsal  artery  for  the  outer  side  of  the  fifth  digit.  At  the  proximal 
ixirt  of  the  metatarsus  it  gives  off  three  deep  dorsal  metatarsal  arteries  which 
descend  in  the  intervals  between  the  metatarsal  bones  and  concur  with  the  sujier- 
ficial  dorsal  and  the  plantar  arteries  in  the  formation  of  the  digital  arteries.  The 
latter  resemble  in  general  arrangement  the  corresponding  arteries  of  the  thoracic 
limb. 

The  internal  iliac  artery  (Fig.  491)  runs  backward  and  a  little  outward  across 
the  ilio-psoas,  and  on  reaching  the  ilium  divides  into  parietal  and  visceral  branches. 
The  parietal  branch  is  the  larger.  It  runs  backward  on  the  lateral  wall  of  the 
pelvis,  passes  out  through  the  lesser  sciatic  notch,  and  breaks  up  into  branches 
which  suppl.y  the  muscles  in  this  region  like  the  posterior  gluteal  (or  ischiatic)  artery 
of  the  horse.  It  gives  off  the  following  branches:  (1)  The  ilio-lmnbar  artery 
passes  outward  between  the  ilio-psoas  and  the  shaft  of  the  ilium  and  ramifies 
in  the  gluteus  medius,  giving  branches  to  the  ilio-psoas  and  tensor  fasciae  lat£p; 
it  may  arise  from  the  internal  iliac.  (2)  The  anterior  gluteal  artery  passes  out 
behind  the  posterior  superior  spine  of  the  ilium  and  supplies  branches  to  the  glutei. 
(3)  Muscular  branches  go  to  the  obturator  internus,  coccygeus,  and  retractor  ani. 
(,4)  The  lateral  coccygeal  artery  (A.  caudalis  lateralis  superficialis)  passes  back  at  first 
on  the  outer  face  of  the  coccygeus  and  continues  beneath  the  skin  along  the  side  of 
the  tail.  The  visceral  branch  or  internal  pudic  artery  passes  back  below  the  parietal 
liranch  on  the  lateral  face  of  the  rectum,  retractor  ani,  and  coccygeus.  Its  chief 
collateral  branches  are:  (1)  The  imibilical  artery,  which  pursues  a  flexuous  course 
and  supplies  twigs  to  the  bladder,  ureter,  and  vas  deferens.  In  the  bitch  it  gives 
off  a  large  uterine  artery  which  ramifies  chieflj-  in  the  body  and  neck  of  the  uteius 
and  the  vagina  and  anastomoses  with  the  utero-ovarian.  (2)  The  middle  haemor- 
rhoidal  artery  arises  near  the  ischial  arch,  passes  upward  and  forward  on  the  lateral 
surface  of  the  rectum,  gains  its  dorsal  surface  and  anastomoses  with  the  posterior 
mesenteric;  it  supplies  the  rectum  and  the  anus,  together  with  its  muscles  and 
glands.  (3)  A  small  perineal  artery  is  detached  to  the  perineum.  In  the  male  the 
trunk  turns  around  the  isc'hial  arch  as  the  artery  of  the  penis  (A.  ])enis).  This 
vessel,  after  giving  off  the  deep  artery  of  the  penis  (A.  profunda  penis),  which 
supplies  the  artery  of  the  bulb  (.\.  bulhi  urethra')  and  enters  the  corpus  cavernosum, 
is  continued  as  the  dorsal  artery  of  the  penis  (A.  dorsalis  penis)  along  the  dorsum 
penis.  In  the  female  the  terminal  branches  of  the  trunk  go  to  the  vulva,  vestibular 
bulb,  and  clitoris. 

The  Veins 

The  arrangement  of  the  veins  is,  of  course,  correlated  in  general  with  the  arterial 
system,  but  a  few  special  features  are  worthy  of  mention. 

The  anterior  vena  cava  is  formed  by  the  junction  of  short  right   and  left 
brachiocephalic  (or  subclavian)  veins,  and  each  of  the  latter  results  from  the  con- 
fluence of  jugular  and  brachial  veins. 
41 


042  CIRCULATOKY    SYSTEM    OF   THE    DOG 

The  vena  azygos  roscmlilcs  that  of  the  horse,  and  receives  at  the  ninth  or 
tenth  thoracic  vertelira  a  vena  hemiazygos. 

Two  jugular  veins  are  present  on  each  side.  The  external  jugular  vein  is 
formed  by  tiie  union  of  external  and  internal  maxillarj'  veins  at  the  posterior  border 
of  the  submaxillary  gland.  The  two  external  jugulars  are  commonly  united  by  a 
transverse  branch  below  the  cricoid  cartilage.  Each  passes  along  the  neck  on  the 
sterno-cephalicus,  covered  only  by  the  skin  and  panniculus,  dips  under  the  cleido- 
cervicalis,  and  joins  the  internal  jugular. 

The  external  maxillary  vein  arises  on  the  lateral  nasal  region  by  the  junction 
of  the  dorsal  nasal  vein  witii  the  angularis  oculi.  Near  the  infraorbital  foramen  it 
receives  the  lateral  nasal  vein,  and  a  little  lower  the  superior  labial.  In  its  course 
along  the  anterior  border  of  the  masseter  it  receives  the  vena  reflexa,  which  arises 
in  the  pterygo-palatine  fossa  by  the  junction  of  infraorbital,  sphenopalatine,  and 
palatine  radicles,  together  with  a  branch  from  the  cavernous  sinus.  At  the  lower 
border  of  the  mandiljle  it  is  joined  by  the  inferior  labial  vein,  which  receives  the 
buccinator  vein.  The  lingual  vein  is  connected  with  its  fellow^  by  a  superficial 
transverse  branch  at  the  insertion  of  the  sterno-hyoidei.  The  sublingual  and 
submental  veins  terminate  in  a  variable  manner,  liut  often  form  a  common  trunk 
which  joins  the  lingual. 

The  internal  maxillary  vein  arises  from  the  pterygoid  plexus,  formed  chiefly 
by  dorsal  lingual,  inferior  alveolar,  deep  temporal,  pterygoid,  and  meningeal  tribu- 
taries. It  receives  the  sujierior  cerebral,  auricular,  superficial  temporal,  transverse 
facial,  and  masseteric  veins,  and  often  a  trunk  formed  by  the  union  of  the  inferior 
cerebral  and  occipital  veins. 

The  internal  jugular  vein  results  usually  from  the  junction  of  laryngeal  and 
thyroid  veins,  but  in  some  cases  it  is  formed  by  the  confluence  of  the  inferior  cerebral 
and  occipital  veins. 

The  brachial  and  radial  veins  are  satellites  of  the  arteries. 

The  ulnar  vein  is  usually  double.  It  unites  below  the  carpus  with  a  branch  of 
the  interosseous  vein  to  form  the  superficial  venous  arch. 

The  cephalic  vein  accompanies  the  ulnar  artery  in  the  forearm  and  joins  the 
superficial  venous  arch  b(>low. 

The  accessory  cephalic  vein  arises  from  the  union  of  three  dorsal  metatarsal 
veins.     It  joins  the  cephalic  about  the  middle  of  the  forearm. 

There  are  three  short  volar  metacarpal  veins  which  open  into  the  superficial 
venous  arch.  They  are  formed  above  the  metacarpo-phalangeal  joints  by  the 
junction  of  the  volar  digital  veins,  of  which  there  are  two  for  each  of  the  chief 
digits.     The  volar  vein  of  the  first  digit  joins  the  superficial  venous  arch. 

Each  of  the  chief  digits  has  two  dorsal  digital  veins,  wliile  the  first  digit  has  one. 

The  posterior  vena  cava,  its  collateral  affluents,  and  common  iliac  radicles 
present  no  s])cciai  features  of  importance. 

The  internal  iliac  vein  corresponds  in  regard  to  its  tributaries  with  the  liranches 
of  the  artery,  except  tiiat  it  is  not  di\-i(ied  into  dorsal  anil  ventral  branches. 

The  external  iliac,  femoral,  and  popliteal  veins  with  tiieir  collateral  tributaries 
are  satellites  of  the  arteries. 

The  anterior  tibial  vein  is  usually  double,  and  the  posterior  tibial  vein  is  very 
small. 

The  internal  saphenous  vein  is  the  upward  continuation  of  the  internal  ]ilantar 
metatarsal  vein.  It  comnmnicates  by  a  large  branch  with  the  dorsal  metatarsal 
vein,  and  ascends  the  leg  as  a  satellite  of  the  saphenous  artery  and  its  plantar 
(posterior)  branch.  The  recurrent  tarsal  or  external  saphenous  vein  is  larger. 
It  is  formed  at  the  lower  part  of  the  leg  by  the  imion  of  dorsal  and  external  plantar 
metatarsal  veins,  crosses  the  outer  surface  of  the  leg  obliquely  upward  and  back- 
ward, ascends  behind  the  gastrocnemius  and  joins  the  posterior  femoral  vein. 


THE    LYMPH    VESSELS    AND    GLANDS  643 

The  metatarsal  and  digital  veins  rosoinl)le  in  general  the  corresponding  vessels 
of  the  fore  Hinl). 

The  Lymph  Vessels  and  glands 

The  cistema  chyli  is  hxrge  and  fusiform.  The  thoracic  duct  may  be  single 
throughout,  hut  often  tlivides  anteriorly  into  two  branches,  which  may  then  unite 
and  form  a  tlilatation  which  receives  the  left  tracheal  duct  and  the  vessels  from  the 
fore  limb.  The  primitive  plexiform  arrangement  persists  in  varying  degree.  The 
duct  terminates  in  the  left  brachiocephalic  vein. 

The  tracheal  ducts  accompany  the  internal  jugular  veins.  The  right  duct 
opens  into  th(>  right  l)racliioc('])halic  vein. 

The  submaxillary  lymph  glands  (Fig.  48G)  are  commonly  three  in  number  on 
each  side.  They  are  situated  in  the  angle  between  the  masseter  and  the  submaxil- 
lary salivarj'  gland,  in  relation  to  the  external  maxillary  vein  and  covered  only 
by  the  skin  and  panniculus.  The  number  may  be  reduced  to  two  or  one  with  a 
corresponding  increase  in  size. 

A  small  round  parotid  or  auricular  lymph  gland  is  situated  superficially  be- 
tween the  upper  part  of  the  posterior  border  of  the  masseter  and  the  parotid  gland. 

Tlie  pharyngeal  (or  retropharj'ngeal)  lymph  glands,  one  or  two  in  numlser 
on  each  side,  lie  on  the  pharynx  chiefly  under  cover  of  the  submaxillary  salivary 
gland. 

The  prescapular  or  superficial  cervical  lymph  glands  lie  on  the  serratus  magnus 
at  the  anterior  ijordcr  of  the  supraspinatus,  embedded  in  a  mass  of  fat.  Usually 
two  or  three  are  present  on  each  side,  Ijut  there  may  be  only  one.  They  are  oval 
and  are  about  an  inch  long  in  a  dog  of  medium  size  when  two  are  present. 

The  axillary  lymph  gland  lies  in  a  mass  of  fat  on  the  inner  face  of  the  lower 
part  of  the  teres  major.     It  is  discoid. 

The  cubital  lymph  gland  is  inconstant.  It  is  situated  on  the  deep  face  of 
the  long  h(>ad  of  the  triceps  or  on  the  latissimus  dorsi. 

The  mediastinal  lymph  glands  are  small  and  quite  variable  in  arrangement. 
Usually  one  or  two  glands  are  found  on  the  course  of  the  internal  thoracic  ves- 
sels at  the  second  segment  of  the  sternum. 

The  bronchial  lymph  glands  are  commonly  four  in  number.  The  largest  is 
situated  in  the  angle  of  divergence  of  the  chief  bronchi,  two  lie  on  the  origin  of 
the  right  apical  bronchus,  and  the  fourth  is  between  the  aortic  arch  and  the  anterior 
face  of  the  left  bronchus.     They  are  commonly  pigmented. 

The  lumbar  lymph  glands  are  small. 

The  mesenteric  lymph  glands  are  represented  chiefiy  by  a  long  flattened  mass 
(formerly  known  as  the  pancreas  Aselli)  which  lies  in  the  mesentery  along  the 
course  of  the  anterior  mesenteric  artery  and  vein.  It  is  succeeded  by  three  or 
four  glands  which  lie  along  the  portal  vein  and  appear  to  receive  vessels  from 
the  stomach,  spleen,  liver,  pancreas,  and  great  omentum.  A  few  very  small 
nodes  occur  along  the  colon. 

The  iliac  lymph  glands  are  relatively  large  and  are  situated  at  the  termination 
of  the  aorta  and  the  origin  of  the  iliac  arteries.  Commonly  four  are  present.  Of 
these,  the  two  largest  lie  on  the  psoas  minor  on  each  side  in  relation  to  the  aorta 
and  vena  cava  respectively.  The  other  two  are  in  the  angle  of  divergence  of 
the  internal  iliac  arteries. 

The  superficial  inguinal  lymph  glands  are  situated  in  the  subcutaneous  fat 
behind  the  external  inguinal  ring.  They  are  relatively  large,  especially  when  there 
is  only  one  on  each  side;   two  smaller  ones  may  be  found  instead. 

The  popliteal  lymph  gland — usually  uniciue,  but  sometimes  double — lies  in 
a  pad  of  fat  on  the  upper  part  of  the  gastrocnemius  between  the  biceps  femoris 
and  semitendinosus.     It  may  project  back  so  as  to  be  superficial  and  palpable. 


NEUROLOGY 

THE  NERVOUS  SYSTEM 

The  nervous  system  is  a  complex  mechanism  by  which  the  organism  is  brought 
into  functional  relation  with  its  environment,  and  its  various  parts  are  coordinated. 
For  purposes  of  gross  description  it  is  divided  primarily  into  two  parts,  central 
and  peripheral. 

The  central  nervous  system  (Systema  nervorum  cent  rale)  comprises  (a)  the 
spinal  cord  (McMhilia  spinalis),  and  {!>)  the  brain  (Encephalon). 

The  peripheral  nervous  system  (.'-Systema  nervorum  periphericum)  includes 
(*))  the  cerebral  and  spinal  nerves  with  their  ganglia,  and  (b)  the  sympathetic 
nervous  system. 

The  division  into  central  and  peripheral  parts  is  quite  arbitrary  and  is  employed  purely 
as  a  matter  of  convenience  of  description.  The  fibers  of  which  the  nerves  are  composed  either 
aiisc  or  end  witliin  the  central  system,  and  therefore  constitute  an  integral  part  of  the  latter. 
Tlie  structural  and  funclidiial  unit  of  the  nervous  system  is  the  neurone,  which  consists  of  the 
cell-body,  usually  termel  the  nerve-cell,  and  all  its  processes.  The  processes  arise  as  out- 
growths from  the  cell-liody  and  conduct  impulses  to  or  from  the  cell.  They  vary  greatly  in 
length,  some  being  less  than  a  millimeter  long,  while  others  extend  from  a  cell  in  the  spinal  cord 
to  t  lie  distal  end  of  a  limb.  A  nerve  is  composed  of  such  processes,  usually  inclosed  in  a  protecting 
and  insulating  shea  I  h,  an  1  iinilid  intcj  liundles  l)y  connective  tissue.  The  neurones  are  embedded 
in  a  in'ciiliar  suppiirtin^j;  li^^uc  ii'iincd  neuroglia.  This  consists  of  a  very  intricate  feltwork 
of  gliu-libers,  many  of  wind;  arc  connected  with  the  small  glia-cells  or  astrocytes.  In  addition 
the  nervous  tissue  is  invested  closely  by  a  vascular  layer  of  connective  tissue,  the  pia  mater,  from 
which  ingrowths  extend  into  the  nervous  substance  proper.' 

To  the  naked  eye  the  central  nervous  system  apjiears  to  he  composed  chiefly 
of  two  kinds  of  substance,  white  and  gray.  The  white  matter  (Substantia  alba)  is 
dead  white  in  color  and  is  soft  in  the  natural  state.  It  consists  larg(>ly  of  medullated 
nerve-fibers,  packed  closely  together  and  arrangerl  more  or  less  clearly  in  large  or 
small  bundles  or  tracts  (Funiculi,  fasciculi).  The  gray  matter  (Substantia  grisea) 
is  usually  brownish-gray  in  color,  often  with  a  tinge  of  pink.  It  is  softer  than  the 
white  sul)stance  and  much  more  vascular.  It  is  composed  chiefly  of  cell-bodies 
and  iion-medulhited  processes.  In  some  situations  it  is  modified  to  form  the 
gelatinous  substance  (Substantia  gelatinosa),  which  is  pale  vellowish-gray  and 
jelly-like. 

Ganglia  are  gray  masses  found  on  the  dorsal  roots  of  the  s]iinal  ner\'es  and  on 
the  course  of  many  nerves.  They  are  commonly  ovoid  in  form  and  are  inclosed  in 
a  fibrous  capsule.  They  are  composed  largely  of  the  cell-bodies  of  neurones,  but 
have  connected  with  and  passing  through  them  nerve-fibers  (processes)  which 
extend  peripherally  and  centrally.  In  origin  and  function  the  spinal  ganglia 
belong  ])roperly  to  the  central  system,  but  it  is  customary  to  include  them  with  the 
peripheral  ]iart  in  gross  anatomical  descriptions. 

Nerves  are  conducting  trunks  composed  of  bundles  of  parallel  nerve-fibers. 
They  are  enveloped  in  a  fibro-elastic  sheath,  the  epineurium,  which  contains  the 
blood  and  lymph  vessels.  They  are  classified  according  to  their  central  connec- 
tions as  cranial  or  cerebral,  spinal,  and  sympathetic.  Th(>  groups  of  cells  of  which 
the  nerve-fibers  are  processes  are  termed  the  nuclei  of  origin  or  termination  of 
the  nerves,  according  as  the  latter  conduct  impulses  in  a  periijheral  or  central  direc- 
tion.    On  the  same  basis  the  nerve-fibers  are  designated  efferent  and  afferent 

'  Limitations  of  space  and  the  purpose  of  this  work  preclude  consideration  of  the  finer 
structure  of  the  nervous  system,  for  which  amjjlc  literature  is  available. 

644 


THE    MENINGES — THE    DURA    MATER  645 

respectively.  A  Imnille  of  fillers  which  passes  from  one  nerve-trunk  to  another  is 
called  an  anastomotic  branch  (Ramus  anastomoticus).  In  some  situations  the 
exchanse  of  branches  between  adjacent  nerves  is  so  free  as  to  constitute  a  nerve- 
plexus  (Plexus  nervorum).  The  term  ramus  commimicans  is  proi)erly  restricted 
to  branches  which  connect  the  ventral  divisions  of  the  spinal  nerves  with  adjacent 
ganglia  or  nerves  of  the  sympathetic  system.  The  terminal  twigs  of  the  nerves  are 
designated  according  to  their  distribution  as  muscular  branches  (Rami  musculares), 
cutaneous  nerves  (Nervi  cutanei),  and  articular  nerves  (Xervi  articulares).  The 
muscular  branches  are  motor  in  function,  the  cutaneous  and  articular  sensory,  but 
all  contain  vasomotor  fibers  which  control  the  caliber  of  the  blood-vessels. 


THE  MENINGES 
The  central  organs  of  the  nervous  system  are  inclosed  in  three  meninges  or 
membranes.     From  without  inward  these  are:    (1)  the  dura  mater,  (2)  the  arach- 
noidea,  and  (3)  the  pia  mater. 

THE  DURA  MATER 

The  dura  mater  is  a  dense  resistant  memlirane  of  white  fibrous  tissue;  in  the 
fresh  state  it  is  bluish-white  in  color.  On  account  of  the  difference  in  its  arrange- 
ment within  the  cranium  from  that  in  the  spinal  canal  it  is  customary  to  describe 
it  as  consisting  of  two  parts,  cereljral  and  spinal;  these  portions  are  continuous  with 
each  other  at  the  foramen  magnum. 

The  cerebral  dura  mater  (Dura  mater  encephali)  is  adherent  to  the  interior 
of  the  cranium,  and  may  lie  regarded  as  forming  an  internal  periosteum  for  the 
bones  here  as  well  as  being  an  envelope  of  the  brain.  Its  outer  surface  is  connected 
with  the  bony  wall  of  the  cranial  cavity  by  numerous  fine  fibrous  strands  and  by 
l)lood-vessels;  hence  it  appears  rough  in  many  places  when  separated  from  the  wall. 
The  degree  of  adhesion  varies  greatly  at  different  points.  It  is  most  firmly  attached 
at  the  various  projections,  e.  g.,  the  internal  sagittal  crest,  the  tentorium  osseum, 
the  petrosal  crest ;  also  at  the  base  and  the  foramen  magnum.  Before  the  sutiu'es 
are  closed  the  dura  is  connected  with  the  sutural  ligaments  and  through  them  is 
continuous  with  the  external  periosteum.  The  cranial  nerves  receive  sheaths  from 
the  dura,  which  is  thus  continuous  without  the  cranium  with  the  epineurium  and 
periosteum.  Along  the  roof  and  sides  (except  as  noted  above)  the  adhesion  is 
relatively  slight,  and  lymph-spaces  are  said  to  exist  between  the  dura  and  the  bone. 
The  internal  surface  of  the  dura  is  smooth  and  glistening,  since  it  is  lined  by 
endothelium  and  is  moistened  by  a  fluid  resembling  lymph;  it  forms  the  outer 
boundary  of  the  subdural  space.  In  accordance  with  its  double  function  tlie  dura 
is  composed  of  two  layers,  which  are,  however,  intimately  adherent  to  each  other 
in  most  places  in  the  adult.  The  venous  sinuses  are  channels  between  the  two 
layers  and  are  lined  by  endothelium.  They  have  been  described  with  the  other 
vessels. 

Several  folds  or  septa  are  given  off  from  the  inner  surface  of  the  dura;  these 
project  into  the  cavity  between  the  gro.ss  subdivisions  of  the  brain.  These  septa 
are;   (1 )  the  falx  cerebri;   (2)  the  tentorium  cerebelli;  and  (3)  the  diaphragma  sellse. 

The  fabc  cerebri  is  a  sickle-shaped  median  partition  which  projects  downward 
in  the  great  longitudinal  fissure  between  the  cerebral  hemispheres.  It  is  attached 
above  to  the  internal  sagittal  crest,  in  front  to  the  crista  galli,  and  behind  to  the 
tentorium  osseum.  Its  superior  border  is  convex  and  separates  into  two  layers 
which  inclose  the  superior  longitudinal  sinus.  Its  lower  border  is  concave  and 
lies  over  the  corpus  callosum.  The  falx  is  thick  above,  but  much  thinner  below, 
and  in  some  places  cribriform. 


646  NEUROLOGY 

In  the  horse  the  posterior  part  of  the  falx  cerebri  does  not  extend  to  the  corpus  callosum,  and 
hence  the  hemispheres  are  here  in  contact  and  adherent  to  each  other  over  a  .small  area.  In  the 
ox  and  pig  the  falx  does  not  descend  so  far  as  in  the  horse,  while  in  the  dog  it  completely  separates 
the  hemispheres. 

The  tentorium  cerebelli  is  a  crescentic  transverse  fold  which  separates  the 
cerebellum  from  the  ])osterior  poles  of  the  cerebral  hemispheres.  It  is  attached 
al)ove  to  the  tentorium  osseuin  and  laterally  to  the  petrosal  crests.  Its  lower 
border  is  thin,  concave,  and  free;  it  forms  the  upper  and  lateral  lioundaries  of  an 
opening  (Incisura  tentorii)  which  incloses  the  mid-brain. 

The  diaphragma  sellae  is  a  small  circular  fold  which  roofs  over  the  sella  turcica 
and  the  pituitary  body.  It  is  perforated  centrally  by  an  opening  (Foramen  dia- 
phragmatis)  for  the  infundibuluiu. 

The  falx  cerebelli,  a  sickle-shaped  fold  which  projects  into  the  median  notch  between  the 
cerebellar  hemispheres  in  man,  is  not  present  in  the  domesticated  animals.  There  is  instead 
merely  a  slight  thickening  of  the  dura. 

The  spinal  dura  mater  (Dura  mater  spinalis)  forms  a  tube  around  the  spinal 
cord  from  the  foramen  magiuun  to  the  second  or  third  segment  of  the  sacrum.  It 
is  separated  from  the  periosteum  of  the  spinal  canal  by  a  considerable  epidural 
space  (Cavuni  ejjidurale)  which  is  occupied  by  fatty  connective  tissue  and  veins. 
It  is  held  in  position  chiefly  by  the  sheaths  which  it  furnishes  to  the  roots  of  the 
spinal  nerves,  and  in  its  anterior  part  by  two  ligaments;  the  latter  connect  it  with 
the  inferior  atlanto-occipital  membrane  and  with  the  odontoid  process.  It  is  large 
in  proportion  to  its  contents,  but  its  diameter  is  not  uniform.  It  is  largest  in  the 
atlas,  small  in  the  thoracic  region,  and  becomes  very  small  in  its  terminal  part, 
where  it  inplos(>s  the  delicate  filum  terminale  of  the  spinal  cord. 

The  subdural  space  (Cavum  subdurale)  is  the  cavity  between  the  inner  surface 
of  the  dura  luater  and  the  arachnoidea.  It  is  a  mere  capillary  space  which  contains 
just  sufficient  fluid  to  moisten  its  surfaces;  this  fluid  is  usually  regarded  as  Ij-niph, 
which  is  replenished  by  filtration  through  the  walls  of  the  blood-vessels.  The 
space  is  in  communication  with  the  lymph-paths  of  the  nerve-sheaths. 


THE  ARACHNOIDEA 

The  arachnoidea  is  a  very  delicate  and  transparent  membrane  situated  between 
the  dura  and  pia  mater.  Its  outer  surface  forms  the  inner  wall  of  the  subdural 
space  and  is  covered  by  a  layer  of  endothelium  continuous  with  that  of  the  diijiosed 
surface  of  the  dura  mater.  Between  it  and  the  pia  mater  is  tlie  subarachnoid  space 
(Cavum  subarachnoideale)  which  contains  the  cerebrospinal  fluid.  An  inner  sur- 
face can  scarcely  be  said  to  exist,  since  deeply  the  membrane  becomes  a  reticulum 
of  fine  fibers  which  traverse  the  subarachnoid  space  and  are  attached  to  the  pia 
mater.  The  arachnoidea  furnishes  sheaths  to  the  cerebral  nerves  from  their  super- 
ficial origins  to  a  variable  but  usually  short  distance  beyond  the  emergence  from 
the  dursal  sac.     In  the  case  of  the  optic  nerve  this  sheath  extends  to  the  eyeball. 

The  arachnoidea  of  the  brain  (Arachnoidea  encephali),  except  in  the  case  of 
the  great  longitudinal  and  transverse  fissures,  does  not  dip  into  the  sulci  on  the 
surface  of  the  brain.  On  the  summits  of  the  gyri  it  is  so  closely  attached  to  the  pia 
mater  that  the  two  form  practically  a  single  membrane.  Its  outer  part  bridges 
over  the  sulci,  and  here  the  subarachnoid  space  is  partially  divided  up  by  the  loose 
arachnoid  tissue  into  intercommunicating  cavities.  In  certain  situations  the 
arachnoidea  is  separated  from  the  pia  by  spaces  of  considerable  depth  and  extent. 
These  enlargements  of  the  subarachnoid  space  are  termed  subarachnoid  cisterns 
(CistcrniB  subarachnoidales).  In  them  the  subarachnoid  tissue  does  not  form  a 
close  network,  but  consists  of  a  relatively  small  number  of  long,  thread-like  strands 
which  traverse  the  cavity. 


PIA  MATER  647 

The  chief  cisternal  are:  (1)  the  cisterna  magna,  which  is  at  the  angle  formed  between  the 
posterior  face  of  tlie  cerebellum  and  the  upper  surfa<-e  of  the  medulla  oblongata.  It  communi- 
cates with  the  fourth  ventricle  through  the  foramen  of  Magendie  (in  man);  and  behind  with  the 
wide  subarachnoid  s[)ace  of  the  spinal  cord;  (2)  the  cisterna  pontis  on  the  ventral  surface  of  the 
pons;  (o)  tlic  cisterna  basalis,  which  lies  at  the  base  of  the  cerebrum  and  is  divided  by  the  optic 
chiasma  into  two  parts  (cisterna  chiasniatis,  cisterna  interpeduncularis);  (4)  the  cisterna  fossae 
lateralis,  situated  at  the  lower  part  of  the  lateral  fissure  (,of  Sylvius),  and  continuous  with  the 
cisterna  basalis. 

Along  the  u]iper  honlcr  of  the  falx  cerebri  the  arachnoidea  bears  bulbous 
excrescences,  the  arachnoid  granulations  or  Pacchionian  bodies.  These  are  in- 
closed in  thin  cvaginations  of  the  dura  mater  and  project  into  the  sagittal  sinus 
or  the  parasinoidal  sinuses  along  either  side  of  it.  In  some  cases  they  are 
sufficiently  large  to  exert  jiressure  on  the  bone  and  produce  in  it  depressions  of 
variable  deptli. 

The  spinal  arachnoidea  (Arachnoidea  spinalis)  is  directly  continuous  with  that 
of  the  brain  at  the  foramen  magnum.  It  forms  a  relativcl.y  witle  tube  around  the 
spinal  cord,  so  that  the  latter  (inclosed  in  the  pia)  is  surrounded  by  a  very  consider- 
able quantity  of  cerebrospinal  fluid.  The  spinal  subarachnoid  space  is  traversed 
by  fewer  arachnoid  trabeculse  than  is  the  case  in  the  cranium.  It  is  partially  sub- 
divided by  three  imperfect  septa.  One  of  these,  the  septum  dorsale,  is  median  and 
dorsal.  The  other  two,  the  ligamenta  denticulata,  are  lateral  and  will  be  described 
with  the  pia  mater. 

PIA  MATER 

The  pia  mater  is  a  delicate  and  very  vascular  memlirane  which  invests  closely 
the  surface  of  the  brain  and  spinal  cord  and  sends  processes  into  their  substance. 
It  also  furnishes  sheaths  to  the  nerves,  which  blend  outside  of  the  dural  sac  with  the 
epineurium. 

The  pia  mater  of  the  brain  (Pia  mater  encephali)  follows  accurately  all  the 
inequalities  of  the  surface,  dipping  into  all  the  fissures  and  sulci  of  the  cerebrum, 
and  into  the  larger  fissures  of  the  cerebellum.  Its  external  surface,  which  forms  the 
inner  boundary  of  the  subarachnoid  space,  is  covered  bj'  a  la.yer  of  endothelium. 
From  its  deep  face  numerous  trabecular  are  given  off  which  penetrate  into  the  sub- 
stance of  the  brain  and  cord,  forming  a  path  for  the  blood-vessels,  and  concurring 
with  the  neuroglia  in  forming  the  supporting  tissue  of  the  nervous  substance  proper. 
The  larger  blood-vessels  of  the  brain  lie  witiiin  the  subarachnoid  space,  but  the 
smaller  vessels  ramify  in  the  pia,  forming  rich  plexuses.  The  twigs  which  penetrate 
into  the  gray  matter  are  inclosed  in  pial  sheaths.  They  are  end-arteries,  i.  e., 
constitute  the  entire  supply  of  the  district  which  thej-  enter  and  do  not  anastomose 
with  adjacent  vessels. 

Two  important  folds  of  the  pia  extend  into  the  two  great  transverse  fissures 
of  the  brain;  these  processes  overlie  the  third  and  fourth  ventricles  and  are  known 
as  the  telae  chorioideae  of  these  cavities.  They  constitute  paths  for  the  deeper 
vessels  and  their  edges  contain  vascular  convolutions  which  are  known  as  chorioid 
plexuses.     They  will  receive  further  consideration  more  appropriately  later. 

The  spinal  pia  mater  (Pia  mater  spinalis)  is  thicker  and  denser  than  that  of 
the  l)rain.  It  has  a  strong  outer  layer  of  fibrous  tissue,  most  of  the  fibers  of  which 
are  longitudinal.  The  inner  layer  is  vascular  and  adheres  closely  to  the  surface 
of  the  cord  because  it  sends  numerous  processes  into  it.  It  sends  a  fold  into  the 
median  ventral  fissure  and  also  helps  to  form  the  median  dorsal  septum  of  the  cord. 
Along  the  median  ventral  line  it  forms  a  band-like  thickening,  the  linea  splendens, 
along  which  the  ventral  spinal  artery  runs.  On  each  side  the  pia  mater  gives  off 
a  strong  longitudinal  band,  the  ligamentmn  denticulattim,  which  is  connected 
externally  with  the  dura  mater.  The  inner  or  pial  border  extends  in  a  line  between 
the  dorsal  and  ventral  roots  of  the  nerves.     The  outer  or  dural  border  is  denticu- 


648  NERVOX'S  SYSTEM  OF  THE  HORSE 

lated  and  to  a  large  extent  free.     The  denticulations  are  attached  to  the  dura 
between  the  nerve-roots. 


NERVOUS  SYSTEM  OF  THE  HORSE 
The  Spinal  Cord 

The  spinal  cord  (Medulla  s])iiialis)  is  the  part  of  the  central  nervous  system 
which  is  situated  in  the  vertebral  canal.  It  extends  from  the  foramen  magnum  to 
about  the  middle  of  the  sacrum. 

In  the  horse  its  average  length  is  about  76  to  78  inches  (ca.  190  to  19.5  cm.), 
and  its  weight  about  8}^  to  9  ounces  (ca.  240  to  255  grams). 

It  is  approximately  cylindrical,  but  more  or  less  flattened  dorso-ventrally. 
There  is  no  line  of  demarcation  between  it  and  the  medulla  oblongata,  but  for  prac- 
tical ])urposes  the  division  is  usually  assumed  to  be  at  the  posterior  border  of  the 
foramen  magnum.  Its  posterior  part  tapers  rapidly  to  a  point,  forming  the  conus 
meduUaris.     This  is  prolonged  for  a  short  distance  by  the  slender  filum  terminale. 

Forty-two  pairs  of  spinal  nerves  are  connected  with  the  sides  of  the  spinal  cord. 
They  are  classified  as  eight  cervical,  eighteen  thoracic,  six  lumbar,  five  sacral,  and 
five  coccygeal.  According  to  the  attachments  of  these  series  of  nerves  the  spinal 
cord  is  divided  into  cervical,  thoracic,  lumbar,  and  sacral  parts. 

In  a  horse  about  I6J-2  hands  high  these  parts  measured  65  cm,  (ca.  26  in.),  86  cm.  (ca.  34.4 
in.),  27  cm.  (ca.  10.8  in.),  and  15  cm.  (ca.  6  in.)  respectively  (Dexler). 

In  the  embryo  these  divisions  correspond  primitively  to  the  regions  of  the 
vertebral  column,  but  later,  through  unequal  growth  of  the  cord  and  spine,  the 
corres]3ondence  between  the  two  is  not  at  all  exact  in  the  anterior  regions  and  is 
lost  in  the  last  two.  The  lumbar  part  of  the  cord  in  the  horse  ends  at  the  junction 
of  the  fifth  and  sixth  lumbar  vertebrae,  so  that  the  roots  of  the  last  lumbar  nerve 
must  run  backward  the  length  of  the  last  lumbar  vertebra  to  reach  the  interverte- 
bral foramen  through  which  it  emerges.  The  conus  medullaris  reaches  only  to  the 
anterior  part  of  the  sacral  canal,  so  that  the  roots  of  the  sacral  and  coccygeal  nerves 
extend  backward  in  the  spinal  canal  for  a  considerable  distance,  forming  a  leash 
of  bundles,  in  the  center  of  which  lie  the  conus  medullaris  and  the  filum  terminale. 
This  arrangement  is  expressively  designated  the  cauda  equina. 

Each  pair  of  spinal  nerves  is  attached  by  its  root-fibers  to  a  certain  length  of 
the  cord,  and  the  latter  is,  therefore,  regarded  as  consisting  of  as  many  segments 
as  there  are  nerves.  It  is  to  be  noted,  however,  that  there  is  no  line  of  demarcation 
between  the  segments  other  than  the  intervals  between  the  root-fibers  of  adjacent 
nerves. 

The  segments  are  of  different  lengtlis;  the  longest  are  the  third  to  tlie  sixth  rcrvical.  wliicli 
measure  11,  10,  10,  and  8.5  cm.  respectively.  Tlie  spinal  nerves  are  in  general  ilesignated  accord- 
ing to  tlie  vertebra;  behind  which  lliey  emerge  from  the  \-ertcbral  canal.  In  tlie  neclc,  however, 
tliore  are  eight  pairs  of  nerves  and  only  seven  vertebra';  here  tlic  first  nerve  emerges  through  tlic 
intervertebral  foramen  of  tlie  atlas  and  the  eightli  lietvveen  tlie  last  cervical  and  tlie  first  thoracic 
vertebra. 

In  the  greater  part  of  the  thoracic  region  the  spinal  cord  is  fairly  uniform  in 
size,  but  there  are  two  conspicuous  wide  enlargements  which  involve  the  segments 
with  which  the  nerves  of  the  limbs  are  connected.  The  cervical  enlargement 
(Intumescentia  cervicalis)  begins  gradually  in  the  fifth  cervical  vcrtebi-a  and  sub- 
sides in  the  second  thoracic.  Its  maximum  transverse  diameter  is  about  an  inch 
(ca.  25  nnn.)  and  its  dorso-ventral  nearly  half  an  inch  (ca.  12  mm.).  The  lumbar 
enlargement  (Intumescentia  lumbalis)  is  situated  in  the  fourth  and  fifth  lumliar 
vertebra;.     It  is  a  little  narrower  than  the  cervical  enlargement,  and   its  dorso- 


THE  SPINAL  CORD 


()49 


ventral  dianu^tcr  is  also  slightly  smaller.  Behind  this  the  cord  tapers  rapidly  to 
form  the  conus  meduUaris.  The  tip  of  the  latter  is  continued  by  a  delicate  glisten- 
ing strand,  tiif  filum  terminale,  which  is  composed  largely  of  fibrous  tissue   con- 

tinuetl  from  the  pia  mater,  covered  by 
arachnoid. 

The  surface  of  the  spinal  cord  is 
divided  into  two  similar  halves  by  a 
dorsal  median  groove  (Sulcus  nudianus 
dorsalis)  and  a  ventral  median  fissure 
(Fissura  mediana  ventralis).  On  citlicr 
side  of  the  former  is  the  dorso-lateral 
groove  (Sulcus  dorsalis  lateralis)  at 
which   the   fibers  of   the  dorsal   nerve- 


-KX 


Fig.  495. — Ventral  Vikw  of  Mkdulla  Oblongata 
AND  First  and  Second  Segments  of  Spinal 
Cord  of  Horse;  the  Membranes  are  CrT 
AND  Reflected. 

i,  Lig.  suspensorium  arachnoideale;  2,  right 
cerebrospinal  artery;  S.  5,  digitations  of  lig.  denticu- 
latum;  4.  free  border  of  lig.  denticulatum;  6,  middle 
spinal  arter.v;  7,  basilar  artery;  S,  pons;  9,  arach- 
noidea;  10,  dura  mater;  //,  12.  ventral  root-bundles 
of  first  and  second  segments  of  spinal  cord;  1"/.,  N. 
abducens;  IX.  X.  glosso-pharyngeus  and  vagus;  XI, 
accessory,  medullary  part;  XT.  accessory,  spinal  part; 
a.  line  between  medulla  oblongata  and  spinal  cord. 
(Dexler,  in  EUenberger-Baum,  .\nat.  d.  Haustiere.) 


Fig.  496.— Cauda  Equina. 
1 .  Dura  and  arachnoidea  divided  and  reflected; 
2.  spinal  cord;  3,  nerve-roots.    (From  Leisering's  .\tlas, 
reduced.) 


roots  enter  the  cord;  it  is  faint  except 
at  the  enlargements,  and  is  represented 
by  two  grooves  in  the  first  cervical 
segment.  The  ventral  root-fibers  as 
they  emerge  from  the  cord  do  not 
form  a  continuous  series,  but  arise 
from  a  zone  (Area  radicularis  ven- 
tralis) 3  to  5  mm.  in  width  a  little  lateral  to  the  ventral  median  fissure, 
and  no  groove  is  found  here.  In  the  greater  part  of  the  cervical  region  and 
the  anterior  part  of  the  thoracic  region  there  is  a  shallow  dorsal  paramedian 
groove    (Sulcus    intermedius    dorsalis)    a  short  distance   lateral    to    the    median 


650 


NERVOUS  SYSTEM  OF  THE  HORSE 


groove.     These  grooves  indicate  the  division   of  the  white   matter  of  the  cord 
into  columns  to  be  described  later. 

Examination  of  cro.ss-sections  of  the  P]iinal  cord  shows  that  it  is  a  bilaterally 
sj-mmctrical  structure,  incompletely  divided  into  ri^dit  antl  left  halves  by  a  ventral 
fissure  antl  a  dorsal  septum.  The  ventral  median  fissure  (Fissura  mediana  ven- 
tralis)  is  narrow  and  penetrates  nearly  to  the  middle  of  the  dorso-ventral  diameter 
of  the  cord.  It  is  occupied  by  a  fold  of  pia  mater.  The  dorsal  median  septum 
(Septum  medianum  dorsale)  is  a  partition  which  descends  from  the  posterior  median 
groove  to  about  the  middle  of  the  cord.  It  apparently  consists  of  condensed  neu- 
roglia with  an  admixture  of  pial  tissue.  The  two  halves  (if  the  cord  are  connected 
by  commissures  of  gray  and  white  matter.  '  The  gray  commissure  (Commissura 
grisea)  is  a  transverse  band  of  gra.y  matter  at  the  ventral  end  of  the  dorsal  septum. 
It  is  divided  into  dorsal  and  ventral  parts  by  the  central  canal  of  the  cord.     The 


Ftg.  497. — Cross-section  of  Spinal  Cord  in  situ,  tx  Part  SrHF:MATir. 
/,  Dorsal  column;  ^,  lateral  column:  .^,  ventral  column;  4.  dorsal  horn;  5,  ventral  horn;  (7,  gray  ( 
sure;  7,  white  commissure;  8,  central  canal;  9,  dorsal  septum;  10,  ventral  fissure;  //,  tlorsal  nerve-root;  12, 
ventral  nerve-root;  13,  .spinal  ganglion;  / 4,  nerve;  i5,  intervertebral  foramen;  75,  arch  of  vertebra;  /7,  epidural 
space;  IS,  dura  mater  (represented  a  little  too  thick);  19,  ligamentum  denticulatum;  20.  20,  longitudinal  venous 
sinuses;  21,  middle  spinal  artery.  The  subdural  and  subarachnoid  si>aces  (black)  are  traversed  by  delicate  trabe- 
cula?.     The  outer  part  of  the  arachnoid  and  the  pia  mater  are  not  shown. 


white  commissure  (Commissura  alba)  is  a  l)ridge  of  white  matter  which  connects 
the  ventral  columns  of  the  cord  over  the  dorsal  end  of  the  ventral  median  fi.ssure, 
and  constitutes  a  conducting  path  from  one  side  to  the  other. 

The  central  canal  of  the  cord  (C'analis  centralis),  the  spinal  vestige  of  the 
lumen  of  the  embryonal  neural  tube,  is  a  minute  passage  which  tunnels  the  gray 
commissure.  It  opens  at  its  anterior  end  into  the  posterior  part  of  the  fourth 
ventricle  of  the  brain,  and  its  terminal  part  in  the  conus  medullaris  forms  a  slight 
dilatation,  the  ventriculus  terminalis.  It  is  lined  by  epithelium  and  is  surrounded 
by  a  layer  of  modified  neuroglia  (Substantia  grisea  centralis). 

The  gray  matter  of  the  spinal  cord  as  seen  in  cross-sections  resembles  roughly 
a  capital  H.  the  cross-bar  of  the  letter  being  formed  by  the  gray  commissure. 
Each  lateral  i)art  is  considered  as  consisting  of  dorsal  and  ventral  gray  columns  or 
horns  (Columna  grisea  dorsalis,  ventralis).     In  the  greater  part  of  the  cord  the 


THE  SPIXAL  CORD  651 

dorsal  column  or  horn  is  elongated  and  narrow  and  tapers  to  a  point  which  extends 
almost  to  the  surface  of  the  cord  at  the  attachment  of  the  dorsal  root-fibers  of  the 
spinal  nerves.  Its  apex  or  tip  consists  of  gray  matter  which  is  lighter  in  color  and 
less  opaque  than  that  of  the  rest  of  the  horn  and  is  termed  the  substantia  gelatinosa 
(Rolandi).  The  ventral  column  or  horn  is  short,  thick  and  rounded,  and  is  sepa- 
rated from  the  surface  of  the  cord  by  a  thick  layer  of  white  matter,  through  which 
the  fibers  of  the  ventral  roots  of  the  spinal  nerves  ]iass.  From  the  middle  of  the 
cervical  region  to  the  lumliar  region  there  is  a  medial  ]iruj(>ction  of  gray  matter  on 
the  lower  part  of  the  dorsal  colunm;  this  is  the  nucleus  dorsalis  or  Clarke's  column. 
In  the  anterior  jiart  of  the  cord  there  is  an  outward  projection  of  the  gray  matter  at 
the  base  of  the  ventral  horn;  this  is  termed  the  lateral  colimin  or  horn.  The 
demarcation  between  the  gray  and  white  matter  is  in  many  places  indistinct;  this 
is  especially  the  case  laterally,  where  processes  of  gray  matter  extend  into  the  white 
substance,  producing  what  is  known  as  the  formatio  reticularis. 

Cross-sections  of  the  spinal  cord  present  the  followinn;  gross  regional  characters:  (1) 
The  cervical  cord  near  the  medulla  is  compressed  dorso-Aentrally.  Its  width  is  about  IS  mm. 
and  its  greatest  tliickness  about  8  mm.  It  has  dorsallj'  a  deep  median  sulcus  and  a  distinct 
dorso-lateral  sulcus.  Lateral  grooves  are  also  present.  The  dorsal  cornua  are  strongly  everted. 
Each  has  an  expanded  head,  which  comes  very  close  to  the  surface  of  the  cord,  and  has  an 
extensive  cap  of  substantia  gelatinosa.  The  neck  is  distinct.  The  ventral  cornua  are 
short  and  Ijhmt  and  diverge  very  little.  The  gray  commissure  is  about  in  the  middle 
of  the  section  and  2.5  mm.  in  length.  .According  to  Dexler  the  column  between  the  median 
and  lateral  grooves  dorsally  is  the  funiculus  cuneatus,  the  funiculus  gracihs  being  very 
small  and  not  showing  on  the  surface  in  this  region.  In  the  middle  of  the  cervical  region 
the  diameters  are  about  16  mm.  and  10  mm.  respectively.  The  ventral  surface  is  somewhat 
flattened.  The  dorsal  cornua  ha\-e  pointeil  ends  and  turn  decitledly  outward.  The  ventral 
cornua  are  short  and  tliick  and  are  directeil  ve;'y  slightly  outward;  their  ends  are  about  4  mm. 
from  the  ventral  surface.  The  gray  commissure  is  just  above  the  middle  of  the  section  and  is 
about  2  mm.  long.  The  cer\'ical  enlargement  measures  aljout  25  nmi.  transversely  and  12  mm. 
vertically.  The  dorsal  cornua  are  smaller  than  the  ^•entral  and  have  a  large  cap  of  substantia 
gelatinosa.  The  ventral  cornua  are  short  and  thick,  curve  strongly  outward,  and  are  about  4  mm. 
from  the  ventral  surface.  Each  bears  a  prominence  on  its  inner  side  near  the  base.  The  gray 
commissure  is  considerably  above  the  middle  of  the  section  and  is  about  4  mm.  long.  (2)  In 
the  middle  of  the  thoracic  region  the  cross-section  is  biconvex,  the  ventral  surface  being  the  more 
strongly  curved.  The  traasverse  diameter  is  about  15  mm.  and  the  dorso-ventral  about  10  mm. 
The  gray  columns  are  close  together,  the  gray  commissure  being  only  about  1  mm.  in  length, 
and  lying  considerably  above  the  middle  of  the  section.  The  tlorsal  cornua  are  short  and  have 
slightly  enlarged  ends.  The  ventral  cornua  have  a  uniform  diameter,  turn  very  little  outward, 
and  end  about  3  mm.  from  the  ventral  surface.  (3)  The  hunl)ar  enlargement  is  much  flattened, 
especially  dorsally.  The  transverse  diameter  is  about  22  mm.  and  the  tlorso-ventral  9  to  10  mm. 
The  cornua  are  very  large.  The  ventral  cornua  are  thick  and  rouniled  and  turn  sharplj-  outward; 
they  end  about  2  mm.  from  the  ventral  surface.  The  dorsal  cornua  are  smaller  and  shorter  and 
do  not  diverge  so  strongly.  The  gray  commissure  is  about  in  the  middle  of  the  section  and  is 
about  3  mm.  long.  In  the  third  lumbar  vertebra  the  cord  is  about  3  mm.  narrower  and  thicker, 
and  both  surfaces  are  about  equally  convex.  The  dorsal  cornua  are  smaller,  considerably 
everted,  and  constricted  in  the  middle.  The  ventral  cornua  are  very  short  and  do  not  turn  out- 
ward. (4)  In  the  first  sacral  vertebra  the  cord  is  almost  round  and  is  5  to  6  mm.  in  diameter; 
the  cornua  are  relatively  very  large  and  the  commissure  has  the  form  of  a  high  intermediate  mass. 

The  ventral  horn  contains  large  cells,  the  axones  of  which  emerge  as  the  fibers  of  the  ventral 
nerve-roots  (Fila  radicularia) .  The  axones  of  many  cells  cross  to  the  opposite  side  in  the  white 
commissure  and  pass  out  in  a  ventral  root  of  that  side,  or  enter  the  white  matter  and  pass  forward 
and  backward,  associating  various  segments  of  the  cord.  Some  pass  to  the  ventral  horn  of  the 
opposite  side  at  the  same  or  at  different  levels.  Others  pass  to  the  periphery  of  the  cord,  join 
the  cerebellospinal  fasciculus,  and  extend  to  the  cerebellum.  Scattered  through  the  gray  matter 
are  many  smaller  cells  with  axones  which  pursue  a  short  course  and  serve  to  connect  different 
parts  of  the  gray  matter. 

The  white  matter  of  the  spinal  cord  is  divided  into  three  pairs  of  columns. 
The  dorsal  columns  (Funiculi  dorsales)  lie  on  either  side  of  the  dorsal  median  septum 
and  extend  outward  to  the  dorso-lateral  groove  and  the  dorsal  gray  column.  The 
ventral  colimms  (Funiculi  ventrales)  are  situated  on  either  side  between  the  median 
fissure  and  the  ventral  gray  coliunns.  Tliey  are  connected  above  the  fissure  by 
the  white  commissure.  The  lateral  columns  (Funiculi  laterales)  lie  external  to  the 
gray  columns  on  either  side;  their  limits  are  indicated  superficially  by  the  dorso- 
lateral groove  and  the  emergence  of  the  ventral  root-fibers.     The  paramedian 


652  NERVOUS  SYSTEM  OF  THE  HORSE 

groove  (where  present)  indicates  a  suhtlivision  of  the  dorsal  column  into  two  fasci- 
culi or  tracts;  the  inner  of  these  is  the  fasciculus  gracilis  (Cioll's  column);  the  outer, 
the  fasciculus  cuneatus  (Burdach's  column). 

The  anKHints  of  gray  and  white  matter  vary  greatly  in  difTcrent  parts  of  the 
cord  both  absolutely  and  relatively.  In  cross-section  the  absolute  areas  of  both  are 
greatest  in  the  enlargements.  The  relative  area  of  gray  matter  is  smallest  in  the 
thoracic  region  (except  at  its  anterior  end),  and  increases  from  the  lumbar  enlarge- 
ment backwani. 

Iiivc'stisialidiis  h.nc  sliown  that  in  man  the  cohimns  of  white  matter  are  subdivided  into 
fa.sriculi  or  tr;iri>,  winch  constitute  definite  conducting  paths  of  greater  or  less  length.  Our 
knowledge  of  tlic  I  racis  in  I  he  domesticated  animals  is  very  limited,  and  it  is  quite  unsafe  to  make 
inferences  from  tin'  ananiiciiicnt  in  man.  As  evidence  of  this  it  may  be  noted  that  the  ventral 
cerebrospinal  oi'  direci  |i\  laiiii^lal  tract  of  man  cannot  be  recognized  as  such. 

The  dorsal  white  ciihinju-  i-i)nsist  essentially  of  two  .sets  of  axones.  The  afferent  or  sensory 
axones  which  come  from  the  cells  of  the  spinal  ganglia  enter  as  the  dorsal  roots  of  the  spinal  nerves 
and  divide  into  two  branches  in  the  vicinity  of  the  dorsal  gray  column.  The  anterior  lascending) 
branches  form  the  direct  sensory  path  to  the  brain  and  extend  in  the  fa.sciculus  cuneatus  and 
fasciculus  gracilis  or  corresponding  tracts  to  nuclei  in  the  medulla  oblongata.  The  posterior 
(descending)  branches  extend  backward  for  varying  distances  and  give  off  numerous  collaterals 
to  cells  of  the  gray  column,  thus  forming  part  of  the  mechanism  for  the  mediation  of  reflex  action. 
Some  collaterals  cross  in  the  white  commissure  to  the  opposite  side.  Many  of  these  fibers  are 
collected  in  the  comma-shaped  tract  between  the  fasciculus  gracilis  and  cuneatus.  The  second 
set  of  axones  arises  from  the  smaller  cells  of  the  gray  colunm.  They  enter  the  white  matter, 
divide  into  anterior  and  posterior  branches,  forming  the  fasciculi  proprii  or  ground  bundles  of  the 
cord.  Some  branches  cross  to  the  opposite  side.  The  function  of  this  set  of  axones  is  cliiefly 
to  associate  various  levels  of  the  cord. 

The  lateral  columns  contain  some  axones  of  the  dorsal  nerve-roots,  which  (in  man)  are 
grouped  in  the  marginal  tract  of  Lissauer,  situated  just  dorsal  to  the  apex  of  the  dorsal  horn. 
The  cerebcUo.spinal  fasciculus  (direct  cerebellar  tract  of  Flech.sig)  extends  along  the  periphery 
of  t  lie  lateral  column.  It  contains  ilic  axones  of  the  cells  of  the  nuclei  is  dmsalis  (Clarke's  column), 
whii'h  pniceeil  to  the  medulla  oliliiiii;ai a  and  enter  the  ecu  liclhiin  liy  I  lie  restiform  body.  The 
rubrospinal  tract  of  Monakou  appears  lo  take  the  place  of  I  he  laleial  ccreliro.spinal  fasciculus  or 
ciii..>e.l  p\  laiiiidal  tract  of  man.     It  lies  at  the  inner  side  of  the  cer  iHlld-pInal  fasciculus.     Its 

tiliei-    H  I  c  111  the  nucleus  ruber  of  the  mid-brain,  cross  the  median  ]ila iccussation  of  Forel), 

ami  |i:i—  li  ickward  in  the  tegmentum  and  medulla  oblongata  to  the  laieial  cnhimn  of  the  cord. 
It  is  a  p.iili  for  motor  impulses  coining  from  the  cerebral  cortex  and  the  cerebellum.  The  lateral 
fasciculus  ])roprius  or  ground-bundle  is  deeply  situated  at  the  side  of  the  gray  columns.  The 
bulk  of  ils  libers  are  axones  of  cells  of  the  posterior  cornu  which  divide  into  anterior  and  posterior 
branches.  They  are  intersegmental  paths  which  associate  different  levels  of  the  gray  matter  of 
the  cord.     The  significance  of  the  remaining  fibers  is  not  yet  known. 

The  ventral  white  columns  do  not  contain  a  ventral  cerebrospinal  or  direct  pyramidal  tract, 
as  in  man.  There  is  a  small  tract  (Fasciculus  intracommissuralis  ventralis)  above  the  white 
commissure,  which  separates  it  from  the  rest  of  the  \'entral  colunm.  It  extends  to  the  middle  of 
the  thoracic  region.  It  consists  of  intersegmental  fibers,  and  contains  in  the  anterior  part  of 
the  cer\ical  cord  in  the  sheep  and  goat  both  crossed  and  direct  pyramidal  fibers.  The  descending 
cerebellospinal  fasciculus  extends  from  the  cerebellum  to  the  lumbar  region.  In  the  cer\ical 
region  it  occupies  a  semilunar  area  which  reaches  almost  to  the  surface  ventro-laterally.  Scattered 
libers  belonging  to  it  lie  also  in  the  medial  part  of  the  ventral  column.  Posteriorly  it  diminishes 
in  size  and  comes  to  occupy  a  position  next  to  the  ventral  median  fissure,  corresponding  to  the 
sulco-marginal  fasciculus  of  man  (Dexler). 


The  Brain 

The  brain  or  encephalon  is  the  part  of  the  central  nervous  system  that  is 
situated  in  th(>  cranial  cavity.  It  is  the  enlarged  and  highly  modified  cephalic 
part  of  the  primitive  neural  tube.  It  conforms  rather  closely  in  size  and  shape  to 
the  cavity  in  which  it  lies. 

Its  average  weight  without  the  dura  mater  is  al)out  23  ounces  (ca.  650  gm.), 
and  forms  about  '  of  1  per  cent,  of  the  body-weight. 

It  is  clesirable  to  examine  the  general  external  configuration  of  the  lirain  before 
studying  its  various  parts  in  detail.' 

When  divested  of  its  membranes  and  vessels   (Figs.  499,  500),  its  ventral 

'  The  description  given  here  is  intended  to  present  the  chief  facts  in  regard  to  the  brain  as 
they  may  be  studied  in  the  dissecting  room.  The  ^•essels  and  membranes  which  must  be  ex- 
amined first  have  been  described. 


THE  BRAIX  653 

surface  or  base  presents  the  median  brain  stem,  which  is  continuous  with  the  spinal 
cord  without  any  natural  line  of  demarcation;  it  divides  in  front  into  two  branches, 
the  cerebral  peduncles,  each  of  which  disappears  into  the  mass  of  the  corresponding 
cerebral  hemisphere.  The  brain  stem  consists  of  three  parts.  The  medulla 
oblongata  is  the  posterior  part  which  extends  forward  as  the  direct  continuation 
of  the  spinal  cord.  The  pons  (Varolii)  is  a  transversely  elongated  mass  which 
appears  to  turn  up  on  either  side  into  the  cerebellum.  The  cerebral  peduncles 
extend  forward  from  the  pons  and  diverge  to  plunge  into  the  ventral  jiart  of  the 
cerebral  hemispheres.  The  area  between  them  is  the  interpedimcular  space.  It 
is  largely  covered  by  the  pituitary  body  nr  hypophysis,  a  yellowish-t)rown,  discoid 
structure,  which  is  connected  with  the  base  of  the  cerebrum  by  a  delicate  tube 
called  the  infimdibulum. '  On  dra^\"ing  the  pituitary  body  gently  aside,  the 
infundil)ulum  is  seen  to  be  attached  to  a  slight  gray  eminence,  the  tuber  cinereum. 
Behind  this  is  the  mammillary  body,  a  well-marked  round  prominence.  The 
posterior  part  of  the  space  is  jierforated  by  numerous  openings  for  the  passage  of 
small  arteries,  and  hence  is  termed  the  locus  perforatus  posticus.  Two  large 
bands  of  white  matter,  the  optic  tracts,  cross  the  anterior  ends  of  the  cerebral 
peduncles  and  unite  at  the  optic  chiasm  or  commissure,  forming  the  anterior 
boundary  of  the  interpeduncular  space.  Above  and  in  front  of  the  chiasm  the 
hemispheres  are  separated  by  the  median  longitudinal  fissure.  In  contact  with 
the  anterior  extremity  of  each  hemisphere  is  the  olfactory  bulb,  an  oval  enlargement 
adapted  to  the  ethmoidal  fossa  of  the  cranium.  This  appears  as  a  gray  swelling 
on  a  wide  flat  band,  the  olfactory  peduncle,  wliich  is  continued  behind  by  two  diver- 
gent bands,  the  olfactory  tracts  or  striae.  The  internal  tract  disappears  after  a 
very  short  course  on  to  the  inner  surface  of  the  hemisphere.  The  external  tract 
is  larger  and  longer;  it  runs  backward,  inclines  at  first  outward  and  then  curves 
inward  and  disappears  on  the  concealed  or  tentorial  surface  of  the  hemispheres. 
It  is  separated  from  the  lateral  cerebral  gyri  by  a  distinct  groove  (Sulcus  rhinalis). 
Along  the  inner  side  of  the  stria  are  two  eminences.  The  anterior  of  these  is  the 
trigonum  olfactorium,  a  gray  elevation  situated  in  the  angle  of  divergence  of  the 
inner  and  outer  striie.  Behind  this  is  a  depression,  the  fossa  transversa,"  which  is 
continued  across  the  external  stria  and  sharply  limits  the  second  and  much  larger 
eminence,  the  pjrriform  lobe. 

The  superficial  origins  of  most  of  the  cranial  nerves  are  visible  on  the  base  of 
the  brain. 

The  olfactory  nerve-fibers  join  the  convex  surface  of  the  olfactory  lobe  and  give 
it  a  shagg>-  ajipearance  in  specimens  which  have  been  removed  intact — a  difficult 
proceeding. 

The  second  or  optic  nerves  converge  to  the  optic  chiasm. 

The  third  or  oculomotor  nerve  arises  from  the  inner  part  of  the  cerebral 
peduncle. 

The  fourth  or  trochlear  nerve  may  be  seen  emerging  between  the  pons  and  the 
hemisphere,  but  its  connection  with  the  brain  is  not  visible. 

The  fifth  or  trigeminal  nerve  is  connected  with  the  lateral  part  of  the  pons. 

The  sixth  or  abducent  nerve  arises  just  behind  the  pons  and  lateral  to  the 
pyramid  of  the  medulla. 

The  seventh  or  facial  and  the  eighth  or  auditory  nerves  arise  close  together 
just  behind  the  pons  proper  on  the  extremity  of  the  corpus  trapezoideum. 

The  ninth  or  glosso-pharyngeal,  the  tenth  or  vagus,  ami  the  eleventh  or  spinal 

'  Unle.ss  care  is  used  in  remo\dng  the  brain  the  infundibulurn  is  likely  to  be  torn  and  the 
pituitary  body  left  in  the  cranium.  In  this  case  there  is  a  small  opening  which  communicates 
with  the  third  ventricle. 

-  The  fossa  corre.sponds  in  position  to  the  locus  perforatus  anticus  of  the  human  brain,  but 
is  not  pierced  by  numerous  openings  for  vessels  in  the  horse. 


654 


NERVOUS  SYSTEM  OF  THE  HORSE 


accessory  nerves  are  connected  by  a  linear  series  of  roots  with  the  lateral  aspect  of 
the  vt'ntral  surface  of  the  medulla.  The  spinal  part  of  the  accessory  nerve  comes 
forward  alonf;-  the  etlge  of  the  medulla  to  join  its  medullary  root. 

The  twelfth  or  hypoglossal  nerve  arises  from  the  posterior  part  of  the  medulla 
along  the  lateral  edge  of  the  pyramid. 

The  parts  that  are  visible  when  the  brain  is  viewed  from  above  are  the  cerebral 
hemispheres,  the  cerebellum,  and  part  of  the  medulla  oblongata.     The  cerebral 


Transverse  fissure 


Olfactory  bidh 

Frontal  pule  of  hemisphere 


^     Cerebrum 


Fig.  498. — Braix  of  HonsE,  Dorsal  Vie 
/,  Entoniarginal  fissure;  2,  marginal  fissure;  S,  ectom 


^ 

^ 

. 

Occipital  pole 
hemisphere 

of 

1 

1 

1 

P 

'., 

rbell 

im 

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dulla  Ohio, 

(jiita 

V      \ 

llOVT 

.  Nai 

URAL 

Size. 

rgii 

al  fi.ssi 

re;  J, 

suprasylvia 

11  fts 

sure. 

hemispheres  fonn  an  ovoid  mass,  and  are  separated  from  each  other  by  the  median 
longitudinal  fissure,  in  which  the  falx  cerebri  is  situated.  Their  surfaces  are  marked 
!)>•  tliick  folds,  the  gyri  cerebri,  separated  by  sulci.  The  upturned  ends  of  the 
olfactory  bulbs  are  seen  in  front  of  the  frontal  poles  of  the  hemispheres.  The 
occiiiital  ])oles  of  the  hemispheres  overlie  the  anterior  part  of  the  cerebellum,  from 
which  they  are  separatetl  l)y  the  transverse  fissure  and  the  tentorium  cerebelli 
contained  in  it.  The  cerebellum  is  a  much  smaller  rounded  mass  which  conceals 
the  greater  part  of  the  medulla  oblongata.     Its  surface  is  divided  into  a  middle 


THE  UHOMHENt'EPIIALON 


655 


lobe,  tho  vermis,  and  two  lateral  hemispheres.  It  is  marked  by  numerous  gyri  and 
narrow  sulri  which  have  in  general  a  transverse  direction.  The  posterior  third  of 
the  medulla  oblongata  is  not  covered  by  the  cerebellum. 

'riie  liiuin  is  developed  from  the  expanded  cephalic  part  of  the  neural  tul)e  of  the  eml)ryo. 
The  process  comprises  a  series  of  thickenings,  fiexures,  and  unequal  growth  and  expansion  of 
various  parts  of  the  tube.  In  the  hifilier  animals  the  result  is  that  the  tubular  character  of  the 
brain  is  not  very  evident,  since  the  lumen  comes  to  consist  of  four  irregular  cavities,  the  ventricles, 
which  are  conni'ctcd  by  narrow  passages.  The  tube  is  first  subdivided  by  two  constrictions  into 
three  biaiii  vesicles,  termed  respectively  the  hind-brain  or  rhoinbcnrephalon,  the  mid-brain  or 
mesencephalon,  and  the  fore-brain  or  prosencephalon.  The  hinil-brain  gives  rise  to  three  secon- 
dary segments  and  the  fore-brain  to  two.  The  annexed  table  indicates  the  origin  of  the  principal 
structures  of  the  fully  developed  brain  from  the  primitive  vesicles.  It  has  become  customary  to 
describe  the  brain  with  reference  to  its  embryological  relations. 


TABLE  INDICATING  THE  DERIVATION  OF  THE  PRINCIPAL  PARTS  OF  THE 

Cavities. 


BRAIN 

Secoxdarv  .Segments.  Derivatives. 

Myelencephalon .Medulla  oblongata. .  . 

Metencephalon J  J."^"^" ',; 

(  (  erebellum 

Isthmus  rhombencephali . . .     J  .\nterior  cerelDt 


Mesencephalon . 


-pe,h. 
[  Anterior  medullary  velu: 
[  Corpora  quadrifremina  . 

:  Cerebral  peduncles 

'  Optic  thaiami 

Subthalamic  tegmenta  . 
.  Pineal  body 


'  Pituitary  body 

Optic  nerves  and  retinae. .  . 

Cerebral  hemispheres 

Olfactory  tracts  and  bulb.. 


Fourth  ventricle 


Cerebral  aqueduct 


Anterior  part  of  third 
ventricle.  Lateral 
ventricles  and  olfac- 
tory continuations. 


THE  RHOMBENCEPHALON 
The  Medulla  Oblongata 

The  medulla  oblongata  lies  on  the  basilar  part  of  the  occipital  bone.  It  is 
quadrilateral  in  outline,  but  much  wider  in  front  than  behind,  and  compressed 
(lorso-ventrally.  Its  length,  measured  from  the  root  of  the  first  cervical  nerve  to 
the  pons,  is  about  two  inches  (ca.  5  cm.). 

Its  ventral  surface  is  convex  in  the  transverse  direction.  It  is  marked  by  a 
median  fissure  (Kissura  mediana  ventralis)  which  is  continuous  behind  with  the 
similar  fissure  of  the  spinal  cord.  The  posterior  part  of  the  fissure  is  faintly  marked, 
but  in  front  it  becomes  deeper  and  ends  in  a  small  depression  (Foramen  caecum) 
behind  the  central  part  of  a  transverse  Ijand,  the  corpus  trapezoideum.  On  either 
side  of  the  fissure  is  a  rounded  tract,  the  pyramid  (Pyramis),  which  is  bounded 
externally  by  a  faint  lateral  groove  (Sulcus  intermedins  ventralis).  The  pyramids 
join  the  pons  in  front;  behind  they  become  narrower  and  disappear  into  the  sub- 
stance of  the  medulla,  in  which  their  fibers  intercross,  forming  the  decussation  of 
the  pyramids  (Decussatio  pyraniidum).' 

The  superficial  origin  of  the  sixth  cranial  nerve  (N.  oculoniotorius)  is  just 
lateral  to  the  anterior  end  of  the  pyramid.  The  corpus  trapezoideum  is  a  trans- 
verse band  which  extends  across  the  surface  immediately  behind  the  pons.  It  is 
crossed  by  the  pyramids,  which  cut  off  a  small  central  part.  The  lateral  part 
extends  out  to  the  roots  of  the  seventh  and  eighth  nerves  on  either  side.  Behind  the 
outer  part  of  the  corpus  trajiezoideum  there  is  a  variably  developed  rounded 
eminence,  the  tuberculiun  faciale.  The  root-fibers  of  the  twelfth  or  hjpoglossal 
nerve  form  an  oblique  linear  series  lateral  to  the  posterior  part  of  the  pyramid. 

The  dorsal  surface  is  largely  concealed  by  the  cerebellum  and  forms  the  greater 
part  of  the  floor  of  the  fourth  ventricle.  The  dorsal  median  fissure  (Fissura 
mediana  dorsalis),  the  direct  continuation  of  the  corresponding  groove  of  the  spinal 

'  The  decussation  varies  superficially  in  different  specimens.  In  some  there  is  a  distinct 
superficial  crossing  of  fibers  so  that  the  median  fissure  is  practically  effaced  at  this  point. 


656 


NERVOUS  SYSTEM  OF  THE  HORSE 


cord,  extends  forward  to  about  the  middle  of  the  surface.  Here  the  restiform 
bodies,  which  constitute  the  hps  of  the  fissure,  diverge  to  form  the  lateral  lx)un- 
dariesof  a  triangular  depression;  this  is  the  posterior  part  of  the  rhomboid  fossa  or 
floor  of  the  fourth  ventricle  of  the  brain.     The  dorso-lateral  fissure  winds  outward 


and  forward  to  tlic  lateral  aspect  of  the  medulla,  where  it  presents  the  roots  of  the 
ninth,  tenth,  and  eleventh  cranial  nerves.  External  to  it  is  a  distinct  oval  eminence 
on  the  anterior  ])art  of  the  lateral  column,  termefl  the  tuberculum  cinereum. 
The  central  canal  of   the  cord  is  continued  in  the  posterior  part  of  the  medulla, 


THE  RHOMBEXCEPHALON 


657 


inclines  dorsally,  and  opens  in  the  posterior  angle  of  the  fourth  ventricle.  Hence  it 
is  customary  to  distinguish  a  closed  and  an  open  part  of  the  medulla.  The  dor.sal 
aspect  of  the  latter,  which  is  concealed  at  present,  will  he  considered  later  in  the 
ilescriptiou  of  the  fourth  ventricle. 

The  lateral  surface  is  narrow  hehinil,  wider  and  rounded  in  front.  From  it 
the  root-fibers  of  the  ninth,  tenth,  and  eleventh  cranial  nerves  arise  in  a  linear 
series,  and  alongside  of  it  the  spinal  part  of  the  eleventh  nerve  passes  forward  to 
join  the  medullary  root.  Close  inspection  reveals  the  presence  of  strise  which 
curve  obliciuely  downward  and  liackward  from  the  surface  of  the  r(>stiform  body 


LoiKjUiiilhial  fissure 


Olfiidonj  bulb 

_  Olfacturij  jwilinide 

I nkriiiil  (AfiuioTij  Intel 

External  olfaclory  tract 

—\- —  Trigonum  olfadorium 
^\~  Fossa  transversa 
Cerebral  peduncle 
Tractus  pelt,  transrersus 


Tuberculum  facial 


_^tJ^_-  Interpeduncular  space 
—  Pons 

Corpus  trapezoideum 

Pijraniid 
Medulla 


~'~-—  Chorioiil  plexus  of  fourth 
nnlnele'   ' 
Median  Jissure   and   de- 
cussation of  pyramids 
—  Spinal  cord 


Fig.  500.— L: 


toward  the  hypoglossal  root-fibers;  these  are  the  external  arcuate  fibers  (Fibrse 
arcuatffi  externa).  The  recess  between  the  lateral  aspect  of  the  medulla  and  the 
cerebellum  is  occupied  by  an  irregular  mass  of  villous  projections  of  tlie  ])ia  mater, 
containing  tufts  of  vessels:  this  is  the  chorioid  plexus  of  the  fourth  ventricle,  and 
is  the  lateral  edge  of  the  tela  chorioidea  of  the  ventricle.  On  raising  the  chorioid 
plexus  it  is  seen  that  the  tela  chorioidea  is  attached  to  the  dorsal  aspect  of  the 
medulla,  and  reinforces  liere  the  wall  of  the  fourth  ventricle;  also  that  the  restiform 
body  terminates  in  front  by  entering  the  Ijase  of  the  cerebellum,  forming  its  pos- 
terior peduncle. 

In  the  medulla  the  fiber  tracts  of  the  spinal  cord  either  terminate  in  the  nuclei  of  the  gray 
matter  or  undergo  changes  in  their  relative  position,  and  new  tracts  appear.  The  gray  matter 
is  highly  modified  and  forms  masses  which  have  no  homologues  in  the  cord.  The  central  canal 
of  the  closed  part  of  the  medulla  is  surrounded  by  a  thicker  layer  of  gray  matter  than  is  the  case 
in  the  spinal  cord.  As  the  medulla  opens  out  this  gray  matter  is  naturally  spread  in  the  floor  of 
42 


658 


NERVOUS  SYSTEM  OF  THE  HORSE 


tlio  fourth  ventricle.  The  dorsal  horns  of  gray  matter  become  wide,  spread  apart,  and  are  broken 
up  to  a  great  extent  in  the  formatio  reticularis.  Two  elongated  masses  of  cells  appear  above 
the  central  gray  matter;  these  are  the  nucleus  gracilis  and  nucleus  cuneatus,  and  in  them  the 
fasciculi  of  like  name  gradually  end.  In  front  of  these  are  the  terminal  nuclei  of  the  aiTerent  or 
sensory  cranial  nerves  and  of  the  sensory  portions  of  the  mixed  nerves.  The  ventral  horns  are 
succeeded  by  the  nuclei  of  origin  of  the  efferent  or  motor  cranial  nerves  and  the  motor  root-fibers 
of  the  mixed  nerves.  Of  the  twelve  pairs  of  cranial  nerves,  the  last  eight  are  connected  with 
nuclei  in  the  medulla  and  pons.  The  posterior  olivary  nucleus  (Nucleus  ohvaris  caudalis)  is  a 
conspicuous  gray  mass  which  lies  above  the  pyramid  on  each  side.  On  cross-sections  it  appears 
as  a  wavy  layer  of  gray  matter  whicli  is  folded  on  itself  so  as  to  inclose  a  mass  of  white  matter. 
It  is  about  2  era.  long  in  the  horse,  but  is  smaller  in  circumference  than  in  man  and  hence  does 
not  cause  any  very  distinct  external  enlargement  (olivary  eminence!,  as  in  the  latter.  It  is  con- 
nected with  the  opposite  side  of  the  cerebrllum  by  the  ccrebello-olivary  fibers.  At  its  inner  side 
are  two  small  accessory  olivary  nuclei.  The  pyramidal  tracts,  which  are  small  in  ungulates,  send 
mo.st  of  thi'ir  fibers  across  to  the  opposite  side  in  the  posterior  part  of  the  medulla,  forming  the 
pyramidal  decussation.  .Some  fibers,  however,  continue  in  the  ventral  column  of  the  .same  side 
of  the  conl.  anil  otliiTs  arc  connected  with  the  nuclei  of  the  motor  nerve-roots.  From  the  nu- 
cleus gracilis  and  nucleus  cimeatus  fibers  arise    which    are   traceable  forward  to  the  thalamus. 


Transverse  fissure 
Vermis 


Hemisplie 


of 
cere- 
bel- 
lum 


Basilar 
(irlery 


Fic.  501. — Brain  of  Horse,  Left  Lateral  View. 
The  larger  arterie-s  are  .shown.  The  nerve-roots  are  indicated  by  Roman  numerals.  P.c.  Chorioid  plexu.s  of 
fourth  ventricle:  B.p.,  middle  peduncle  of  cerebellum;  P,  pons;  //,  pituitary  body;  L.p.,  pyriform  lobe;  A. p., 
trigonum  olfactorium;  li.u,  olfactory  bulb;  iS'.r.a.,  sulcus  rhinalLs  anterior;  S.r.p.,  .sulcus  rhinalis  posterior;  /''./., 
lateral  fissure  (of  Sylvius) ;  F./.a.,  anterior  branch  of  lateral  fissure;  iS.p.,  presylvian  fissure;  S.p.n.,  anterior  presyl- 
vian  fissure;   S.s.,  suprasyivian  fissure:    .S.e.,  ectomarginal  fissure. 


These  are  the  internal  arcuate  fibers  (Fibra?  arcuata-  interns'),  which  curve  across  the  median 
plane  below  the  central  gray  matter  and  form  with  those  of  the  opposite  side  the  decussation  of 
the  fillet  iDecussatio  lemniscorum).  Beyond  the  decussation  the  fibers  form  an  iiii]>()rtant 
longitudinal  tract  which  extends  forw-ard  in  the  mid-brain.  This  is  the  fillet  or  lemniscus,  the 
chief  continuation  of  the  sensory  conducting  path  from  the  donsal  roots  of  the  spinal  nerves. 
The  external  arcuate  fibers,  some  of  which  were  seen  on  the  lateral  aspect  of  the  medulla,  have  a 
similar  origin.  Part  of  them  (Fibr;e  dorsales)  pass  directly  to  the  dorsal  aspect  of  the  restiform 
body  of  the  s;une  side;  others  (Fibrae  ventrales)  cross  to  the  opposite  side,  descend  clo.se  to  the 
ventral  fi.ssurc,  and  then  curve  upward  and  forward  to  the  restiform  body.  The  dccii.^sation  of 
the  arcuate  fibers  forms  the  distinct  median  raphe  seen  on  cross-sections  of  the  nu'dulhi  anterior 
to  (he  pynunidal  (h-cu.ssation.  The  restiform  body,  silu:ilrd  dorso-latcrally,  contains,  in  addi- 
tion to  the  :ircuate  fibers,  the  cerebello-olivary  fasciculus  bcfnrr  nuntiDiicd,  and  the  cerebello- 
spinal fasciculus  or  direct  cerebellar  tract.  Tiic  dorsal  longitudinal  fasciculus  corresponds  to 
the  ventral  ground-btmdle  of  the  spinal  cord,  displaced  dorsally  by  the  decussation  of  the  pyra- 
mids and  fillet.  In  the  posterior  part  of  the  medulla  it  is  not  marked  off  from  the  fillet,  along 
the  dorsal  e  Ige  of  which  it  lies.  From  the  level  of  the  hypoglossal  nucleus  forward  it  is  di.stinct 
and  can  be  traced  as  a  conspicuous  tract  in  the  ventral  margin  of  the  gray  matter  of  the  floor  of 
the  fourth  ventricle  and  of  the  central  gray  matter  of  the  mid-brain.  Below  the  restiform  body 
and  related  externally  to  the  external  arcuate  fibers,  there  is  a  considerable  bimdle  of  longitud- 
inal fibers,  the  spinal  root  (Tractus  spinalis)  of  the  fifth  nerve;  internal  to  it  is  the  terminal  nu- 
cleus of  the  sensory  root  of  the  nerve. 


THE  PONS 


659 


THE  PONS 


The  pons  (Varolii)  is  that  part  of  the  brain  stem  which  Hes  between  the  medulla 
and  the  cerel)ral  peduncles;   it  is  marked  off  from  these  ventrally  by  anterior  and 


(ir 


Fig.  502. — Cross-section  of  Medulla  Oblong.i.ta  of  Horse,  Passing  through  Facial  Nicleus. 
Cr,  Corpus  restiforme;  D,  dorsal  longitudinal  fasciculus;  Fa,  ascending  part  of  facial  nerve:  L,  fillet; 
.V7.  nucleus  of  facial  nerve;  iVS,  triangular  nucleus  of  vestibular  root  of  eighth  nerve;  .VS' ,  spinal  root  of  eighth 
nerve;  Pi),  pyramid;  Ra,  raphe;  R7,  radicular  part  of  facial  nerve;  RS,  vestibular  root  of  eighth  nerve;  Sg, 
substantia  gelatinosa;  Ta,  posterior  end  of  tuberculuni  acusticum;  V,  spinal  root  of  trigeminus.  (Ellenberger- 
Baum,  Anat.  d.  Haustiere.) 


posterior  grooves.     Viewed  from  below  it  is  elongated  transversely,  convex  in  both 
directions,  and  presents  a  wide  shallow  median  groove  (Sulcus  basilaris),  which 


Fig.  503  — Cross-sectiom  of  Medulla  Oblongata  of  Horse;    Section  Passes  through  Middle  of  Corpus 

Trapezoideum. 
Cr,  Corpus  restiforme;  D,  dorsal  longitudinal  bundle;  Fa,  ascending  part  of  facial  nerve;  Fa',  emergent  or 
descending  part  of  facial  nerve;  fl7,  root  of  facial  nen-e;  i.  fillet;  .U,  central  white  matter  of  cerebellum;  N6, 
abducens  nucleus;  X8,  triangular  nucleus;  .VS'.  nucleus  of  Deiters;  A'S".  tuberculum  acusticum;  Oo,  anterior 
ohve;  Pi/,  pyramid;  R6,  root  of  abducens  nerve;  R7,  root  of  facial  nerve;  Re.  cochlear  nerve;  if  r.  vestibular  nerve; 
.Sff,  substantia  gelatinosa;  T.  corpus  trapezoideum;  V,  spinal  root  of  trigeminus.  (Ellenberger-Baum,  .\nat.  d. 
Haustiere.) 

lodges  the  basilar  artery.  Laterally  a  large  part  of  its  mass  curves  upward  and 
backward  into  the  base  of  the  cerebellum,  forming  the  middle  cerebellar  peduncle 
(Brachium  pontis).     The  superficial  origin  of  the  trigeminal  (fifth)  nerve  is  at  the 


660  NERVOtS  SYSTEM  OF  THE  HORSE 

lateral  limit  of  the  ventral  surfaee.  Transverse  striations  indicate  the  course  of 
its  sujierficial  (ventral)  fibers  which  connect  the  two  sides  of  the  cerebellum.  The 
dorsal  surface  is  blended  on  either  side  with  the  overlying  anterior  i)eduncles  of  the 
cerebellum;  the  central  free  portion  forms  the  anterior  part  of  the  floor  of  the  fourth 
ventricle,  and  will  be  considered  in  the  account  of  that  cavity. 

On  cross-section  tlip  pons  is  seen  to  1)6  composed  of  dorsal  and  central  parts.  The  dorsal 
part  (Pars  dorsalis  pontis)  consists  superficially  of  a  layer  of  gray  matter  co\ered  by  the  epen- 
clyma  of  the  fourth  ventricle,  lieneath  this  the  median  raphe  of  the  medulla  is  continued  into 
the  pons,  dividing  it  into  similar  halves.  In  the  anterior  part  of  the  pons  the  fillet  divides  into 
an  inner  and  outer  part,  the  medial  and  lateral  fillets  (Lemniscus  medialis,  latcmlisl;  tin-  latter 
arches  outward  to  reach  the  outer  side  of  the  anterior  cerebellar  peduncle.  The  dorsal  longitudinal 
fasciculus  becomes  sharply  defined  into  a  round  bundle  which  lies  close  to  the  raphe  under  the 
gray  matter  of  the  floor  of  the  fourth  \entricle.  In  cross-section  the  fonnatio  reticularis  forms 
a  large  area  below  the  superficial  gray  matter  and  the  longitudinal  bundles.  Dorso-laterally  is 
the  la'rge  rounded  section  of  the  anterior  cerebellar  peduncle.  Lower  down  is  a  large  bundle,  the 
sensory  root  of  the  fifth  nerve.  In  front  of  this  is  tlic  motor  nucleus  of  the  same  nerve,  exter- 
nal to  whicli  is  its  motor  root.  Tlie  ventral  part  of  the  pons  (Pars  basilaris  pontis)  is  composed 
of  transverse  and  longitudinal  filx'rs,  and  a  Uu-gc  auiount  of  gray  matter  which  is  broken  up  into 
small  masses  (Xuclei  i)i>iilis)  by  the  iiitrrsci'iioii  of  the  fibers.  The  transverse  fibers  are  gath- 
ered laterally  into  a  com])act  mass  wliich  turns  upward  and  backward  and  enters  tlie  central  white 
matter  of  tlie  cerebellum,  forming  the  middle  cerebellar  pedtincle.  Centrally  the  fibers  are  ar- 
ranged in  bundles  which  intercross.  The  transverse  fibers  are  chiefly  of  two  kinds.  Some  arise 
from  the  Piu-kinje  cells  of  the  cerebellar  cortex  and  pass  either  to  the  opposite  side  of  the  cere- 
bellum or  turn  at  the  raphe  and  run  forward  and  backward  in  the  brain-stem.  (Jthers  are  ax- 
ones  of  cells  of  the  nuclei  ponti.s,  and  pass  to  the  hemispheres  of  the  cerebellum.  The  corpus 
trapezoideum  is  mainly  the  central  continuation  of  the  cochlear  division  of  the  auditory  ner\-e. 
Above  it  is  the  small  anterior  olivary  nucleus  (Nucleus  olivaris  nasalis).  The  longitudin.al 
fibers  of  the  ventral  part  of  the  pons  consist  chiefly  of  the  cerebrospinal  or  pyramidal  fasciculi. 
These  come  from  the  ventral  part  (pes)  of  the  cerebral  peduncles  and  are  situated  laterally, 
intersperseil  among  the  deep  transverse  fibers  in  the  anterior  part  of  the  pons.  Toward  the  poste- 
rior part  the  bundles  incline  toward  the  median  plane  and  become  collected  into  a  compact  mass 
which  appears  superficially  at  the  posterior  border.  Many  fibers  come  from  the  cerebral  cortex 
and  terminate  in  the  nuclei  of  the  gray  matter  of  the  pons;  they  may  be  designated  cortlco- 
pontile  fibers. 

THE  CEREBELLUM 

Tlie  cerebellum  is  situated  in  the  jxtsterior  fossa  of  the  cranium,  and  is  sep- 
arated from  the  cerebral  hemispheres  bj-  the  trans\'erse  fissure  and  the  tentorium 
cerebelli  which  occupies  it.  It  overlies  the  pons  and  the  greater  part  of  the  medulla, 
from  which  it  is  separated  by  the  fourth  ventricle.  Its  average  weight  is  about  two 
ounces  (ca.  60  gm.)  or  about  9  per  cent,  of  the  weight  of  the  entire  brain.  Its 
shape  is  approximatel.v  globular  but  very  irregular.  It  is  somewhat  comj^ressed 
dorso-vont rally  and  its  transverse  diameter  is  the  greatest. 

The  anterior  surface  faces  ujiward  and  forward  and  is  co\-ered  partially  by 
the  tentorium  cerebelli.  The  posterior  surface  is  almost  vertical.  The  ventral 
surface  or  base  lies  over  the  fourth  ventricle,  and  is  connected  by  three  jiairs  of 
peduncles  with  the  medulla,  pons,  and  mid-brain. 

It  is  customary  to  recognize  three  gro.ss  divisions  of  the  cerebellum,  viz.,  the 
median  vermis  and  two  lateral  hemispheres.  The  vermis  (cerebelli)  is  curved  in  a 
circular  manner  so  that  its  two  extremities  are  close  together  or  even  in  contact 
on  the  ventral  surface.  The  anterior  extremity  is  termed  the  lingula;  it  lies 
between  the  cerebellar  peduncles  and  gives  attachment  to  the  anterior  meduUary 
velum,  a  thin  lamina  which  forms  the  anterior  part  of  the  roof  of  the  fourth  ven- 
tricle. The  posterior  extremity,  the  nodulus,  gives  attachment  to  the  posterior 
medullary  velum  which  covers  the  posterior  recess  of  the  fourth  ventricle.  The 
hemispheres  (Ilemisplueria  cerebelli)  are  clearly  sejiarated  from  the  vermis  by 
two  deep  ]mramedian  fis.sures.  They  lie  in  the  lateral  depressions  of  the  cereliellar 
compartment  of  the  cranium. 

In  tracing  the  fi.ssures  from  behind  forward  it  will  be  noticed  that  they  .are  nearly  sagittal 
as  far  as  the  anterior  surface,  where  they  diverge  widely,  so  that  the  \ermis  forms  all  of  the  fore 
part  of  the  cerebellum. 


THK  CEREBELLUM  661 

The  surface  of  the  cerebellum  is  further  cut  up  into  numerous  gyri  or  folia 
by  narrow  and  relatively  deep  sulci,  many  of  which  approach  a  transverse  direction. 
Certain  of  the  sulci  arc  more  j)ronounced  than  the  others,  and  l)y  means  of  them  it 
is  possible  to  define  groups  of  gyri.  Such  groups  are  termed  lobes,  and  have 
received  specific  names,  derived  chiefly  from  the  systematic  descriptions  of  the 
human  cerebellum. 

The  lobes  of  the  vermis  are  readily  distinguished  on  a  median  section.  Enumerated  from 
the  anterior  to  the  posterior  extremity  they  are:  (1)  lingula,  (2)  lobus  centralis,  (o)  lobus  ascendens, 
(4)  lobus  culminis,  (.5)  lobus  clivi,  (6)  tuber  vermis,  (7)  pyramis,  (8)  uvula,  (9)  nodulus.  Each 
hemisphere  is  cut  into  laterally  by  two  sulci  which  mark  off  two  sagittal  discoid  masses,  termed  by 
Ziehen  tabulations.  The  external  tabulation  consists  of  four  or  five  lobules,  the  lowest  of  which 
is  regarded  as  the  flocculus.  The  inner  part  of  the  hemisphere  is  divided  into  three  or  four  lobes. 
In  the  absence  of  a  satisfactory  morphological  basis  it  seems  undesirable  to  deal  with  the  lobation 
of  the  cerebellum  in  further  detail. 

The  cerebellar  peduncles,  three  on  each  side,  join  the  central  white  matter  of 
the  cerebellum  at  the  base.  The  posterior  peduncle  is  the  restiform  body  of  the 
medulla,  a  large  rounded  tract  derived  from  the  lateral  and  ventral  cohmins  of 
the  cord.  Near  the  middle  of  the  medulla  it  inclines  outward,  forms  the  lateral 
wall  of  the  fourth  v(MitricIe,  and  ends  bj'  entering  the  central  white  matter  of  the 
cerebellum.  The  middle  peduncle  is  formed,  as  previously  seen,  by  the  brachium 
pontis.  The  anterior  peduncles  (Brachia  conjunctiva)  pass  forward  on  either  side 
on  the  dorsal  siu'face  of  the  pons,  forming  the  lateral  boimdary  of  the  fore  part  of 
the  fourth  ventricle.  They  disappear  under  the  corpora  quadrigemina  into  the 
substance  of  the  mid-brain.  At  the  point  of  disappearance  the  trochlear  (fourth) 
nerve  emerges  from  the  mid-brain.  In  some  cases  two  or  three  bundles  of  fibers 
(Fila  lateralia  pontis)  arise  in  the  angle  between  the  middle  and  anterior  peduncle, 
curve  obliquely  forward  and  downward  over  the  outer  aspect  of  the  latter,  and 
spread  out  on  the  ventral  face  of  the  cerebral  peduncle  just  in  front  of  the  pons. 

On  sagittal  section  the  cerebellum  is  seen  to  consist  of  a  layer  of  cortical  gray 
matter  (Substantia  corticalis)  and  the  medullary  white  matter.  The  white  matter 
consists  of  a  large  basal  mass  (Corpus  meduUare),  which  is  joined  by  the  peduncles, 
and  gives  off  primary  laminae  to  the  lobules;  from  these  secondary  and  tertiary 
laminiE  arise,  the  latter  entering  the  gjTi.  The  arrangement  on  sagittal  section  is 
tree-like,  hence  the  classical  term  "arbor  vitse"  which  is  applied  to  it.  The  central 
gray  matter  consists  of  groups  of  cells  which  form  small  nuclei  embedded  in  the 
central  white  substance. 

.\s  noted  above  the  central  gray  matter  does  not  form  a  large  nucleus,  the  corpus  dentatum, 
which  is  so  conspicuous  an  object  on  sagittal  sections  of  the  cerebellar  hemisphere  in  man. 

The  principal  connections  established  by  the  peduncular  fibers  of  the  cerebelhmi  are  as 
follows:  The  posterior  pedimcle  (Corpus  restiforme)  is  composed  of  afferent  and  efferent  fibers 
which  connect  the  cerebellum  with  the  medulla  and  spinal  cord.  The  cerebello-spinal  fascicu- 
lus or  direct  cerebellar  tract,  which  arises  from  the  cells  of  the  nucleus  dorsalis  i(  larkc's  column) 
of  the  cord,  ends  in  the  cortex  of  the  vermis;  many  of  its  fibers  cro.*s  to  the  cippusite  side. 
Numerous  arcuate  fibers  from  the  nucleus  gracilis  and  nucleus  cuneatus  of  the  .-amc  and  op- 
posite sides  estabUsli  connections  \\ith  cells  of  the  cerebellar  cortex.  Clivo-cerebellar  fibers 
(chiefly  afferent )  connect  with  the  olivary  nucleus  of  the  same  and  of  the  opposite  side  of  the  me- 
dulla oblongata.  The  nucleo-cerebellar  fasciculus  comprises  fillers  derived  from  the  nuclei  of 
the  fifth,  eighth,  and  tenth  cranial  nerves  (Edinger).  The  descending  cerebello-spinal  fascicu- 
lus consists  of  fibers  wliich  terminate  in  relation  witli  cells  of  the  ventral  horns  of  the  spinal 
cord.  The  chief  facts  concerning  the  middle  peduncle  have  been  mentioned  in  the  description 
of  the  pons.  The  anterior  peduncle  is  essentially  an  efferent  tract,  the  fibers  of  which  pass  for- 
ward to  the  tegmentum  of  the  cerebral  peduncle,  the  subthalamic  region,  and  the  thalamus. 
After  the  peduncles  disappear  under  the  corpora  quaihigeniina,  they  converge  and  many  of  their 
fibers  intercross,  forming  the  decussation  of  the  superior  peduncle.  A  considerable  numljer  of 
fibers  end  in  the  nucleus  ruber.  Thence  impulses  are  transmitted  in  two  directions:  first,  by 
thalamo-cortical  fibers  to  the  cerebral  cortex;  second,  by  the  rubro-spinal  tract  through  the 
braiii-sfrni  unci  lateral  columns  of  the  cord  to  the  ventral  horn  cells.  The  ventro-latcral  cere- 
licllijspinal  fasciculus  (Gowers'  tract)  is  an  ill-defined  tract  wliich  connects  the  spinal  cord  with 
the  cerebeUum.  Its  fibers  appear  to  be  axones  of  cells  of  the  posterior  horns  of  the  cord;  they 
pa.ss  in  the  lateral  column  of  the  cord,  become  scattered  in  passing  through  the  reticular  forma- 
tion of  the  medulla  and  pons,  and  enter  the  cerebellum  by  waj- of  the  anterior  medullary  velum. 


662 


NERVOUS  SYSTEM  OF  THE  HOHSE 


The  Fourth  Ventricle 

The  fourth  ventricle  (\'entriculus  quartus)  is  the  cavity  of  the  rhombencepha- 
lon; it  coniniunicatcts  witli  the  central  canal  of  the  spinal  cord  behind,  and  through 
the  aqueduct  with  tlie  third  ventricle  in  front.  It  is  somewhat  rhomboid  in  out- 
line, elongated  from  l)efore  backward  and  narrowest  behind.  It  is  lined  complete!}' 
by  an  cijitlieliuui  (Ependyma)  and  contains  a  small  amount  of  fluid. 

Its  floor  (Fossa  rhomboidea)  is  formed  by  tiie  medulla  and  pons  and  is  marked 
by  tln-ee  longitudinal  furrows  whicli  converge  l^ehind.  It  is  widest  and  deepest 
a  little  in  front  of  its  middle.  The  i)osterior  part  narrows  to  a  point  at  the  opening 
of  the  central  canal,  and  on  account  of  its  appearance  in  man  it  has  been  termed  the 


FaciuL  eminence   -' 


Columns  of  fornix 

Corpus  striatum 

Chorioid  plexus  of 
lateral  ventricle 

SIriii  /<rininalis 
ihinl  re  utricle 
ThuUunus 
Fimbria 

Corpus  genie,  externum 
Pineal  body 
--^__     "  Corpus  genie,  internum 
'''  ■  Corpora  quadrigemina 

.\- Anterior  prdunele  of  cerebdlum 

Middle  peduncle  of  eereli<lluvi 

Median  sulcus 

Limiting  sulcus 

.1-41 Corpus  restiforme 

Tcenia 
Obex 

Tubcrculum  cinereum 

Dorso-lateral  sulcus 
Median  sulcus 


:,    DORSM 

numerals 


calamus  scriptorius.  The  median  sulcus  (Sulcus  medianus)  extends  the  entire 
length  of  the  floor  and  is  deepest  toward  the  ends.  The  limiting  sulci  (Sulci 
limitantes)  begin  on  either  side  of  the  opening  of  the  central  canal  and  extend  for- 
ward as  the  lateral  limits  of  the  rhomlioid  fossa.  Just  beyond  the  middle  of  the 
fossa  they  expand  into  a  shallow  depression,  the  anterior  fovea  (Fovea  nasalis). 
On  either  side  of  the  median  sulcus  and  margined  by  the  limiting  sulcus  is  a  slightly 
rounded  column,  the  eminentia  medialis.  Opposite  the  fovea  this  presents  an 
elongated  prominence,  the  colliculus  facialis,  so  named  becau.se  it  overlies  the  bend 
formed  by  the  fibers  of  origin  of  the  facial  nerve.  External  to  the  limiting  sulcus 
is  a  long  fusiform  elevation,  the  area  acustica,  from  which  a  band  of  fibers  (Striie 
acusticip)  winds  over  the  anterior  end  of  the  restiform  body  to  the  sujierficial 
origin  of  the  cochlear  nerve. 


THE  MESENCEPHALON  663 

The  lateral  wall  is  foriiictl  by  the  restiform  body  and  tlie  anterior  peduncle 
of  the  cerebelkun. 

The  roof  is  formed  in  its  middle  part  by  the  vermis  of  the  cerebellum,  covered 
by  the  epithehum  before  mentioned.  There  is  commonly  a  dorsal  recess  (Recessus 
tecti  s.  fastigium)  between  the  extremities  of  the  vermis.  The  anterior  ])art  of  the 
roof  is  formed  by  a  thin  lamina  of  white  substance,  the  anterior  medullary  veliun 
(or  valve  of  Vieussens),  which  extends  backward  from  the  corpora  quach'igemina, 
and  is  attached  on  either  side  to  the  anterior  peduncles  of  the  cerebellum.  Its 
anterior  part  is  relatively  thick  and  contains  the  decussation  of  the  fillers  of  the 
trochlear  nerves.  Posteriorly  it  blends  with  th(>  white  matter  of  the  cereliellum. 
A  thin  lamina  of  white  matter,  the  posterior  medullary  velum,  l)acked  l)y  pia  mater, 
completes  the  roof  posteriorly.  After  removal  of  the  cerebellum  the  line  of 
attachment  (Twnia  ventriculi  quarti)  to  the  medulla  is  seen;  it  begins  centrally 
over  the  opening  of  the  central  canal,  runs  forward  on  the  inner  face  of  the  restiform 
body,  ancl  turns  outward  behind  the  brachium  pontis.  The  thick  part  which 
stretches  over  the  posterior  angle  of  the  ventricle  is  termed  the  obex.  The  pos- 
terior part  of  the  ventricle  forms  three  recesses,  of  which  two  are  lateral  and  the 
third  median  and  posterior.     The  lateral  recesses  communicate  with  the  sub- 


FiG.  50.5. — Brain  Stem  and  Basal  Ganglia  of  Hohse,  Right  View. 
F.a.,  External  arcuate  fibers;   Cr.,  corpus  restiforrae;   P,  pyramid;    T,  corpus  trapezoideum;   B.p.,  middle 
peduncle  of  cerebellum;    P.c,  cerebral  peduncle;    S.  sulcus  lateralis;    T.t.,  tractus  transversus;    /,,  trigonum  lem- 
nisci;   Ca.,  corpus  quad,  ant.;   f.p.,  corpu.s  quad,  post.;   i?,  commissure  of  Cp.;  G,  corpus  geniculatum  internum; 
T.O.,  olfactorj-  peduncle;   B.o.,  olfactory  bulb. 

arachnoid  space  by  distinct  openings  (Aperturse  laterales).  The  layer  of  pia 
which  strengthens  the  roof  here  is  named  the  tela  chorioideaof  the  fourtli  ventricle. 
It  is  triangular  in  outline  and  closely  adherent  to  the  velum.  It  forms  three 
fringed  masses  which  contain  vascular  convolutions  and  are  designated  the  median 
and  lateral  chorioid  plexuses  of  the  fourth  ventricle.  They  ajipear  to  lie  within 
the  ventricle,  but  are  really  excluded  from  the  cavity  by  the  epithelial  lining,  which 
they  invaginate. 

THE  MESENCEPHALON 

The  mesencephalon  or  mid-brain  connects  the  rhomliencephalon  with  the 
fore-brain.  In  the  undissected  Itrain  it  is  covered  dorsally  by  the  cerebral  hemi- 
spheres. It  consists  of  a  dorsal  part,  the  corpora  quadrigemina,  and  a  larger  ventral 
part,  the  cerebral  peduncles,  which  are  visible  on  the  base  of  the  brain.  It  is  tra- 
versed longitudinally  by  a  narrow  canal,  the  cerebral  aqueduct,  which  connects  the 
fourth  ventricle  with  the  third. 

The  corpora  quadrigemina'  are  four  rounded  eminences  which  lie  under  the 
posterior  part  of  the  cerebral  hemispheres.  They  consist  of  two  pairs,  separated 
by  a  transverse  groove.     The  anterior  pair  (Colliculi  nasales)  are  larger  and  much 

'  In  the  new  nomemclature  the  term  lamina  quadrigemina  is  applie-]  to  the  dorsal  mass  of 
the  n.id-brain,  and  the  four  eminences  which  it  bears  are  the  corpora  qua.aiscmina. 


664  NERVOUS  SYSTEM  OF  THE  HORSE 

higher  than  the  posterior  pair.  They  are  gray  in  color,  almost  hemispherical,  and 
are  separated  by  a  narrow  furrow  which  leads  forward  to  the  suhpineal  fovea. 
A  wide  groove  intervenes  between  them  and  the  optic  thalami.  The  posterior  pair 
(CoUiculi  caudales)  are  relatively  small  and  are  paler  than  the  anterior  iwir.  They 
are  marked  liy  a  wide  median  dcjiression,  and  are  limited  below  by  a  transverse 
furrow  (Sulcus  postquadrigeminus),  at  cither  side  of  which  the  trochlear  (fourth) 
nerve  emerges.  Laterally  each  is  jjrolonged  to  the  inner  geniculate  botly  by  a 
band  of  white  matter  termed  the  inferior  brachium.' 

The  cerebral  peduncles  or  (Tura  cerebri  (Pedunculi  cereljri)  appear  on  the 
base  of  the  brain  as  two  large  roix'-like  stalks  which  emerge  from  the  pons  close 
together  and  di\-crge  as  they  extend  forward  to  enter  the  cerebrum.  At  the  point 
of  disajiiiearance  the  optic  tract  winds  obliquely  across  the  peduncle.  About  half 
an  inch  further  back  a  small  tract  (Tractus  peduncularistransversus)  curves  across 
the  peduncles,  and  behind  this  near  the  median  line  is  the  superficial  origin  of  the 
oculomotor  (third)  nerve.  The  triangular  depression  between  the  diverging 
peduncles  is  the  interpeduncular  space  (Fossa  interpeduncularis).  It  is  covered 
to  a  large  extent  by  tlie  pituitary  body,  a  discoid  brown  mass  which  is  connected 
with  the  base  of  the  l>rain  by  a  hollow  stalk,  the  infundibulum.  The  posterior 
part  of  the  space  is  pierced  by  numerous  minute  openings  wliicii  transmit  blood- 
vessels, and  is  therefore  termed  the  locus  perforatus  posticus.  The  objects  in  the 
space  belong  to  the  dicncephalon,  and  will  be  dcscrilx'd  later.  The  lateral  asjiect 
of  the  peduncle  is  marked  by  a  groove  (Sulcus  lateralis  mcsence]ihali)  which  indi- 
cates the  division  into  a  dorsal  part,  the  tegmentum,  and  a  ventral  part  the  basis 
pedunculi;  these  are  separated  by  a  hyn-  of  dark  gray  matter,  the  substantia 
nigra.  Tiie  triangular  area  (Trigonum  lemnisci)  above  the  lateral  groove  is  faintly 
marked  by  fibers  passing  obliquely  upwaril  and  backward  to  the  anterior  cerebellar 
peduncle;  these  belong  to  the  fillet  or  lemniscus,  an  important  tract  that  connects 
the  thalamus  and  corpora  quadrigemina  with  the  sensory  reception  nuclei  of  the 
opposite  side  of  the  medulla. 

The  aqueduct  of  the  cerebrum  or  of  Sylvius  (Aquseductus  cerebri)  is  the  canal 
which  extends  through  the  mid-brain  from  the  fourth  to  the  thirtl  ventricle.  It  is 
surrounded  by  a  layer  of  gray  matter  (Stratum  griseum  centrale),  in  the  ventral 
part  of  which  are  the  nuclei  of  origin  of  the  oculomotor  and  trochlear  nerves,  and 
laterally  nuclei  of  the  mesencephalic  roots  of  the  trigeminal  nerves. 


THE  DIENCEPHALON 

The  diencephalon  or  inter-brain  comprises  the  thalamus  and  a  number  of 
other  structures  grouped  aljout  the  third  ventricle,  the  cavity  of  this  division  of  the 
brain.-'  To  expose  its  dorsal  aspect,  the  greater  part  of  the  cerebral  hemispheres, 
the  corpus  callosum,  the  fornix,  the  hippocampus,  and  the  tela  chorioidea  of 
the  third  ventricle  must  be  removed. 

The  thalamus  (or  optic  thalamus)  is  the  ])rincipal  body  in  this  jjart  of  tiie  lirain. 
It  is  a  large  ovoid  gray  mass  placed  obliquely  across  the  dorsal  face  of  each 
cerebral  peduncle,  so  that  the  long  axes  of  the  two  thalami  would  meet  in  front 
about  at  a  right  angle.  Medially  th(>y  are  fused  to  a  large  extent,  and  around  the 
area  of  adhesion  they  are  separated  by  a  sagittal  circular  space,  the  third  ventricle. 
The  dorsal  surface  is  convex  in  both  directions,  and  is  separated  from  the  overlying 
hippocampus  by  the  tela  chorioidea  (or  velum  interpcsitum).    Laterally  it  is  sep- 

'  In  man  a  distinot  superior  brachium  eonnocts  the  superior  pair  with  the  lateral  geniculate 
body,  liut  in  the  (lonicsticatol  animals  the  union  with  I  he  optic  thalamus  is  too  direct  to  allow  of 
any  definite  arm  hcinfj  rocojfiiized. 

=  On  a  strictly  embryological  basis  the  optic  part  of  the  hypothalamus,  comprising  the 
anterior  part  of  the  third  ventricle  and  the  structures  associated  with  it,  belong  to  the  telen- 
cephalon, but  will  be  considered  here  as  a  matter  of  convenience. 


THE  DIENCEPHALON  665 

arated  from  the  nucleus  caudatus  l)y  an  oblique  groove  in  which  there  is  a  band 
of  white  matter  termed  the  stria  terminalis  or  tienia  semicircularis.  Internallj'  it  is 
bounded  by  a  narrow  band,  the  stria  meduUaris,  on  which  is  a  delicate  ridge  of 
ependyma  termed  the  taenia  thalami.  The  striie  unite  posteriorly  and  blend  with 
the  stalk  of  the  pituitary  i)ody.  Near  this  point  they  present  a  small  enlargement 
caused  by  the  nucleus  habenulie.  Anteriorly  there  is  a  small  eminence,  the  anterior 
tubercle.  The  posterior  part  of  the  thalamus  has  the  form  of  a  rounded  ridge  which 
is  continuous  laterallj  with  the  optic  tract.'  Behind  the  point  of  origin  of  the 
tract,  in  the  angle  between  the  thalamus  and  the  cerebral  peduncle,  is  the  internal 
geniculate  body  (Corpus  geniculatum  mediale),  a  well-defined  oval  prominence. 

The  outer  surface  is  separated  from  the  lenticular  nucleus  by  the  internal  capsule,  au 
important  mass  of  white  matter  compo.sed  of  fibers  pa.ssing  to  and  from  the  (■ciclinil  cortex. 
These  fillers  go  to  form  a  large  part  of  the  ventral  portion  (basis)  of  the  cerebral  ]ie(linu-le.  From 
the  entire  external  surface  of  the  thalamus  fibers  pass  into  the  internal  capsule  and  radiate  to 
reach  the  cerebral  cortex;  similarly  fibers  coming  from  the  cortex  converge  in  the  internal  capsule 
to  enter  the  thalamus.  This  arrangement  is  termed  the  thalamic  radiation,  ^'entral  to  the 
thalamus  proper  is  the  subthalamic  tegmental  region.  This  is  the  continuation  of  the  tegmental 
part  of  the  cerebral  peilunclc  inlo  the  clicmcphalun.  It  contains  the  red  nucleus  ( Nucleus 
ruber)  an  important  ganglion  on  the  coin-se  of  tlie  motor  tracts.  It  receives  numerous  fibers 
from  the  cerebral  cortex  and  the  corpus  striatum.  From  it  fibers  proceed  to  the  thalamus 
and  to  the  spinal  cord;  the  fibers  to  the  cord  (Tractus  rubro-spinalis  of  Monakow)  cross  to  the 
oppo.site  side  and  extend  back  in  the  tegmentum  to  the  lateral  columns  of  the  cord.  Lateral  to 
the  red  nucleus  a  conspicuous  lenticular  area  of  dark  gray  matter  is  visible  on  cro.ss-.sections  of 
the  subthalamic  region;  this  is  the  subthalamic  nucleus  (Xucleus  hypothalamicus  s.  corpus 
Luysi),  which  consists  of  pigmented  nerve-cells  scattered  throughaden.se  network  of  fine  medul- 
lated  fibers,  and  is  riclily  supplied  with  capillary  blood-vessels.  The  two  nuclei  are  connected 
by  a  transverse  commissure  (( 'onnnisstu'a  hypothalamica),  which  crosses  the  floor  of  the  third 
ventricle  above  the  maminillary  liody. 

The  pineal  body  or  epiphysis  is  a  small  ovoid  or  fusiform  red  Inown  mass 
situated  in  a  deep  central  depression  l)etween  the  thalami  and  corpora  (juadrigemina. 
It  is  variable  in  size,  but  is  commonly  about  10  to  12  mm.  long  and  6  mm.  wide. 
It  is  attached  at  the  postero-superior  quadrant  of  the  third  ventricle  by  a  short 
stalk,  in  which  is  a  small  recess  of  that  cavity.  Its  base  blends  in  front  with  the 
junction  of  the  striae  medullares  of  the  thalamus.  Immediately  under  the  posterior 
part  of  the  stalk  is  a  short  transverse  band  of  white  matter,  the  posterior  commis- 
sure. 

The  pineal  body  is  inclosed  in  a  fibrous  capsule  from  which  numerous  trabecule  pass  inward, 
dividing  the  organ  into  spaces  occupied  by  round  epithelial  cells  of  the  same  origin  as  the  epen- 
dyma of  the  ventricle. 

The  mammillary  body  (( 'orpus  manunillare)  is  a  white  round  elevation  a  little 
larger  than  a  pea  which  projects  ventrally  at  the  anterior  end  of  the  median  furrow 
of  the  interpeduncular  space.  While  it  is  a  single  body  in  external  form  in  the  horse, 
sections  show  that  it  is  double  in  structure  and  contains  a  nucleus  of  gray  matter 
on  either  side. 

Three  sets  of  fibers  are  connected  with  the  mammillary  body.  The  anterior  pillar  of  the 
fornix  curves  down  in  the  lateral  wall  of  the  third  ventricle  to  the  body  and  many  of  the  fornix 
fibers  end  in  it.  A  bundle  (Fasciculus  thalamo-mammillaris)  passes  upward  and  backward 
from  it  into  the  anterior  part  of  the  thalamus,  and  a  tract  (Fasciculus  pedunculo-mammillaris) 
extends  back  in  the  floor  of  the  third  ventricle  to  the  tegmentum  of  the  mid-brain. 

The  pituitary  body  or  hypophysis  was  mentioned  as  covering  part  of  the  inter- 
jicduncular  space.  It  is  oval  in  outline,  flattened  dorso-ventrally,  and  nearly  an 
inch  (ca.  2  cm.)  in  width.  It  is  attached  by  a  delicate  tubular  stalk,  the  infundi- 
bulum,  to  the  tuber  cinereum,  a  small  gray  prominence  situated  between  the  optic 
chiasm  in  front  and  the  mammillary  body  behind. 

The  pituitary  body  consists  of  two  parts  which  can  be  distinguished  readily  on  sections  by 
their  color.     The  glandular  (or  anterior)  lobe  is  brown  in  color  and  is  inclosed  in  a  fibrous  capsule. 

'  This  backward  projection  of  the  thalamus  is  equivalent  to  the  pulvinar  and  lateral  genicu- 
late body  of  man,  which  are  not  superficially  divided  in  the  domestic  animals. 


666 


NERVOUS  SYSTEM  OF  THE  HORSE 


It  is  glandular  in  character  and  there  is  good  ground  for  tlie  view  that  it  is  an  organ  of  internal 
secretion.  Besides  the  chief  cells  which  stain  lightly,  it  contains  large  deeply  staining  chromophile 
colls.  It  arises  as  an  outgrowth  from  the  primitive  mouth  cavity.  The  cerebral  (.or  posterior) 
lobe  is  pale  and  is  connected  with  the  infundibulum  so  as  to  form  a  rather  flask-shaped  arrange- 
ment. It  is  almost  entirely  inclosed  by  the  glandular  part.  It  arises  as  an  outgrowth  from  the 
I)rimitive  diencephalon,  but  loses  most  of  its  earlier  ner\-ous  character. 

The  optic  chiasm  and  tracts  form  the  anterior  boundary  of  the  interpeduncular 
space.  The  optic  chiasm  or  commissure  (C'hiasma  opticuin)  is  formed  by  the 
convergence  of  the  optic  nerves  and  the  crossing  of  the  major  part  of  the  fibers  of 
the  nerve  of  one  side  to  the  tract  of  the  opposite  side.  From  the  chiasm  each 
optic   tract   (Tractus   ojjticus)  curves  over  the  cerebral  jXHUincle  outward,  l>ack- 


Djitic  tract 


Fiu.  506. — Cross-section  of  Brain  of  Horse,  N.^tirai.  Size. 
Section  passes  through  posterior  part  of  third  ventricle  an<.i  is  viewed  from  behind.  1 ..  Longitudinal  fissure; 
2,  hippocampus;  2',  fimbria;  3,  septum  pellucidum;  4,  lateral  ventricle;  5,  thalamus;  6,  habenula;  7,  third  ven- 
tricle; 8,  cerebral  peduncle;  S',  hypothalamus;  9,  mammillary  body;  10,  pituitary  body;  //,  pyriform  lobe; 
12,  ventral  end  of  hippocampus;  l.i,  amygdaloid  nucleus.  Between  the  upper  parts  of  the  ta?nia!  thalami  is  the 
chorioid  plexus  of  the  third  ventricle,  and  above  this  are  the  internal  cerebral  veins 


ward,  and  upward  to  the  posterior  part  of  the  thalamus  and  the  internal  geniculate 
body;   some  fibers  reach  the  anterior  quadrigeminal  body. 

All  the  fibers  in  the  chiasm  are  not  derived  from  the  optic  nerves.  The  posterior  part 
contains  fibers  which  pass  from  one  tract  to  the  other  and  are  connected  with  the  internal  genicti- 
late  bodies;  this,  bundle  is  called  Cludden's  commissure  (Commissura  inferior).  Above  it  is 
Meynert's  commissure  (Commissura  superior),  the  fibers  of  which  enter  the  subthalamic  body. 

The  third  ventricle  (Ventriculus  tertius)  is  the  narrow  annular  space  between 
the  thahuiii.  It  conniiunicates  by  means  of  the  aqueduct  with  the  fourth  ven- 
tricle behinil,  and  in  front  it  is  continuous  with  the  lateral  ventricle  on  each  side 
through  the  interventricular  foramen.  Its  floor  is  formed  by  the  structtires  of  the 
interpeduncular  space  and  to  a  small  extent  1)V  the  tegmentum  of  the  cerebral 
peduncles.  The  roof  is  formed  in  the  strict  sense  only  by  the  epcndyma,  above 
which  is  a  fold  of  pia  mater,  termed  the  tela  chorioidea  of  the  third  ventricle  or 
velum  interpositum.     The  roof  is  invaginated  by  two  dcliratc  chorioid  plexuses 


THE  TELENCEPHALON  6(37 

which  appear  to  lie  within  the  ventricle,  although  they  are  excluded  from  the  cavity 
Ijy  the  epithelium.  When  the  tela  is  removed,  the  delicate  ependyma  of  the 
roof  is  torn  away  with  it,  leaving  the  line  of  attachment  to  the  stria  medullaris  to 
constitute  the  tajnia  thalami.  The  anterior  wall  is  formed  by  the  lamina  terminalis 
(s.  cinerea),  a  thin  layer  of  gray  matter  which  extends  upward  from  the  optic 
chiasm  to  the  corpus  callosum.  A  distinct  rounded  band  of  white  matter  extends 
across  its  posterior  face,  bulging  into  the  ventricle.  This  is  the  anterior  commissure 
(Commissura  nasalis)  of  the  cerebrum;  its  fibers  extend  to  the  olfactory  bulb  and 
to  the  pyriform  lobe.  A  similar  but  more  slender  posterior  commissure  (Commis- 
sura caudalis)  crosses  the  posterior  wall  above  the  entrance  to  the  acjueduct; 
the  connections  of  its  fibers  are  not  yet  clearly  known.  The  interventricular 
foramen  (of  Monroe)  is  situated  on  either  side  of  the  anterior  part  of  the  \i'ntricle 
and  leads  outward  and  slightly  upward  between  the  anterior  pillar  of  the  fornix  and 
the  anterior  tubercle  of  the  thalamus.  The  cavity  presents  three  recesses  or 
diverticula,  of  which  two  are  ventral  and  the  third  is  supero-posterior.  The 
optic  recess  (Recessus  opticus)  lies  above  the  optic  chiasm.  Just  behind  it  is  the 
infundibular  recess  (Recessus  infundibuli)  which  extends  through  the  infundibu- 
lum  to  the  pituitary  body.  The  pineal  recess  (Recessus  pinealis)  is  in  the  stalk  of 
the  pineal  body. 

THE  TELENCEPHALON 
The  telencephalon  or  end-brain  comprises  two  principal  parts,  the  cerebral 
hemispheres  and  the  oi)tic  part  of  the  hypothalamus.     The  latter  has  been  con- 
sidered as  a  matter  of  convenience  in  the  ilescription  of  the  diencephalon. 

The  Cerebral  Hemispheres 

The  cerebral  hemispheres  (Hemisphteria)  form  the  greater  part  of  the  fully 
develo]>ed  brain.  Viewed  from  above  (Fig.  498)  they  form  an  ovoid  mass,  of 
which  the  broader  end  is  posterior,  and  the  greatest  transverse  diameter  is  a  little 
l)ehind  the  middle.  The  two  hemispheres  arc  separated  by  a  deep  median  cleft, 
the  longitudinal  fissure  of  the  cerebrum,  which  is  occupied  by  a  sickle-shaped 
fold  of  dura  mater,  the  falx  cerebri.  In  front  the  separation  is  complete,  and  it 
apjiears  to  be  behind  also,  but  here  the  two  hemispheres  are  attached  to  each  other 
over  a  small  area  by  the  pia  mater.  When  the  hemispheres  are  gently  drawn 
apart,  it  is  seen  that  the  fissure  is  interrupted  in  its  middle  part  at  a  depth  of  a 
little  more  than  an  inch  (ca.  3  cm.)  by  a  white  commissural  mass,  the  corpus 
callosum;  this  connects  the  hemispheres  for  about  half  of  their  length.  The 
transverse  fissure  separates  the  hemispheres  from  the  cerebellum,  and  contains 
the  tentorium  cerelielli. 

The  convex  or  dorso-lateral  surface'  conforms  closely  to  the  cranial  wall. 
The  medial  or  internal  siuiace  is  flat  and  sagittal  and  bounds  the  longitudinal 
fissure;  to  a  large  extent  it  is  in  contact  with  the  falx  cerebri,  but  behind  the  great 
cerebral  vein  the  two  hemispheres  are  in  contact  and  are  attached  to  each  other 
over  a  small  area  as  noted  above.  In  well  hardened  specimens  there  is  usually  an 
impression  for  the  vein  in  front  of  the  area  of  adhesion.  The  base  or  ventral 
surface  (Fig.  499)  is  irregular.  Its  anterior  two-thirds  is  adapted  to  the  cerebral 
fossa  of  the  cranial  floor.  Crossing  this  area  in  front  of  the  optic  tract  is  a  de- 
pression, the  transverse  fossa  (vallecula  or  fossa  of  Sylvius),  which  leads  outward 
to  the  lateral  fissure  (fissure  of  Sylvius),  and  lodges  the  middle  cerebral  artery. 
In  front  of  the  fossa  there  is  a  considerable  rounded  elevation  known  as  the 
trigonum  olfactorium.    The  trigonum  and  the  inner  part  of  the  fossa  are  pierced 

'  In  order  to  study  the  configuration  of  the  hemi.sphere  it  should  be  separated  from  its  fellow 
by  median  section  ami  from  the  brain  stem  by  cutting  across  the  mid-brain.  Material  for  this 
purpose  should  be  hardened  in  sita. 


668  NEKVOUS  SYSTEM  OV  THE  HORSE 

bj-  numerous  openings  for  the  passage  of  small  l)lood-vessels  and  are  equivalent, 
to  the  locus  perforatus  anticus  of  man.  Behind  the  outer  part  of  the  fossa  is  the 
rounded  anterior  end  of  the  pyriform  lobe.  Traced  backward  the  lobe  curves  up- 
ward and  inward  over  the  optic  tract  and  the  thalamus  to  the  tentorial  aspect  of  the 
hemisphere;  its  continuation,  the  hippocampus,  forms  part  of  the  floor  of  the 
lateral  ventricle,  and  will  be  examined  later. 

The  posterior  part  or  tentorial  area  is  flattened,  faces  inward  and  backward  as 
well  as  downward,  and  rests  largely  on  the  tentorium  cerebelli;  on  its  anterior  part 
there  is  a  shallow  depression  adaiJted  to  tlie  corpora  quadrigemina  and  the  pineal 
Iwdy. 

The  frontal  pole  or  anterior  extremity  (exclusive  of  tlie  olfactory  bulb)  is 
compressed  laterally,  and  the  occipital  pole  or  posterior  extremity  forms  a  blunt 
point. 

The  hemisphere  comprises:  (1)  the  pallium  or  mantle,  which  consists  of  an 
outer  layer  of  gray  matter,  the  cortex  (Substantia  corticalis),  covering  a  large  mass 


Fui.  507. — Left  Cerebral  Hemisphere  of  Horse,  L.^ter.^i.  View.     The  Olfactory  Bulb  is  Ci't  Off. 
/.  Lateral  fissure  (of  Sylvius);   2,  3,  4,  middle,  posterior,  and  anterior  branches  of  /,"  5,  presylvian  fissure; 
6,  6,'  sulcus  rhinalis,   anterior  et   posterior;    7,  suprasylvian  fissure;    S,  ectomarginal  fissure;    9,  & ,  ectosylvian 
fissure. 

of  white  matter  (Centrum  semiovale);  (2)  the  rhinencephalon  or  olfactory  ]X)rtion 
of  the  brain;  (;5)  the  corpus  callosum  and  fornix,  the  great  commissural  white 
masses;  (4)  the  lateral  ventricle  and  certain  ini])ortant  structures  associated  there- 
with. 

The  pallium  is  tiu-own  into  numerous  folds,  the  gyri  cerebri,  which  are  seji- 
arated  l)y  sulci  or  fissures  of  varying  ilei)tli.  The  general  pattern  of  the  gyri  antl 
sulci  is  similar  in  normal  brains  of  the  same  species,  but  the  details  are  very  variable 
and  are  never  alike  on  the  two  hemispheres  of  the  same  brain.  In  the  horse  the 
arrangement  is  complicated  by  the  existence  of  numerous  short  accessory  fissures 
which  cut  into  the  gyri  at  right  angles  and  tend  to  confuse  the  observer.  The 
principal  fissures  and  sulci  of  the  convex  surface  (Figs.  497,  507)  are  as  follows: 

1.  The  lateral  fissure  (Fissura  lateralis  Sylvii)  ascends  on  the  lateral  surface 
of  the  hemisj)here  as  the  continuation  of  the  fossa  transversa  in  front  of  the  pyriform 
lobe.  After  crossing  the  external  olfactory  tract  it  divides  into  three  branches; 
of  these  one  pass(>s  ujiward,  one  runs  oblitiuely  forward  and  upward,  and  the  third 
is  directed  upward  and  backward. 

2.  The  suprasylvian  fissure  (F.  suprasylvia)'  is  long  and  divides  a  large  ])art 
'  Termed  by  l^esljre  tlie  parietal  fissure  ami  by  M'Fadyean  the  great  oblique  fis.sure. 


THE  CEREBRAL  HEMISPHERES  669 

of  the  convex  surface  of  the  hemisphere  into  dorsal  and  lateral  portions.  It  begins 
on  the  dorso-medial  border  near  its  anterior  end  and,  inclining  graduallj-  downward, 
passes  back  to  end  on  reaching  the  tentorial  surface.  It  is  continuous  intemallj' 
with  the  transverse  fissure  usually  and  in  front  with  the  presj'lvian  fissure. 

3.  The  presylvian  fissure  (F.  prasylvia)  is  the  continuation  forward  of  the 
preceding.  It  i)asscs  forward,  outward,  and  downward  almost  to  the  frontal  pole, 
and  then  inclines  backward  to  end  at  the  groove  which  marks  the  u])per  limit  of 
the  rhinenccphalon  (Sulcus  rhinalis). 

4.  The  marginal  fissure  (F.  marginalis)  extends  along  the  dor.so-mcdial  Iwrder. 
It  begins  a  little  in  front  of  the  middle  of  the  border  and  turns  around  the  occipital 
pole  to  end  on  its  tentorial  aspect. 

5.  The  entomarginal  fissure  (F.  entomarginalis)  lies  internal  to  the  dorso- 
medial  border.  It  docs  not  extend  quite  as  far  forward  as  the  marginal  fissure, 
from  which  it  is  si'iiarated  by  a  narrow  gyrus. 

6.  The  ectomarginal  fissure  (F.  ectomarginalis)  lies  about  midway  between  the 
marginal  fissure  and  the  posterior  part  of  the  suprasylvian  fissure. 

7.  The  sulcus  rhinalis  is  a  very  distinct  furrow  on  the  lower  part  of  the  lateral 
surface  which  marks  off  the  olfactory  part  of  the  brain  (rhinenccphalon)  from  the 
rest  of  the  hemisphere.  It  is  undulating  and  is  highest  where  it  is  crossed  by  the 
lateral  fissure  (of  Sylvius).' 

On  the  medial  surface  (Fig.  50S)  the  main  fissures  and  sulci  are  as  follows: 

1.  The  calloso-marginal  fissure  (F.  calloso-marginalis)  is  extensive  and  well- 
defined.  It  is  a]iproximately  parallel  to  the  dorso-medial  border  of  the  hemisphere, 
from  which  it  is  aliout  half  an  inch  distant.  It  begins  in  front  a  short  distance 
below  and  in  front  of  the  anterior  bend  (genu)  of  the  corpus  callosum  and  forms  a 
C-shaped  curve,  its  posterior  part  extending  on  the  tentorial  surface  to  a  point 
behind  the  depression  for  the  corpora  quadrigemina.  It  separates  the  marginal 
gyri  above  from  the  gyrus  fornicatus,  which  extends  down  to  the  corpus  callosum. 

2.  The  transverse  fissure  (F.  transversa)  begins  a  little  behind  the  middle  of 
the  calloso-marginal  fissure,  passes  obliquely  upward  and  forward  to  the  dorso- 
medial  border — into  which  it  cuts  deeply — and  usually  joins  the  suprasylvian 
fissure." 

3.  The  sublimbic  fissure  (F.  sublimbica)  curves  over  the  gyrus  fornicatus  a 
short  distance  above  the  corpus  callosum.  Its  middle  part  is  commonly  indistinct, 
and  it  is  often  divided  into  anterior  and  posterior  parts. 

4.  The  callosal  sulcus  (Sulcus  corporis  callosi)  separates  the  corpus  callosum 
from  the  gyrus  fornicatus. 

The  hippocampus  (or  cornu  Ammonis)  is  a  gyrus  which  curves  from  the  deep 
face  of  the  pyriform  lobe  around  the  thalamus  and  forms  the  posterior  part  of  the 
floor  of  the  lateral  ventricle.  It  can  be  displayed  by  cutting  away  the  brain-stem 
up  to  the  optic  tract  and  the  interventricular  foramen.  Viewed  from  below  the 
hippocampal  gyrus  is  seen  to  form  a  semicircular  curve  from  the  apex  of  the  pjTiform 
lobe  to  the  angle  of  divergence  of  the  posterior  pillars  of  the  fornix,  i.  e.,  to  a  point 
under  the  central  part  of  the  corpus  callosum.  It  is  .separated  deeply  by  the  hippo- 
campal fissure  from  the  gyrus  dentatus.  Along  the  concave  margin  of  the  latter 
is  a  band  of  white  matter,  termed  the  fimbria,  which  is  the  prolongation  of  the 
greater  part  of  the  posterior  pillar  of  the  fornix  into  this  region.  The  ventricular 
surface  of  the  hippocampus  (Fig.  511)  is  covered  with  a  thin  layer  of  white 
matter,  the  alveus,  which  is  also  derived  from  the  posterior  pillar  of  the  fornix,  and 

'  Just  .above  this  point  is  a  lobe  which  is  homologous  with  the  insula  of  man.  When  the 
overhanging  gyri  which  partly  conceal  it — forming  tlie  operculum — are  removed,  there  are  dis- 
closed several  short,  deeply  placed  gj'ri  (Gyri  breves). 

-  By  some  authors  this  is  regarded  as  the  homologue  of  the  cruciate  fissure  of  the  dog,  but  it 
seems  likely  that  the  latter  is  represented  by  a  short  and  inconstant  sulcus  situated  further  forward. 


070 


NERVOUS  SYSTEM  OF  THE  HORSE 


is  tlierpfore  continuous  with  the  fimliria.  The  two  hippocampi  are  connected  at 
their  highest  parts  by  transverse  fibers  wliieh  constitute  the  hippocampal  commis- 
sure. 

The  interval  lietween  tlie  hippocampus  and  fimbria  on  the  one  hand  and  the 
brain-stem  on  the  other  is  a  lateral  continuation  of  the  great  transverse  fissure  of 
the  brain,  and  is  termed  the  chorioid  fissure.  It  is  occupied  by  a  fold  of  pia  mater, 
the  tela  chorioidea  of  the  third  ventricle,  or  velum  interpositum.  This  fold  is 
triangular  in  outline  and  its  apex  reaches  to  the  interventricular  foramen.  Its  base 
is  continuous  at  the  transverse  fissure  with  the  pia  which  covers  the  surface  of  the 
brain.     Its  middle  part  lies  over  the  epithelial  roof  of  the  third  ventricle,  as  has 


Gyruti  fornicaliis 


Transverse     Calloso-mar- 
jissare        ginal  Jia 


Marginal  fissure 


Entomarginal  fissure 


Lamina     Chiasma 
termmabs  opticum 


Posterior 
,  commissure  \       ^\^^^.^^ 

Pituitary       Cerebral    niedul- 
body  aqueduct      lary 

velum 


Fourth 
ventricle 


The  membranes  and  ^ 
P.r.,  cerebral  peduncle;  (\q,. 
r.  optic  recess;  r',  infundibuli 
C,  genu  of  corpus  callosuni; 


Fig.  508. — Medi.vn  Section  of  Brain  of  Horse. 
essels  are  removed.     C,  Central  white  matter  (corpus 

corpora  quadrigemina;  P,  pineal  body;  7Vi.,  thalam 
ir  recess;  C.tti.,  mammillary  body;  s,  subcallosal  gj-ru; 
>S',  splenium  of  same;    /,  callosal  sulcus;    2,  interventrii 


medydlare>  of  cerebellum; 
is;  V.lll.,  thir.l  ventricle; 
;  A. p.,  area  parolfactoria; 
lular  foramen;  S,  olfactory 


bulb.     The  cerebral  lobe  of  the  pituitary  body  is  distinguished  by  its  lighter  colo 


been  seen  (Fig.  500).  The  lateral  borders  will  be  seen  on  the  floor  of  the  lateral 
ventricles,  where  they  form  thick  roundt'd  bands  containing  convolutions  of 
blood-ve,s.sels,  known  as  the  chorioid  plexuses  of  the  lateral  ventricles  (Fig.  511). 

When  the  tela  is  pulled  out  one  may  easily  get  the  impression  that  the  lateral  \eiitriele 
communieates  with  the  exterior  by  means  of  the  ehorioid  fis.sure.  Sueh  is  not  the  ease,  sinee  the 
chorioid  plexus  is  eovered  liy  the  epithelial  hninfc  of  tlie  ventricle,  which  has  been  torn  away. 

The  rhinencephalon  or  olfactory  jiart  of  the  brain  comprises  the  olfactory 
bulb,  peduncle  and  tracts  or  roots,  the  trigonum  olfactoriuin,  the  area  parolfactoria, 
and  the  pyriform  lobe.' 

'  From  the  morphological  point  of  view  other  structures  should  be  included,  but  in  descriptive 
anatomy  it  is  usual  to  limit  the  appHcation  of  the  term  to  the  parts  enumerated  above. 


THE  CEREBRAL  HEMISPHERES 


G71 


The  olfactory  bulb  (Bulhus  olfactorius)  is  an  oval  enlargement  which  curves 
upward  in  front  of  the  frontal  pole  of  the  hemisphere.  Its  convex  superficial  face 
tits  into  the  ethmoidal  fossa  and  receives  numerous  olfactory  nerve-fihers  through 
the  cribriform  plate;  hence  it  is  very  difficult  to  remove  the  Ijulb  intact.  It  con- 
tains a  considerable  cavity  (Ventriculus  bulbi  olfactorii)  which  is  connected  with 
the  lateral  ventricle  by  a  small  canal  in  the  middle  olfactory  tract.  The  deep 
face  is  largely  in  contact  with  the  frontal  pole  of  the  hemisphere  and  is  connected 
with  the  olfactory  peduncle. 

The  gray  matter  of  the  bulb  is  external  and  is  thickest  on  the  convex  anterior  surface.  The 
posterior  surface  consists  to  a  large  extent  of  filjers  which  are  the  axones  of  the  mitral  cells  of  the 
deep  layer  of  the  gray  substance  and  go  to  form  the  peduncle  and  stria-. 

The  olfactory  peduncle  (Tractus  olfactorius)  is  a  very  short  but  wide  band  of 
white  substance  which  arises  in  the  olfactory  bulb  and  extends  back  to  be  continued 
by  tile  olfactory  tracts. 

The  olfactory  tracts  or  striae   (.Striie  olfactorii)   are  three  in  number.     The 


Inkri'cntricular  Jura 
Gyrus  fornicalu 
Sublimbic  fissxtre  (ant.  pari) 


Transverse  fissure 

( '  alloso-marginal  fissure 

Sublimbic  fissure  (post,  part) 

Entomarginal  fissure 

Marginal  fissure 


Sulcus  rhinalis  anterior 


Ectomarginal  fissure 


Hippocampal  fissure         ^,^^^^  ^^^^^^  posterior 

Fig.  509. — Medio-vextr.<.l  .\spect  of  Right  Cerebr.^l  Hemisphere  of  Horse. 
The  olfactory  bulb  is  cut  off.     T.ol..  Olfactory  peduncle;    A.p..  area  parolfactoria  ;  Tr.O., 


facforium;  T.op.,  optic  tract;  Co.,  chiasm 
pellucidum;  F,  fornix;  G.c,  callosal  gyn 
L  p.,  pyrifonn  lobe;   G.k.,  hippocampal  gy; 


I  opticum;   G.s..  subcallosal  gyr 
s;    T,  cut  surface  of  thalamus 


c,  corpus  callo 
tirabria;    G.d., 


trigonum  ol- 
.S.p.,  septum 


gyr 


external  tract  (Stria  lateralis)  is  much  the  largest  and  most  distinct.  It  passes 
Imckwanl,  upward,  and  outward,  widens  out  and  joins  the  pyrifonn  lolje.  It  is 
clearly  defined  dorsally  by  the  sulcus  rhinalis  and  is  marked  off  from  the  trigonum 
olfactorium  by  the  sulcus  arcuatus.  The  intermediate  tract  (Stria  intermedia) 
is  short,  ill  defined,  and  flat;  it  contains  the  canal  which  opens  into  the  anterior 
horn  of  the  lateral  ventricle.  The  internal  tract  (Stria  medialis)  is  small,  short, 
and  not  well  defined;  it  bends  over  to  the  parolfactory  area  (of  Broca)  on  the  inner 
face  of  the  hemisphere  below  the  genu  of  the  corpus  callosum. 

The  trigonum  olfactorium  is  the  prominent  gray  area  situated  in  the  angle  of 
divergence  of  the  internal  and  external  olfactory  striae.  It  is  bounded  externally 
by  the  external  olfactory  stria,  from  which  it  is  defined  by  the  arcuate  sulcus.  It 
is  continuous  with  the  area  parolfactoria  on  the  medial  surface;  behind  the  latter 
a  band  descends  from  the  rostrum  of  the  corpus  callosum  and  is  continuous  below 
with  the  anterior  perforated  space;  it  is  termed  the  subcallosal  gyrus  or  peduncle 
of  the  corpus  callosum. 


672 


NERVOUS  SYSTEM  OF  THE  HORSE 


The  pyriform  lobe  (Lobus  piriformis)  is  the  well-marked  prominence  on  the 
base  lateral  to  tlic  optic  tract  and  cerebral  peduncle,  from  which  it  is  separated  by  a 
deep  fissure.  Its  nipple-like  apex  lies  behind  the  fossa  transversa  and  covers  the 
optic  tract.  The  external  surface  is  marked  by  one  or  two  sulci  (lobi  piriformis). 
The  lobe  contains  a  cavity,  the  ventral  horn  of  the  lateral  ventricle. 

Tlie  fibers  of  the  olfactory  tract.s  go  to  the  pyriform  lobe  and  hippocampus,  the  trigonum 
olfactorium,  the  area  parolfactoria,  the  Mil.call.i-^al  sjynis,  and  part  of  the  gyrus  fornicatus.  The 
central  connections  of  the  olfactory  apparni  ii-  mv  complex  and  are  not  yet  fully  understood.  The 
anterior  cerel)ral  commissure  contains  lil.n-^  «liirh  pass  from  the  olfactory  bulb  of  one  side  by 
way  of  the  inner  tracts  to  the  bulb  of  the  uppn>iic  side;  also  fibers  ulii.li  cni-^s  in  it  from  the  uiner 
tract  of  one  side  to  the  pyriform  lobe  of  i  lir  opimMlc  side.  Many  lil.n-  |ki-  l.y  \yay  of  the  septum 
pellucidum,  fornix,  and  fimbria  to  th.'  InppocaTiipus.  Otlier  til.c'i.-  p.i>s  m  ilie  anterior  pillar  of 
tlie  fornix  to  the  mammillary  body  and  thence  to  the  thalamus  l)y  the  tlialamo-mamniillary 
bundle. 

The  corpus  callostun  is  the  great  transverse  commissure  which  connects  the 
two  cerebral  hcniisplicrcs  through  about  half  of  their  length.  On  median  section 
(Fig.  508)  it  is  seen  to  be  arched  from  before  backward,  white  in  color,  and  coin- 


Fir,.  .510. — Laterai.  View  of  Cast  of  Cavities  of  Brain  of  Horsk. 
Bo,  Cavity  of  olfactory,  which  communicates  through  the  canal  /  with  a  lateral  ventricle;  Ca,  anterior 
hum.  Cm,  boily,  Ci',  ventral  horn  of  lateral  ventricle;  M,  isthmus  which  connects  lateral  ami  third  ventricles 
Ep,  suprapineal  rece.ss,  below  which  is  the  small  infrapineal  recess;  Ro,  optic  recess;  Rh .  infuiulibular  and  jjitnitary 
recess;  .S,  aqueduct;  Fl,  ridge  corresponding  to  sulcus  limitans;  Rl,  lateral  recess,  Rm,  posterior  recess,  of  fourth 
ventricle;  Cc,  beginning  of  central  canal  of  spinal  cord.     (Dexler.) 


po.sed  substantially  of  transverse  fibers.  The  middle  part  or  truncus  (Trunctis 
corporis  callosi)  slopes  downward  and  forward  and  is  thinner  than  the  (>nds.  The 
anterior  thickened  end,  the  genu,  bentls  downward  and  backward  and  thins  out  to 
form  the  rostrum  ;  tlie  latter  is  continuous  with  the  lamina  terminalis.  The  pos- 
terior end,  tlic  splenium,  also  thick,  lies  at  a  considerably  higher  level  than  the 
genu.  The  upper  surface  is  convex  in  its  length,  concave  transversely.  Its  central 
part  forms  the  floor  of  the  longitudinal  fissure.  It  is  covered  by  a  thin  layer  of 
gray  matter  (Indus;'um  griseum),  in  which  are  strands  of  longitudinal  fibers  (Striaj 
longitudinales) ;  the  latter  are  arranged  in  median  and  lateral  bundles  (.Str>a 
mcdialis,  striic  laterales).'  The  lower  surface  has  the  reverse  configuration,  and 
forms  the  roof  of  the  lateral  ventricles.  Along  the  median  line  the  septum 
pellucidum  is  attached  to  it.  The  fibers  of  the  corpus  callosum  (with  the  exception 
of  tlie  iongitudintil  striie)  run  transversely  and  spread  out  laterally  in  all  directions  in 
the  central  wiiite  matter  of  the  hemispheres  to  the  cortex,  forming  the  radiation  of 
the  corpus  callosum  (Radiatio  corporis  callosi). 

'  It  is  generally  lielieyetl  that  these  constitute  an  oKactory  path. 


THE  CEREBRAL  HEMISPHERES 


673 


The  fornix  is  a  bilateral  structure  composed  of  white  fibers  which  arch  chiefly 
over  the  thalamus  and  the  third  ventricle.  It  is  described  as  consisting  of  a  body 
and  two  pairs  of  pillars.  The  body  (Corpus  fornicis)  is  formed  by  the  fusion  of  the 
two  arches  of  which  the  fornix  is  composed.  It  is  triangular  and  overlies  the  an- 
terior parts  of  the  thalami  and  the  third  ventricle.  The  upper  surface  gives 
attachment  to  the  septum  pellucidum  and  on  either  side  forms  part  of  the  floor  of 
the  lateral  ventricle.  The  lateral  border  is  related  to  the  chorioid  plexus  of  the 
lateral  ventricle  and  forms  the  inner  boundary  of  the  interventricular  foramen. 
The  anterior  pillars  or  columns  (Columnae  fornicis)  (Fig.  512)  are  two  slender 
round  Ijundles  which  emerge  from  the  bodj^  in  front  of  the  interventricular  foramen 


Olfactory  bulb 


Corjyus  viedullnre 
Caudate  nucleus 

^  r"     Chorioiil  plexus 
--W  -  Fornix 

II  ippocampus 


Fig.  511. — Brain  of  Horse,  with  L- 


;ntricles  Opened  by  Remova 
Hemispheres. 


OF  Upper  Part  of  Cerf.bral 


and  diverge  slightlj-  as  they  curve  downward  and  backward  to  the  mammillary 
body. 

From  the  mammillary  body  the  greater  part  of  these  fornix  fibers  are  continued  to  the 
thalamus  by  the  thalamo-mammillary  fa.sciculus  (or  bundle  of  Vicq  d'.\zyr).  Others  pas,s  to 
the  cerebral  peduncle.  A  portion  of  the  fibers  cross  to  the  opposite  thalamus  and  cerebral 
peduncle. 

The  posterior  pillars  (Crura  fornicis)  are  much  larger  bands  which  diverge 

widely  from  the  posterior  angles  of  tlie  body.     Each  curves  outward  and  backward 

over  the  thalamus  (from  which  it  is  separated  by  the  tela  chorioidea)  and  is  chiefly 

continued  as  the  fimbria  along  the  concave  border  of  the  hippocampus.     The  pillars 

43 


674 


NERVOIS  SYSTEM  OF  THE  HORSE 


give  off  fibers  to  form  the  alveus  or  white  matter  which  covers  the  ventricular  face 
of  the  hippocampi,  and  tjetween  them  are  transverse  fibers  which  constitute  the 
hippocampal  coniniissiin'. 

The  septum  pellucidum  is  the  mechan  partition  lietween  the  two  lateral  ven- 
tricles. Its  convex  upper  border  blends  with  the  corpus  callosum  and  its  concave 
lower  border  joins  the  fornix.  Its  anterior  part  is  received  into  the  genu  of  the 
corpus  callosum.  Traced  backward  it  diminishes  in  height  and  the  two  edges  meet 
at  an  acute  angle  at  the  splenium. 

The  septum  consists  of  two  layers  (Laminze  scpti  pellucidi)  which  are  in  direct  contact  with 
each  other.  They  consist  of  nerve-filiers  and  gray  matter.  The  latter  exists  in  considerable 
amount  in  the  thicker  part  of  tlic  septum  adjacent  to  the  anterior  pillars  of  the  fornix.  Many 
of  the  fibers  of  the  septum  pass  up  through  the  corpus  callosum  to  the  gyrus  fornicatus.  Others 
are  connected  with  the  subcallosal  gyrus  and  the  parolfactory  area. 


512.— Cross- 

Section  passes  through  cliiasni:] 

pellucidum;   S,  columns  (anterior  pill: 

(centra!  white  matter)  of  hemisphere: 

capsule:    //,  insula. 


1  tihrreiitricular  foramen 
Anterior  coininissure 


SECTION  OF  Brain-  of  Horse,  about  Natura 

opticum,  and  is  viewed  from  in  front,     i,  Longitudinal  fissure:    S,  septum 
irs)  of  fornix;   4.  lateral  ventricle;    5,  chorioid  plexus:  6,  corpus  meduUare 

7,  caudate  nucleus;   S,  lenticular  nucleus;   9,  internal  capsule;    10,  external 


The  lateral  ventricle  (^'entriculus  lateralis)  is  the  irregular  cavity  in  the 
interior  of  each  ccrel^ral  hemisphere.'  Each  communicates  with  the  third  ventricle 
through  till"  interventricular  foramen  (of  ]\Ionro),  and  by  a  small  canal  with  the 
cavity  of  the  olfactory  bulb.  It  is  usual  to  describe  the  ventricle  as  consisting 
of  three  parts,  viz.,  the  central  ]mrt  or  body,  and  anterior  and  inferior  horns.  The 
anterior  horn  (Cornu  nasale)  is  the  part  in  front  of  the  interventricular  foramen; 
it  communicates  ventrally  with  the  olfactory  cavity.  The  central  part  (Pars 
centralis)  extends  back  to  the  siilenium  of  the  corpus  callcsum.  It  opens  into  the 
third  ventricle  through  the  interventricular  foramen,  which  is  situated  between  the 
fornix  and  the  anterior  part  of  the  thalamus.     The  inferior  horn  (Cornu  ventrale) 

'  It  is  hardly  po.ssible  to  get  an  accurate  idea  of  the  shape  of  the  ventricle  except  by  studying 
a  cast  of  it.  The  size  of  the  ventricles  varies  in  different  subjects,  and  it  is  not  rare  to  find  more 
or  less  disparity  between  the  two  ventricles  of  the  same  brain. 


THE  CEREBRAL  HEMISPHERES  675 

curves  downward  and  forward  into  the  pyriform  lobe.  The  roof  of  the  ventricle 
is  formed  by  the  corpus  callosuni  and  the  inner  wall  is  the  septum  pellucidum. 
After  removal  of  the  roof  the  floor  is  seen  to  be  formed  chiefly  by  two  bodies.  The 
anterior  one  is  the  caudate  nucleus  (Nucleus  caudatus),  a  somewhat  pear-shaped 
gray  eminence,  the  long  axis  of  which  is  directed  obliquely  upward,  backward,  and 
outward.  Its  anterior  large  end  is  termed  the  head,  and  the  posterior  long  tapering 
end  the  tail.  The  posterior  body,  the  hippocampus,  is  white  on  its  ventricular 
surface,  which  is  strongly  convex.  It  curves  outward  and  backward  and  then  turns 
downward  and  forward  to  join  the  jiyriform  lobe.  The  two  bodies  are  separated 
by  an  ol)lique  groove  which  is  occupied  l)y  the  chorioid  plexus  of  the  lateral  ven- 
tricle. This  is  the  thickened  edge  of  a  fold  of  pia  mater,  tiie  tela  chorioidea  (or 
velum  interpositum),  which  lies  l)etween  the  hippocam]nis  and  the  thalamus.  It 
contains  convolutions  of  small  l)lood-vessels  and  in  old  sut)jects  there  may  be 
calcareous  concretions  in  it.  The  plexuses  of  the  two  sides  are  continuous  through 
the  interventricular  foramen.     On  drawing  the  chorioid  plexus  backward  a  narrow 


Fig.  513. — S.\gitt.\l  Section  of  Brain  of  Horse. 
Section  is  cut  about  1.5  cm.  to  the  right  of  the  median  plane.     M,  Medulla  oblongata;  P.  pons;  P.c.  (above 
M),  chorioid  plexus  of  fourth  ventricle;    Cm.,  central  white  matter  (corpus  meduUare)  of  cerebellum  and  of  cere- 
brum;   P. c.  tin  front  of  P),  cerebral  peduncle;   //.hippocampus;    V,  lateral  ventricle;    T,  thalamus;  A'. c,  caudate 
nucleus;   C'.i.,  internal  capsule;    .V.^,  lenticular  nucleus;   B.o.,  olfactory  bulb. 

white  band,  the  stria  terminalis  (or  taenia  semicircularis),  is  seen  along  the  margin 
of  the  caudate  nucleus,  where  it  bounds  the  intermediate  groove.  The  plexus 
partiallj'  covers  a  wider  white  band  whicli  is  blended  with  the  white  substance  of 
the  hippocampus;  this  is  the  posterior  pillar  of  the  fornix  and  its  continuation, 
the  fimbria. 

The  corpus  striatum'  is  the  great  basal  ganglion  of  the  hemisphere.  It  is 
situated  in  front  of  the  thalamus  and  the  cerebral  peduncle,  and  its  anterior  rounded 
end  appears  on  the  base  of  the  hemisphere  at  the  trigonum  olfactorium.  It  is 
composed  of  two  masses  of  gray  matter,  the  caudate  and  lenticular  nuclei,  separated 
incompletely  by  tracts  of  white  matter  which  are  knowni  collectively  as  the  internal 
capsule.  The  caudate  nucleus  (Nucleus  caudatus)  is  the  dorso-medial  and  larger 
of  the  two  gray  masses;  it  has  been  seen  in  the  examination  of  the  floor  of  the  lateral 
ventricle.  The  lenticular  nucleus  (Nucleus  lentiformis)  lies  ventro-laterally,  over 
the  trigonum  olfactorium  and  the  fossa  transversa.  It  is  related  externally  to  a 
layer  of  white  matter  termed  the  external  capsule,  which  separates  it  from  a  stratum 
of  gray  substance  knowni  as  the  claustrum.     The  two  nuclei  are  fused  in  front,  and 

'  The  term  arose  from  the  striated  appearance  of  the  mas.s  in  sections  cut  in  certain  planes, 
the  gray  matter  being  cut  up  into  strands  by  tracts  of  white  fibers. 


G7G  NERVOUS  SYSTEM  OF  THE  HORSE 

further  back  they  are  connected  by  strands  of  gray  matter  which  intersect  the  in- 
ternal capsule. 

The  amygdaloid  nucleus  (Nucleus  amygdalae)  (Fig.  506)  is  an  ovoid  mass  of 
gray  matter  .situated  external  to  the  ventral  horn  of  the  lateral  ventricle  and  below 
the  posterior  part  of  the  lenticular  nucleus.  Some  fibers  of  the  stria  terminalis 
are  connected  with  it. 

The  internal  capsule  (C'apsula  interna)  is  a  broad  band  of  white  matter  situated 
between  the  thalamus  and  caudate  nucleus  internally  and  the  lenticular  nucleus 
externally.  A  sagittal  section  through  the  brain  shows  that  it  is  in  great  part 
directly  continuous  with  the  liasis  or  ventral  part  of  the  cerebral  peduncle.  It 
contains  most  of  the  so-called  projection  fibers  of  the  hemisphere,  which  connect  the 
cerebral  cortex  with  nuclei  of  other  and  more  posterior  parts  of  the  brain.  When 
the  fibers  of  the  internal  capsule  are  traced  forward  it  is  evident  that  they  spread 
out  in  all  directions  to  reach  the  cerebral  cortex.  This  arrangement,  in  which  the 
fibers  of  the  corpus  callosum  participate,  is  termed  the  corona  radiata. 

The  internal  capsule  also  contains  fibers  which  connect  the  corpus  striatum  with  the  thala- 
mus. These  are  termed  the  thalamo-striate  and  strio-thalamic  fibers  respectively,  according  to 
the  direction  in  which  they  conduct  impulses. 

The  fibers  of  the  stria  terminalis  connect  the  amygdaloid  nucleus  with  the  septum  pelluci- 
dum  and  trigonum  olfaetorium.  It  is  therefore  probably  part  of  the  complex  comiections  be- 
tween the  primary  and  secondary  olfactory  centers. 


The  Cranial  Nerves 

The  cranial  or  cerebral  nerves  (Nn.  cerebralcs)  comprise  twelve  pairs  which 
are  designated  from  before  backward  numerically  and  by  name.  Their  number, 
names,  and  functional  characters  are  given  in  the  subjoined  table: 

1.  Olfactory Sensory  (Smell) 

II.  Optic .  .'- Sen.sory  (Sight) 

III.  Oculomotor Motor 

IV.  Trochlear Motor 

V.  Trigeminal Mixed 

VI.  Abducent Motor 

VII,   Facial Mixed 

VIII.  Auditory Sen.sory  (Hearing  and  Equihbration) 

IX.  Glosso-pliaryngeal Mixed 

X.  Vagus  or  Pneumogastric Mixed 

XI.  Spinal  accessory Motor 

XII.  Hj'poglossal IMotor 


THE  FIRST  OR  OLFACTORY  NERVE 
The  olfactory  nerve  (X.  olfactorius)  is  peculiar  in  that  its  fibers  are  not  aggre- 
gated to  form  a  trunk,  but  are  connected  in  small  bundles  with  the  olfactory  bulb. 
They  are  non-medullated,  and  are  the  central  processes  of  the  olfactory  cells  which 
are  situated  in  the  olfactory  region  of  the  mucous  membrane  of  the  nasal  cavity. 
This  region  is  distinguished  by  its  brown  color  and  comprises  most  of  the  lateral 
mass  of  the  ethmoid,  a  small  adjacent  area  of  the  superior  turbinal,  and  the  corre- 
sponding surface  of  the  septum  nasi.  The  nerve-bundles  are  inclosed  in  sheaths 
derived  from  the  membranes  of  the  brain  and  pass  through  the  foramina  of  the 
cribriform  plate  to  join  the  convex  surface  of  the  olfactory  bulb.  Some  fibers  come 
from  the  vomero-nasal  organ  of  Jacobson. 


THE  SECOND  OR  OPTIC  NERVE 
The  optic  nerve  (N.  opticus)  is  composed  of  fibers  which  are  the  central  pro- 
cesses of  the  ganglion  cells  of  the  retina.     The  fibers  converge  within  the  eyeball  to 


THE  FIFTH,  TRIGEMINAL,  OR  TRIFACIAL  NERVE  677 

the  optic  papilla,  where  they  are  collected  into  a  round  trunk,  the  optic  nerve.  The 
nerve  thus  formed  pierces  the  chorioid  and  sclera,  emerges  from  the  pos- 
terior part  of  the  eyeball,  and  passes  backward  and  inward  to  the  optic  foramen. 
After  traversing  the  latter  it  decussates  with  its  fellow  of  the  oiiposite  side  to  form 
the  optic  chiasma  or  commissure.  In  the  orbit  the  nerve  is  slightly  flexuous  and  is 
embedded  in  the  fat  behind  the  eyeball  and  surrounded  by  the  retractor  oculi 
muscle.  Its  intraosseous  part  is  an  inch  or  more  (ca.  3  cm.)  long.  The  sheath 
of  the  nerve  is  formed  bj-  i)rolongations  of  the  membranes  of  the  brain,  and  includes 
continuations  of  the  subdural  and  subarachnoid  spaces. 

The  greater  part  of  the  fibers  of  the  optic  nerve  cross  in  the  chiasma  to  the  tract  of  the  oppo- 
site side.  In  the  tract  the  fibers  proceed  to  (1)  the  internal  geniculate  liody,  (2)  the  |)()stciior 
part  of  the  thalamus,  and  (.3)  the  anterior  quadrigeminal  body  (indirectly).  The  fibers  which 
go  to  the  internal  geniculate  body  appear  to  belong  to  Gudden's  commissure  and  to  be  non- 
visual  in  function.  The  visual  fibers,  which  come  from  the  outer  part  of  the  retina  of  the  same 
side  and  the  inner  part  of  the  retina  of  the  opposite  side,  terminate  about  cells  in  the  interior 
quadrigeminal  body  and  the  part  of  the  thalamus  which  corresponds  to  the  pulvinar  and  external 
geniculate  body  of  man.  From  the  cells  of  the  former  fibers  pass  to  the  nuclei  of  the  motor 
nerves  of  the  eyeball,  and  complete  the  reflex  arc.  Fillers  proceed  from  the  cells  of  the  thalamus 
to  the  visual  area  of  the  cortex  in  the  occipital  part  of  the  hemisphere. 


THE  THIRD  OR  OCULOMOTOR  NERVE 
The  oculomotor  nerve  (N.  oculomotorius)  arises  by  several  radicles  from  the 
basal  surface  of  the  cerebral  peduncle,  a  little  lateral  to  the  interpeduncular  furrow. 
It  turns  sharply  outward  and  forward,  crosses  over  the  cavernous  sinus,  and  con- 
tinues above  the  maxillarj-  nerve  and  iii  company  with  the  ophthalmic  nerve  to  the 
foramen  lacerum  orbitale.  It  emerges  through  the  foramen  with  the  latter  nerve 
and  the  abducens  ami  divides  into  two  branches.  The  superior  branch  is  short  and 
divides  into  twigs  wliich  sup])ly  the  rectus  superior,  retractor,  and  levator  palpebrs 
superioris.  The  inferior  branch  (Figs.  438,  439)  is  larger  and  much  longer.  It 
supplies  the  motor  fibers  to  the  ciliary  ganglion  (which  lies  directl.v  on  this  branch 
in  the  horse)  and  short  branches  to  the  rectus  internus  and  rectus  inferior,  and 
continues  forward  on  the  latter  to  end  in  the  inferior  obliciue  muscle. 

The  deep  origin  of  the  fibers  of  the  oculomotor  nerve  is  in  the  oculomotor  nucleus  .situated 
in  the  gray  matter  of  the  floor  of  the  cerebral  aqueduct  in  the  region  of  the  anterior  corpora 
quadrigemina. 

THE  FOURTH  OR  TROCHLEAR  NERVE 
The  trochlear  or  pathetic  (X.  trochlearis)  is  the  smallest  of  the  cranial  nerves. 
It  arises  from  the  anterior  cerebellar  peduncle  just  behind  the  corpora  quadrigemina, 
curves  outward  and  forward,  pierces  the  tentorium  cerebelli,  and  passes  forward 
along  the  outer  border  of  the  maxillary  nerve  (Figs.  504,  505).  It  emerges  from 
the  cranium  through  a  small  foramen  immediately  above  the  foramen  lacerum 
orbitale  or  through  the  latter  and  passes  forward  along  the  inner  wall  of  the  orbit 
to  end  in  the  posterior  part  of  the  superior  oblicjue  muscle  of  the  ej'eball  (Fig.  439). 

The  fibers  of  the  fourth  nerve  spring  from  a  nucleus  in  the  gray  matter  of  the  floor  of  the 
cerebral  aqueduct  behind  the  oculomotor  nucleus.  The  fibers  run  backward  in  the  tegmentum, 
then  turn  upward  and  inward  and  undergo  total  decussation  with  those  of  the  opposite  nerve  in 
the  anterior  part  of  the  anterior  medullary  velum.  In  addition  to  this  peculiarity  it  is  the  onlj' 
nerve  which  is  connected  with  the  dorsal  aspect  of  the  brain. 


THE  FIFTH,  TRIGEMINAL.  OR  TRIFACIAL  NERVE 
The  trigeminal  nerve  (X.  trigeminus)  is  the  largest  of  the  cranial  series.     It 
is  connected  with  the  lateral  part  of  the  pons  by  a  large  sensory  root  and  a  smaller 
motor  root  (Fig.  499). 


678  NERVOUS  SYSTEM  OF  THE  HORSE 

The  sensory  root  (Portio  major)  extends  forward  through  a  notch  on  the  lower 
part  of  the  jietrosal  crest  and  widens  out  to  join  the  semilunar  ganglion. 

The  semilunar  (or  Gasserian)  ganglion  (Ganglion  semilunare)  is  a  crescent- 
shaped  mass  of  nerve-fibers  and  cells  which  overlies  the  antero-external  part  of 
the  foramen  lacerum  basis  cranii,  and  is  partly  embedded  in  the  dense  fibrous  tissue 
which  occupies  the  foramen  except  where  vessels  and  nerves  pass  through.  Its 
long  axis,  which  is  about  an  inch  (2.5  cm.)  in  length,  is  directed  forward  and  inward 
and  its  convex  anterior  face  gives  rise  to  the  ophthalmic,  the  maxillary,  and  the 
sensory  part  of  the  mandibular  division  of  the  nerve.  The  surface  of  the  ganglion 
is  irregularly  striated.  It  is  connected  by  filaments  with  the  adjacent  carotid 
plexus  of  the  sympathetic,  and  sends  delicate  twigs  to  the  dura  mater. 

The  fibers  of  the  sensory  root  arise  from  the  ganglion  as  axones  of  the  ganglion  celts,  and  the 
fibers  of  the  nerve?  whicli  oxtentl  pcriphrrally  from  the  gangHon  are  dendrites  of  the  I'clls.  The 
sensory  root-fibers  cuicr  i  he  ti'i;iiiiiii  iim  cf  ilic  pons  and  cH  vide  into  anterior  and  posterior  branches, 
which  terminate  alioiil  iIh'  rclls  uf  llir  sensory  nucleus  of  termination  of  the  trigeminus.  This 
nucleus  extends  frum  llu-  pons  tn  Ihr  sixtli  cervical  segment  of  the  spinal  cord  (Dexler).  The 
posterior  liranchcs  of  the  Hliers  arc  collected  into  a  compact  bundle,  the  spinal  tract  or  root  of  the 
trigeminus,  which  lie<  lateral  to  the  sul)stantia  gclatinosa  in  the  medulla.  The  centr.al  connections 
of  till'  sensory  |i:irt  of  the  trigemiiuis  are  very  extensive.  The  most  impnrtriiit  paths  are:  (1) 
Axone-  (if  .ell-  nf  the  sensory  nucleus  and  the  ~ul'-i,inii:i  gelatinosa  pass  eliiell\  ;i~  arcuate  fibers 
across  I  lie  raphe  to  the  thalamus,  whence  impuNes  aie  transmitted  by  i  lialaiim-eiirtical  fibers 
to  the  cerebral  cortex.  In  ungulates  a  distinei  i  raei  extends  from  the  anterior  jiai  I  of  the  sensory 
nucleus  to  the  thalamus  of  the  same  side  (\\  allenhernl.  It  is  probable  that  cnllaterals  of  the 
arcuate  fibers  go  to  the  motor  nuclei  of  the  lillli,  sexenth,  ninth,  and  tenth  cranial  nerves.  (2) 
Axones  of  cells  of  the  sensory  nucleus  enter  the  jjustciior  cerebellar  pciluncle  of  the  same  sirle 
and  reach  the  cerebellar  cortex.  (3)  Collaterals  are  distributed  to  the  nuclei  of  origin  of  the 
hypoglossal  and  of  the  motor  part  of  the  trigeminal  and  facial  nerves. 

The  motor  root  (Portio  minor)  extends  forward  beneath  the  sensory  root  and 
the  semilunar  ganglion  and  is  incorporated  with  the  mandibular  division  of  the 
nerve.  Its  fibers  arise  chiefly  from  the  so-called  masticatory  nucleus,  which  is 
situated  in  the  pons  near  the  inner  face  of  the  sensory  nucleus;  a  few  of  these  fibers 
come  from  the  nucleus  of  the  opposite  side  and  cross  in  the  raphe.  Other  fibers, 
which  constitute  the  mesencephalic  root,  arise  from  cells  in  the  outer  part  of  the 
central  gray  matter  of  the  mid-brain. 

It  is  evident  from  the  foregoing  statements  that  the  trigeminus  has  essentially 
the  same  arrangement  as  a  typical  spinal  nerve.     It  divides  into  three  branches. 

I.  The  ophthalmic  nerve  (N.  ojihthalmicus)  (Figs.  438,  439,  440)  is  purely 
sensory  and  is  tlie  smallest  of  the  three  branches  of  the  trigeminus.  It  arises  from 
the  inner  part  of  the  front  of  the  semilunar  ganglion,  passes  forward  along  the  outer 
side  of  the  cavernous  sinus,  and  is  blended  with  the  maxillary  nerve  for  some  dis- 
tance. It  enters  the  foramen  lacerum  orltitale  with  the  third  and  sixth  nerves  and 
divides  into  three  branches. 

1.  The  lacrimal  nerve  (N.  lacrimalis)  runs  forward  on  the  rectus  superior  and 
the  levator  i)alix'l)r;e  superioris  and  ramifies  chiefly  in  the  lacrimal  gland  and  the 
upper  eyelid.  A  Ijranch  (Ramus  zygomatico-temporalis)  exchanges  twigs  with  the 
zygomatic  branch  of  the  maxillary  nerve,  perforates  the  periorbita,  and  emerges 
from  the  orbital  fossa  behind  the  supraorbital  process;  it  forms  a  plexus  with 
branches  of  the  auriculo-palpehral  ;uid  frontal  nerves,  and  ramifies  in  the  skin  of 
the  temporal  region. 

2.  The  frontal  nerve  (N.  frontalis),  also  termed  the  supraorbital,  runs  forward 
almost  parallel  with  the  su])erior  oblique  muscle,  at  first  within,  then  outside  of,  the 
])eriorbita.  It  passes  through  the  supraorbital  foramen  with  the  artery  of  like 
name  and  ramifies  in  the  skin  of  the  forehead  and  upper  eyelid,  forming  a  plexus 
with  the  lacrimal  :uid  atu-iculo-palpebral  nerves.     It  divides  into  three  branches. 

3.  The  naso-ciliary  nerve  (N.  naso-ciliaris),  also  termed  the  palpebro-nasal, 
runs  forward  along  the  inner  side  of  the  optic  nerve  between  parts  of  the  retractor 
muscle  and  divides  into  two  branches.     Of  these  the  ethmoidal  nerve  (N.  ethmoi- 


THE  FIFTH,  TRIGEMIXAL,  OR  TRIFACIAL  NERVE  G79 

dalis)  is  the  continuation  of  the  parent  trunk.  It  accompanies  the  ethmoidal 
artery  through  the  foramen  of  lilve  name  into  the  cranial  cavity  and  crosses  the 
lower  part  of  the  ethmoidal  fossa.  Leaving  the  cranium  through  an  opening  in  the 
cribriform  plate  close  to  the  crista  galli,  it  enters  the  nasal  cavity  and  ramifies  in 
the  mucous  membrane  of  the  septum  nasi  and  the  superior  turbinal.  The  in- 
fratrochlear  nerve  (N.  infratrochlearis)  runs  forward  to  the  inner  canthus  and  rami- 
fies in  the  skin  in  this  region;  it  detaches  twigs  to  the  conjunctiva  and  caruncula 
lacrimalis,  and  a  long  branch  which  supjilics  the  third  eyelid  and  the  lacrimal  ducts 
and  sac.  The  naso-ciliary  nerve  furnishes  the  sensory  or  long  root  (Radix  longa) 
of  the  ciliary  ganglido. 

The  ciliary  ganglion  is  placed  on  the  inferior  branch  of  the  cjculomotor  nerve. 
It  is  usually  not  larger  than  a  millet-seed,  and  is  liest  found  by  following  the  nerve 
to  the  inferior  oblique  muscle  back  to  its  origin.  The  ganglion  receives  (a)  sensory 
fibers  from  the  naso-ciliary  nerve;  (6)  motor  fibers  from  the  oculomotor  nerve; 
and  ((■)  S)mipathetic  fibers  from  the  sphenopalatine  plexus.  It  detaches  filaments 
which  unite  with  twigs  from  the  ophthalmic  and  maxillary  nerves  and  from  the 
sphenopalatine  ganglion  to  form  the  ciliary  plexus.  From  the  latter  emanate  five 
to  eight  delicate  short  ciliary  nerves  (Nn.  ciliares  breves),  which  pursue  a  .somewhat 
flexuous  course  along  the  optic  nerve,  pierce  the  sclera  near  the  entrance  of  that 
nerve,  and  run  forward  lietween  the  sclera  and  chorioidea  to  the  circumference  of 
the  iris.  Here  the  branches  of  adjacent  nerves  anastomose  to  form  a  circular 
plexus  (Plexus  gangliosus  ciliaris),  from  which  filaments  go  to  the  ciliary  body,  iris, 
and  cornea. 

The  circular  fibers  of  the  iris  and  the  ciliary  muscle  are  innervated  by  fibers  derived  from  the 
oculomotor  nerve,  the  radial  fibers  of  the  iris  by  the  sympathetic. 

II.  The  maxillary  nerve  (X.  maxillaris),  also  termed  the  superior  maxillary, 
is  purely  sensory  and  is  mucli  larger  than  the  ophthalmic.  It  extends  forward  from 
the  semilunar  ganglion  in  the  middle  cranial  fossa  in  the  large  groove  on  the  root 
of  the  temporal  v/ing  of  the  sphenoid.  It  is  related  internally  to  the  cavernous  sinus 
and  superiorly  to  the  ojihthalmic  nerve,  with  which  it  is  blended  for  some  distance. 
It  emerges  through  the  foramen  rotuudum,  passes  forward  in  the  pterygo-palatine 
fossa  above  the  internal  maxillary  arterj-  and  embetlded  in  fat,  and  is  continued  in 
the  infraorbital  canal  as  the  infraorbital  nerve  (Fig.  439).  Its  branches  are  as 
follows : 

1.  The  zygomatic  nerve  (X.  zygomaticus  s.  subcutaneus  malae),  also  termed 
the  orbital  branch,  arises  before  the  maxillary  nerve  reaches  the  pterygo-palatine 
fossa  (Figs.  438,  439,  514).  It  pierces  the  periorbita  and  divides  into  two  or  three 
delicate  branches  which  pass  along  the  surface  of  the  external  straight  muscle  to 
the  external  canthus  and  ramify  chieflj-  in  the  lower  lid  and  the  adjacent  skin. 
Anastomoses  are  formed  with  branches  of  the  lacrimal  nerve. 

2.  The  sphenopalatine  nerve  (X'^.  sphenopalatinus)  is  given  ofT  in  the  pterygo- 
palatine fossa  from  tin-  lower  l)order  of  the  maxillary  nerve  (Fig.  439).  It  is  broad 
and  flat  and  forms  a  jilexus  in  which  several  small  sphenopalatine  ganglia  are  inter- 
posed.    It  divides  into  posterior  nasal,  and  greater  anil  lesser  palatine  nerves. 

(1)  The  posterior  nasal  nerve  (X.  nasalis  aboralis)  passes  through  the  sphenopala- 
tine foramen,  in  which  it  bears  one  or  more  minute  ganglia,  enters  the  nasal  cavity, 
and  divides  into  internal  and  external  branches  (Figs.  440,  464).  The  internal 
branch  (X.  septi  narium)  runs  forward  in  the  submucous  tissue  of  the  lower  part  of 
the  septum  nasi,  gives  twigs  to  the  mucous  membrane  here  and  to  the  vomero-nasal 
organ  (of  Jacobson),  passes  through  the  palatine  cleft  and  ramifies  in  the  anterior 
part  of  the  hard  palate.  The  external  branch  (Ramus  lateralis)  ramifies  in  the 
mucous  membrane  of  the  inferior  turbinal  and  the  middle  and  inferior  meatus  nasi. 

(2)  The  greater  or  anterior  palatine  nerve  (X.  palatinus  major  s.  anterior)  (Figs. 


680 


NERVOUS  SYSTEM  OF  THE  HORSE 


438,  439)  is  the  largest  of  the  three  branches.  It  runs  forward  in  the  palatine  canal 
and  groove  and  ramifies  in  the  hard  palate  and  gums.  It  also  supplies  twigs  to  the 
soft  palate,  and  gives  off  branches  which  pass  through  the  accessory  jialatine  fora- 
mina to  supply  the  mucous  membrane  of  the  inferior  meatus. 

The  branclie.s  of  tlie  two  nerves  anastomose  in  the  hard  palate  and  form  a  plcxii.s  about  the 
branches  of  the  palatine  arteries. 


Fig.  514. — Di.ssEmoN  of  Head  of  Horse. 
The  masseter  and  superficial  muscles  and  the  parotid  gland  are  in  great  part  removed,  a,  a.  Levator  labii 
superioris  proprius;  h,  b.  levator  nasolabialis;  c,  dilatator  naris  inferior;  d,  buccinator;  e,  common  mass  of  buc- 
cinator and  depressor  labii  inferioris;  /,  depressor  labii  inferioris;  g,  masseter;  h,  orbicularis  oculi;  ?',  temporalis; 
k,  occipito-hyoideus;  k',  stylo-maxillaris;  /,  sterno-cephalicus;  /'.  tendon  of  same;  m,  omo-hyoideus; 
n,  crico-pharyngeus;  o,  mastoid  tendon  of  mastoido-humeralis;  p,  splenius;  i/,  inferior  buccal  and  labial  glands; 
r,  superior  buccal  glands;  s,  remnant  of  parotid  gland;  t,  submaxillary  gland;  u,  anterior  cervical  (subparotid) 
lymph  glands;  i',  probe  passed  into  diverticulum  nasi;  w,  cornu  of  alar  cartilage;  x.  internal  palpebral  ligament; 
H,  wing  of  atlas;  z,  scutiform  cartilage  of  ear;  /,  external  nasal  nerve;  5,  anterior  nasal  nerve;  S,  superior  labial 
nerve;  4.  anterior  part  of  superior  buccal  nerve;  5,  buccinator  nerve;  6,  6',  inferior  alveolar  nerve;  6",  mental 
nerve-continuation  of  6;  7,  masseteric  nerve;  S,  facial  nerve  (cut);  9,  superficial  temporal  nerve;  W,  anastomosis 
between  9  and  S;  II,  internal  auricular  nerve;  J£,  posterior  auricular  nerve;  13,  digastric  nerve;  14,  cervical 
branch  of  facial  nerve  (cut) ;  /S,  auriculo-palpebral  nerve;  /S  lacrimal  nerve;  /7,  frontal  nerve;  AS,  infratroch- 
lear  nerve;  19,  n.  zygomaticus  s.  subcutaneus  malcp;  30,  spinal  accessory  nerve;  SI,  ventral  branch  of  spinal  ac- 
cessory nerve  (to  sterno-cephalicus);  S3,  ventral  end  branch  of  first  cervical  nerve;  23,  thyro-laryngeal  artery; 
Si,  internal  maxillary  artery;  3S,  masseteric  artery;  S9,  great  (posterior)  auricular  artery;  27,  external  branch  of 
eS;  5S,  deep  auricular  artery;  29,  superficial  temporal  artery;  SO,  transverse  f.acial  artery;  31,  facial  artery;  S3, 
inferior  labial  artery;  55,  superior  labial  artery;  3.4,  lateral  nasal  artery;  35,  dorsal  nasal  artery;  SS,  angular.artery 
of  eye;  37,  labial  twigs  of  palato-labial  artery— loft  uncolored  by  oversight:  33,  branch  of  buccinator  artery;  39, 
buccinator  vein;  40,  vena  reflexa;  41 ,  43,  jugular  vein;  43.  external  maxillary  vein;  44.  inferior  cerebral  vein; 
4S,  stump  of  great  auricular  vein;  46,  ramus  of  mandible;  47,  facial  crest;  4S.  zygomatic  arch;  49,  parotid  duct. 
(.\ftcr  Kllenberger-Baum,  Top.  .\nat.  d.  Pferdes.) 


(3)  The  lesser  or  posterior  palatine  nerve  (N.  ])alatinus  minor  s.  posterior), 
also  termed  the  stapiiylinc  is  much  tlic  smallest  of  the  three  branches  (Figs.  438, 
439).  It  passes  downward  and  forward  with  the  palatine  vein  in  the  groove  at  the 
inner  side  of  the  tuber  maxillare  and  ramifies  in  the  soft  palate. 

The  sphenopalatine  ganglia  and  plexus  (Fig.  ,51.5)  lie  on  the  perpendicular  part  of  the  palate 
bone  and  the  pterygoid  process  under  cover  of  the  maxillary  nerve.     The  afferent  fibers  of  the 


THE  FIFTH,  TRIGEMINAL,  OU  TRIFACIAL  NERVE  681 

plexus  and  ganglia  come  chiefly  from  tlie  branches  of  the  sphenopahitine  nerve  and  the  nerve  of 
the  pterygoid  canal.  Interspersed  in  these  are  several  minute  ganglia  and  one  or  more  larger 
ones.  The  nerve  of  the  pterygoid  canal  or  Vidian  nerve  (X.  canalis  pterygoidei)  is  formed  by 
the  union  of  sympathetic  til)ers  with  the  superficial  petrcsal  branch  of  the  facial  nerve.  It  pa.sses 
forward  at  first  l)etween  the  Eustachian  tube  and  the  sphenoid  bone,  enters  the  canal  between 
the  pterygoid  bone  and  process,  and  joins  the  posterior  part  of  the  plexus.  It  is  probable  tliat 
it  furnishes  the  motor  fibers  to  the  levator  palati  and  palatinus  muscles.  Efferent  filaments  go  to 
the  periorbita  and  the  ophthalmic  vessels,  and  others  accompany  the  branches  of  the  maxil- 
lary nerve,  around  whicli  they  have  a  plexiforni  arrangement. 

3.  The  infraorbital  nerve  (X.  infraorbitalis)  is  the  continuation  of  the  maxillary 
trunk.  It  traverses  the  infraorbital  canal,  emerges  through  the  infraorlntai  fora- 
men, and  divides  into  nasal  and  superior  labial  branches.  Along  its  course  it  gives 
off  superior  alveolar  or  dental  branches  (Rami  alveolares  maxillse),  which  supply 
the  teeth,  alveolar  periosteum,  and  gums. 

The  delicate  posterior  alveolar  branches  are  given  off  in  the  pterygo-palatine  fossa,  pass 
through  small  foramina  in  the  tuber  ma.xillare,  and  supply  the  posterior  molar  teeth  and  the 
raa.xillary  sinus.  The  middle  alveolar  branches  are  given  off  in  the  infraorbital  canal,  and  consti- 
tute the  chief  nerve-supply  to  the  cheek  teeth  and  the  maxillary  sinus.  The  anterior  or  incisor 
branch  runs  forward  in  the  anterior  alveolar  or  incisor  canal  and  supplies  branches  to  the  canine 
and  incisor  teeth.  The  foregoing  unite  with  each  other  to  form  the  superior  dental  plexus, 
from  which  the  dental  and  gingival  branches  are  given  off. 

The  external  nasal  branches  (Rami  nasales  externi),  two  or  three  in  number, 
accompany  the  levator  labii  superioris  proprius  and  ramify  in  the  dorsum  nasi  and 
the  nasal  diverticulum. 

The  large  anterior  nasal  branch  (Ramus  nasalis  anterior)  passes  over  the  nasal 
process  of  the  premaxilla  under  cover  of  the  dilatator  naris  inferior,  gives  branches 
to  the  nasal  mucous  membrane,  and  terminates  in  the  skin  of  the  upper  lip. 

The  superior  labial  branch  (Ramus  labialis  dorsalis)  is  the  largest  of  the  termi- 
nals of  the  infraorbital  nerve.  It  passes  downward  and  forward  under  the  levator 
nasolabialis  and,  after  supplying  the  skin  of  the  anterior  part  of  the  cheek,  forms  a 
rich  terminal  ramification  in  the  skin  and  mucous  membrane  of  the  upper  lip.  It 
anastomoses  with  the  superior  buccal  branch  of  the  facial  nerve. 

III.  The  mandibular  nerve  (X.  mandibularis),  also  termed  the  inferior  maxil- 
lary branch,  is  formed  tjy  the  union  of  two  roots;  of  these  the  large  sensory  root 
comes  from  the  semilunar  ganglion,  and  the  small  motor  root  is  the  pars  minor  of 
the  trigeminus.  It  emerges  from  the  cranium  through  the  oval  notch  of  the  fora- 
men lacerum,  between  the  temporal  wing  of  the  sphenoid  bone  and  the  muscular 
process  of  the  petrous  temporal,  and  gives  off  the  following  Ijranches: 

1.  The  masseteric  nerve  (X.  massetericus)  (Figs.  437,  515)  passes  outward 
through  the  sigmoid  notch  of  the  mandible  and  enters  the  deep  face  of  the  masseter 
muscle,  in  which  it  ramifies. 

2.  The  deep  temporal  nerves  (Xn.  tcmporales  profundi)  (Fig.  437),  two 
or  three  in  number,  arise  by  a  common  trunk  mth  the  masseteric.  They 
supply  the  temporal  muscle. 

3.  The  buccinator  nerve  (X.  buccinatorius)  passes  obliquely  forward  through 
the  anterior  part  of  tlie  external  pterygoid  muscle,  then  between  the  internal 
pterygoid  and  the  tuber  maxillare  (Fig.  514).  It  continues  forward  in  the  sub- 
mucous tissue  of  the  cheek  along  the  lower  border  of  the  buccinator  and  divides 
into  Ijranches  which  ramify  in  the  mucous  meml^rane  and  glands  of  the  lips  in  the 
vicinity  of  the  commissure.  It  supplies  small  branches  to  the  external  pterygoid 
and  temporal  muscles  and  detaches  numerous  collateral  twigs  to  the  mucous  mem- 
brane of  the  cheek  and  to  the  buccal  glands.  It  also  communicates  with  the  in- 
ferior buccal  branch  of  the  facial  nerve. 

4.  The  pterygoid  nerve  (X.  pterygoideus)  arises  in  common  with  the  preceding, 
passes  forward  on  the  guttural  pouch,  and  divides  into  branches  for  the  pterygoid 
muscles  (Fig.  515). 

The  otic  ganglion  (G.  oticum)  is  situated  near  the  origin  of  the  pterygoid  and 


682  NERVOUS  SYSTEM  OF  THE  HORSE 

buccinator  nerves,  and  is  related  internally  to  the  tensor  palati  and  the  Eustachian 
tube.  It  receives  motor  fibers  from  the  pterygoid  nerve  and  sensorj-  fibers  by  the 
small  superficial  petrosal  nerve  from  the  tympanic  plexus,  through  which  communi- 
cations are  made  with  the  facial  and  glosso-pharyngeal  nerves.  Sympathetic 
fibers  are  derived  from  the  plexus  on  the  internal  maxillary  artery.  Efferent  fila- 
ments go  to  the  tensor  palati,  tensor  tympani,  and  pterygoid  muscles,  and  to  the 
Eustachian  tube. 

The  Ranglion  is  .small  and  sonipwhat  difficult  to  demonstratt'.  In  many  cases  it  is  replaced 
by  a  number  of  minute  sanslia  interspersed  in  a  fine  plexus. 

5.  The  superficial  temporal  nerve  (N.  temporalis  superficialis)  (Figs.  437, 
514,  515)  runs  outward  across  the  pterygoideus  externus,  passes  between  the  parotid 
gland  and  the  neck  of  the  ramus  of  the  mandible,  turns  around  the  latter,  and  di- 
vides into  two  branches.     The  upper  branch  (Ramus  transversus  faciei)  accom- 


FiG.  515. — Deep  Dissection  of  Bask  of  Cranittm,  Viewed  from  the  Right  and  Below. 
The  tympanic  cavity  is  opened  and  the  paramastoid  process  is  sawn  off.  a.  Occipital  condyle;  h,  body  of 
sphenoid;  c,  external  auditory  meatus  (part  removed);  d,  malleus;  c,  incus;  1,  stump  of  ophthalmic  nerve;  £, 
ina?dllary  nerve  (cut  off);  S,  sphenopalatine  plexus;  4>  Vitlian  nerve;  4,  deep  petrosal  nerve;  4" •  branch  to 
tympanic  plexus;  4'".  superficial  petrosal  nerve;  o,  superficial  temporal  nerve  (cut  otT) ;  6,  masseteric  nerve  (cut 
off);  7,  mandibular  nerve  (raised) ;  S,  lingual  nerve  (cut  otT);  9.  pterygoid  ner\'e  (cut);  /O.  nerve  to  tensor  tympani; 
77,  otic  ganglion;  /^,  facial  nerve;  i.^,  stapedial  nerve;  14,  chorda  tympani;  16,  glosso-jjliaryngeal  nerve  (cut); 
76,  tympanic  nerve;  77,  vagus  (cut  off);  7<!?.  auricular  branch  of  vagus;  75,  spinal  accessory  nerve  (cut  off);  20, 
hypoglossal  nerve  (cut  off);  21,  sympathetic  nerve  (cut  off);  22,  internal  carotid  artery,  (.\fter  EUenberger, 
in  Leisering's  .\tlas.) 

panics  the  transverse  facial  vessels  and  ramifies  in  the  skin  of  the  cheek.  The  larger 
inferior  branch  unites  with  the  inferior  buccal  division  of  the  facial  nerve. 

Before  its  division  the  nerve  gives  ofT  twigs  to  the  guttural  pouch,  the  jiarotid 
gland,  the  external  ear,  and  the  skin  of  the  external  auditory  meatus  and  the  mem- 
brana  tympani.  Branches  from  it  concur  with  filaments  from  the  cervical  branch 
of  the  facial  nervi>  in  the  formation  of  tlie  auricular  plexus. 

6.  The  inferior  alveolar  or  dental  nerve  (N.  alveolaris  mandibuhr)  (Figs. 
436,  437,  514)  arises  with  the  lingual  by  a  common  trunk  which  passes  forward  at 
first  on  the  external  pterygoid  muscle,  then  inclines  ventrally  between  the  internal 
pterygoid  and  the  ramus  of  the  mandible.  The  lingual  and  alveolar  separate  at  an 
acute  angle,  and  the  latter  enters  the  mandibular  foramen  and  courses  in  the  canal 
within  the  ramus  (Fig.  516).  Emerging  at  the  mental  foramen,  it  terminates  by 
dividing  into  six  to  eight  inferior  labial  and  mental  l)ranches,  which  ramify  in  the 
lower  lip  and  chin.  Before  entering  the  bone,  the  nerve  detaches  the  mylo-hyoid 
nerve  (N.  mylohyoideus),  which  runs  tlownward  and  forward  between  the  ramus 
and  the  mylo-hyoid  muscle;  it  supplies  that  muscle,  the  anterior  belly  of  the 
digastricus,  and  the  skin  of  the  anterior  part  of  the  submaxillar^'  space.     The  dental 


THE  SIXTH  OR  ABDUCENT  NERVE 


G83 


and  gingival  branches  detached  from  the  nerve  within  the  inaiuHhle  are  arranged 
lilve  the  corresponding  nerves  of  the  ujiper  jaw. 

7.  The  lingual  nerve  (X.  lingualis)  arises  by  a  common  trunk  with  the  inferior 
alveolar  or  dental  nerve  (Figs.  430,  437).  After  separating  from  the  latter  it  runs 
downward  and  forward,  lying  at  first  between  the  ramus  of  the  mandible  and  the 
internal  pterygoid  muscle,  then  on  the  inner  face  of  the  mylo-hyoid.  On  reaching 
the  root  of  the  tongue  it  divides  into  superficial  and  deep  branches.  The  super- 
ficial branch  (Ramus  superficialis)  runs  forward  on  the  stylo-glossus  and  accom- 
panies the  submaxillary  duct  on  the  deep  face  of  the  sublingual  gland.  It  supplies 
the  mucous  membrane  of  the  tongue  and  the  floor  of  the  mouth.  At  the  root  of  the 
tongue  it  gives  off  a  recurrent  branch  to  the  isthmus  faucium,  which  connnunicates 
with  the  lingual  branch  of  the  glosso-pharyngeal  nerve.  The  larger  deep  branch 
(Ramus  profundus)  turns  around  the  lower  edge  of  the  hyo-glossus,  jjasses  ujiward 
and  forward  Isetween  that  muscle  and  the  genio-glossus,  and  continues  forward  on 
tlie  latter  to  the  tip  of  the  tongue.  It  gives  branches  to  the  mucous  membrane  and 
the  fungiform  papillse  of  the  tongue,  and  anastomoses  with  branches  of  the  hypo- 


& 


.a^^-oci^^ 


Fig.  516. — Part  of  Branch  op  Lower  Jaw  of  Horse.  Internal  Vi 
The  bone  has  been  removed  to  show  the  vessels  and  nerves.     /,  i',  Inferior  alveolar 
branches  to  cheek  teeth  and  gums;   2' ,  branch  to  canine  and  incisor  teeth;   S^  3\ 
4,  satellite  vein.     (After  Leisering's  .\tlas.) 


ntal  nerv'e;   S,  2, 
ferjor  alveolar  or  dental  artery: 


glossal  nerve  and  with  the  superficial  branch.  Minute  ganglia  occur  on  the  finer 
branches  of  the  lingual  nerve.  The  chorda  tympani  branch  of  the  facial  joins  the 
lingual  nerve  at  the  origin  of  the  latter  and  is  incorporated  with  it  in  its  distribution 
to  the  tongue. 


THE  SIXTH  OR  ABDUCENT  NERVE 
The  abducent  nerve  (N.  abducens)  emerges  from  the  brain  behind  the  ]X)ns 
and  just  external  to  the  pyramid  (Fig.  499).  It  passes  forward  across  the  pons, 
jMcrces  the  dura  mater,  and  accompanies  the  third  and  ophthahnic  nerves,  below 
which  it  emerges  through  the  foramen  lacerum  orbitale.  In  the  orbit  it  divides 
into  two  branches;  the  larger  of  these  enters  the  external  rectus,  the  smaller  sup- 
plies the  superior  and  external  parts  of  the  retractor  muscle  of  the  eyeball.  "Within 
the  cranium  it  receives  filaments  from  the  carotid  plexus  of  the  sympathetic. 

The  fibers  ot  the  abducent  nerve  are  axones  of  the  large  muUipolar  cells  of  the  abducent 
nucleus  which  is  situated  beneath  the  eminentia  teres  of  the  floor  of  the  fourth  ventricle.  The 
nucleus  lies  within  the  loop  formed  by  the  fibers  of  origin  of  the  facial  nerve.  It  is  connected 
with  (n)  the  anterior  olive;  ib)  the  oculomotor  nucleus  of  the  oppasite  side;  (c)  the  motor  area  of 
the  cerebral  corte.x  bj-  means  of  the  pyramidal  tract  of  the  opposite  side. 


684  NERVOUS  SYSTEM  OF  THE  HORSE 

THE  SEVENTH  OR  FACIAL  NERVE 
The  facial  nerve  (X.  facialis)  has  its  suiierficial  origin  at  the  lateral  part  of  the 
corpus  trapfzoidcuni.  immediately  behind  the  j^ons  (Fig.  499).  It  passes  outward 
in  front  of  the  eighth  nerve  and  enters  the  internal  auditory  meatus.  At  the  bottom 
of  the  meatus  the  two  nerves  part  company,  the  facial  coursing  in  the  facial  canal 
of  the  petrous  temporal  bone.  The  canal  and  nerve  are  at  first  directed  outward 
lietween  the  vestibule  and  the  cochlea,  then  curve  backward  and  downward  in  the 
jjosterior  wall  of  the  tympanum  to  end  at  the  stylo-mastoid  foramen.  The  bend 
formed  by  the  nerve  is  called  the  knee  (Cleniculum  n.  facialis)  and  liears  at  its 
highest  point  the  round  geniculate  ganglion  (G.  geniculij. 

The  nerve  consists  of  two  parts,  motor  and  sensory.  The  motor  part  constitutes  the  bulk 
ofjthe  nerve.  Its  deep  origin  is  from  the  cells  of  the  facial  nucleus,  which  is  situated  in  the  medulla 
aliove  the  facial  tubercle.  On  lea\ing  the  nucleus  the  root-fibers  pass  upward  and  inward,  in- 
cline forward  close  to  the  median  plane,  and  then  bend  sharply  downward  to  the  point  of  emer- 
gence. The  highest  point  of  the  bend  is  subjacent  to  the  gray  matter  of  the  erainentia  teres  in 
the  floor  of  the  fourth  ventricle,  and  the  abducent  nucleus  lies  in  the  concavity  of  the  curve. 
The  small  sensory  part  iX.  intermedins)  consists  of  axones  of  cells  of  the  geniculate  ganglion, 
which  i,<  interp(jsed  on  the  facial  nerve  as  it  bends  downward  in  the  facial  canal.  The  fibers  of 
this  part  after  entering  the  medulla,  pass  to  the  nucleus  of  termination  which  it  shares  with  the 
ninth  and  tenth  nerves.  The  peripheral  fibers  from  the  geniculate  ganglion  constitute  the  chorda 
tympaiii. 

After  its  emergence  through  the  stylo-mastoid  foramen  (Fig.  514)  the  nerve 
passes  downward,  forward,  and  outward  on  the  guttural  pouch  under  cover  of  the 
parotid  gland,  and  crosses  between  the  origin  of  the  superficial  temporal  and  internal 
maxillary  arteries  internally  and  the  superficial  temporal  vein  externally.  It  then 
crosses  the  posterior  border  of  the  raiiius  of  the  mandible  ventral  to  the  transverse 
facial  artery  and  about  an  inch  and  a  half  (ca.  3.5  to  4  cm.)  below  the  articulation 
of  the  jaw.  Emerging  from  beneath  the  j^arotid  gland  upon  the  masseter  muscle, 
it  receives  the  lower  branch  of  the  superficial  temporal  nerve,  and  divides  into  supe- 
rior and  inferior  buccal  branches.  The  following  collateral  branches  are  given  off, 
the  first  five  being  detached  within  the  facial  canal,  and  the  others  between  the 
stylo-mastoid  foramen  and  the  border  of  the  jaw. 

1.  The  great  superficial  petrosal  nerve  (N.  petrosus  superficialis  major)  arises 
from  the  geniculate  ganglion.'  It  passes  through  the  petrosal  canal,  contributes  a 
filament  to  the  tympanic  plexus,  receives  the  great  deep  petrosal  nerve  from  the 
carotid  plexus  of  the  sympathetic,  emerges  through  the  foramen  lacerum,  and  is 
continued  as  the  Vidian  nerve  to  the  sphenopalatine  plexus  and  ganglia  (Fig.  515). 

2.  A  delicate  branch  (R.  anastomoticus  cum  plexu  tympanico)  emerges  from 
the  geniculate  ganglion  antl  tmites  with  a  filament  issuing  from  the  tympanic  plexus 
to  form  the  small  superficial  petrosal  nerve  (N.  petrosus  superficialis  minor); 
this  ends  in  the  (itir  ganglion. 

3.  The  stapedial  nerve  (N.  stapedius)  (Fig.  515)  is  a  short  filament  tletached 
from  the  facial  nei\c  as  it  turns  down  in  the  facial  canal.  It  innervates  the  sta]ie- 
dius  muscle. 

4.  The  chorda  tympani  (Fig.  515)  is  a  small  nerve  which  arises  a  little  l)elow  the 
preceding  and  pursues  a  recurrent  course  in  a  small  canal  in  the  mastoid  part  of 
the  temporal  bone  to  reach  the  tympanic  cavity.  It  traverses  the  latter,  passing 
between  the  handle  of  the  malleus  and  the  long  branch  of  the  incus.  Emerging 
through  the  petrotymjianic  fissure,  the  nerve  passes  downward  and  forward,  crosses 
beneath  the  internal  maxillary  artery,  and  joins  the  lingual  nerve.  It  sends  twigs 
to  the  submaxillary  and  sublingual  glands,  and  through  its  incorporation  with  the 
lingual  nerve  furnishes  fibers  to  the  mucous  membrane  of  the  anterior  two-thirds 
of  the  tongue  which  are  believed  to  mediate  the  sense  of  taste. 

'  Although  this  nerve  springs  directlj-  from  the  ganglion,  it  contains  motor  as  well  as  sensory 
fibers. 


THE  SEVENTH  OR  FACIAL  NERVE  685 

5.  Anastomotic  tilanu'iits  unit(>  with  tlie  auricular  t)rancli  of  the  vagus  near 
the  stylomastoid  foramen. 

6.  The  posterior  auricular  nerve  (X.  auricularis  posterior)  arises  from  the 
-facial  at  its  emergence  from  the  facial  canal  (Fig.  514).     It  runs  upward  and  l)ack- 

ward  with  the  posterior  auricular  artery  under  cover  of  the  parotid  gland  and  sup- 
plies the  posterior  auricular  muscles  and  the  skin  of  the  convex  surface  of  the 
external  ear.  It  anastomoses  with  branches  of  the  first  and  second  cervical 
nerves. 

7.  The  internal  auricular  nerve  (X.  auricularis  internus)  springs  from  the 
facial  close  to  or  in  common  with  the  preceding  (Fig.  514).  It  ascends  in  the  paro- 
tid gland  just  Ijchind  the  styloid  process  of  the  conchal  cartilage,  passes  through 
an  opening  in  the  cartilage,  and  ramifies  in  the  skin  of  the  concave  surface 
of  the  ear. 

8.  The  digastric  branch  (R.  digastricus)  (Fig.  514)  arises  from  the  facial  below 
the  auricular  nerves.  Its  branches  innervate  the  posterior  belly  of  the  digastricus, 
the  stylo-hyoideus,  and  the  occipito-hyoidcus.  At  its  origin  it  gives  off  a  small 
branch  which  forms  a  loop  around  the  great  auricular  arter.v  or  its  posterior  branch 
and  rejoins  the  tnnik. 

9.  The  auriculo-palpebral  nerve  (X'.  auriculo-palpebralis)  (Fig.  514)  arises 
from  the  upper  edge  of  the  facial  near  the  posterior  border  of  the  ramus.  It  ascends 
in  the  parotid  gland  behind  the  superficial  temporal  artery,  and  terminates  in 
anterior  auricular  and  temporal  branches.  The  anterior  auricular  branches  form 
with  branches  of  the  trigeminus  the  anterior  auricular  plexus.  They  innervate 
the  anterior  auricular  and  parotido-auricularis  muscles.  The  temporal  branch 
runs  forward  and  inward  over  the  temporal  muscle  to  the  inner  canthus  of 
the  eye,  forms  a  plexus  with  the  terminal  branches  of  the  ophthalmic  nerve, 
and  is  distril.iuted  to  the  orbicularis  oculi,  corrugatur  supercilii,  anil  levator  naso- 
labialis. 

10.  The  cervical  branch  (R.  colli)  (Fig.  435)  arises  from  the  ventral  border 
of  the  facial  opposite  to  the  preceding  nerve.  It  emerges  obliquely  through  the 
parotid  gland,  passes  downward  and  backward  on  or  near  the  jugular  vein,  and 
anastomoses  with  the  cutaneous  branches  of  the  cervical  nerves.  It  gives  branches 
to  the  parotido-auricularis  and  the  cervical  panniculus.  In  its  course  along  the 
neck  the  nerve  is  reinforced  by  twigs  from  the  cutaneous  branches  of  the  second  to 
the  sixth  cervical  nerves. 

11.  Small  branches  are  detached  to  the  guttural  pouch  and  the  parotid  gland. 
The  latter  (Rami  parotidei)  concur  with  branches  of  the  superficial  temporal  nerve 
in  forming  the  parotid  plexus. 

The  facial  nerve  usually  terminates  after  a  short  course  on  the  surface  of  the 
masseter  by  dividing  into  two  buccal  liranches  (Figs.  435,  461). 

1.  The  superior  buccal  nerve  (X.  buccalis  dorsalis)  passes  forward  on  the 
upper  part  of  the  masseter,  dips  under  the  zygomaticus,  and  continues  along  the 
lower  border  of  the  dilatator  naris  lateralis.  It  then  runs  under  the  last-named 
muscle  and  anastomoses  with  branches  of  the  infraorbital  nerve,  and  is  distributed 
to  the  muscles  of  the  cheek,  upper  lip,  and  nostril. 

2.  The  inferior  buccal  nerve  (X".  buccalis  ventralis)  crosses  the  masseter 
obliciuely  and  continues  forward  along  the  depressor  labii  inferioris.  It  is  connected 
by  variable  anastomotic  branches  with  the  superior  nerve.  It  gives  collateral 
branches  to  the  panniculus,  buccinator,  and  depressor  labii  inferioris,  and  ramifies 
with  the  terminal  branches  of  the  inferior  alveolar  nerve  in  the  lower  lip. 

The  buccal  nerves  are  .'subject  to  much  variation  in  regard  to  their  course,  anastomose.s, 
and  relations  to  the  sensory  components  derived  from  the  superficial  temporal  nerve.  Their 
distribution  is  constant.  The  point  at  which  the  branch  of  the  superficial  temporal  nerve  joins 
the  facial  is  variable. 


686  NERVOUS  SYSTEM  OF  THE  HORSE 

THE  EIGHTH  OR  AUDITORY  NERVE 
The  auditory  nerve  (X.  acusticus)  is  connected  with  the  lateral  aspect  of  the 
medulla  just  hchind  and  external  to  the  facial  (Fig.  499).     It  has  two  roots,  vesti- 
bular and  cochlear  (Radix  vestibularis  et  cochlearis). 

The  auditory  nerve  consists  of  two  distinct  parts  which  might  well  be  regarded  as  separate 
nerves.  The  cochlear  part  mediates  the  sense  of  hearing,  while  the  vestibular  part  is  not  auditory 
in  function,  but  is  concerned  in  the  sense  of  the  position  of  the  body  and  the  mechanism  of 
equilibration. 

The  nerve  passes  outward  to  the  internal  auditory  meatus,  which  it  enters 
behind  the  facial  nerve.  In  the  meatus  it  divides  into  two  nerves,  of  which  the 
upper  is  the  vestibular  and  the  lower  is  the  cochlear  nerve. 

1.  The  vestibular  nerve  (N.  vestibuli)  is  distributed  to  the  utriculus,  the  saccu- 
lus,  and  to  the  ampullae  of  the  semicircular  canals,  of  the  internal  ear.  In  the  in- 
ternal auditory  meatus  the  nerve  is  connected  by  filaments  with  the  geniculate 
ganglion  of  the  facial  nerve.  At  the  bottom  of  the  meatus  it  bears  the  vestibular 
ganglion  (G.  vestibulare),  from  the  cells  of  which  the  fibers  of  the  nerve  arise. 

2.  The  cochlear  nerve  (N.  cochleae)  detaches  a  filament  to  the  sacculus,  passes 
through  the  lamina  cribrosa  to  the  labyrinth,  and  is  distributed  to  the  organ  of 
Corti  in  the  cochlea. 

The  fibers  of  the  \'estibiilar  ner\-e  arise  from  the  vestibular  ganglion  as  central  processes 
(axones)  of  the  bipolar  colls  of  the  f;anglion.  Tlic  peripheral  processes  (rlendrites)  of  the  cells 
form  arborizations  about  the  (Icrp  ends  of  the  hair-cells  of  the  macuke  and  iii<l:i'  acustica.'  of  the 
utriculus,  sacculus,  and  >iiiiiriicular  canals.  The  fibers  enter  the  iiu-dulla,  iki->  between  the 
re.stiform  body  and  the  spinal  tract  of  the  trigeminus,  and  spread  out  tu  end  m  the  vestibular 
nucleus  in  the  floor  of  the  fourth  ventricle.  Among  the  central  connections  of  tlie  vestibular 
nerve  are:  (1)  fibers  vi'hich  connect  its  nucleus  with  centers  in  the  cerebellum  (chiefly  of  the  oppo- 
site side);  (2)  the  vestibulo-spinal  tract,  which  convej-s  impulses  to  the  motor  cells  of  the  ventral 
columns  of  the  spinal  cord;  (3)  fibers  which  connect  the  nucleus  with  those  of  the  abducent  nerve 
of  the  same  side,  the  third  antl  fourth  nerves,  and  the  motor  part  of  the  trigeminus  of  both  sides. 

The  fibers  of  the  cochlear  nerve  are  the  central  processes  of  the  bipolar  cells  of  the  spiral 
ganglion  of  the  cochlea.  The  peripheral  processes  of  these  cells  end  in  relation  to  the  hair-cells 
of  the  organ  of  Corti.  Some  of  the  nerve-fibers  enter  the  ventral  cochlear  nucleus  in  the  medulla 
close  to  the  superficial  origin  of  the  nerve;  others  end  in  the  dorsal  nucleus  of  the  tuberculum 
acusticum  at  the  lateral  angle  of  the  floor  of  the  fourth  \-entricle.  From  the  ventral  nucleus 
fillers  pass  in  the  corpus  trapezoideinn  to  the  anterior  olivary  nucleus  of  the  same  and  of  the 
opposite  side.  Thence  tracts  pass  to  the  nuclei  of  the  motor  nerves  of  the  eye,  and  through  the 
lateral  fillet  to  the  posterior  quadrincriiiiial  binly  ;ind  llic  inh  rnal  geniculate  body.  The  axones 
of  the  cells  of  the  dorsal  nucleus  jiass  largely  i:iN  llic  sirur  arn-^lica')  over  the  restiform  body  and 
acro.ss  the  floor  of  the  fourth  ventricle  toward  tlie  inedian  plane.  They  then  turn  ventrally, 
cross  to  the  opposite  side,  and  are  continued  by  the  lateral  fillet.  From  the  mid-l)rain  a  tract 
proceeds  to  the  cortex  of  the  temporal  lobe  of  the  hemisphere. 


THE  NINTH  OR  GLOSSOPHARYNGEAL  NERVE 
The  glosso-pharyngeal  nerve  (N.  glossopharyngeus)  is  attached  to  the  anterior 
part  of  the  lateral  aspect  of  the  medulla  by  several  filaments  (Fig.  499).  The  root- 
bundles  enter  the  furrow  ventral  to  the  restiform  bodj-;  they  are  separated  by  a 
short  interval  from  the  origin  of  the  facial  nerve,  but  are  not  marked  off  behind  from 
the  roots  of  the  vagus.  The  bundles  converge  laterally  to  form  a  nerve  which  ])er- 
forates  the  dura  mater  and  emerges  through  the  foramen  lacerum  posterius  just 
in  front  of  the  tenth  nerve  (Fig.  515).  As  it  issues  from  the  cranium  the  nerve 
bears  a  considerable  ovoid  gray  enlargement,  the  petrous  ganglion  (G.  petrosum).' 
It  then  curves  downward  and  forward  over  the  guttural  pouch  and  behind  the  great 
coriui  of  the  hyoid  l)one,  crosses  the  deep  face  of  the  external  carotid  artery,  and 
divides  into  pharyngeal  and  lingual  branches  (Fig.  437).  The  collateral  branches 
are  as  follows: 

1.  The  tympanic  nerve  (N.  tymjianicus)  (Fig.  515)  arises  from  the  petrous 
'  This  ganglion  appears  to  be  equivalent  to  the  jugular  or  superior  and  petrous  ganglia  of  man. 


THE  TENTH,  VAGIJS,  OR  PNEUMOGASTRIC  NERVE  687 

ganglion  and  passes  upward  between  the  petrous  and  tympanic  parts  of  the  temporal 
hone  to  reach  the  cavity  of  the  tympanum.  Here  it  breaks  up  into  branches 
to  form,  along  with  branches  from  the  carotid  plexus  of  the  sympathetic,  the  tym- 
panic plexus.  From  the  jilexus  branches  pass  to  the  mucous  membrane  of  the 
tympanum  and  the  Eustachian  tube.  The  continuation  of  the  nerve  issues  from 
the  plexus  and  unites  with  a  filament  from  the  geniculate  ganglion  of  the  facial  to 
form  the  small  superficial  petrosal  nerve;  this  runs  forward  and  ends  in  the  otic 
ganglion. 

Filaments  also  connect  the  petrous  ganglion  with  the  jugular  ganglion  of  the  \'agus  nerve 
and  with  the  superior  cervical  ganglion  of  the  sympathetic. 

2.  A  consideralile  branch  runs  backward  on  the  guttural  pouch,  contributes 
filaments  to  the  ])haryngeal  plexus,  and  concurs  with  twigs  from  the  vagus  and  the 
sympathetic  in  forming  the  carotid  plexus  on  the  terminal  part  of  the  carotid 
artery  and  on  its  chief  branches.     In  this  plexus  is  the  small  ganglion  intercaroticum. 

The  pharyngeal  branch  (R.  pharyngeus)  (Fig.  437)  is  the  smaller  of  the  two 
terminal  V)ranches.  It  runs  forward  across  the  deep  face  of  the  great  cornu  of  the 
hyoid  bone  and  concurs  with  the  pharyngeal  branches  of  the  vagus  and  with  sym- 
pathetic filaments  in  forming  the  pharj'ngeal  plexus;  from  this  liranches  pass  to 
the  muscles  and  mucous  membrane  of  the  pharynx. 

The  lingual  branch  (R.  lingualis)  is  the  continuation  of  the  trunk  (Fig.  437). 
It  runs  along  the  ])osterior  border  of  the  great  cornu  of  the  hyoid  bone  in  front  of 
the  external  maxillary  artery  and  dips  under  the  hyo-glossus  muscle.  It  gives 
collateral  branches  to  the  soft  palate,  isthmus  faucium,  and  tonsil,  and  ends  in 
the  mucous  membrane  of  the  posterior  part  of  the  tongue,  where  it  supplies  gusta- 
tory fibers  to  the  vallate  papillae.  A  considerable  branch  unites  with  a  twig  from 
the  lingual  nerve. 

The  glosso-pharyngeal  is  a  mixed  nerve,  containing  both  motor  and  sensory  fil)ers.  The 
latter  constitute  the  bulk  of  the  nerve  and  include  those  which  mediate  the  special  sense  of  taste. 
They  are  processes  of  the  cells  of  the  petrous  ganglion.  The  central  pmi'isx^  nf  ihc  ganglion 
cells  enter  the  medulla,  pass  upward  and  inward  through  the  formatio  retiiiilaris,  and  end  in  the 
nucleus  of  termination  in  the  floor  of  the  fourth  ventricle.  The  motor  fibers  arise  fruin  dorsal 
and  ventral  efferent  nuclei  in  the  medulla.  The  glosso-pharyngeal  shares  these  nuclei  with  the 
vagus  and  has  practically  the  same  central  connections  as  that  nerve  {q.  v.). 


THE  TENTH,  VAGUS,  OR  PNEUMOGASTRIC  NERVE 
The  vagus  or  pneumogastric  (N.  vagus)  is  the  longest  and  most  widely  dis- 
tributed of  the  cranial  nerves;  it  is  also  remarkable  for  the  connections -which  it 
forms  with  adjacent  nerves  and  with  the  sympathetic.  It  is  attached  to  the  lateral 
aspect  of  the  medulla  by  several  filaments  which  are  in  series  with  those  of  the 
ninth  nerve  in  front  and  the  eleventh  nerve  behind  (Fig.  499).  The  bundles  con- 
verge to  form  a  trunk  which  passes  outward,  pierces  the  dura  mater,  and  emerges 
from  the  cranium  through  the  foramen  lacerum  posterius  (Fig.  51.5).  In  the 
foramen  the  nerve  bears  on  its  lateral  aspect  the  elongated  flattened  jugular  gang- 
lion (G.  jugulare). 

The  ganglion  communicates  with  (a)  the  tympanic  nerve,  (h)  the  petrous  ganglion  of  the 
nintli  nerve,  (c)  the  spinal  acce.s.sory,  and  (rf)  the  hypoglo-ssal.  It  also  gives  off  the  auricular 
branch  (R.  auricularis),  which  runs  forward  below  the  petrous  ganglion  and  passes  through  a 
small  canal  in  the  petrous  temporal  bone  to  gain  the  facial  canal.  Here  it  gives  hlamcnts  to  the 
facial  and  emerges  with  that  nerve  through  the  stylo-mastoid  foramen.  It  ascends  behind  the 
external  auditory  meatus,  dips  under  the  rotator  longus  muscle,  and  passes  through  a  foramen 
in  the  conchal  cartilage  to  ramify  in  the  integument  which  lines  the  meatus  and  the  adjacent 
part  of  the  ear. 

Beyond  the  ganglion  the  vagus  runs  backward  and  downward  with  the  spinal 
accessory  in  a  fold  of  the  guttural  pouch  (Fig.  437).  Then  the  two  nerves  separate, 
allowing  the  hypoglossal  to  pass  between  them,  and  the  vagus  descends  with  the 


688 


NERVOUS  SYSTEM  OF  THE  HORSE 


internal  carotid  artery  and  crosses  tiie  inner  face  of  the  origin  of  the  occipital 
artery.  Here  it  is  joined  by  the  cervical  trunk  of  the  sympathetic,  and  the  two 
nerves  continue  along  the  dorsal  aspect  of  the  common  carotid  artery  in  a  common 
sheath  (Fig.  433).     At  the  root  of  the  neck  the  vagus  separates  from  the  sym- 


Lig.  nucha 
Splenius^ 


Nuchal  fal 


Branch  oj  occipital  artery 
Corn-plexus 


Complexus  tendon 
Intertransversalis 

Rectus  capitis 
posterior  major 


Spinal 

accessory 

nerte 

(dorsal 

branch) 

Mantoido- 
hiimiralis 
'ayus 


accessory 
nerte  (dorsal 
branch) 
Rectus  capitis   ante- 
rior major 

Jugular  vein 

Thyro-laryngeal 
artery 

Anterior  cervical 
lymph  glands 


Extrninl  nia.r- 
illury  nin 


Sterno-ccphiilic 
Omo-hyoideus  and  sterttu-hyoidcu 


Tliyroid  gland 
SUriio-lliyroideus 


Fig.  517. — Cross-section  of  Neck  of  Horse,  Passing  throdoh  Posterior  Part  of  Atlas. 
The  head  and  neck  were  extended,     i,  Dorsal  arch  of  atlas;   2,  odontoid  process;   S,  odontoid  ligament; 
4,  vertebral  siniises;   6,  dura  mater;   6,  spinal  cord;   7.  vertebral  artery;    8,  wing  of  atlas;   9,  atlanto-axial  joint 
cavity;   10.  ccsophagus;   11,  11,  recurrent  nerves:   12,  12,  ventral  branches  of  spinal  accessory  nerves.       By  an 
oversight  the  ubliquus  cai).  i>ost.  (above  wing  of  atlas)  is  unmarked. 


pathetic,  and  from  this  point  backward  the  relations  of  the  right  and  left  vagi  differ 
somewhat  and  must  be  described  separately. 

The  right  vagus  (Fig.  429)  enters  the  thorax  in  the  angle  of  divergence  of  the 
right  l)rachial  artery  and  the  truncus  bicaroticus.  It  then  passes  backward  and 
slightly  upward,  crossing  oblitiuely  the  outer  surface  of  the  brachiocephalic  artery 
and  the  right  face  of  the  trachea.  Reaching  the  dorsal  surface  of  the  latter  near 
the  bifurcation,  it  divides  into  dorsal  and  ventral  branches. 


THE  TENTH,  VAGUS,  OR  PNEUMOGASTRIC  NERVE  689 

The  left  vagus  (Fig.  428)  enters  the  thorax  on  the  ventral  face  of  the  crsophagus, 
crosses  obliquely  under  the  left  brachial  artery,  and  passes  back  on  the  external 
surface  of  that  vessel  in  company  with  a  large  cardiac  nerve.'  Separating  from 
the  latter,  the  vagus  continues  backward  on  the  left  face  of  the  aorta,  inclines  to 
the  upper  surface  of  the  left  bronchus,  and  divides  into  dorsal  and  ventral  branches. 

The  dorsal  and  ventral  branches  unite  with  the  corresponding  branches  of  the 
opposite  nerve,  thus  forming  dorsal  and  ventral  oesophageal  trunks  (Truncus 
ocsophageus  dorsalis,  ventralis).  These  run  backward  in  the  posterior  mediastinum, 
above  and  below  the  oesophagus  resjDeetively,  and  enter  the  abdominal  cavity 
through  the  hiatus  cesophageus;  they  supply  branches  to  the  oesophagus  and 
anastomose  with  each  other.  The  dorsal  trunk  receives  the  major  part  of  its  fibers 
from  the  right  vagus.  After  entering  the  abdomen  it  passes  to  the  left  of  the 
cardia,  gives  branches  to  the  visceral  surface  of  the  stomach,  and  ends  in  the 
celiac  and  subsidiary  plexuses.  The  ventral  trunk  passes  to  the  lesser  curva- 
ture of  the  stomach  and  ramifies  on  the  parietal  surface  of  the  stomach;  it  forms 
here  the  anterior  gastric  plexus,  from  which  branches  are  supplied  also  to  the  first 
part  of  the  duodenum  and  to  the  liver. 

The  collateral  liranches  of  the  vagus  are  as  follows: 

1.  The  pharyngeal  branch  (R.  pharyngeus)  is  given  off  in  relation  to  the  supe- 
rior cervical  ganglion,  turns  around  the  internal  carotid  artery,  and  runs  downward 
and  forward  on  the  guttural  pouch  to  the  dorsal  wall  of  the  pharynx  (Fig.  437). 
Here  its  branches  concur  with  the  pharyngeal  branch  of  the  ninth  nerve  and  with 
filaments  from  the  spinal  accessory  and  the  sympathetic  in  forming  the  pharyngeal 
plexus.  This  supplies  numerous  twigs  to  the  pharynx,  and  a  larger  branch  which 
l^asses  along  the  side  of  the  oesophagus  and  ramifies  in  its  cervical  part. 

According  to  Ellenberger  and  Baum  the  pliaryngeal  plexus  receives  filaments  also  from  the 
digastric,  superior  laryngeal,  hypoglossal,  and  first  cervical  nerves.  The  branches  of  the  plexus 
form  secondary  intermuscular  and  submucous  ple.xuses,  in  which  there  are  numerous  minute 
ganglia. 

2.  The  superior  or  anterior  laryngeal  nerve  (N.  laryngeus  cranialis)  is  larger 
than  the  preceding  and  arises  a  little  behind  it  (Fig.  437).  It  crosses  the  deep  face 
of  the  origin  of  the  external  carotid  artery,  runs  downward  and  forward  over  the 
lateral  wall  of  the  pharynx  behind  the  hypoglossal  nerve,  and  passes  through  the 
foramen  below  the  anterior  cornu  of  the  thyroid  cartilage.  Its  terminal  branches 
ramify  in  the  mucous  membrane  of  the  larynx,  the  floor  of  the  jjharynx,  and  the 
entrance  to  the  oesophagus;  they  anastomose  with  those  of  the  recurrent.  At 
its  origin  the  nerve  gives  off  its  small  external  branch  (R.  externus);  this  descends 
to  the  crico-thyroid  muscle,  which  it  supplies,  and  sends  filaments  to  the  crico- 
pharyngeus  also.  It  may  arise  from  the  trunk  of  the  vagus  or  from  the  pharyngeal 
branch. 

.\t  the  point  of  origin  of  the  superior  laryngeal  nerve  there  is  a  plexiform  widening  which  is 
regarded  by  some  authors  as  the  homologue  of  the  gangUon  nodosum  of  man.  From  it  a  filament 
arises  which,  after  a  short  course,  rejoins  the  vagus  or  enters  the  sympathetic  trunk.  Stimulation 
of  its  central  end  causes  a  reduction  of  the  blood-pressure,  and  it  is  therefore  termed  the  depressor 
nerve  (N.  depressor). 

3.  The  recurrent  nerve  (N.  recurrens),  also  termed  the  inferior  or  posterior 
laryngeal  nerve,  differs  on  the  two  sides  in  its  point  of  origin  and  in  the  first  part  of 
its  course.  The  right  nerve  (Fig.  429)  is  given  off  opposite  the  second  rib,  turns 
around  the  dorso-cervical  artery  from  without  inward,  runs  forward  on  the  lower 
part  of  the  lateral  surface  of  the  trachea,  and  ascends  in  the  neck  on  the  ventral 
face  of  the  common  carotid  artery.  The  left  nerve  (Fig.  428)  arises  from  the  vagus 
where  the  latter  begins  to  cross  the  aortic  arch.     It  passes  back  over  the  ligamentum 

'  In  some  cases  the  left  vagus  passes  back  below  the  junction  of  the  jugular  veins  and  the 
termination  of  the  left  brachial  vein.     It  then  runs  backward  and  somewhat  dorsally  across  the 
left  face  of  the  anterior  vena  cava  to  reach  its  usual  position. 
44 


CM  NERVOUS  SYSTEM  OF  THE  HORSE 

arteriosum,  winds  aimind  tlic  concavity  of  the  aortic  arch  from  without  inward, 
runs  forward  on  the  lower  part  of  the  left  face  of  the  trachea,  and  continues  in  the 
neck  in  a  similar  position  to  the  right  nerve. 

It  is  wortliy  of  note  that  the  left  nerve  passes  beneath  the  bronchial  lympli  glands  as  it 
winds  around  the  aorta;  also  that  in  the  next  part  of  its  course  it  lies  between  the  left  surface  of 
the  trachea  and  the  deep  face  of  the  aorta,  and  is  then  related  to  lymph  glands  which  lie  along 
the  ventral  aspect  of  the  trachea.  Tlic  left  recurrent  is  often  incorporated  in  part  of  its  course 
in  the  anterior  mediastinum  with  a  deep  cardiac  nerve.  Further,  the  left  nerve  lies  at  first 
ventral  to,  and  then  upon,  the  tesophagus  in  the  neck.  The  right  recurrent  is  given  off  from  or 
in  common  with  a  consiJcrable  trunk  which  connects  the  vagus  witli  the  first  thoracic  ganghon 
of  the  sympathetic.  The  arrangement  here  is  commonly  more  or  less  plexiform,  and  from  it 
one  or  two  cardiac  nerves  arise. 

The  terminal  part  of  eachnerve  (Fig.  517)  lies  on  the  dorsal  surface  of  thetrachea, 
in  relation  to  the  oesophagus  internally  and  the  carotid  artery  above.'  It  passes 
hetween  the  crico-arytenoideus  posterior  and  the  crico-pharyngeus ;  the  terminal 
branches  supply  all  the  muscles  of  the  larj^nx except  the  crico-thyroid,  and  communi- 
cate with  branches  of  the  superior  laryngeal  nerve.  Collateral  branches  are  given 
off  to  the  cardiac  plexus  (Rr.  cardiaci),  to  the  trachea  (Hr.  tradieales),  to  the 
rcsophagus  (Rr.  a-sophagei),  and  to  the  inferior  cervical  ganglion  of  the  sympathetic. 

4.  Cardiac  branches  (Rr.  cardiaci),  usually  two  or  three  in  number,  are  given 
off  from  each  vagus  within  the  thorax  (Figs.  428,  429).  These  concur  with  the 
cardiac  branches  of  the  sj'mpathetic  and  recurrent  nerves  to  form  the  cardiac 
plexus,  which  innervates  the  heart  and  great  vessels. 

5.  Small  tracheal  and  oesophageal  branches  (Rr.  tracheales  et  cesophagei) 
are  given  off  from  both  vagi  in  the  thorax.  These  concur  with  branches  from  the 
recurrent  nerves  and  the  inferior  cervical  and  anterior  thoracic  ganglia  of  the 
.sympathetic  in  forming  the  posterior  tracheal  and  oesophageal  plexuses,  from 
which  twigs  go  to  tlu'  trachea,  ffsophagus,  heart,  and  large  vessels. 

6.  Bronchial  branches  (Rr.  bronchiales)  are  detached  at  the  roots  of  the  lungs 
and  unite  with  sympathetic  filaments  in  forming  the  pulmonar^  plexuses.  From 
the  latter  numerous  branches  proceed  in  a  plexiform  manner  along  the  bronchi  and 
vessels  into  the  substance  of  the  lungs. 

The  vagus  and  glosso-pharyngeal  nerves  are  so  closely  associated  in  origin  and  central 
connections  that  they  may  be  described  together  in  this  re.spect. 

The  sensory  fibers  arise  from  the  petrous  and  jugular  ganglia,  and  their  central  parts  enter 
the  lateral  aspect  of  the  medulla  and  divide  into  anterior  and  posterior  branches  like  the 
fibers  of  the  dorsal  roots  of  the  sjiimd  nerves.  Most  of  the  fibers  end  in  arborizations  about  the 
cells  of  the  v:ig(i-t;losso-]ilmryni;i-:il  iiUfli-iH  nf  1  rrniiii;ilion,  which  consists  of  two  parts.  Of  these 
the  dorsal  sensory  nucleus  (XihI.iik  ,iI;c  ciiH-n;!!  is  -ituated  in  the  posterior  part  of  the  floor  of 
the  fourth  ventricle  and  in  the  adjaci'iit  part  uf  llic  rlosed  portion  of  the  medulla  near  the  me- 
dian plane.  The  other  part  is  termed  the  nucleus  of  the  solitary  tract,  and  is  so  named  lnrauM' 
its  cells  are  grouped  about  the  bundle  (Tracius  solilariiis)  foniicii  by  the  posterior  diN  i-mn- nl' 
the  afferent  nerve-fibers.  It  ends  about  th<>  lc\  el  of  the  pyramidal  decussation.  Tlic  si'iuiidui  y 
central  connccticms  are  siinil;ir  to  those  of  the  sensory  part  of  the  trigeminus. 

The  motor  fibers  land  those  of  the  nuMlulIary  part  of  the  acce.s.sory)  arise  from  the  dor- 
sal motor  nucleus  and  the  ventral  motor  nucleus.  The  cells  of  the  former  lie  in  groups  along 
the  ventro-medial  side  of  the  tlorsal  sensory  nucleus.  The  latter,  also  termed  the  nucleus  am- 
biguus,  is  situated  more  deeply  in  the  lateral  part  of  the  formatio  reticularis. 


THE  ELEVENTH  OR  SPINAL  ACCESSORY  NERVE 
The  spinal  accessory  nerve  (N.  accessorius)  is  ]3urely  motor.     It  consists  of 
two  parts  which  differ  in  origin  and  function. 

The  medullary  part  arises  from  the  lateral  aspect  of  the  medulla  by  several 
rootlets  which  are  behind  and  in  series  with  those  of  the  vagus  (Fig.  499).  The 
spinal  part  arises  from  the  cervical  part  of  the  spinal  cord  by  a  series  of  fasciculi 

'  The  nerve  lies  here  about  a  finger's  breadth  aliove  the  thyroid  gland.  If.  however,  the 
gland  is  enlarged  it  may  come  in  contjvct  with  the  nerve.  The  same  is  true  in  regard  to  the  rela- 
tion to  the  anterior  cervical  lymph  glands. 


THE  ELEVENTH  OR  SPINAL  ACCESSORY  NERVE 


691 


which  emerge  between  the  dorsal  antl  ventral  roots.  The  bundles  unite  to  ft)rm 
a  trunk  which  is  very  small  at  its  origin  at  the  fifth  segment  of  the  cord,  but  in- 
creases in  size  when  traced  toward  the  brain,  since  it  continually  receives  accessions 
of  fibers.  It  passes  through  the  foramen  magnum  and  joins  the  medullary  part. 
The  trunk  thus  formed  sends  its  medullary  fibers  to  the  tenth  antl  ninth  nerves  and 
emerges  through  the  foramen  laccrum  posterius.     It  then  runs  backwaril  and  down- 


FiG.  31S. — Neck  of  Horse,  after  Removal  of  Part  of  Panxicttlcs  asd  Trapezits. 
a,  a',  Ma^toiUo-humeraUs;  6.  anterior  superficial  pectoral  imigcie;  c,  cer\*ical  pannicultis;  d,  sterno-cephal- 
icils;  e,  omo-hyoideus;  /.  sterao-thyro-hyoideus;  {/,  trachea;  h,  h' ,  h",  teadons  of  splenitis,  mastoido-humeralis, 
and  trachelo-ma^toideus;  i,  trapezius  cenicalis:  t.supraspinatus;  /, anterior  deep  pectoral  muscle;  m,  rhomboideus 
cer\-icalis;  n,  serratus  cer\-icis;  o,  splenitis,  upper  and  lower  borders  of  which  are  indicated  by  dotted  lines;  p,  parotid 
gland;  <j,  parotido-auricularis  muscle;  r,  wing  of  atlas;  «.  spine  of  scapula;  J,  external  inaxillarj  vein;  3,  S, 
jugular  vein;  4.  carotid  artery;  5,  descending  branch  of  inferior  ceriical  arterj-;  S.  cephalic  vein;  7-;/,  ventral 
branches  of  second  to  seventh  cervical  nerves;  1£,  cutaneous  branch  of  second  cer\-ical  ner\e;  13,  cer\ical  branch 
of  facial  nen-e;  14.  terminal  branches  of  dorsal  dirisions  of  cervical  nenes;  15,  dorsal  branch  of  spinal  accessory 
ner\-e.     (After  EUenberger-Baum,  Top.  .\nat.  d.  Fferdes.) 


ward  with  the  vagus  in  a  fold  of  the  guttural  pouch,  separates  from  that  nerve, 
crosses  the  deep  face  of  the  submaxillary  gland  and  the  occipital  artery,  antl  divides 
in  the  recessus  atlantis  into  dorsal  and  ventral  branches. 

It  is  connected  by  anastomotic  branclies  n-ith  tlie  vagus  and  hypoglo.s.saI  nerves  and  the 
superior  cervical  ganglion  of  the  s^^npathetic,  and  contributes  a  branch  to  the  pharyngeal  plexus. 

The  dorsal  branch  (R.  dorsalis)  (Figs.  433,  517,  518)  receives  a  twig  from  the 
second  and  third  cervical  nerves  and  turns  around  the  atlantal  tendon  of  the  splenius 


692  NERVOUS  SYSTEM  OF  THE  HORSE 

under  cover  of  the  mastoido-humeralis.  It  then  passes  obhquely  through  the 
latter  muscle  and  continues  backward  on  the  splenius  and  the  cervical  part  of  the 
serratus,  inclines  upward  across  the  anterior  deep  pectoral  and  the  supraspinatus, 
and  enters  the  deep  face  of  the  trapezius,  in  which  it  ramifies. 

The  ventral  branch  (R.  ventralis)  (Fig.  436)  is  smaller.  It  enters  the  sterno- 
cephalicus  muscle  Ijchind  the  cervical  angle  of  the  parotid  gland. 

The  fiber.s  of  the  spinal  part  of  the  accessory  arise  from  the  ventro-lateral  cells  of  the  ventral 
gray  column  of  tlie  cord  as  far  back  as  the  fifth  cervical  segment.  The  fibers  of  the  medullary 
part  come  chiefly  from  the  nucleus  ambiguus  in  common  with  the  motor  fibers  of  the  vagus. 

THE  TWELFTH  OR  HYPOGLOSSAL  NERVE 
The  hypoglossal  nerve  (N.  hypoglossus)  is  jiurcly  motor  and  innervates  the 
muscles  of  the  tongue  (Fig.  437).  Its  root-fibers  arise  from  the  ventral  face  of  the 
medulla  in  linear  series  about  3  to  4  mm.  lateral  to  the  posterior  half  of  the  pyramid 
(Fig.  499).  The  filaments  converge  to  three  or  four  bundles  which  perforate  the 
dura  mater  and  unite  to  form  the  trunk.  The  latter  emerges  through  the  hypoglos- 
sal foramen  (Fig.  515)  and  runs  downward  and  backward  between  the  guttural 
pouch  and  the  capsule  of  the  atlanto-occipital  articulation  for  a  distance  of  a  little 
less  than  an  inch  (ca.  2  cm.).  It  then  passes  between  the  tenth  and  eleventh 
nerves,  turns  downward  and  forward,  crosses  the  external  face  of  the  external 
carotid  artery,  and  continues  over  the  pharynx  parallel  with  the  great  cornu  of 
the  hyoid  bone  and  behind  the  external  maxillary  artery.  It  then  crosses  beneath 
the  artery,  runs  forward  on  the  external  face  of  tlie  hyo-glossus  nmscle,  and  divides 
into  its  terminal  branches  (Rami  linguales).  The  smaller  branch  supplies  the 
stylo-glossus,  hyo-glossus,  and  lingualis.  The  larger  branch  ramifies  on  the  genio- 
glossus  and  supplies  the  remaining  muscles.  Anastomoses  occur  with  branches  of 
the  lingual  nerve. 

In  the  first  part  of  its  course  the  nerve  communicates  with  the  superior  cervical 
ganglion  and  with  the  ventral  branch  of  the  first  cervical  nerve,  and  gives  filaments 
to  the  pharyngeal  branch  of  the  vagus  and  the  pharyngeal  plexus. 

The  libers  of  the  nerve  arise  from  the  hypoglossal  nucleus,  an  elongated  group  of  large 
multipolar  cells  situated  chiefly  under  the  posterior  part  of  the  floor  of  the  fourth  ventricle  close 
to  the  median  plane.  The  two  nuclei  are  connected  by  commissural  fibers.  The  other  central 
connections  include:  (a)  communications  by  the  medial  longitudinal  fasciculus  with  the  nuclei 
of  termination  of  other  cranial  nerves;  (6)  cortico-nuclear  fibers  which  come  from  the  cortex 
by  way  of  the  internal  capsule  and  the  pyramids  and  go  largely  to  the  nucleus  of  the  opposite 
side;  (c)  fibers  which  join  the  dorsal  longitudinal  bundle  of  Schiltz,  a  tract  which  underlies  the 
floor  of  the  fourth  ventricle  and  is  traceable  forward  below  the  cerebral  aqueduct. 

The  Spinal  Nerves 

The  spinal  nerves  (Xcrvi  spinales)  are  arranged  in  pairs,  of  which  there  are 
usually  forty-two  in  the  horse.  They  are  designated  according  to  their  relations  to 
the  vertebral  column  as  cervical  (8),  thoracic  (18),  lumbar  (0),  sacral  (5),  and 
coccygeal  (5).  Each  nerve  is  connected  with  the  si^inal  cord  by  two  roots,  dorsal 
and  ventral  (Fig.  497). 

The  dorsal  (or  superior)  root  (Radix  dorsalis)  is  the  larger  of  the  two.  Its 
iiliers  (Fila  radicularia)  spread  out  in  fan  shape  and  join  the  cord  in  a  linear  series 
along  the  dorso-lateral  groove.  Laterallj'  the  fibers  converge  to  form  a  compact 
bundle,  on  which  is  a  gray  nodular  enlargement,  the  spinal  ganglion  (Ganglion 
spinale).  Beyond  the  ganglion  the  dorsal  root  joins  the  ventral  root  to  constitute 
the  nerve.  The  ganglia  are  external  to  the  dura  mater,  and  are  situated  in  the 
intervertebral  foramina,  except  in  the  case  of  the  sacral  and  coccygeal  nerves,  the 
ganglia  of  which  lie  within  the  vertebral  canal.  Those  of  the  coccygeal  nerves  are 
intradural. 


THE  SPINAL  NERVES 


C93 


The  ganglia  vary  greatly  in  size;  that  of  the  first  cervical  neri'e  is  scarcely  as  large  as  a  hemp- 
seed,  while  that  of  the  eighth  cervical  is  about  2  cm.  long  and  1  cm.  wide.  On  the  large  roots 
connected  with  the  cervical  and  lumbar  enlargement  of  the  cord  there  are  multiple  ganglia  of 
varying  sizes  interposed  in  the  course  of  the  root-lnmdle.s.  The  fibers  of  the  dorsal  roots  arise 
from  the  cells  of  the  spinal  ganglia;  each  cell  gives  off  a  fiber  which  enters  the  spinal  cord  and 
another  which  passes  into  the  nerve. 

The  ventral  (or  inferior)  root  (Radix  ventralis)  contains  fewer  fillers  than  the 
dorsal  root,  except  in  the  case  of  the  first  cervical  nerve.  It  arises  from  the  ventral 
surface  of  the  spinal  cord  (Fig.  495)  by  means  of  numerous  small  bundles  of 
fibers  which  do  not  form  a  linear  series  but  emerge  from  the  cord  over  an  area 
three  to  five  millimeters  in  width  (ventral  root  zone).  The  fibers  are  processes  of 
the  large  cells  of  the  ventral  gray  columns  of  the  spinal  cord.  There  is  no  gang- 
lion on  the  ventral  root. 

In  the  cer^^cal,  thoracic,  and  anterior  lumbar  regions  the  bundles  of  both  roots  pa.ss  through 
separate  openings  in  Hnear  series  in  the  dura  mater  before  uniting  into  a  root  proper.  Further 
back  the  bundles  of  each  root  unite  within  the  dura.  In  the  anterior  part  of  the  cervical  region 
and  in  the  thoracic  part  of  the  cord  there  are  intervals  of  varying  length  between  adjacent  roots, 
but  in  some  places  the  fibers  of  adjacent  roots  overlap  and  an  exchange  of  fibers  may  be  observed. 


Fig.  519. — Vertebral  Ca 


Conjugal  ligament 

:  S.4WING  OFF  THE  .\rCHES. 


Spinal  branch  of  inlercostal  artery 


Spinal  ganglion 

Dura  mater 

Lig.  (ienliculatum 

Dors':l  root  bundles 


Superior  common  ligament 


(.\fter  Schmaltz,  .\tlas  d.  .\nat.  d.  Pferdes.) 


Many  of  the  roots  are  directed  almost  straight  outward  or  incline  slightly  backward,  but  the  pos- 
terior lumbar,  sacral,  and  coccygeal  roots  and  nerves  run  backward  to  reach  the  foramina  through 
wliich  they  emerge.  The  distance  thus  to  be  tra\-ersed  increases  from  before  backward,  so  that 
these  nerves  form  a  tapering  sheaf  around  the  conus  meduUaris  anil  filum  terminale  in  the  last 
lumbar  vertebra  and  the  sacrum  which  is  known  as  the  Cauda  equina. 

The  size  of  the  spinal  nerves  varies  greatly.  The  largest  are  connected  with 
the  cervical  and  lumbar  enlargements. 

In  or  immediately  after  its  emergence  from  the  intervertebral  foramen  each 
spinal  nerve  gives  off  a  small  meningeal  or  recurrent  branch  (Ramus  meningeus). 
This  is  joined  by  a  bundle  of  fibers  from  the  ramus  communicans  and  enters  the 
vertebral  canal,  in  which  it  is  distributed.  Each  nerve  then  divides  into  two  pri- 
mary branches,  dorsal  and  ventral  (Ramus  dorsalis,  ventralis).  The  dorsal 
branches  are  smaller  than  the  ventral,  except  in  the  cervical  region.  They  are 
distributed  chiefly  to  the  muscles  and  skin  of  the  dorsal  part  of  the  body.  The 
ventral  branches  supply  in  general  the  muscles  and  skin  of  the  ventral  parts  of  the 
body,  including  the  limbs.  Each  nerve  or  its  ventral  branch  is  connected  with  an 
adjacent  ganglion  of  the  sympathetic  system  by  at  least  one  small  short  branch 
known  as  a  ramus  communicans.     Many  nerves  have  two  and  some  have  three 


694  NERVOUS  SYSTEM  OF  THE  HORSE 

such  rami.     A  norve  may  bo  connected  with  two  ganglia,  and  a  ganghon  may  be 
connected  with  two  nerves. 

The  dorsal  root  is  sensory  or  afferent,  i.  e..  it  conveys  impulses  to  the  central  system.  Its 
fibers  are  axones  of  the  cells  of  the  spinal  ganglion.  The  ventral  root  is  motor  or  efferent,  and 
conveys  impulses  toward  the  periphery.  Its  fibers  are  axones  of  the  large  cells  in  tlie  ventral 
gray  columns  of  the  spinal  cord.  The  common  trunk  or  nerve  formed  by  the  union  of  the  two 
roots  contains  both  kinds  of  fibers,  as  do  also  their  primary  divisions.  In  addition  to  thc.«!e  fibers, 
which  are  distributed  to  the  skeletal  muscles  and  the  skin,  the  spinal  nerves  contain  fibers  derived 
from  the  .sympathetic  .system  through  the  r.ami  communicantcs;  these  go  to  the  glands  and 
unstriped  muscle  ami  arc  tiesignated  secretory  and  vasomotor  fibers. 


THE  CERVICAL  NERVES 

The  cervical  nerves  (Xervi  cervicales)  (Figs.  431,  433,  518,  523)  number  eight 
pairs.  Of  these  the  first  emerges  through  the  interverteliral  foramen  of  the  atlas, 
the  second  through  that  of  the  axis,  and  the  eighth  between  the  last  cervical 
and  the  first  thoracic  vertebrie. 

The  dorsal  branches  are  distributed  to  the  dorso-lateral  muscles  and  skin  of 
the  neck.  They  divide  usually  into  inner  and  outer  branches.  The  internal 
branches  (Rami  mediales)  ruii  in  general  across  the  multifidus  and  the  lamellar  part 
of  the  ligamentum  nuchse  to  the  skin  of  the  upper  border  of  the  neck;  they  supply 
the  deep  lateral  muscles  and  the  skin.  The  external  Ijranches  (Rami  laterales)  are 
chiefly  muscular  in  their  distribution.  The  dorsal  branches  of  the  third  to  the 
sixth  nerves  are  connected  by  anastomotic  branches  to  form  the  dorsal  cervical 
plexus. 

The  ventral  branches  are  smaller  than  the  dorsal  ones — an  exception  to  the 
general  rule.  They  increase  in  size  from  first  to  last.  They  supply  in  general  the 
muscles  and  skin  over  the  lateral  and  ventral  aspect  of  the  vertebrae,  but  the  last 
three  enter  into  the  formation  of  the  brachial  plexus,  and  the  three  preceding  the 
last  give  off  the  roots  of  the  phrenic  nerve.  An  irregular  ventral  cervical  plexus  is 
formed  by  anastomoses  established  between  the  ventral  branches.  The  following 
special  features  may  be  noted: 

The  first  cervical  nerve  emerges  through  the  intervertebral  (antero-internal) 
foramen  of  the  atlas.  Its  dorsal  branch  (N.  occipitalis)  passes  upward  and  outward 
between  the  obliqui  capitis  and  the  recti  capitis  dorsales  and  supplies  branches  to 
these  muscles,  the  scutularis  and  posterior  auricular  muscles,  and  the  skin  of  the 
poll.  The  ventral  branch  descends  through  the  alar  (antero-external)  foramen  of 
the  atlas,  crosses  over  the  ventral  straight  nmscles  and  the  carotid  arterj'  under 
cover  of  the  parotid  gland,  and  divides  into  two  branches.  The  anterior  branch 
enters  the  omo-hyoideus  muscle.  The  posterior  branch  passes  downward  and 
backward  under  cover  of  that  muscle,  unites  with  a  branch  of  the  ventral  division 
of  the  second  cervical  nerve,  and  continues  its  course  on  the  ventro-lateral  surface 
of  the  trachea  to  enter  the  .sterno-thyro-hyoideus  behind  the  intermediate  tendon. 
In  the  recessus  atlantis  the  ventral  branch  is  connected  l)y  one  or  more  twigs  with 
the  superior  cervical  ganglion  of  the  sympathetic,  and  a  little  lower  with  the  hypo- 
glossal nerve.  It  also  sends  l)ranches  to  the  ventral  straight  muscles  of  the  head 
and  the  thyro-hyoideus.  Below  the  atlas  the  ventral  liranch  is  crossed  super- 
ficially by  the  spinal  accessory  nerve,  the  occipital  artery,  and  the  inferior  cerebral 
vein. 

The  second  cervical  nerve  is  larger  than  the  first.  It  emerges  from  the  verte- 
bral canal  through  the  intervertebral  foramen  of  the  anterior  part  of  the  arch  of  the 
axis.  Its  dorsal  branch  ascends  between  the  comph-xus  and  the  ligamentum 
nuchse  and  ramifies  in  the  skin  of  the  poll.  The  ventral  branch  gives  off  muscular 
branches  to  the  rectus  capitis  anterior  major,  anil  anastomotic  branches  to  the 
spinal  accessory  and  the  ventral  divisions  of  the  first  and  third  cervical  nerves; 


PHRENIC  NERVE  695 

one  of  these  crosses  over  the  earotiil  artery  and  concurs  in  the  formation  of  tiie  nerve 
to  the  sterno-thyro-hyoideus  mentioned  above.  The  ventral  branch  then  becomes 
superficial  by  passing  between  the  two  parts  of  the  mastoido-humeralis,  and  divides 
into  posterior  auricular  and  cutaneous  branches.  The  posterior  auricular  nerve 
inisses  upwartl  and  forward  on  the  parotid  gland  parallel  with  the  ])osterior  border 
of  the  parotido-auricuiaris  to  ramify  on  the  convex  face  of  the  external  ear.  Tlie 
cutaneous-  nerve  of  the  neck  (N.  cutaneus  colli)  crosses  the  mastoido-humeralis 
muscle  and  turns  backward  along  the  course  of  the  jugular  vein.  On  the  lower 
part  of  the  parotid  gland  it  is  connected  bj-  a  twig  with  the  cervical  cutaneous 
branch  of  the  facial  nerve.  It  gives  off  twngs  to  the  subcutaneous  muscles  and 
the  skin  of  the  parotid  and  laryngeal  regions  and  a  long  branch  which  passes  for- 
ward in  the  submaxillary  space. 

The  third  cervical  nerve  leaves  the  vertebral  canal  through  the  foramen  be- 
tween the  second  and  third  cervical  vertebrae.  Its  dorsal  branch  emerges  between 
two  bundles  of  the  intertransversalis  muscle  accompanied  l)y  a  liranch  of  the  verte- 
bral artery,  turns  upward  on  the  multifitlus,  and  divides  into  several  branches  which 
radiate  on  the  tleep  face  of  the  complexus.  It  gives  branches  to  these  muscles  and 
to  the  skin,  and  a  twig  which  joins  the  corresponding  branch  of  the  fourth  nerve. 
The  ventral  branch  emerges  through  the  intertransversalis  below  the  bundle  above 
which  the  dorsal  branch  appears.  It  gives  branches  to  the  trachelo-ma.stoideus, 
rectus  capitis  anterior  major,  longus  coUi,  splenius,  and  mastoido-humeralis.  It 
also  gives  off  a  large  cutaneous  nerve  which  passes  out  between  the  two  parts  of  the 
mastoido-humeralis  and  divides  into  several  divergent  branches. 

The  fourth  and  fifth  cervical  nerves  are  distributed  in  general  like  the 
third.  Their  dorsal  branches  are  united  by  anastomotic  t^xngs  with  each  other 
and  with  those  of  the  third  and  sixth  nerves  to  form  the  dorsal  cervical  plexus. 
The  ventral  branch  of  the  fifth  nerve  often  contributes  a  small  twig  to  the 
phrenic  nerve. 

The  sixth  cervical  nerve  has  a  smaller  dorsal  branch  than  the  fifth.  Its 
ventral  branch  is  larger  and  goes  in  part  to  the  brachial  plexus;  it  supplies  twigs 
to  the  intertransversales,  the  longus  colli,  the  mastoido-humeralis,  and  the  cervical 
parts  of  the  serratus  and  rhomboideus,  furnishes  a  root  of  the  phrenic  nerve,  and 
gives  off  several  considerable  subcutaneous  branches.  One  of  the  latter  ramifies 
on  the  thick  part  of  the  cervical  panniculus,  to  which  it  gives  branches;  another  and 
larger  branch  (X.  supraclavicularis)  sends  twigs  to  the  skin  over  the  shoulder  joint, 
and  descends  to  the  skin  over  the  superficial  pectoral  muscles  (Fig.  466). 

The  seventh  and  eighth  cervical  nerves  have  small  dorsal  branches,  which 
ascend  between  the  longissimus  and  inultifidus,  giving  twigs  to  these  muscles,  the 
spinalis  and  semispinalis,  the  rhomboideus,  and  the  skin.  Their  ventral  branches 
are  very  large  and  concur  in  the  formation  of  the  brachial  plexus;  that  of  the 
seventh  nerve  contributes  the  posterior  root  of  the  phrenic  nerve. 

Phrenic  Nerve 
The  phrenic  nerve  (X.  phrenicus)  (Figs.  428,  429,  433),  the  motor  nerve  to  the 
diaphragm,  is  formed  by  the  union  of  two  or  three  roots  which  cross  the  superficial 
face  of  the  scalenus  muscle  obliquely  downward  and  backward.  The  chief  roots 
come  from  the  ventral  branches  of  the  sixth  and  seventh  cervical  nerves.  The  root 
derived  from  the  fifth  nerve  is  small  and  inconstant.  The  root  from  the  seventh 
cervical  comes  by  way  of  the  brachial  plexus.  The  course  of  the  nerve  is  not  the 
same  on  both  sides.  On  the  right  side  the  nerve  enters  the  thorax  by  passing  be- 
tween the  brachial  artery  and  the  anterior  vena  cava.  It  then  courses  backward 
and  somewhat  downward  over  the  right  face  of  the  anterior  vena  cava,  crosses  the 
pericardium,  and  continues  along  the  posterior  vena  cava  to  the  diaphragm.  In  the 
latter  part  of  its  course  it  is  inclosed  in  a  special  fold  of  the  right  pleura  and  inclines 


696  NERVOUS  SYSTEM  OF  THE  HORSE 

gradually  to  the  ventral  face  of  the  vein.  On  the  left  side  the  nerve  enters  the 
thorax  between  the  left  brachial  and  inferior  cervical  arteries,  and  then  runs  its 
entire  course  in  the  mediastinum.  In  the  anterior  mediastinum  it  lies  along  the 
brachiocephalic  artery  ventral  to  the  left  vagus  and  cardiac  nerves,  and  crosses 
over  the  dorso-cervical  vein.  It  then  passes  over  the  upper  part  of  the  pericardium 
and  runs  backward  in  the  posterior  mediastinum  to  reach  the  tendinous  center  of 
the  diaphragm  considerably  to  the  left  of  the  median  plane.  Each  nerve  is  usually 
connected  near  its  origin  with  the  first  thoracic  ganglion  of  the  sympathetic  by  a 
ramus  communicans,  and  each  terminates  by  dividing  into  several  branches  which 
are  distributed  to  the  corresponding  part  of  the  diaphragm. 

The  Brachial  Plexus 

The  brachial  plejnis  (Plexus  brachialis)  (Fig.  433)  results  from  anastomoses 
estal:)lished  Ix'tween  the  ventral  branches  of  the  la-st  three  cervical  and  first  two 
thoracic  nerves.  It  appears  as  a  thick,  wide  band  between  the  two  parts  of  the 
scalenus  muscle,  and  is  covered  by  the  anterior  deep  pectoral  and  subscapularis 
muscles.  The  largest  root  of  the  plexus  is  derived  from  the  first  thoracic  nerve, 
while  the  root  supplied  \>y  the  sixth  cervical  nerve  is  quite  small.  Each  of  the 
three  chief  roots,  /.  e.,  those  from  the  last  two  cervical  and  the  first  thoracic  nerve, 
is  connected  with  the  sympathetic  by  a  ramus  communicans. 

The  branches  emanating  from  the  plexus  go  for  the  most  part  to  the  thoracic 
limb,  but  some  are  distributed  on  the  chest-wall.  The  names  of  the  branches,  and 
their  arrangement  so  far  as  they  can  be  conveniently  examined  before  removal  of 
the  fore  limb,  are  as  follows:' 

1.  The  large  suprascapular  nerve  (N.  suprascapularis)  turns  outward  and  for- 
ward and  disappears  between  the  su]iras])inatus  and  subscapularis. 

2.  The  much  smaller  subscapular  nerves  (Nn.  subscapulares),  usually  two 
primary  trunks,  arise  close  behind  the  suprascapular,  run  backward  a  short  dis- 
tance, and  divide  into  several  branches  which  enter  the  lower  third  of  the  subscap- 
ularis. 

3.  The  anterior  thoracic  or  pectoral  nerves  (N.  pectorales  craniales),  three  or 
four  in  numt)cr,  arise  from  the  anterior  jiart  of  the  plexus  and  from  the  loop  formed 
by  the  musculo-cutaneous  and  median  nerves.  One  enters  the  anterior  deep 
pectoral  muscle.  Another  passes  out  between  the  divisions  of  the  deep  pectoral  to 
supply  the  superficial  pectoral,  giving  a  twig  u.sually  to  the  posterior  deep  muscle. 
The  latter  receives  one  or  two  other  nerves. 

4.  The  musculo-cutaneous  nerve  (N.  musculocutaneus)  arises  from  the  an- 
terior part  of  the  ]ilexus  and  passes  over  the  outer  face  of  the  brachial  artery,  below 
which  it  is  connected  by  a  large  l:>ut  short  branch  with  the  median  nerve,  thus  form- 
ing a  loop  in  which  the  artery  lies.  One  or  two  branches  to  the  pectoral  muscles 
are  given  off  from  the  nerve  or  the  loop. 

5.  The  median  nerve  (N.  medianus)  is  usually  the  largest  branch  of  the  bra- 
chial plexus.  It  lies  at  first  above  the  brachial  artery,  then  passes  between  the 
arterj'  and  vein  to  reach  the  anterior  border  of  the  former.  It  is  easily  recognized 
by  its  large  size  and  the  loop  which  it  forms  with  the  musculo-cutaneous  nerve. 

6.  The  ulnar  nerve  (N.  ulnaris)  arises  with  the  median  by  a  short  common 
trunk.  It  descends  liehind  the  brachial  artery  and  is  accompanied  a  short  distance 
by  the  radial  nerve. 

7  The  radial  nerve  (X.  radialis)  arises  from  the  posterior  part  of  the  plexus 
and  is  sometimes  the  largest  branch.  It  descends  behind  the  ulnar  nerve  over 
the  origin  of  the  subscapular  artery  and  the  lower  part  of  the  teres  major,  and 

'  In  orflor  to  examine  the  plexus  and  the  oriRins  of  its  chief  brandies  eonveniently  and  with 
as  Httle  disturbance  of  relation  as  possil)lo,  the  suliject  should  be  suspended  in  imitation  of  the 
natural  position  and  tlie  fore  limb  abducted  as  much  as  is  necessary. 


SUPRASCAPILAR    NERVE — AXILLARY   NERVE  697 

dips  into  the  interstice  between  that   muscle  and  the  long  and  internal  heads  of 
the  triceps. 

8.  The  axillary  or  circximflex  nerve  (X.  axillaris)  arises  behind  the  musculo- 
cutaneous. It  passes  downward  and  backward  on  the  inner  face  of  the  sub.scapu- 
laris  and  disajijiears  between  that  muscle  and  the  subscapular  artery. 

9.  The  long  thoracic  nerve  (X.  thoracalis  longus)  is  wide  and  thin.  It  passes 
backward  across  the  surface  of  the  serratus  magnus.  to  which  it  is  di.stributed. 
The  branches  which  enter  the  muscle  are  given  off  both  upward  and  dowiiward  in 
fairly  regular  fashion. 

10.  The  thoraco-dorsal  nerve  (X.  thoracodorsalis)  passes  upward  and  back- 
ward across  the  subscapularis  nuisclc  to  ramify  in  the  teres  major  and  tlie  latissimus 
(.lorsi. 

11.  The  external  (or  subcutaneous)  thoracic  nerve  arises  by  a  common  trunk 
with  the  ulnar.  It  runs  liackward  and  downward  across  the  inner  face  of  the  tensor 
fasciae  antibrachii,  communicates  with  the  anterior  pectoral  branches,  and  gives 
twigs  to  the  deep  pectoral  muscle.  It  then  runs  backward  in  company  with  the 
external  thoracic  or  "spur"  vein,  gives  branches  to  the  latissimus  dor.si  and  the 
deep  pectoral,  and  ramifies  in  the  panniculus  and  the  skin  of  the  abdominal  wall. 
It  communicates  with  perforating  branches  of  the  intercostal  nerves.  A  branch 
from  it,  accompanied  by  a  large  perforating  intercostal  branch,  winds  around 
the  lower  border  of  the  latissimus  dorsi  and  ramifies  in  the  panniculus  on  the  outer 
surface  of  the  arm. 

The  term  posterior  thoracic  or  pectoral  nerves  CSn.  pectorales  caudales)  may  be  used  to 
include  S,  9,  and  10. 

Suprascapular  Nerve 

The  suprascapular  (Fig.  441)  is  a  large  nerve  derived  chiefly,  if  not  exclusively, 

from  the  si.xth  and  seventh  cervical  components  of  the  brachial  plexus.     It  passes 

lietween  the  supraspinatus  and  subscapularis  muscles  and  turns  around  the  distal 

fourth  of  the  anterior  border  of  the  scapula  to  reach  the  supraspinous  fcssa.     It 

gives  branches  to  the  supraspinatus  and  continues  backward  and  upward  into  the 

infraspinous  fossa,  where  it  supplies  the  infraspinatus,  deltoid,  and   teres  minor 

muscles. 

The  direct  relation  of  this  nerve  to  the  scapula  renders  it  liable  to  injury,  the  result  of  which 
may  be  paralysis  and  atrophy  of  the  muscles  supphed  by  it. 

HUSCULO-CUTANEOUS  NERVE 

The  musculo-cutaneous  nerve  (Fig.  441)  arises  close  behind  the  suprascapular, 
and  is  derived  chiefly  from  the  part  of  the  brachial  plexus  which  is  supplied  by  the 
seventh  and  eighth  cervical  nerves.  It  descends  across  the  outer  surface  of  the 
brachial  artery,  below  which  a  great  part  of  the  nerve  unites  with  the  median  to 
form  the  loop  previously  mentioned.  It  gives  off  a  liranch  which  enters  the  upper 
part  of  the  belly  of  the  coraco-brachialis,  passes  downward  and  forward  between  the 
two  parts  of  that  muscle  or  between  the  muscle  and  the  bone,  and  divides  into 
branches  which  enter  the  biceps  brachii.  It  contributes  one  of  the  nerves  to  the 
pectoral  muscles.  In  some  cases  this  nerve  sends  a  branch  to  join  the  cutaneous 
branch  of  the  median. 

Axillary  Nerve 

The  axillary  nerve  (Figs.  441,  520),  also  termed  the  circumflex,  derives  its 
fibers  from  the  eighth  cervical  and  first  thoracic  roots  of  the  brachial  plexus.  It 
runs  downward  and  backward  across  the  lower  part  of  the  subscapularis  and  dips 
in  between  that  muscle  and  the  subscapular  artery  at  the  level  of  the  shoulder  joint. 
Continuing  outward  in  the  interval  between  the  teres  minor  and  the  long  and  ex- 
ternal heads  of  the  triceps,  it  reaches  the  deep  face  of  the  deltoid  and  divides  into 


G98 


NERVOUS  SYSTEM  OF  THE  HORSE 


several  divergent  branches.     The  muscular  branches  supplj-  the  teres  major,  cap- 
sularis,  teres  minor,  infraspinatus,  deltoid,  and  niastoido-humeralis.     The  cutane- 
ous branch  (X.  cutaneus  brachii  lateralis)  runs  downward  and  a    little   forward 
across  the  external  head  of  the  triceps  and  ramifies  on  the 
fascia  on  the  front  of  the  forearm  and  on  the  superficial 
pectoral  muscle. 

Radial  Nerve 
The  radial  nerve  (Figs.  441,  443,  520),  also  called 
the  musculo-spira!,  is  sometimes  the  largest  branch  of 
the  brachial  plexus.  Its  fibers  are  derived  from  the 
seventh  and  eighth  cervical  and  first  thoracic  roots  of 
the  plexus.  It  passes  downward  and  backward  over 
the  inner  surface  of  the  subscapular  arterj-  and  the  teres 
major.  In  this  part  of  its  course  it  is  related  in  front  to 
the  ulnar  nerve,  which  separates  it  from  the  brachial 
vein.  It  detaches  a  branch  to  the  tensor  fasciae  antibrachii, 
passes  outward  in  the  interval  between  the  teres  major  and 
the  long  and  internal  heads  of  the  triceps,  and  gains  the 
musculo-spiral  groove  of  the  humerus.  Accompanied  by  a 
branch  of  the  deep  brachial  artery,  it  runs  obliquely  down- 
ward and  outwartl  in  the  groove,  covered  externally  by  the 
external  head  of  the  triceps  and  the  extensor  carpi  radialis, 
and  reaches  the  flexion  surface  of  the  elbow  joint.  In  this 
part  of  its  course  it  gives  off  a  muscular  branch  which 
ramifies  in  the  long  and  external  heads  of  the  triceps  and  in 
the  anconeus,  and  a  cutaneous  nerve  (N.  cutaneus  anti- 
brachii dorsalis);  brandies  of  the  latter  emerge  below  or 
through  the  external  head  of  the  triceps  and  ramify  on  the 
dorso-lateral  surface  of  the  forearm.  At  the  elbow  the  nerve 
descends  with  the  anterior  radial  vessels  on  the  joint  capsule 
between  the  brachialis  and  extensor  carpi  radialis,  and  sup- 
plies branches  to  the  extensor  carpi  and  the  common  or 
anterior  extensor  of  the  digit  and  (inconstantly)  to  the 
brachialis.  Below  the  elbow  joint  the  nerve  detaches  a 
large  branch  which  passes  back  to  the  flexor  carpi  ex- 
ternus,  and  terminates  by  small  branches  which  descend 
on  the  radius  to  enter  the  radial  and  ulnar  heads  of  the 
common  extensor,  the  lateral  extensor,  and  the  oblique 
extensor  of  the  carpus.  Thus  the  radial  nerve  innervates 
the  extensors  of  the  elbow,  carpal  and  digital  joints,  and 
supplies  also  the  flexor  carpi  externus.' 


Fig.      520.  —  Cit 

Nf.rves  of  Right 
Fore  Limb  op 
Hor.se,  External 
Face. 

a.  Cutaneous  branch 
of  axillary  nerve:  b,  cu- 
taneous branches  of  radial 
nerve;  c,  posterior  cutane- 
ous branch  of  ulnar  nerve; 
fl,  cutaneous  branch  of  me- 
dian nerve;  e,  superficial 
branch  of  ulnar  nerve;  /, 
external  metacarpal  nerve; 
ff,  anastomotic  branch  con- 
necting internal  and  exter- 
nal metacarpal  nerves;  1, 
external  head  of  triceps;  2, 
extensor  carpi  radialis;  3, 
anterior  extensor;  .(,  flexor 
carpi  extertms.  C.\ftcr  El- 
lenberger,  in  Leisering's 
Atlaa.) 


Ulnar  Nerve 

The  ulnar  nerve  (Figs.  441,  442,  443,  520)  arises  with 

the  median  from  the  thoracic  components  of  the  brachial 

plexus.      It    descends    between    the    brachial    artery    and 

vein,   accompanied    for    a    short    distance   by    the    radial 

nerve.     It   then   crosses    the   vein    and    continues    behind 

the  latter  along  the  anterior  border  of  the  tensor  fasciae 

antibrachii    and   dips    under   that    muscle   near   the   elbow.      Here   it  is   joined 

by  the  ulnar  vessels  and  passes  downward  and  backward  over  the   internal 

'  Morphologically  the  last-named  muscle  belongs  to   the  extensor  group.     In  man  and  in 
the  dog  and  many  other  animals  it  is  an  extensor  in  function. 


MEDIAN  NERVE 


699 


ppicondyle  of  the  humenis.  In  the  fort-arm  it  crosses  obliquely  the  deep  faee  of  the 
ulnar  head  of  the  flexor  carpi  ineilius  and  descends  under  the  deep  fascia  with  the 
vessels,  at  first  on  the  ulnar  head  of  the  perforans,  and  then  between  the  midtUe  and 
external  flexors  of  the  carpus.  Near  the  level  of  the  accessory  carpal  bone  it  divides 
into  two  terminal  branches,  su])erficial  and  deep.  It  gives  off  two  i)rinci]ial  col- 
lateral branches.  The  cutaneous  branch  (Ramus  cutaneus  palnuiris)  is  detached 
just  before  the  nerve  passes  under  the  tensor  fasciae  antibrachii;  it  runs  downward 
and  backward  on  that  muscle  under  cover  of  the  posterior  superficial  pectoral, 
becomes  superficial  below  the  elbow  and  ramifies  on  the  posterior  surface  and  both 
sides  of  the  forearm.  The  muscular  branch  is  given  off  at  the  elbow  joint  and 
divides  to  supply  the  flexors  of  the  digit  and  the  middle  flexor  of  the  carpus.     Of 


Jij.li  uxor  carpi  rudiulis 


Inlenntiscular  septum 


Anlcrior  extensor  of  digit 


Intermuscular  septum 

Lateral  extensor  of  dii/it 
Iniermusndar  septum 


Flexor  carpi  externus 
Flexor  perforans. 
{humeral  head) 


Flexor  perforatum 
Flexor  perforans  {ulnar  head) 


Ulnar  rein      j  Ulnar  nerve 
Ulnar  artery 

21. — Cross-section  of  Forearm  of  Horse  about  Three  ] 
The  rleep  fa.scia  is  flesignateil  by  re^l  line.     .V,  .1    V , 


Accessory  cephalic  vein 

Vein 

Cephalic  vein 
Intiriinl  lateral  ligament 
of  elbow 

Median   nerre 
Posterior  radial  reins 

Puslerior  radial  artery 

Flexor  carpi  intemus 


Fl'xor  carpi  medius 


I.)   BELOW  1 

essels  and  i 


:  Elbow  Joint. 


the  two  terminals,  the  superficial  branch  (Ramus  superficialis)  emerges  between  the 
tendons  of  insertion  of  the  external  and  middle  flexors  of  the  carpus  and  ramifies 
on  the  dorso-lateral  aspect  of  the  carpus  and  metacarpus.  The  deep  branch  (Ramus 
profundus),  after  a  very  short  course,  unites  under  cover  of  the  tendon  of  the  flexor 
carpi  medius  with  the  outer  branch  of  the  median  nerve  to  form  the  external  meta- 
carpal or  volar  nerve. 

Median  Nerve 

The  median  nerve  (Figs.  441,  442,  447,  520,  521)  derives  its  fibers  chiefly  from 

the  first  thoracic  root  of  the  brachial  plexus.      It  is  usually  the  largest  branch  and 

it  accompanies  the  chief  arterial  trunks  to  the  distal  part  of  the  limb.    It  descends 

over  the  inner  face  of  the  brachial  artery,  which  it  crosses  obliquely,  and  continues 


700 


NERVOUS  SYSTEM  OF  THE  HORSE 


down  the  arm  in  front  of  the  artery.  Near  its  origin  it  is  joined  by  a  large  branch 
with  the  musculo-cutaneous  nerve,  thus  forming  a  loop  in  which  the  artery  appears 
to  be  suspended.  Near  the  elbow  it  crosses  obliquely  over  the  artery  (posterior 
radial)  and  lies  behind  it  on  the  internal  lateral  ligament.  Below  the  joint  it 
again  crosses  the  artery  and  lies  behind  the  radius  and  the  lower  part  of  the  long 
int(>rnal  lateral  ligament. 

.\t  the  elbow  the  nerve  is  covered  by  the  posterior  superficial  pectoral  muscle  and  is  crossed 
by  the  large  oblique  connection  between  the  cephalic  and  Ijrachial  veins.  The  ^■arial3le  and  often 
piexiform  venous  arrangement  renders  approach  to  the  nerve  here  undesirable.     It  can  be  reached 


hdcrnnl  mdacarpal  vein 

MdaciiriHil  or  rolar  nerve 

Digital  artery 


Dorsal  or  anterior  digital  branch 
Volar  or  posterior  digital  branch 


Distal  end  of  cxtcrned  small  meta- 
carpal bone 

Large  metacarpal  hone 
Suspensory  ligament 

Superficial  flexor  tendon 

Posterior  annular  ligament  of 
fetlock 


Exlensiir  branch  of  suspensory 

lii/ainent 

Olilii/ue  or  middle  inferior 

scxdnidiilean  lig. 

I  'ular  lig,  of  paslem  joint 

Proximal  annular  lig.  of  digit 

Deep  flexor  tendon 
Distal  annular  lig.  of  digit 


2.— Dissection  or  Dibta 

.  Part  ui-    Ku. 

IT     Im.KK 

.JMi.    >,K    Ho 

rtil;igc;    2,  .i,  4.  ligaments 

rom  first  phala 

nx  to  thin 

sesamoi.l,  1 

(.\fte 

Schmaltz,  .\tla 

s  d,  Anat. 

d.  Pferdes.) 

ulli  of   heel,  and  la 


best  liy  an  incision  just  l)eliinil  the  lower  part  of  the  long  internal  lateral  ligament:  here  the  nerve 
lies  umlcr  the  deep  fascia  in  the  furrow  between  the  radius  anil  the  anterior  border  of  the  flexor 
carpi  internus,  overlapped  by  the  latter.  In  some  cases  the  nerve  retains  its  position  in  front  of 
the  artery  at  the  elbow,  apd  in  others  it  crosses  the  deep  face  of  the  artery. 

Passing  beneath  the  internal  flexor  of  the  carpus,  the  nerve  continues  downward 
in  the  forearm  with  the  posterior  radial  vessels,  and  divides  at  a  variable  distance 
above  the  carpus  into  two  branches;  these  are  the  internal  volar  or  metacarpal 
nerve  and  the  branch  which  unites  with  the  ulnar  to  form  the  corresponiling 
external  nerve. 

At  the  proximal  part  of  the  forearm  tlic  nerve  nms  almost  straiglit  downward  along  the 
posterior  border  of  tlie  long  internal  lateral  ligament,  while  the  artery  here  inclines  somewhat 
backward.  Thus  the  nerve  is  superficial  to  the  artery  for  a  short  distance,  then  lies  in  front  of 
the  latter  to  about  the  middle  of  the  region,  where  it  inclines  a  little  backward  and  arrives  at  the 


MEDIAN  NERVE  701 

interval  between  the  internal  and  mifliile  flexors  of  the  carpus.     The  division  may  occur  about  the 
middle  of  the  region,  but  commonly  takes  place  in  the  distal  third  or  fourth. 

The  collateral  branches  are  as  follows: 

1.  The  musculo-cutaneous  branch  is  in  reality  the  continuation  of  the  nerve  of 
that  name.  It  is  given  off  about  the  niicUUe  of  the  arm,  passes  beneath  the  lower 
liart  of  the  biceps,  and  divides  into  muscular  and  cutaneous  branches.  The  mus- 
cular branch  enters  the  lirachialis.  The  cutaneous  branch  emerges  between  the 
mastoido-humeralis  and  the  biceps  and  divides  into  two  branches;  these  descend 
on  the  fascia  of  the  forearm  with  the  cephalic  vein  and  its  accessory,  and  ramify 
on  the  front  and  inner  face  of  the  forearm,  carpus,  and  metacarpus. 

2.  Muscular  branches  to  the  internal  flexor  of  the  carpus  and  the  flexors  of 
the  digit  are  given  off  just  as  the  nerve  jxisses  under  the  first  named  muscle. 

3.  The  very  small  interosseous  nerve  passes  through  the  interosseous  space 
and  is  distributed  chiefly  to  the  periosteum,  but  in  some  cases  twigs  maj'  go  to  the 
extensor  muscles. 

The  metacarpal  or  volar  nerves,'  internal  and  external,  are  the  continuations 
of  the  median  and  ulnar  nerves  in  the  distal  part  of  the  limb. 

The  internal  metacarpal  or  volar  nerve  (X.  volaris  medialis)  arises  as  the  inner 
terminal  branch  of  the  median  nerve  at  a  variable  distance  above  the  carpus  (Fig. 
442).  It  descends  through  the  carpal  canal  along  the  inner  border  of  the  super- 
ficial flexor  tendon,  and  lies  at  first  in  front  of  the  large  metacarpal  or  common 
digital  artery.  It  then  passes  behind  the  artery  to  the  distal  third  of  the  metacar- 
pus, where  it  lies  behind  the  vein,  the  artery  here  becoming  deeper  in  position.  In 
addition  to  cutaneous  twigs,  the  nerve  gives  off  about  the  middle  of  the  metacar- 
pus a  considerable  anastomotic  branch  which  winds  obliquely  downward  and 
outward  over  the  flexor  tendons  and  joins  the  external  nerve  at  the  lower  third 
of  the  metacarpus  (Fig.  447).  Near  the  fetlock  the  nerve  divides  into  two  digital 
branches. 

1.  The  dorsal  or  anterior  digital  branch  (Ramus  dorsalis)  descends  at  first 
between  the  digital  artery  and  vein,  then  crosses  over  the  vein  and  ramifies  in  the 
skin  and  the  matrix  of  the  hocjf  on  the  dorsal  (anterior)  face  of  the  digit. 

2.  The  volar  or  posterior  digital  branch  (Ramus  volaris)  is  the  direct  continua- 
tion of  the  tnmk.  It  tlescends  liehind  the  digital  artery,  which  it  accompanies  in 
its  ramification.  A  middle  digital  branch  is  sometimes  described  as  descending 
behind  the  vein.  In  some  cases  this  branch  is  distinct,  but  usually  there  are  instead 
several  small  twigs  derived  from  the  posterior  branch,  which  cress  very  obliquely 
over  the  artery  and  anastomose  in  a  variable  manner  with  each  other  and  with  the 
anterior  branch. 

The  external  metacarpal  or  volar  nerve  (X.  volaris  lateralis)  is  formed  by  the 
union  of  the  external  terminal  branch  of  the  median  with  the  deep  branch  of  the 
ulnar  nerve  (Fig.  442).  It  descends  with  the  internal  volar  or  small  metacarpal 
artery  in  the  texture  of  the  posterior  annular  ligament  of  the  carpus.  In  the 
metacarpus  it  descends  along  the  outer  border  of  the  deep  flexor  tendon  behind 
the  external  metacarpal  vein,  and  is  accompanied  l^y  a  small  artery  from  the  volar 
subcarpal  arch.  Toward  the  distal  end  of  the  metacarpus  it  is  joined  by  the 
oblique  laranch  from  the  internal  nerve,  and  beyond  this  is  arranged  like  the  lat- 
ter. Below  the  carpus  it  detaches  a  deep  branch  to  the  suspensory  ligament  and 
the  interossei,  and  also  supplies  twigs  to  the  skin. 

Anastomoses  are  established  between  the  digital  branches,  and  the  areas  innervated  by  them 
are  not  well  defined,  but  really  overlap  each  other.  In  certain  diseased  conditions,  however, 
in  which  the  lesions  are  confined  to  the  volar  structures,  relief  from  pain  may  be  afforded  by 
section  of  the  volar  branches  only. 

'  In  veterinary  works  these  arc  frequently  termed  plantar  nerves,  which  is  an  unfortunate 
misnomer.  The  writer  inclines  to  the  use  of  tlie  old  term  metacarpal  or  common  digital  to  desig- 
nate the  nerves  as  far  as  their  divisions,  and  the  term  digital  beyond  this. 


702  NERVOUS  SYSTEM  OF  THE  HORSE 

THE  THORACIC  NERVES 

The  thoracic  nerves  (Xn.  thorucalos)  number  eighteen  on  either  side  in  the 
horse.  They  are  designated  numerically  according  to  the  vertebrae  behind  which 
they  emerge.  Most  of  them  are  arranged  in  a  very  similar  manner  and  therefore 
tlo  not  require  separate  description.  Each  divides  into  a  dorsal  and  a  ventral 
branch,  the  latter  being  the  larger. 

The  dorsal  branches  (Rami  dorsales)  emerge  behind  the  levatores  costarum 
and  divide  into  internal  and  external  branches.  The  internal  branches  ascend  on 
the  multifidus  and  supply  the  dorsal  spinal  muscles.  The  external  branches  run 
outward  under  the  longissimus  and  emerge  between  that  muscle  and  the  trans- 
versalis  costarum;  after  giving  twigs  to  these  muscles  they  pass  through  the 
latissimus  dorsi  and  the  lumbo-dorsal  fascia  and  ramify  as  dorsal  cutaneous  nerves 
under  the  skin  of  the  back  (Fig.  523).  In  the  region  of  the  withers  the}'  give 
branches  to  the  serratus  anticus  and  rhomboideus,  and  their  cutaneous  terminals 
pass  through  these  muscles  and  the  dorso-scapular  ligament  to  supply  the  skin 
over  the  ligamentum  nucha>  and  the  scapular  cartilage. 

The  ventral  branches  or  intercostal  nerves  (Nn.  intercostales)  are  mucli  larger 
than  the  preceding,  and  are  conne<'ted  with  the  sympathetic  by  rami  communi- 
cantes.  The  first  goes  almost  entirelj'  to  the  Israchial  plexus,  but  sends  a  fine  branch 
downward  in  the  first  intercostal  space  which  is  expended  in  the  muscle  there  with- 
out reaching  the  lower  end  of  the  space.  The  second  ventral  branch  furnishes  a 
considerable  root  to  the  brachial  plexus,  but  its  intercostal  continuation  is  typical. 
The  intercostal  nerves  (Fig.  184)  descend  in  the  intercostal  spaces  with  the  vessels  of 
like  name,  at  first  between  the  intercostal  muscles,  and  lower  down  chiefly  between 
the  pleura  and  the  internal  intercostal  muscle.  In  the  anterior  spaces  the  artery  lies 
along  the  posterior  border  of  the  rib,  with  the  nerve  in  front  of  it;  further  back  the 
nerve  lies  behind  the  border  of  the  ril),  with  the  artery  in  front  of  it.  They  supply 
the  intercostal  muscles,  give  off  lateral  perforating  branches,  and  terminate  in  the 
following  manner:  The  second  to  the  sixth  inclusive  emerge  through  the  spaces 
between  the  costal  cartilages  and  concur  in  supph'ing  the  pectoral  muscles.  The 
second  to  the  eighth  give  branches  to  the  transversus  thoracis.  The  succeeding 
ones  give  branches  to  the  diaphragm,  pass  between  the  transverse  and  internal 
oblique  muscles,  give  twigs  to  these,  and  end  in  the  rectus  abdominis.  There  are 
three  series  of  cutaneous  nerves  given  off  by  the  intercostal  nerves.  The  upper 
nerves  emerge  through  the  serratus  magnus  and  the  external  intercostals  about 
parallel  with  the  digitations  of  the  external  oblique.  The  middle  set  perforate  the 
origin  of  the  latter  muscle.  The  lower  ones  appear  through  the  abdominal  tunic. 
They  supply  branches  to  the  abdominal  muscles,  the  panniculus,  and  the  skin. 
Some  of  the  anterior  ones  anastomose  with  the  posterior  thoracic  branches  of  the 
brachial  plexus.  The  posterior  three  supply  in  part  the  skin  of  the  flank.  The 
ventral  branch  of  the  last  thoracic  nerve  runs  outward  behind  the  la.st  rib  across 
the  dorsal  surface  of  the  psoas  major  and  divides  into  superficial  and  deep  branches. 
The  superficial  branch  passes  between  the  obliquus  internus  and  transversus  ab- 
dominis, perforates  the  obliquus  externus,  and  ramifies  under  the  skin  of  the  flank 
(Fig.  525).  The  deep  branch  descends  on  the  inner  face  of  the  internal  oblique 
to  the  rectus  abdominis,  in  which  it  ends. 


THE  LUMBAR  NERVES 
There  are  six  pairs  of  lumbar  nerves  (Xn.  lumbales)  in  the  horse,  the  last  of 
which  emerge  between  the  last  lumbar  vertebra  and  the  sacrum.     The  anterior  two 
or  three  are  about  the  same  size  as  the  thoracic  nerves,  but  the  others  are  much 
larger. 


fe  H  s 


703 


704 


NERVOUS  SYSTEM  OF  THE  HORSE 


Their  dorsal  branches  are  small  in  comparison  with  the  ventral  ones.  They 
are  distrilxitcd  to  the  muscles  and  skin  of  the  loins  and  croup  in  a  fashion  similar 
to  those  of  the  thoracic  nerves. 

The  ventral  branches  are  connected  with  the  sympathetic  by  small  rami 
communicautes,  anil  give  branches  to  the  sublumbar  muscles.  Those  of  the  first 
two  nerves  are  arranged  in  a  manner  analogous  to  the  corresponding  brancli  of  the 
last  thoracic  nerve. 

The  ventral  branch  of  the  first  lumbar  nerve  is  termed  the  ilio-hypogastric 
nerve  (N.  iliohypogastricus).  It  passes  outward  between  the  cjuadratus  lum- 
borum  and  the  psoas  major,  and  divides  at  the  outer  border  of  the  latter  into  an 
anterior  or  superficial  and  a  posterior  or  deep  branch.  The  anterior  or  superficial 
branch  passes  over  the  upper  edge  of  the  internal  oblique,  descends  between  that 
muscle  antl  the  external  oblique,  perforates  the  latter,  and  runs  downward  and  back- 
ward and  ramifies  under  the  skin  of  the  posterior  part  of  the  flank  and  the  outer 
surface  of  the  thigh.  It  gives  branches  to  the  transversus  and  obliquus  externus 
abdominis.     The  posterior  or  deep  branch  is  smaller;  it  runs  downward  and  back- 


Crura  of  ti'mphragm 

Diaphragm 
Last  intercostal 
ne 

Ilio-hypngnxtric 
nerve  - 
Ilin-inguinal  nerve- 
Exlernal  spermatic 
nerve 
External  cutaneous^     ,// 
nerve 

Sympathetic 
trunks 

Insertion  of  quad- 
ratus  lumhorum' 

Anterior  part  of  j^ 
lumbosacral  plexus  [Z 

Obturator  nerve 
Femoral  nerve 


Splanchnic  nerve 
Last  intercostal  arteries 
First  lumbar  arteries 


Attachments  of  psoas  major 
—  Body  of  vertebra 

External  spermatic  nerve 
Trunk  of  lumbar  arteries 


I'Es  OF  Horse,  Ven' 


Sixth  lumbar  artery 


Ventral  sacro-iliac 
ligament 


(After  Schmaltz,  .\tlas  d.  .\nat.  d.  Pferdes.) 


ward  beneath  the  pcritoneimi  to  the  outer  ])order  of  the  rectus  abdominis,  gives 
branches  to  the  internal  oblique,  and  terminates  in  the  rectus  abdominis. 

The  ventral  l:(ranch  of  the  second  lumbar  nerve  is  comiected  by  an  anastomotic 
branch  with  that  of  the  third  nerve.  It  gives  off  a  large  branch  to  the  psoas  muscle 
and  an  inguinal  branch,  and  is  continued  as  the  ilio-inguinal  nerve.  The  inguinal 
branch  (N.  spermaticus  externus)  runs  backward  in  the  substance  of  the  psoas 
minor,  emerges  a  short  distance  in  front  of  the  circumflex  iliac  vessels,  and  runs 
backward  and  downward  under  the  peritoneum  to  the  internal  inguinal  ring.  It 
gives  branches  to  the  internal  oblique  muscle  and  descends  in  the  inguinal  <'anal 
along  the  outer  border  of  the  cremaster  (to  which  it  detaches  filaments)  and  ends 
suhcutaneously  in  the  scrotum  and  prepuce  in  the  male,  the  mammary  gland  in  tlie 
female.  The  ilio-inguinal  nerve  (N.  ilioinguinalis)  may  be  regarded  as  the  con- 
tinuation of  the  ventral  branch.  It  runs  ]iarall('l  with  tlie  iho-hypogastric  nerve 
and  has  a  similar  arrangement.  Its  anterior  or  superficial  branch  perforates  the 
external  oblique  muscle  a  little  in  front  of  the  point  of  the  hip,  runs  downward  on 
the  front  of  the  thigh  and  the  outer  surface  of  the  stifle,  and  gives  off  cutaneous 
branches.     The  posterior  or  deep  branch  runs  behind  and  parallel  with  that  of  the 


LUMBO-SACRAL  PLEXUS 


705 


ilio-hypogastricus,  detaches  branches  to  the  internal  obhciue  muscle,  and  descends 
the  inguinal  canal  with  the  inguinal  l)ranch,  to  be  distributed  to  the  external  genital 
organs  and  the  surrounding  skin  in  the  inguinal  region. 

The  ventral  branch  of  the  third  lumbar  nerve  is  connected  Ijy  a  small  anasto- 
motic branch  with  the  second  nerve  and  furnishes  a  root  of  the  lumlio-sacral  plexus. 
It  gives  off  a  branch  to  the  psoas  muscles,  an  inguinal  branch,  and  is  continued 
as  the  external  cutaneous  nerve.  The  inguinal  btanch  (N.  spermaticus  externus) 
passes  backward  in  the  substance  of  the  psoas  minor,  from  which  it  emerges  under 
cover  of  or  near  the  circumflex 
iliac  vessels.  It  then  runs  ex- 
ternal to  and  parallel  with  the 
external  iliac  artery  and  de- 
scends in  the  inner  part  of  the 
inguinal  canal.  It  emerges  at 
the  external  ring  with  the  ex- 
ternal pudic  artery  and  rami- 
fies in  the  external  genital 
organs  and  the  skin  of  the 
inguinal  region.  The  external 
cutaneous  nerve  of  the  thigh 
(X.  cutaneus  femoris  lateralis) 
runs  backward  in  the  sub- 
stance of  the  psoas  muscles 
and  emerges  at  the  outer  bor- 
der of  the  psoas  minor.  It 
then  passes  outward  and  back- 
ward on  the  iliac  fascia  and 
accompanies  the  posterior 
branch  of  the  circumflex  iliac 
artery.  With  this  vessel  it 
perforates  the  abdominal  wall 
by  passing  between  the  ex- 
ternal oblique  and  the  iliacus 
a  short  distance  below  the 
point  of  the  hip,  and  descends 
on  the  inner  face  of  the  tensor 
fasciae  latae  (near  its  anterior 
border)  and  ramifies  subcuta- 
neously  in  the  region  of  the 
stifle. 


Pig.  525. — Soperficiai.  Nerves  of  Pel- 
vic Limb  and  Posterior  Part  op 
Trunk  of  Horse. 
a.  Cutaneous  branches  of  sixteenth 
and  seventeenth  thoracic  nerves,  b.  cuta- 
neous branches  of  lumbar  ner\'es,   c,  cu- 
taneous   branches    of    sacral     nerves;    d, 
cutaneous  branches  of  coccygeal  ner%'es, 
e.  /.  (7,  cutaneous  branches  of  last  inter- 
costal,   iUo-hypogastric,   and    ilio-inguinal 
nerves;  *;'.  end  of  external  cutaneous  nerve 
of  thigh;  k,  posterior  cutaneous  nerve  of 
thigh;    i,  i,  cutaneous  branches  of  great 
____^  sciatic  nerve;  t,  posterior  cutaneous  nerve 

The   origin   and    disposition  of  of  the  leg;    I.  superficial   peroneal   nerve, 

some   of    the    foregoing    nerves    arc        „|^  terminal  part  of  deep  peroneal  nerve;   n    external  plantar  nerve, 
variable.      In    some    cases    the    ilio-        ;^   obliquus  abdominis  externus;   2,  tensor  fasci.-E   lat£e;  3    gluteus 
inguinal    nerve    ends    in   the    psoas       superficialis;  i.  biceps  femoris;  b,  semitendinosus.  6,  ante 
major,  and    appears   then   to  be  ab-        tensor;    7,  lateral  extensor;    S,  flexor  tendo 
sent.      The    mode    of    formation    of        artery.     (After  EUenberger,  in  Leisering'a  Atlas  ) 
the  inguinal  nerves  is  very  incon- 
stant.    The  inner  nerve  mav  arise  m.     •        •     i  i  i, 
^\-ith  one  of  the  outer  ones  from  a  common  trunk,  or  they  may  anastomose.      Ihe  inguinal  branch 
of  the  ilio-inguinal  nerve  often  receives  a  twig  from  the  ilio-hypogastric  nerve. 

The  ventral  branches  of  the  fourth,  fifth,  and  sixth  lumbar  nerves  concur  in 
the  formation  of  the  lumbo-sacral  plexus. 

LuMBO-SACRAL  Plexus 
This  plexus  (Fig.  451)   results  substantially  from  the  union  of  the  ventral 
branches  of  the  last  three  lumbar  and  the  first  two  sacral  nerves,  but  it  derives  a 


great  metatarsal 


706  NERVOrS  SYSTEM  OF  THE  HORSE 

small  root  from  the  third  lumbar  nerve  also.  The  anterior  part  of  the  plexus  lies 
in  front  of  the  internal  iliac  artery  between  the  lumbar  transverse  processes  and  the 
psoas  minor.  The  posterior  part  lies  partly  upon  and  partly  in  the  texture  of  the 
sacro-sciatic  ligament.  From  the  plexus  are  derived  the  nerves  of  the  pelvic  limb, 
which  are  now  to  be  described. 

Femoral  Nerve 

The  femoral  (or  anterior  crural)  nerve  (N.  femoralis)  is  derived  chiefly  from 
the  fourth  and  fifth  lumbar  nerves,  but  commonly  receives  a  fasciculus  from  the 
third  nerve  also  (Fig.  524).  It  is  the  larger  of  the  two  nerves  which  are  given  off 
from  the  anterior  part  of  the  lumbo-sacral  plexus.  It  runs  backward  at  first  be- 
tween the  psoas  major  and  minor,  then  crosses  the  deep  face  of  the  tendon  of  in- 
sertion of  the  latter,  and  descends  under  cover  of  the  sartorius  in  the  furrow  between 
the  two  heads  of  the  iliacus.  It  gives  off  the  saphenous  nerve,  crosses  the  lower 
part  of  the  outer  head  of  the  iliacus,  and  divides  into  several  branches  which  dip 
into  the  interstice  between  the  rectus  femoris  and  the  vastus  internus  (Fig.  450). 
These  branches  are  accompanied  by  the  anterior  femoral  vessels  and  innervate  the 
quadriceps  femoris.  Collateral  muscular  branches  are  supplied  to  the  ilio-psoas 
and  sartorius. 

The  saphenous  nerve  (N.  saphenus)  (Figs.  450,  451,  457)  is  given  off  as  the 
parent  trunk  crosses  the  furrow  between  the  psoas  major  and  the  outer  head  of 
the  iliacus.  It  descends  with  the  femoral  vessels  in  the  femoral  canal,  and  gives 
branches  to  the  sartorius,  gracilis,  and  pectineus.  About  the  middle  of  the  thigh 
it  divides  into  several  branches  which  emerge  from  between  the  sartorius  and  gracilis, 
perforate  the  deep  fascia  and  ramify  on  the  inner  surface  and  the  front  of  the  limb 
as  far  downward  as  the  hock.  The  longer  posterior  branches  accompany  the 
saphenous  vessels,  while  the  anterior  branches  deviate  forward  toward  the  stifle 
and  the  anterior  surface  of  the  leg. 

Obturator  Nerve 
This  nerve  (N.  ol)turatorius)  is  derived  from  the  ventral  liranches  of  the  last 
three  lumbar  nerves  (Fig.  524).  It  runs  downward  and  backward,  at  first  above 
and  then  upon  the  external  iliac  vein,  inclines  inward  across  the  obturator  vein, 
and  passes  through  the  anterior  part  of  the  obturator  foramen  in  front  of  that  vessel 
(Fig.  451).  It  continues  downward  through  the  obturator  externus,  and  divides 
into  several  liranches  which  innervate  the  obturator  externus,  pectineus,  adductor, 
and  gracilis  muscles  (Fig.  456). 

Anterior  Gluteal  Nerve 
This  nerve  (N.  glutanis  cranialis)  is  derived  chiefly  from  the  last  lumbar  and 
first  sacral  nerves.  It  divides  into  four  or  five  liranches  which  emerge  through  the 
great  sacro-sciatic  foramen  with  the  divisions  of  the  anterior  gluteal  artery  and 
supply  the  gluteal  and  tensor  fascia  latie  muscles.  The  nerve  to  the  latter  and 
the  anterior  part  of  the  superfic'ial  gluteus  passes  l:)etween  the  deeji  jiart  of  the  glu- 
teus medius  and  the  deep  gluteal  muscle,  and  is  accompanied  on  the  iliacus  by 
branches  of  the  external  circumflex  vessels. 

Posterior  Gluteal  Nerve 
The  posterior  gluteal  nerve  (N.  glutceus  caudalis)  is  derived  mainly  from  the 
sacral  roots  of  the  lumbo-sacral  plexus  (Figs.  451,  526).  It  divides  into  two  trunks 
which  emerge  above  the  great  sciatic  nerve.  The  upper  nerve  passes  backward 
on  the  sacro-sciatic  ligament  and  divides  into  branches  which  enter  the  two  heads 
of  the  biceps  femoris ;  it  supjilies  a  branch  to  the  posterior  part  of  the  middle  gluteus, 
and  a  nerve  which  turns  around  the  posterior  border  of  the  latter  and  enters  the 


GREAT  SCIATIC  NERVE 


707 


posterior  head  of  the  superficial  gkitcus.  The  inferior  nerve  runs  downward  and 
backward  on  the  sacro-sciatic  Hgainent  and  divides  into  the  posterior  cutaneous 
nerve  and  muscular  branches  which  supply  the  semitendinosus.  The  former  (N. 
cutaneus  femoris  caudalis)  passes  through  the  biceps  femoris,  emerges  between 
that  muscle  and  the  semitendinosus  a  little  below  the  level  of  the  tuber  ischii,  and 
ramifies  subcutaneously  on  the  outer  and  posterior  surfaces  of  the  hip  and  thigh 
(Fig.  525). 

Great  Sciatic  Nerve 
The  great  sciatic  nerve  (N.  ischiadicus)  (Figs.  451,  455,  526),  the  largest  in 
the  body,  is  deriveil  cliieHy  from  the  last  lumbar  and  the  sacral  roots  of  the  lumbo- 
sacral plexus,  but  may  receive  a  fasciculus  from  the  third  sacral  nerve  also.     It 


CoCCIIQKll 

i;  rt,  hr.r 


Sacral  spines 


Lateral  sacro-  / 
iliac  ligament  \ 


"^111  t 

^^vr^>^-=itftt!s:-izi 

TuhlT 

ischii^ 

Gemel-    Anastomosis' 
lus         between  ob- 
turator and 
internal  pudic 

\\.      Obturator  artery 
\    Obturator  internus 
Obturator  vein 

Lesser 
sciatic 
foramen 

Fig.  526. — Vessels  and  Nerves  on  Pelvic  Wall  of  Horse. 

Ner\'U9  ischiadicus  =  great  sciatic  nerve:  n.  glut.  inf.  =  anterior  gluteal  nerve;  n.  pudendus  =  internal  pudic  ner\'e. 

(After  Schmaltz,  Atlaa  d.  Anat.  d.  Pferdes.) 


emerges  through  the  great  sacro-sciatic  foramen  as  a  broad  flat  band — blended  at 
first  with  the  posterior  gluteal  nerve — which  passes  downward  and  backward  on 
the  lower  part  of  the  sacro-sciatic  ligament  and  on  the  origin  of  the  deej)  gluteus 
muscle.  It  turns  downward  in  the  hollow  between  the  trochanter  major  and  the 
tuber  ischii  over  the  gemellus,  the  tendon  of  the  obturator  internus,  and  the  quad- 
ratus  femoris.  In  its  descent  in  the  thigh  it  lies  between  the  biceps  femoris  ex- 
ternally and  the  adductor,  semimembranosus,  and  semitendinosus  internally,  and 
it  is  continued  between  the  two  heads  of  the  gastrocnemius  as  the  tibial  nerve.  Its 
chief  branches  are  as  follows: 


708  NERVOUS  SYSTEM  OF  THE  HORSE 

1.  In  the  pelvic  part  of  its  course  the  sciatic  nerve  supphes  small  branches  to 
the  obturator  internus,  gemellus,  and  quadratus  femoris;  the  branch  to  the  obtura- 
tor internus  reaches  the  muscle  bj'  passing  through  the  anterior  end  of  the  lesser 
sacro-sciatic  foramen. 

2.  As  the  sciatic  nerve  turns  down  behind  the  hip  joint  it  gives  off  a  large 
branch  (Ramus  muscularis  proxinialis)  which  divides  to  supply  the  semimembran- 
osus and  the  short  heads  of  the  l)iceps  femoris  and  semitcndinnsns. 

3.  The  posterior  cutaneous  nerve  of  the  leg  or  external  saphenous  nerve  (X. 
cutaneus  surae  posterior)  is  detached  from  the  sciatic  about  the  middle  of  the  thigh. 
It  receives  a  fasciculus  from  the  peroneal  nerve  and  descends  with  the  recurrent 
tarsal  vein  on  the  outer  face  of  the  gastrocnemius  to  the  distal  third  of  the  leg. 
Here  it  perforates  the  deep  fascia  and  ramifies  under  the  skin  on  the  outer  surface 
of  the  tarsus  and  metatarsus  (Fig.  525). 

4.  The  peroneal  or  external  popliteal  nerve  (N.  peronseus)  (Figs.  455,  460,  527) 
is  a  large  trunk  which  arises  from  the  great  sciatic  nerve  very  shortly  after  the  latter 
emerges  from  the  pelvic  cavity.  It  descends  with  the  parent  trunk  to  the  origin 
of  the  gastrocnemius;  here  the  peroneal  nerve  deviates  outward  and  forward 
across  the  external  face  of  the  gastrocnemius  under  cover  of  the  biceps  femoris,  and 
divides  at  the  origin  of  the  lateral  extensor  muscle  into  superficial  and  deep  branches. 
The  collateral  branches  inchule  a  twig  to  the  biceps  femoris,  the  reinforcing  fasci- 
culus detached  about  the  middle  of  the  thigh  to  the  posterior  cutaneous  nerve,  and, 
lower  down,  the  external  cutaneous  nerve  of  the  leg  (Ramus  cutaneus  sura>  later- 
alis). The  latter,  also  known  as  the  jieroneal  cutaneous  nerve,  emerges  between  the 
middle  and  posterior  divisions  of  the  bice]is  femoris  at  the  level  of  the  stifle  joint 
and  ramifies  under  the  skin.  The  superficial  peroneal  or  musculo-cutaneous  nerve 
(N.  peronteus  superficialis)  furnishes  branches  to  the  lateral  extensor,  and  descends 
in  the  furrow  between  that  muscle  and  the  anterior  extensor,  perforates  the  deep 
fascia  of  the  leg,  and  ramifies  under  the  skin  on  the  front  and  the  outer  face  of  the 
tarsus  and  metatarsus.  The  deep  peroneal  or  anterior  tibial  nerve  (N.  perona^us 
profundus)  is  the  direct  continuation  in  i)oint  of  siz(>  of  the  peroneal  trunk.  It  dips 
in  between  the  lateral  and  anterior  extensors  of  the  digit,  gives  Ijranches  to  these 
muscles  and  the  tibialis  anterior,  and  descends  in  front  of  the  intermuscular  septum 
which  separates  the  former.  It  continues  downward  behind  the  tendon  of  the 
anterior  extensor  and  divides  on  the  front  of  the  hock  into  internal  and  external 
branches.  The  internal  branch  (Ramus  medialis)  passes  down  under  the  skin  on 
the  anterior  face  of  the  metatarsus  and  supplies  the  cutaneous  fibers  of  this  region. 
The  external  branch  (Ramus  lateralis)  furnishes  a  twig  to  the  extensor  brevis 
muscle  and  descends  with  the  great  metatarsal  artery.  It  supplies  the  skin  on  the 
outer  face  of  the  metatarsus  and  the  fetlock. 

In  the  greater  part  of  its  course  in  the  leg  the  deep  peroneal  nerve  is  separated  from  the 
anlrrior  til)ial  vessels  by  the  tibiahs  anterior  (muscular  part  of  the  flexor  metatarsi).  It  should 
he  noted  that  the  outer  of  the  two  veins  which  almost  always  accompany  the  artery  here  is  fre- 
<iuciitl.\-  \cry  large,  and  the  layer  of  muscle  which  intervenes  between  it  and  the  nerve  is  often 
cxcccilingly  thin.  In  the  distal  part  of  the  leg  the  nerve  is  in  direct  contact  with  the  vein,  and  on 
the  front  of  the  hock  it  lies  behind  the  ve.s.sels. 

Tibial  Nerve 
The  tibial  nerve  (N.  tibialis),  also  termed  the  posterior  tibial,  is  the  direct 
continuation  of  the  great  sciatic  nerve  (Figs.  451,  455,  458,  459,  527).  It  passes 
down  between  the  two  heads  of  the  gastrocnemius,  and  accompanies  the  recurrent 
tibial  vessels  to  the  distal  third  of  the  leg,  where  it  divides  into  internal  and  external 
jilantar  nerves.  In  the  upper  third  of  the  leg  it  lies  along  the  inner  side  of  the 
superficial  flexor  under  cover  of  the  internal  head  of  the  gastrocnemius;  lower  down 
it  is  covered  by  the  common  deep  fascia  and  is  situated  in  the  space  between  the 
deep  flexor  and  the  inner  border  of  the  tendo  Achillis. 


PLANTAR  NERVES 


ro9 


At  tlie  usual  point  of  olcetion  for  tibial  neurectomy,  i.  e.,  about  a  handbreadtli  above  the 
level  of  the  tuber  calcis,  the  nerve  lies  in  areolar  tissue  and  fat  in  a  fascial  compartment  formed  by 
the  special  fascia  of  the  deep  flexor  in  front  and  by  the  common  fascia  and  the  accessory  or  tarsal 
tendon  of  the  semitendinosus  and  biceps  femoris  behind  and  internally. 

At  its  origin  the  tibial  nerve  gives  off  a  muscular  branch  (Ramus  muscularis 
(listalis),  the  divisions  of  which  pass  lietween  the  two  heads  of  the  gastrocnemius 
and  radiate  to  supply  that  muscle,  the  popliteus,  the  soleus,  and  the  flexors  of  the 
digit.     Small  cutaneous  twigs  are  also  detached  along  the  course  of  the  nerve. 


Anlerior  tiigiUd  extensor 
Anterior  tibial  vessels 


Deep  peroneal  nerve 
Superficial  peroneal 
nerve 
Intermuscular  septum 
Fibrous  band 


Peroncus  tertiits 


Lateral  extensor 
Intermuscular  septum 


Deep  head  of  deep 
flexor  {Flex,  hall.' 

longus)  \V 


Tibialis  posterior 

N.  cuianeus  suroe 
Recurrent  tarsal  artery 
and  vein 
Soleus 


Tibialis  anterior 


Saphenous  vein 
Saphenous  artery 


Posterior  tibial  vessels 

Tetidon  of  long  digital 
flexor  or  flexor  accessorius 


Recurrent  tibial  vein 
Recurrent  tibial  artery 
Tibial  nerve 

Tarsal  tendon  of  biceps  femoris 
and  sem  itendinosus 

Gastrocnemius  tendon 


Superficial  flexor  tendon 
Fig.  527. — Cross-section  of  Dist.\l  Third  of  Left 
The  deep  fascia  is  shown  by  red  line. 


Plantar  Nerves 
The  plantar  nerves,  internal  and  external  (X.  plantaris  medialis,  lateralis), 
result  from  the  Ijifureation  of  the  tibial  nerve  in  the  lower  part  of  the  leg  (Figs. 
4.58,  459).  They  continue  at  first  in  the  same  direction  and  relations  as  the  parent 
trunk,  in  direct  apposition  and  inclosed  in  a  common  sheath.  At  the  hock  they 
diverge  at  a  very  acute  angle  and  descend  m  the  tarsal  canal  behind  the  deep  flexor 
tendon  in  company  with  the  plantar  arteries.  The  internal  plantar  nerve  supplies 
cutaneous  nerves  to  the  inner  aspect  of  the  tarsus  and  metatarsus,  descends  along 
the  inner  border  of  the  flexor  tendons  behind  the  superficial  plantar  metatarsal 
vessels,  and  is  otherwise  arranged  like  the  corresponding  volar  nerve  of  the  fore 
limb.  The  external  plantar  nerve  deviates  outward  between  the  two  flexor 
tendons   to  reach  their  outer  border.     It  supplies  a  branch  to  the  suspensory 


710  •  NERVOUS  SYSTEM  OF  THE  HORSE 

ligament,  and  in  its   furtlier   course   rescnililos  tlio  corresponding   nerve  of  the 
fore  limb. 

In  so-called  "tibial"  npurectomy  the  operator  really  cuts  the  two  plantar  nerves  which 
have  not  yet  separated.  Tlie  anastoniotic  l)ranch  between  the  two  plantar  nerves  is  smaller  than 
that  which  connects  the  correspondiiig  ner\ps  of  the  fore  liinli,  and  is  absent  in  30  per  cent,  of  the 
cases,  according  to  Rudert. 

Sacral  Nerves 

Five  pairs  of  sacral  nerves  (Nn.  sacrales)  are  present  in  the  horse. 

The  small  dorsal  branches  emerge  through  the  dorsal  sacral  foramina  and  the 
space  between  the  sacrum  and  the  first  coccygeal  vertebra,  and  ramify  in  the 
muscles  and  skin  of  tlic  sacral  region  and  the  adjacent  part  of  the  tail  (Fig.  525). 
The  fifth  anastoinosi-s  with  the  dorsal  branch  of  the  first  coccygeal  nerve. 

The  ventral  branches  leave  the  vertebral  canal  through  the  ventral  sacral 
foramina  and  the  interval  between  the  sacrum  and  first  coccygeal  vertebra.  They 
are  connected  with  the  sympathetic  by  rami  communicantes,  and  contribute 
branches  to  the  pelvic  jilexus.  The  first  and  second  are  the  largest,  and  unite  with 
each  other  and  with  those  of  the  last  three  hmibar  nerves  to  form  the  luml)o-sacral 
plexus.  The  third  anil  fourth  are  connected  with  each  other,  and  the  majority  of 
their  fibers  go  to  form  the  pudic  and  posterior  htemorrhoidal  nerves. 

The  pudic  nerve  (N.  pudendus)  (Figs.  451,  455,  526)  accompanies  the  internal 
pudic  artery  to  the  ischial  arch,  turns  around  the  latter,  parting  company  with  the 
artery,  and  pursues  a  flexuous  course  along  the  dorsum  penis  as  the  nervus  dorsaUs 
penis  and  ramifies  in  the  glans  and  the  penile  layer  of  the  prepuce.  Within  the 
pelvis  it  anastomoses  with  the  posterior  htemorrhoidal  nerve,  and  gives  branches 
to  the  bladder  and  urethra,  the  terminal  part  of  the  rectum,  and  the  skin  and 
muscles  of  the  anus  (Fig.  452).  It  also  supplies  the  nerve  to  the  ischio-cavernosus 
muscle  and  numerous  branches  to  the  corpus  cavernosum  and  corpus  spongiosum. 
In  the  female  it  terminates  in  the  clitoris  and  vulva  (Fig.  453). 

The  posterior  haemorrhoidal  nerve  (N.  hsemorrhoidalis  caudalis)  ]5asses  down- 
ward and  backward  above  the  pudic  nerve,  with  which  it  anastomoses.  It  gives 
twigs  to  the  terminal  j^art  of  the  rectum,  the  sphincter  ani  externus,  and  the  sur- 
rounding skin  (Fig.  452).  In  the  female  it  supplies  twigs  to  the  \-ulva  also  (Fig. 
4.5.3). 

The  ventral  branch  of  the  fifth  nerve  is  small.  It  gives  twigs  to  the  sacro- 
coccygeus  ventralis  lateralis  and  the  skin  of  the  root  of  the  tail  and  joins  the  first 
coccygeal  nerve. 

Coccygeal  Nerves 

The  coccygeal  nerves  (Nn.  coccygei)  commonly  number  five  pairs.  Their 
dorsal  and  ventral  branches  anastomose  to  form  respectivelj'  two  trunks  on  either 
side,  which  extend  to  the  tip  of  the  tail  and  supply  its  muscular  and  cutaneous 
nerves.  The  dorsal  trunk  runs  with  the  dorso-lateral  artery  between  the  sacro- 
coccygeus  tlorsalis  and  intertransvcrsales  muscles  (Fig.  454).  The  ventral  trunk 
accompanies  the  ventro-lateral  artery  below  the  intertransversales. 


The  Sympathetic  Nervous  System' 

The  sympathetic  nervous  system  (Systema  nervorum  sympathicum)  is  that 
part  of  tiie  nervous  system  which  serves  (1)  to  transmit  stimuli  to  the  heart -muscle, 
unstriped  nmscle,  and  glands;  (2)  to  conduct  impulses  from  the  viscera  to  the  cere- 
brospinal system. 

Many  of  the  fibers  are  derived  from  the  cerebrospinal  system  and  are  rearranged  and  dis- 
tributed in  the  sympathetic  system.     Numerous  sympathetic  filjers  are  contributed  to  the  cerebro- 

'  The  special  statements  of  this  description  refer  to  the  system  of  the  horse.  A  few  important 
differential  features  will  be  mentioned  in  the  account  of  the  nervous  system  of  the  other  animals. 


THE  SYMFATHKTIC  NERVOUS  SYSTEM  711 

spinal  nerves,  through  which  they  are  distributed  to  the  unstriped  muscuhir  tissue  and  glands, 
as  vasomotor,  pilomotor,  and  secretory  nerves.  The  sympathetic,  like  the  cerebrospinal  system, 
consists  of  neurones,  each  of  which  comprises  the  cell-body,  an  axone,  and  numerous  branched 
dendrites.  The  cell-bodies  are  aggregated  into  ganglia,  some  of  wliich  are  large  and  more  or 
less  constant  in  position  and  form,  while  others  are  microscopic  and  are  scattered  in  an  irregular 
manner  through  the  peripheral  part  of  the  system.  It  is  probable  that  simple  visceral  reflexes 
may  be  mediated  by  sj'mpathctic  neurones  alone. 

In  descriptive  anatomy  the  sympathetic  system  is  regarded  as  consisting  of 
(1)  a  chain  of  ganglia  extending  along  eithiT  side  of  the  vertebral  colvunn  and  con- 
nected by  association  fibers  to  form  the  sympathetic  trunk;  (2)  central  branches 
to  and  from  the  cerebrospinal  nerves;  (3)  peripheral  branches,  which  form  plexuses 
with  each  other  and  the  cerebrospinal  nerves;  (41  the  peripheral  ganglia  which  are 
interposed  in  the  plexuses. 

The  sympathetic  trunk  (Truncus  sympathicus)  extends  on  either  side  from 
the  ba.se  of  the  cranium  to  the  tail.  In  it  arc  interposed,  at  intervals  of  varying 
regularity,  the  ganglia  of  the  sympathetic  trunk  (Ganglia  trunci  sympathici). 
These  are  connected  with  the  cerebrospinal  nerves  by  central  branches,  the  rami 
communicantes. 

Two  kinds  of  rami  communicantes  occur.  Of  these,  one  type  consists  largely  of  mcilullated 
fibers  derived  from  the  spinal  nerves  and  gangha;  thej-  have  therefore  a  white  a|)piarani'c,  and 
are  termed  white  rami.  They  contain  both  efferent  and  afferent  fibers.  The  efferent  splanch- 
nic fibers  are  derived  from  the  ventral  roots  of  the  spinal  nerves  and  terminate  in  great  part 
about  the  cells  of  the  nearest  sympathetic  ganglion;  others  end  in  more  distant  or  in  periph- 
eral ganglia.  The  afferent  splanchnic  fibers  are  chiefly  peripheral  processes  of  the  cells  of  the 
spinal  gangha,  but  some  are  sympathetic  fibers  which  enter  the  spinal  nerve-trunk  and  terminate 
about  cells  of  the  spinal  ganglion.  The  gray  rami  consist  mainly  of  non-medullated  fillers  derived 
from  the  sympathetic  gangha  directly  or  through  the  trunk,  which  proceed  centrally  to  the 
spinal  nerves  and  are  distributed  along  the  somatic  divisions  of  the  latter  to  unstriped  muscle  and 
glands  as  vasomotor,  pilomotor,  and  secretory  fibers.  Some  go  to  the  membranes  of  the  spinal 
cord,  and  a  few  terminate  about  cells  of  the  spinal  ganglia  as  sensory  sympathetic  fibers. 

Similar  but  more  complex  and  irregular  communications  which  exist  between 
the  spnpathetic  system  and  the  cranial  nerves — with  the  exception  of  the  first 
and  second — have  been  referred  to  in  the  accounts  of  the  latter. 

It  is  convenient  for  descriptive  purposes  to  divide  the  sympathetic  system  into 
cephalic,  cervical,  thoracic,  abdominal,  and  pelvic  parts. 

1.  The  cephalic  part  (Pars  cephalica  systematis  sympathici)  comprises  the 
otic,  sphenopalatine,  and  ciUary  ganglia,  which  luay  be  regarded  as  homologues  of 
the  ganglia  of  the  trunk  of  other  regions.  It  also  includes  three  plexuses  formed  by 
branches  derived  from  the  superior  cervical  ganglion.  The  ganglion  gives  off  two 
or  three  filaments  which  subclivide  to  form  the  internal  carotid  plexus  around  the 
artery  of  like  name.  The  cavernous  plexus  surrounds  the  artery  within  the  caver- 
nous sinus  and  communicates  with  that  of  the  opposite  side.  The  external  carotid 
plexus  is  foriued  around  the  homonymous  artery,  and  filaments  from  it  go  to  the 
vessel  and  its  branches  and  to  the  salivary  glands. 

2.  The  cervical  part  (Pars  cervicalis  s.  sympathici)  includes  two  ganglia  and 
the  trunk  which  connects  them. 

The  superior  or  anterior  cervical  ganglion  (G.  cervicale  craniale)  lies  on  the 
guttural  pouch  below  the  occipito-atlantal  articulation  (Fig.  437).  It  is  reddish- 
gray  in  color,  fusiform,  and  about  an  inch  (ca.  2  to  3  cm.)  in  length.  It  is  connected 
by  rami  communicantes  vdth  the  last  four  cranial  and  first  cervical  nerves,  sends 
branches  to  form  the  plexuses  mentioned  above,  and  contributes  to  the  pharyngeal 
plexus. 

The  cervical  tnmk  of  the  sympathetic  connects  the  superior  and  inferior 
cervical  ganglia.  On  leaving  the  former  it  is  associated  in  a  common  sheath  with 
the  vagus  along  the  dorsal  face  of  the  common  carotid  artery.  At  the  root  of  the 
neck  it  separates  from  the  vagus  and  joins  the  inferior  ganglion. 

The  inferior  or  posterior  cervical  ganglion  (G.  cervicale  caudale)  is  situated 
under  the  first  rib  and  the  insertion  of  the  scalenus  (Figs.  428,  429).     On  the  right 


712  NERVOUS  SYSTEM  OF  THE  HORSE 

side  it  lies  ui)on  tho  longus  colli  and  tlii'  trachea,  on  the  left  side  ujion  the  same 
muscle  and  the  oesophagus.  It  is  flattened,  very  irregular  and  variable  in  outline, 
and  is  blended  more  or  less  with  the  first  thoracic  ganglion.  It  is  connected  by 
large  gray  rami  with  the  ventral  branches  of  the  last  two  cervical  nerves,  and  by 
small  filaments  with  the  recurrent  nerve.  It  receives  a  nerve — termed  by  Schmaltz 
the  nervus  transversarius — which  accompanies  the  vertebral  artery;  through  it 
rami  come  from  the  second  to  the  sixth  cervical  nerves  inclusive. 

A  middle  cervical  ganglion  may  be  jiresent,  and  occurs  oftenest  on  the  right 
side.  It  lies  on  thi'  carotid  artery  an  inch  or  two  in  front  of  the  first  rili  and  is 
intercalated  in  the  vago-sympathetic  trunk. 

The  cardiac  nerves  (Nn.  cardiaci)  are  formed  l^y  branches  from  the  inferior 
cervical  antl  first  tlioracic  ganglia,  together  with  twigs  from  the  s.ympathetic  trunks 
and  the  vagi.  They  form  a  plexus  (P.  cardiacus)  on  the  ventral  face  of  the  trachea 
with  each  other  and  with  branches  of  the  vagus  and  recurrent  nerves.  They  are 
subject  to  considerable  variation,  but  their  general  arrangement  may  be  stated  as 
follows : 

(f()  On  the  right  side  there  are  usually  two  cardiac  nerves.  Of  these  one 
passes  back  with  the  vagus  in  the  angle  between  the  right  brachial  artery  and  the 
common  carotid  trunk,  pierces  the  pericardium,  crosses  the  aortic  arch,  and  divides 
into  branches  which  are  mingled  with  those  of  the  left  nerves.  The  second  crosses 
obliquely  over  the  right  face  of  the  trachea  and  joins  the  vagus,  where  the  latter 
gives  off  the  right  recurrent  nerve;  a  small  plexus  is  formed  here,  from  which 
two  or  three  cardiac  branches  are  detached.  These  pass  back  beneath  the  trachea 
and  ramify  on  the  atria  and  ventricles. 

(6)  On  the  left  side  there  are  commonly  three  cardiac  nerves.  One  of  these  is 
distributed  to  the  great  vessels  in  the  anterior  mediastinum.  The  largest  passes 
back  at  first  with  the  vagus  beneath  the  arch  of  the  left  brachial  artery,  inclines 
downward,  perforates  the  pericardium,  and  divides  into  two  branches.  One 
branch  passes  beneath  the  bifurcation  of  the  pulmonary  artery  and  is  distributed 
to  the  left  atrium.  The  larger  branch  dijjs  in  between  the  aorta  and  the  pulmonary 
artery,  gives  twigs  to  these  vessels,  and  ramifies  on  the  ventricles,  especially  along 
the  course  of  the  right  coronary  artery.  The  third  nerve  crosses  the  deep  face  of 
the  left  brachial  artery,  passes  back  below  the  trachea,  and  unites  with  filaments 
of  a  right  cardiac  nerve.  It  passes  around  the  aorta  and  ramifies  chiefly  along  the 
course  of  the  left  coronary  artery  on  the  left  face  of  the  ventricles. 

3.  The  thoracic  part  (Pars  thoracalis  systematis  sympathici)  extends  below 
the  costo-vertebral  joints  from  the  inferior  cervical  ganglion  to  the  upper  border 
of  the  diaphragm,  and  passes  between  the  latter  and  the  psoas  minor  to  be  con- 
tinued by  the  abdominal  part. 

The  trunk  is  concealed  in  the  first  part  of  its  course  by  the  outer  border  of  the 
longus  colli,  but  further  back  it  is  visible  under  the  pleura. 

The  ganglia  are  arranged  segmentally  at  each  intercostal  sjiace  and  partly  on 
the  heads  of  the  ribs.  They  are  flattened  and  are  small  and  fusiform,  with  the 
exception  of  the  first.  This  ((J.  thoracale  primum)  is  extensive,  irregularly  quadri- 
lateral in  outline,  and  is  united  with  the  inferior  cervical  ganglion.  The  ganglia 
are  connected  with  the  thoracic  nerves  by  white  and  graj'  rami  communicantes. 

The  visceral  branches  comprise  aortic,  cardiac,  pulmonary,  and  a'sophageal 
branches,  and  the  splanchnic  nerves.  The  aortic  branches  ramify  on  the  thoracic 
artery,  forming  around  that  vessel  the  thoracic  aortic  plexus  (P.  aorticus  thoracalis). 
The  cardiac  branches  concur  with  those  of  the  vagus  in  forming  the  cardiac  plexus 
(P.  cardiacus).  From  this  branches  go  to  form  the  coronary  plexuses  (P.  <'()r(inarii) 
along  the  course  of  the  vessels  of  like  name.  The  pulmonary  branches  join  with 
corresijonding  branches  of  the  vagus  and  filaments  from  the  cardiac  ])lexus  in 
forming  the  pulmonary  plexus  (P.  pulmonalis)  at  the  root  of  the  hmg.     Branches 


THE  ABDOMINAL  AND  PELVIC  PLEXUSES  713 

of  the  plexus,  on  which  are  minute  ganglia,  ramify  with  the  bronchi  in  the  substance 
of  the  lung.'  The  oesophageal  branches  join  with  those  of  the  vagus  in  the  forma- 
tion of  the  oesophageal  plexus  (P.  trsoi^hageus). 

The  great  splanchnic  nerve  (X.  splanehnicus  major)  arises  by  a  series  of  roots 
derived  from  the  sixth  or  seventh  to  the  fifteenth  or  sixteenth  thoracic  ganglia 
inclusive.  It  extends  at  first  along  the  inner  side  of  the  thoracic  trunk,  then  crosses 
the  latter  ventrally,  passes  back  between  the  crus  of  the  diaphragm  and  the  outer 
border  of  the  psoas  minor,  and  joins  the  cccliac  ganglion.  It  is  small  at  its  origin, 
Init  becomes  considerably  larger  than  the  sympathetic  trunk.  Near  its  termination 
it  bears  the  small  splanchnic  ganglion,  from  which  and  from  the  nerve,  filaments  go 
to  the  aorta,  the  cesojihagus,  and  the  vertebrae. 

The  small  splanchnic  nerve  (X.  splanehnicus  minor)  is  formed  by  roots  derived 
from  the  last  two  or  three  thoracic  ganglia.  It  runs  back  with  the  great  splanchnic 
nerve,  but  ends  in  the  cceliac  or  in  the  renal  and  adrenal  plexuses. 

This  ner\'e  is  not  always  present  and  is  variable  in  arrangement.  Tlie  roots  communicate 
by  filaments  with  the  great  splanchnic. 

4.  The  abdominal  part  of  the  sj-mpathetic  trunk  (Pars  abdominalis  systematis 
sympathici)  lies  along  the  inner  border  of  the  psoas  minor,  above  the  aorta  on  the 
left  side  and  the  posterior  vena  cava  on  the  right  (Fig.  524).  The  trunk  is  smaller 
than  the  thoracic  part,  and  presents  usually  six  small  fusiform  lumbar  ganglia  (G. 
lumbalia),  which  are  connected  by  rami  communicantes  with  the  ventral  divisions 
of  the  lumbar  nerves.  Visceral  branches  go  to  the  aortic  and  hypogastric  plexuses, 
and  to  the  cceliac  and  mesenteric  ganglia. 

5.  The  pelvic  part  of  the  sympathetic  trunk  (Pars  pelvina  systematis  sympa- 
thici) begins  at  the  last  lumbar  ganglion  and  extends  along  the  pelvic  surface  of 
the  sacrum  internal  to  the  emergence  of  the  ventral  branches  of  the  sacral  nerves 
(Fig.  451).  At  the  third  segment  of  the  sacrum  the  trunk  divides  into  internal 
and  external  branches.  The  internal  branch  inclines  to  the  median  plane  and 
unites  with  the  opposite  branch.  At  the  junction  there  is  often  found  the  small 
coccygeal  ganglion  (G.  irapar),  which  lies  on  the  coccygeal  artery  at  the  joint 
between  the  first  and  second  coccygeal  vertebrae.  A  filament  from  the  ganglion 
accompanies  the  artery.  The  external  branch  communicates  with  the  last  two 
sacral  nerves  and  joins  the  ventral  coccj'geal  nerves.  Ganglia  occur  near  each  of 
the  first  three  sacral  foramina,  and  are  connected  by  gray  rami  communicantes 
with  the  adjacent  spinal  nerves.  The  visceral  branches  are  distributed  through  the 
hypogastric  plexus.  They  supph'  motor  fibers  to  the  longitudinal  and  inhibitory 
fibers  to  the  circular  muscular  coat  of  the  rectum,  motor  fibers  to  the  bladder  and 
uterus,  and  the  vaso-dilator  fibers  (X^n.  erigentes)  to  the  penis. 


THE  ABDOraNAL  AND  PELVIC  PLEXUSES 
The  chief  plexuses  which  distribute  nerves  to  the  viscera  and  vessels  of  the 
abdominal  and  pelvic  cavities  are  two  in  number,  the  solar  and  the  pelvic.     From 
them  fibers  proceed  to  form  numerous  subsidiar.y  plexuses  which  are  named  accord- 
ing to  the  organs  which  they  supply  or  the  vessels  which  they  enlace. 

The  Solar  Plexus 
The  solar  plexus  (Fig.  4.50)  is  situated  on  the  dorsal  wall  of  the  abdominal 
cavity  in  relation  to  the  aorta  and  the  origin  of  its  chief  visceral  branches.     It  com- 
prises  the   cceliaco-mesenteric   ganglia   and   the   cceliac   and   anterior   mesenteric 
plexuses. 

'  The  right  and  left  plexuses  communicate  with  each  other,  so  that  both  lungs  receive  fibers 
from  both  vagi. 


714  NERVOUS  SYSTEM  OF  THE  HORSE 

The  coeliaco-mesenteric  ganglia'  are  two  in  number,  right  and  left.  They  arc 
situated  on  each  side  of  the  aorta,  in  relation  to  the  origin  of  the  ca'liac  and  anterior 
mesenteric  arteries.  The  right  ganghon  is  concealed  by  the  posterior  vena  cava; 
it  is  irregularly  quadrilateral  and  is  about  two  inches  (4  to  6  cm.)  in  length.  The 
left  ganglion  is  largely  covered  by  the  left  adrenal;  it  is  narrower  than  the  right 
one  and  is  three  or  four  inches  (ca.  8  to  10  cm.)  long.  The  two  ganglia  are  united 
by  irregular  connecting  branches  in  front  of  and  behind  the  anterior  mesenteric 
artery.-  Each  receives  the  splanchnic  nerve  of  its  own  side  and  branches  from  the 
dorsal  ccso])hageal  continuation  of  the  vagus  nerves.  Branches  from  the  ganglia 
and  the  cords  which  connect  them  pass  back  to  the  small  stellate  posterior 
mesenteric  ganglia,  which  are  situated  at  the  origin  of  the  posterior  mesen- 
teric artery. 

The  coeliac  plexus  (P.  cceliacus)  consists  of  a  felt-work  of  nerve-fibers  in  which 
are  small  ganglia.  It  surrounds  the  coeliac  artery  and  from  it  proceed  the  following 
unpaired  secondary  ])lexuses  which  accompany  the  arterial  branches: 

1.  The  gastric  plexus  (P.  gastricus)  enlaces  the  gastric  artery  and  divides  like 
the  artery  into  two  parts,  forming  the  anterior  and  posterior  gastric  plexuses. 
These  r(-ceive  branches  of  the  vagus  nerves. 

2.  The  hepatic  plexus  (P.  hepaticus)  is  formed  l)y  several  nerves  of  considerable 
size  which  accompany  the  hepatic  artery  and  the  portal  vein.  It  receives  fibers 
from  the  left  vagus,  ramifies  in  the  liver,  and  gives  off  branches  which  accompany 
the  collateral  branches  of  the  hepatic  artery  and  supply  the  areas  in  which  these 
vessels  are  distributed. 

3.  The  splenic  plexus  (P.  lienalis)  resembles  the  preceding  in  its  arrangement. 
In  addition  to  its  terminal  l)ranches  to  the  spleen,  it  gives  collateral  twigs  to  the 
pancreas  and  the  left  part  of  the  greater  curvature  of  the  stomach. 

The  anterior  mesenteric  plexus  (P.  mesentericus  cranialis)  is  formed  mainly 
by  branches  from  the  posterior  i)art  of  the  cceliaco-mesenteric  ganglia;  it  is  con- 
tinuous with  the  cceliac  plexus  in  front  and  the  posterior  mesenteric  behind.  It 
surrounds  the  anterior  mesenteric  trunk  and  its  branches,  and  supplies  the  viscera 
to  which  these  vessels  are  distributed. 

Tlie  posterior  mesenteric  plexus  (P.  mesentericus  caudalis)  accompanies  the 
artery  of  like  name  in  its  distribution. 

The  secondary  plexuses  which  accompany  the  branches  of  the  mesenteric  arteries  give  off 
brandies  whieli  foni\  two  fine  peripheral  plexuses  in  the  wall  of  the  intestine.  One  of  these,  the 
myenteric  plexus  (P.  mycnteri(nis)  or  plexus  of  Auerbach,  lies  between  the  layers  of  the  mus- 
cular coat,  and  is  provided  with  microscopic  ganglia.  The  other  is  in  the  submucous  tissue,  and 
is  therefore  termed  the  submucous  plexus  (P.  submucosus)  or  plexus  of  Meissner. 

The  following  ])aired  i^lexuses  are  derived  mainly  from  branches  of  the  coeliac 
and  aortic  jilexuses: 

1.  The  renal  plexuses  (P.  renales)  proceed  largely  from  the  coeliaco-mesenteric 
ganglia,  but  receive  fibers  also  from  the  small  splanchnic  nerves.  They  enlace  the 
renal  arteries  and  supply  the  kidneys.  Minute  renal  ganglia  occur  on  the  course 
of  the  nerves  along  the  renal  vessels. 

2.  The  adrenal  plexuses  (P.  suprarenales)  are  formed  by  a  relatively  very 
large  number  of  tine  tibt'rs  derived  in  great  part  directly  from  the  coeliaco-mesen- 
teric ganglia.     Nmnerous  minute  ganglia  occur  in  their  meshes. 

3  a.  The  spermatic  plexuses  (P.  si)ermatici)  proceed  largely  from  the  aortic 
and  renal  plexuses.  Each  acconii)anies  the  corresponding  (internal)  spermatic 
artery  to  the  testicle. 

3  b.  The  utero-ovarian  plexuses  (P.  ovarici)  are  the  homologues  in  the  female 

'  It  hsus  been  customary  to  designate  these  in  veterinary  works  as  the  semilunar  or  CCeliac 
ganglia,  but  in  the  horse  they  e\-idently  include  the  anterior  mesenteric  ganglia  as  well. 

'  A  good  preparation  of  the  ganglia  in  the  horse  is  often  difficult  to  obtain  on  account  of 
aneurysm  of  the  artery  and  the  formation  of  a  quantity  of  connective  tissue  about  it. 


THE  NERVOUS  SYSTEM  OF  THE  OX 


715 


of  the  prefeding.     Thoy  acooniiiany  tho  utoro-ovarian  arteries  to  the  ovar.y  and  tlie 
coniua  of  tlic  uterus. 

The  hypogastric  or  pelvic  plexus  (P.  hypogastricus)  is  tlie  jjelvic  continuation 
of  the  aortic  and  posterior  mesenteric  plexuses.  The  chief  nerves  which  form  it 
enter  the  pelvic  cavity  ventral  to  the  large  vessels,  anastomose  with  each  other  and 
with  branches  from  the  thirtl  and  fourth  sacral  nerves,  and  ramify  on  the  pelvic 
viscera.  The  perijiheral  plexuses  derived  therefrom  are  named  according  to  the 
organs  which  they  supjily;  the  chief  of  these  are  the  haemorrhoidal,  vesical,  utero- 
vaginal, prostatic,  cavernous  (of  the  penis  or  clitoris). 


THE  NERVOUS  SYSTEM  OF  THE  OX^ 
The  spinal  cord  resembles  that  of  the  horse  in  conformation  and  structure. 
In  cattle  of  medium  size  its  length  is  about  165  to  170  cm.  (ca.  65  to  67  inches)  and 
its  weight  about  2-10  to  250  grams 
(ca.  8  ounces). 

In  a  cow  140  cm.  in  height  Dexler 
found  the  weight  of  the  cord  (inckiding 
the  intradural  nerve-roots)  to  be  2lit)  g. 
and  the  length  162  cm.  The  lengths  of 
the  region.s  were:  cervical  41  cm.,  tho- 
racic 72  cm.,  lumbar  32  cm.,  sacral  7  cm. 

The  brain  has  an  average 
weight  of  about  500  grams  (ca. 
16  to  17  ounces).  Its  differences 
in  general  form  are  correlated  with 
those  noted  in  the  consideration  of 
the  cranial  cavity. 

The  medulla  is  short,  wide, 
and  thick.  Its  ventral  face  is 
strongly  convex.  The  pyramids 
are  narrow,  short,  and  close  to- 
gether in  front.  Near  the  decus- 
sation there  is  a  well-defined  oval 
prominence  on  either  side  which 
indicates  the  position  of  the  pos- 
terior olive.  The  corpus  trape- 
zoideum  is  large;  it  has  no  cen- 
tral part  between  the  pyramids. 
The  external  arcuate  fibers  are 
distinct.  The  restiform  bodies  are 
short  and  thick  and  diverge  more 
strongly  than  in  the  horse.  The 
floor  of  the  fourth  ventricle  is  only 
about  two-thirds  as  long  as  in  the 
horse.  The  area  acustica  is  a  well- 
marked  oval  prominence  lateral  to 
the  middle  part  of  the  limiting  sul-  •'<"■<'■> 
cus.     The   tuberculum   acusticum 

at  the  origin  of  the  auditory  nerve  is  very  large.  The  anterior  fovea  is  distinct. 
The  posterior  recess  of  the  fourth  ventricle  communicates  through  the  foramen  of 
Magendie  (Apcrtura  mediana)  with  the  subarachnoid  space. 

'  Only  the  most  salient  differences  as  compared  with  the  horse  will  be  mentioned. 


Fig.  528. — Br.\in  of  Cow,  Dorsal  View. 
J,  Sulcus  transversus;  B,  longitudinal  fissure;  3.  antero- 
internal  frontal  gyrus;  4.  olfactory  bulb;  6,  marginal  or  sagittal 
pole  of  hemisphere;  S,  lateral  fissure  (of  Sylvius);  7,  hemisphere 
of  cerebellum;  S,  vermis  of  same;  9,  accessory  nerve;  10.  dorsal 
root  of  first  cervical  nerve.     (EUenberger-Baum,  .\nat.  d.  Haus- 


716 


THE  NEUVOUS  SYSTEM  OF  THE  OX 


to  the  pineal  body: 


The  pons  is  smaller,  l)oth  transversely  and  longitudinally,  than  that  of  the 
horse.     It  is  stroniiJA'  convex  and  has  a  distinct  central  depression. 

The  cerebellum  is  smaller  and  more  angular  in  form  than  in  the  horse.  The 
vermis  is  large  and  has  a  distinct  depression  on  its  anterior  face  for  the  posterior 
corpora  quadrigemina.  The  hemispheres  are  relatively  small  and  are  not  clearly 
divided  into  tal dilations.     The  anterior  peduncles  are  very  short. 

The  cerebral  peduncles  are  short.  A  small  eminence  in  the  locus  jierforatus 
posticus  is  caused  by  the  presence  of  the  interpeduncular  ganglion.  The  internal 
geniculate  body  is  iirominent.  The  pineal  body  is  long  and  fusiform,  and  is  dften 
pigmented  in  spots.  The  third  ventricle  forms  two  considerable  recesses  in  relation 
one  (R.  pinealis)  extends  up  into  the  body;  the  other  (R. 
supra]5inealis)  is  a  long  tuliular  prolongation 
in  front  of  it. 

The  optic  tracts  cross  the  cerebral  pedun- 
cles almost  at  a  right  angle. 

The  pituitary  body  is  situated  in  a 
deep  fossa  and  is  surrounded  by  a  plexus 
of  vessels. 

The  cerebral  hemispheres  are  shorter, 
higher,  and  reiati\-ely  wider  than  in  the 
horse.  The  frontal  jjoles  are  small,  the 
occipital  large.  Viewed  from  the  side,  the 
dorsal  surface  is  strongly  convex.  The 
highest  point  of  the  dorso-medial  border 
is  a  little  in  front  of  its  middle  and 
forms  a  marked  prominence  termed  the 
sagittal  or  marginal  pole  (Polus  sagittalis 
s.  prominentia  marginalis  dorsalis).  An- 
terior to  this  the  border  drops  abruptly, 
being  cut  into  by  the  deep  transverse 
fissure.  The  arachnoid  on  the  basal  and 
anterior  parts  of  the  hemispheres  is  usually 
pigmented.  The  corpus  callosum  extends 
through  a  little  more  than  a  third  of  the  length  of  the  hemisphere.  The  iiattern 
of  the  fissures  and  gyri  of  the  ]iallium  is  somewhat  simpler  than  in  the  horse. 

1.  The  lateral  fissure  (of  Sylvius)  is  very  deep.  It.s  middle  branch  extends  almost  ver- 
tically upward  on  tlie  iniildle  of  the  lalei-al  surface  of  the  hemisphere,  and  is  separated  by  a 
gyrus  of  varialile  widtli  frorii  tlie  suprasylvian  fissure.  The  anterior  branch  runs  forward  about 
parallel  with  the  sulcus  rhinalis  anterior,  from  which  it  is  separated  by  the  short  gyri  of  the  insula. 
The  latter  are  covered  to  a  small  extent  only  by  the  overhanging  gyri  "(operculum).  The  posterior 
branch  may  run  baek  a  distance  of  only  about  1.5  cm.  and  end  in  T-shaped  manner,  or  it  may 
join  the  sulcus  rhinalis  posterior. 

2.  The  suprasylvian  fissure  is  deep  and  very  distinct.  It  extends  in  an  undulating  manner 
from  the  lateral  surface  of  the  occipital  pole  to  the  outer  side  of  the  sagittal  pole.  Here  it  may 
be  interrupted  or  may  be  continued  by  the  coronal  fissure,  which  descends  to  the  frontal  pole 
and  divides  into  two  short  branches. 

3.  The  diagonal  fissure  (S.  diagonalis)  begins  in  front  of  the  stem  of  the  lateral  fissure  and 
runs  upward  and  .''orwanl.     Its  form  is  very  variable. 

4.  The  transverse  fissure  cuts  obliquely  into  the  dorsal  border  in  front  of  the  sagittal 
pole.  It  is  short  ami  di'cp  and  commonly  communicates  with  the  suprasylvian  and  coronal 
fissures. 

5.  The  marginal  fissure  is  distinct.  It  extends  from  the  sagittal  pole  to  the  occipital 
pole.     It  is  flexuous  and  deviates  outward  somewhat  in  its  posterior  two-thirds. 

6.  The  entomarginal  fissure  lies  medial  and  parallel  to  tlie  postcTior  part  of  the 
preceding. 

7.  The  ectomarginal  fissure  is  lateral  and  parallel  to  the  marginal  fissure.  It  does  not  ex- 
tend so  far  in  either  direction  as  the  latter  and  is  often  more  or  h-ss  broken  up  by  annectcnt  gyri. 

S.  The  sulcus  rhinalis  is  more  open  than  in  the  horse,  since  it  is  not  overlapped  by  the 
gyri  above  it. 

9.  The  calloso-marginal  fi.ssure  is  flexuous  and  not  .so  regular  as  in  the  horse.     It  is  often 


Fig.  529. — Cerebral  Hemispheres  of 
Dorsal  View. 
a,  Transverse  fissure;  b.  lateral  fissure  (of 
Sylvius);  c,  coronal  fissure:  rf,  diagonal  fissure; 
c,  entomarginal  fissure;  /,  marginal  fissure;  g, 
ectomarginal  fissure;  h,  suprasylvian  fissure. 
(After  Ellenherger,  in  Leisering's  .\tlas.) 


THE  NERVOUS  SYSTEM  OF  THE  OX  717 

interrupted  at  or  near  the  level  of  the  genu  of  the  corpus  callosum,  in  which  case  the  genual  fissure 
continues  it  downward. 

10.  The  crucial  fissure  is  faint  and  is  confined  to  the  medial  surface.  It  lies  about  one 
centimeter  iu  front  of  the  transverse  fissure  and  commonly  joins  the  calloso-marginal  fissure 
below. 

11.  Short  and  variable  fissures  occur  in  front  of  and  liehind  the  middle  branch  of  the  lateral 
fissure  (F.  ectosylvia  anterior,  posterior). 

The  olfactory  bulb  is  much  smaller  than  in  the  horse.  The  external  olfactorj- 
tract  is  large,  the  inner  one  small  and  not  distinct. 

The  cranial  nerves  have  in  general  the  same  superficial  origin  as  in  the  horse. 
The  more  important  differences  in  other  respects  are  as  follows: 

The  oculomotor  nerve  is  larger  than  in  the  horse.  It  emerges  with  the  fourth, 
sixth,  ophtlialmic,  and  maxillary  nerves  through  the  large  foramen,  which  is 
equivalent  to  the  foramen  lacerum  orbitale  and  foramen  rotundum  of  the  horse. 

The  internal  branch  of  the  lacrimal  nerve  supplies  twigs  to  the  mucous  mem- 
brane of  the  frontal  sinus:  tlie  large  outer  branch  runs  backward  and  supplies  the 
matrix  of  the  horn.  The  frontal  nerve  emerges  from  the  orbit  below  the  supraor- 
bital process.  The  naso-ciUary  nerve  is  large  and  sends  filaments  to  the  ocular 
muscles.  The  ciliary  ganglion  is  somewhat  larger  than  in  the  horse  and  is  connected 
with  the  lower  divi-sion  of  the  oculomotor  nerve  bj-  several  short  filaments.  In 
consequence  of  the  absence  of  the  canine  and  upper  incisor  teeth  the  corresponding 
branch  of  the  infraorbital  nerve  is  naturahy  wanting.  The  mandibular  nerve 
emerges  through  the  foramen  ovale.  The  superficial  temporal  nerve  gi\es  off  a 
large  branch  which  joins  the  superior  buccal  division  of  the  facial  on  the  masseter, 
about  half-way  between  the  zygomatic  arch  and  the  angle  of  the  jaw.  The  otic 
ganglion  is  larger  than  in  the  horse.  According  to  ^loussu  the  buccinator  nerve 
furnishes  excito-secretory  twigs  to  the  parotid  and  inferior  buccal  glands. 

The  facial  nerve  divides  into  its  two  terminal  branches  before  reaching  the 
border  of  the  jaw.  The  superior  buccal  nerve  is  the  larger  of  the  two:  it  crosses 
the  masseter  much  lower  than  in  the  horse.  The  relatively  small  inferior  buccal 
nerve  runs  beneath  the  parotid  or  in  the  gland  substance  parallel  with  the  border 
of  the  lower  jaw,  crosses  under  the  insertion  of  the  sterno-cephalicus,  and  runs  for- 
ward along  the  depressor  labii  inferioris.  At  the  point  where  it  crosses  the  facial 
vein  and  parotid  duct  it  gives  off  an  ana,stomotic  branch  to  the  superior  nerve. 
The  auriculo-palpebral  nerve  is  large. 

The  vagus  bears — in  addition  to  the  relatively  large  jugular  ganglion — a 
ganglion  nodosum  at  the  point  of  origin  of  the  superior  laryngeal  nerve.  The 
trunk  is  large.  The  pharyngeal  branch  is  large  and  anastomoses  with  the  superior 
and  external  laryngeal  nerves.  The  latter  commonly  arises  directly  from  the  trunk. 
The  superior  oesophageal  trunk  communicates  with  the  splanchnic  nerve,  contri- 
butes t'\\'igs  to  the  hepatic  plexus,  and  ramifies  chiefly  on  the  riglit  surface  of  the 
rumen  and  the  adjacent  surface  of  the  abomasum.  The  inferior  oesophageal  trunk 
supplies  branches  to  the  hepatic  plexus  and  to  all  the  divisions  of  the  stomach. 

The  spinal  accessory  nerve  presents  two  special  features.  The  part  which 
joins  the  jugular  ganglion  bears  a  small  ganglion.  The  ventral  branch  supplies 
both  parts  of  the  sterno-cephalicus. 

The  hypoglossal  nerve  is  large.  It  is  connected  with  the  ventral  division  of 
the  first  cervical  nerve  liy  a  branch  of  considerable  size,  and  detaches  a  long  branch 
which  runs  backward  along  the  carotid  artery. 

The  spinal  nerves  resemble  those  of  the  horse  in  origin  and  general  arrange- 
ment. The  thoracic  nerves  number  thirteen  pairs.  The  more  important  differ- 
ences in  the  limb-plexuses  and  their  branches  are  as  follows: 

The  brachial  plexus  is  formed  by  the  ventral  branches  of  the  last  three  cervical 


718 


THE  NERVOUS  SYSTEM  OF  THE  OX 


and  first  thoracic  nerves;  the  second  thoracic  nerve  furnishes  no  root,  but  the  ven- 
tral branch  of  the  sixth  cervical  goes  almost  entirely  to  the  plexus  after  giving  off 
the  nerve  to  the  rhomboideus  and  the  cervical  part  of  the  serratus  magnus. 

The  differences  in  the  nerves  above  the  elbow  are  not  of  sufficient  moment 
to  receive  notice  in  this  brief  account,  but  below  this  point  there  are  naturally 
important  special  features  correlated  chiefly  with  the  arrangement  of  the 
digits. 

The  radial  nerve  is  continued  below  the  elbow  by  a  large  cutaneous  branch 
(N.  cutaneus  antibrachii  dorsalis)  which  emerges  at  the  lower  border  of  the  exter- 


Median  lurve- 


'Ulnar  nerve 


Anastomotic 
branch 


Fig.  530. — Nerves  of  Distal  Part  op  Right  Fore 

Limb  ok  Ox,  Anterior  View  (Schematic). 

p.  Dorsal  digital  nerves. 


Fig.  531. — Nerves  of  Distal  Part  of  Right  Fore 

Limb  of  Ox,  Posterior  View  (Schematic). 

p,  Volar  digital  nerve.s. 


nal  head  of  the  triceps  and  descends  on  the  dorsal  aspect  of  the  limb.  It  commu- 
nicates above  the  carpus  with  the  cutaneous  branch  of  the  median  nerve  and 
terminates  in  three  dorsal  digital  nerves;  two  of  these  descend  along  the  axial 
or  interdigital  side  of  the  dorsal  surface  of  the  chief  digits,  and  the  third  along 
the  inner  (abaxial)  side  of  the  inner  chief  digit. 

The  ulnar  nerve  divides  at  a  variable  distance  down  the  forearm  into  two 
branches.  The  dorsal  or  superficial  branch  emerges  lietween  the  tendons  of  the 
external  and  middle  flexors  of  the  carpus,  and  is  continued  as  the  external  dorsal 
digital  nerve  on  the  outer  chief  digit.  The  volar  or  deep  branch  tlescends  along  the 
superficial  digital  flexor,  gives  a  branch  to  the  suspensory  ligament  below  the  carpus, 


THE  NERVOUS  SYSTEM  OF  THE  OX 


719 


and  unites  with  the  external  l)ranch  of  the  nietUan  nerve  to  form  the  external 
volar  digital  nerve. 

Tlie  median  nerve  is  much  larger  than  the  uhiar.  It  passes  beneath  the  prona- 
tor teres,  descends  the  forearm  as  in  the  horse,  and  divides  in  the  distal  part  of  the 
metacarpus  into  two  branches.  Tlie  internal  branch  gives  twigs  to  the  inner  small 
digit  and  is  continued  on  the  inner  side  of  the  volar  surface  of  the  inner  chief  digit 
as  the  internal  volar  digital  nerve  (N.  digitalis  medialis  digiti  III);  it  also  concurs 
with  the  outer  branch  in  forming  the  two  digital  nerves  which  descend  along  the 
interdigital  aspect  of  the  chief  digits.     The  external  branch  is  larger.     It  bifurcates, 


Superficial 
peroneal  nerve 
Deep  peronealy-- 
nerce     ,-■ 
Internal  sa-/ 
phenous  nerve 


Tibial  nerve 


Internal  planiar 
nerve 


Kitcrnal  saphen- 
ous nerve 


External  plantar 
nerve 


' — Deep  branch 


Fig.  532. — Nerves  of  Distal  Part  of  Right  Hind 

Limb  of  Ox,  Anterior  View  (Schematic). 

p,  Dorsal  digital  nerves. 


Fig.  533. — Nerves  of  Distal  Part  op  Right  Hind 

Limb  of  Ox,  Posterior  View  (Schematic). 

p,  Plantar  digital  nerves. 


and  one  division  unites  with  the  twig  from  the  internal  branch  to  form  a  common 
digital  trunk.  From  the  latter  two  digital  nerves  proceed  as  mentioned  above; 
these  are  the  external  and  internal  volar  digital  nerves  of  the  internal  and  external 
chief  digits  respectively  (X.  digitalis  volaris  lateralis  digiti  III,  medialis  digiti  IV). 
The  other  division  unites  with  the  volar  branch  of  the  ulnar  nerve  to  form  the 
external  volar  digital  nerve  of  the  external  chief  digit  (N.  digitalis  lateralis  digiti 
IV). 

The  lumbo-sacral  plexus  and  its  branches  to  the  pelvis  and  thigh  present  no 
very  striking  special  features. 

The  superficial  peroneal  nerve  is  much  larger  than  in  the  horse.     After  crossing 


720  THE  NERVOUS  SYSTEM  OF  THE  PIG 

bi'iu'iitli  llie  jjcroiicus  loiisins  it  passes  down  on  the  front  of  the  tarsus  and  meta- 
tarsus and  divides  into  three  l)ranehes.  Tlie  internal  and  external  branches  descend 
as  the  internal  and  external  dorsal  digital  nerves  on  the  chief  digits.  The  larger 
middle  branch  joins  a  l)ranch  of  the  deep  peroneal  nerve  in  the  interdigital  space, 
and  from  this  union  proceed  the  dorsal  digital  nerves  which  descend  on  the  opposed 
surfaces  of  the  cliief  digits. 

The  deep  peroneal  nerve  descends  in  the  leg  as  in  the  horse  and  continues 
down  the  anterior  groove  of  tlie  metatarsus  with  the  dorsal  metatarsal  artery.  Its 
terminal  branches  concur  with  brandies  from  the  superficial  peroneal  nerve  in  the 
formation  of  the  two  axial  dorsal  digital  nerves  (N.  dig.  dors.  lat.  dig.  Ill  et  dig. 
dors.  med.  dig.  I\'  i)edis),  and  with  a  branch  of  the  internal  ijlantar  nerve  in  the 
formation  of  corresi)onding  plantar  digital  nerves. 

The  tibial  nerve  divides  at  the  back  of  the  hock  into  internal  and  external 
plantar  nerves.  The  internal  plantar  nerve  descends  between  the  superficial  flexor 
tendon  and  the  suspensory  ligament  and  divides  into  two  branches;  the  inner 
branch  descends  as  the  internal  plantar  digital  nerve  (X.  dig.  plant,  med.  dig.  Ill) 
along  the  inner  side  of  the  fle.xor  tendons  of  the  inner  chief  digit;  the  outer  branch 
turns  around  the  flexor  tendons  to  reach  the  interdigital  space,  where  it  concurs 
with  a  brancli  of  tlie  deep  peroneal  nerve  in  the  formation  of  two  axial  plantar 
digital  nerves  (N.  dig.  plant,  lat.  dig.  Ill  et  dig.  jilant.  med.  dig.  IX)  which  descend 
on  the  opposed  surfaces  of  the  chief  digits.  The  external  plantar  nerve  descends 
along  the  outer  border  of  the  flexor  tendons,  gives  a  branch  to  the  suspensory  liga- 
ment and  to  the  external  small  digit,  and  continues  along  the  outer  face  of  the  ex- 
ternal digit  as  the  external  plantar  digital  nerve  (X.  dig.  jilant.  lat.  dig.  IV). 

The  sympathetic  system  closelj-  resembles  that  of  the  horse  in  its  general 
arrangement,  and  only  a  few  differential  features  will  receive  attention.  The 
superior  cervical  ganglion  is  closer  to  the  cranial  base  and  is  thicker  than  in  the 
horse;  its  branches  to  the  carotid  and  cavernous  plexuses  are  large,  and  no  con- 
nection is  formed  with  the  spinal  accessory  nerve.  The  cervical  trunk  is  smaller 
than  in  the  hor.se,  and  arises  by  two  or  three  bundles  from  the  su]ierior  cervical 
ganglion  behind  its  middle.  The  inferior  cervical  ganglion  is  distinctly  sejiarable 
from  the  first  thoracic;  the  latter  is  large.  There  are  thirteen  pairs  of  thoracic 
ganglia.  The  cceliaco-mesenteric  ganglia  are  plexiform,  not  compact.  There 
are  five  pairs  of  sacral  ganglia,  and  the  right  and  left  trunks  are  connected  here  by 
transverse  anastomoses. 


THE  NERVOUS  SYSTEM  OF  THE  PIG 
The  spinal  cord  weighs  about  42   grams  (KUenberger-Baum).     It  is  almost 
circular  in  cross-section,  except  at  the  enlargements,  where  it  is  somewhat  flattened 
dorsoventrally.     The  conus  medullaris  extends  to  the  anterior  part  of  the  third 
sacral  segment.     The  epidural  space  is  occujiied  by  a  large  (juantity  of  fat. 

The  brain  in  adults  of  medium  size  weighs  about  125  grams  (ca.  4  to  4^2  ounces). 
When  viewed  from  above,  it  is  seen  to  have  an  elongated  oval  form.  The  occipital 
poles  overlie  the  cerebellum  to  a  small  extent  only;  the  frontal  poles  are  rounded 
and  relatively  large,  but  do  not  conceal  the  ends  of  the  olfactory  bulbs.  The 
medulla  is  relatively  liroad.  The  cuneatc  tubercle  is  very  large  and  is  limited 
externally  by  a  groove.  The  corpus  trapezoideum  is  very  wide  laterally.  The  pons 
is  less  prominent  than  in  the  ox.  The  cerebellum  is  very  wide  and  short.  Its 
anterior  face  is  flattened  and  i^resents  a  depression  for  the  corpora  quadrigemina. 
The  vermis  is  large.  The  hemispheres  consist  of  an  inner  large  and  an  outer  small 
part.     The  cerebral  peduncles  are  very  short.     The   posterior  corpora  quadri- 


THE  NERVOUS  SYSTEM  OF  THE  PIG 


721 


geraiiia  are  wide  apart,  rounded,  and  relatively  large.  The  internal  geniculate 
bod}-  is  prominent.  The  cerebral  hemispheres  are  somewhat  bean-shaped  in 
lateral  profile,  the  convex  border  being  dorsal.  The  arrangement  of  the  gyri 
and  sulci  is  simpler  than  in  the  horse  or  ox.  The  principal  fissures  are  as 
follows : 

1 .  The  lateral  fissure  (of  Sylvius)  begins  at  the  sulcus  rhinalis  and  runs  upward 
and  somewhat  bat  kward  on  the  depressed  part  of  the  lateral  surface  of  the  hemi- 
sphere: it  appears  unliranched  on  superficial  examination,  but  when  the  gyrus 
which  almost  completely  conceals  the  insula  is  raised,  an  anterior  branch  is  exposed 
which  forms  the  dorsal  lidundary  of  the  insula. 

2.  The  suprasylvian  fissure  pursues  a  curved  course  approximately  parallel 
with  the  dorso-medial  l)order  of  the  hemisphere.  Its  posterior  end  is  separated  by  a 
short  interval  from  the  sulcus  rhinalis  posterior.  From  its  highest  point  a  branch 
proceeds  obliquely  upward  and  forward,  crosses  the  dorso-medial  border,  and 
joins  the  splenial  fissure. 

3.  The  diagonal  fissure  crosses  the  anterior  part  of  the  lateral  surface.  It  is 
directed  obliquely  downward  and  backward. 

4.  The  coronal  fissure  is  constant  and  deep.     It  is  directed  upward  and  inward 
over  the  frontal  pole,  continues  backward  near  the 
dorso-medial  border,  antl   usually  ends  by  passing 
obliquely  over  the  border  to  the  inner  surface  of  the 
hemisphere. 

5.  The  presylvian  fissure  begins — apparently  as 
a  branch  of  the  sulcus  rhinalis  anterior — about  2  cm. 
in  front  of  the  lateral  fissure,  and  curves  over  the 
lateral  aspect  of  the  frontal  pole. 

6.  The  marginal  fissure  Ijegins  behind  the  cruci- 
ate fissure  close  to  the  dorsoniedial  border  and  ex- 
tends in  a  gentle  curve  backward  almost  to  the  occi- 
pital pole. 

7.  The  ectomarginal  fissure  lies  above  and 
nearly  parallel  to  the  posterior  part  of  the  supra- 
sylvian fissure. 

8.  The  entomarginal  fissure  lies  along  the  pos- 
terior part  of  the  dorso-medial  liorder. 

9.  The  calloso-marginal  fissure  consists  of  two 
separate  parts.  The  more  extensive  posterior  part 
is  termed  the  splenial  fissure.  It  extends  from  the 
tentorial  aspect  of  the  hemisphere  in  a  direction 
parallel  with  the  corpus  callosum  nearly  to  the  middle 
of  the  medial  surface;  it  is  continued  by  the  cruciate 

fissure  and  is  also  connected  with  the  suprasylvian  and  coronal  fissures  by  branches 
which  pass  obliquely  upward  and  forward.  The  anterior  part,  the  genual  fissure, 
lies  about  midway  between  the  anterior  part  of  the  corpus  callosum  and  the  dorso- 
medial  border. 

10.  The  cruciate  fissure  is  short  and  shallow.  It  runs  obliquely  upward  and 
forward  from  the  anterior  end  of  the  splenial  fissure  on  the  inner  surface  of  the 
hemisphere. 

11.  The  sulcus  rhinalis  extends  in  an  undulating  manner  along  the  entire 
lower  part  of  the  lateral  surface  of  the  hemisphere  and  forms  the  upper  limit  of  the 
rhinencephalon. 

The  olfactory  bulbs  are  very  large  and  the  tracts  extremely  liroati  anrl  short. 
The  trigonum  olfactorium  is  so  prominent  as  to  be  termed  the  tuberculiun  olfac- 
torium. 

46 


Fig.  534. — Cerebral  Hemispheres 
OF  Pig,  Dors.\l  View. 
a,  Upper  part  of  lateral  fissure 
(of  Sylvius);  6,  cruciate  fissure;  c, 
suprasylvian  fissure,  with  its  anterior 
branch  ((f)  and  upper  branch  (c"); 
d,  diagonal  fissure;  e,  coronal  fissure; 
/,  presylvian  fissure;  g,  marginal 
fissure;  k,  ectomarginal  fissure;  i, 
entomarginal  fissure,  (.\fter  Ellen- 
berger,  in  Leisering's  .-Vtlas.) 


722 


THE  NERVOUS  SYSTEM  OF  THE  PIG 


The  cranial  nerves  present  the  following  special  features: 

The  third,  fourth,  sixth,  and  the  ophthalmic  and  maxillary  divisions  of  tlio 
fifth  nerve,  cmcriic  tosetiier  as  in  tlie  ox. 

The  lacrimal  nerve  resenil)les  that  of  the  horse,  the  frontal  that  of  the  ox. 
The  naso-ciliary  nerve  is  rehitively  large  and  sends  numerous  filaments  to  the  ocular 
muscles.  The  maxillary  nerve  has  a  very  short  course  in  the  pterygo-palatinc 
fossa.  The  infraorbital  nerve  is  large  in  correlation  with  the  development  of  the 
snout  which  receives  numerous  Ijranches.  The  mandibular  nerve  emerges  through 
the  foramen  lacerum  anterius.  The  superficial  temporal  nerve  is  small;  according 
to  Moussu  it  furnishes  the  c-xcito-secretory  fibers  to  the  ujij^er  ])art  of  the  ])arotid 
gland,  wiiile  those  going  to  the  lower  jjart  are  derived  from  tlie  mylo-hyoid  nerve. 

The  inferior  buccal  nerve  jiasses  downward  and  forward  under  cover  of  the 


Median 

Ulnar  inrre        1      \ 

\         Radial 

nerve 

{dorsal  branch)  -~ 

\ 

\ 

-\—    nerve 
\        {ridaneuus 
\       branch) 

L-       Ulmir  ncm- 
f        Dor!i(d  branch 


Diip  branch 


Fig.  .535. — Nerves  of  Distal  Part  of  Riout  Fore 

Limb  op  Pig,  Anterior  View  (Schematk). 

c,   Dorsal   common   digital    nerves;     p,   dorsal   proper 

digital  nerves. 


Fig.  536. — Nerves  of  Distal  Part  of  Right  Fore 

Limb  of  Pig,  Posterior  View  (Schematic). 

p,  \'oIar  proper  digital  nerves. 


parotid  gland  and  accomi)anies  tlie  parotid  duct,  with  which  it  turns  around  the 
lower  border  of  the  jaw  in  front  of  the  masseter. 

The  vagus  bears  a  jugular  ganglion  and  a  gangUon  nodosum ;  the  latter  occurs 
at  the  point  of  origin  of  the  superior  laryngeal  nerve,  and  may  be  as  large  as  a  small 
pea.  Proximal  to  this  the  vagus  is  easily  divided  into  two  strands,  one  of  which  is 
the  accessory  comjionent.  The  cesophageal  trunks  form  a  posterior  cpsophageal 
plexus,  as  in  man,  from  which  two  nerves  issue.  The  inferior  nerve  is  small  and 
ramifies  on  the  parietal  surface  of  the  stomach.  The  superior  trunk  is  much  larger; 
it  gives  branches  to  the  stomach,  crosses  the  lesser  curvature  of  that  organ,  and 
joins  the  solar  jilexus. 

The  hypoglossal  nerve  may  present  a  small  dorsal  root,  on  which  there  is  a 
minute  hjiiogiossal  ganglion  (of  Froriep). 


THE  NERVOUS  SYSTEM  OF  THE  PIG 


723 


The  spinal  nerves  numlier  on  each  side  eight  in  the  cervical  region,  fourteen 
(commonly)  in  the  thoracic,  seven  in  the  lumbar,  and  four  in  the  sacral.  Some 
of  the  special  features  of  the  nerves  of  the  limbs  are  as  follows: 

The  brachial  plexus  is  derived  from  the  same  nerves  as  in  the  ox,  but  the  root 
furnished  by  the  sixth  cervical  is  relatively  smaller.  The  plexus  consists  of  two 
parts,  the  upper  of  which  emerges  above  the  scalenus,  the  lower  between  the  two 
parts  of  that  muscle.  The  more  important  differences  in  the  nerves  emanating 
from  the  plexus  from  the  arrangement  in  the  ox  occur  in  the  lower  part  of  the  limb. 
The  cutaneous  branch  of  the  radial  nerve  divides  at  the  carpus  into  branches  which 
concur  with  the  dorsal  branch  of  the  ulnar  nerve  in  supplying  the  dorsal  digital 
nerves,  two  for  each  digit.  The  volar  digital  nerves,  also  two  for  each  digit,  are 
formed  by  the  terminal  branches  of  the  median  nerve  and  the  volar  or  deep  branch 


Dap  pcruntat 
nerve 


Superficia, 
peroneal  nerix 


Internal  plantar 
nerve 


Fig.  537. — Nerves  of  Distal  Part   of  Right  Hikd 

Limb  of  Pig,  .\nterior  View  (.Schem.itic). 

p.  Dorsal  proi>er  digital  nerves. 


Fig.  53S.— Nerv 
Limb  o 


Right  Hind 


of  the  ulnar  nerve.  The  formation  and  arrangement  of  the  digital  nerves  are 
indicated  in  the  annexed  schematic  figures. 

The  lumbo-sacral  plexus  is  derived  from  the  ventral  branches  of  the  last  three 
lumbar  and  first  sacral  nerves.  The  distribution  of  the  branches  of  the  ])lexus 
differs  chiefiy  in  the  distal  part  of  the  limb.  The  superficial  peroneal  nerve  is 
large  and  terminates  by  forming  the  greater  part  of  the  dorsal  digital  nerves. 
The  latter,  two  for  each  digit,  are  also  in  part  formed  by  the  terminal  branches  of 
the  deep  peroneal  nerve. 

The  tibial  nerve  divides  at  the  tarsus  into  internal  and  external  plantar  nerves. 
The  latter  divitle  to  form  the  plantar  digital  nerves,  two  for  each  digit.  In  addi- 
tion, the  external  plantar  nerve  supplies  a  branch  to  the  dorsal  aspect  of  the  outer 
(fifth)  digit.  The  arrangement  of  the  digital  nerves  is  indicated  by  the  annexed 
schematic  figures. 


724 


THE  NERVOUS  SYSTEM  OF  THE  DOG 


Tile  sympathetic  system  of  tlip  pig  has  received  wry  little  attention  from 
anatomist.s.  The  superior  cervical  ganglion  is  long  and  fusiform.  It  gives  off 
filaments  which  jtjin  the  vagus  n(^ar  the  ganglion  nodosum.  The  cervical  tnmk  is 
short  and  relatively  larger  tiiau  in  the  ox;  it  is  inclosed  in  a  common  sheath  with 
the  vagus  in  the  neck  and  separates  from  that  nerve  to  join  the  middle  cervical 
ganglion  at  the  thoracic  inlet. 


THE  NERVOUS  SYSTEM  OF  THE  DOG 
The  spinal  cord  is  almost  circular  in  cross-section  except  at  the  well-marked 
cervical  and  lum})ar  enlargements,  where  it  is  compressed  dorso-vent rally.     The 
conus  medullaris  lies  over  the  junction  of  the  sixth  and  seventh  lumbar  vertebrae. 


Fig.  539— Basi:  of  Brain  of  Dog. 
a,  Olfactory  bulb;  a,'  a",  external  and  internal 
olfactory  tracts;  6,  optic  nerve;  c,  oculomotor  ner\'e 
d,  trochlear  nerve;  c,  trigeminua;  /,  abducens;  n,  facial 
h,  auditory;  i,  gloaso-pharyngeal;  k,  vaRUs;  /,  spinal 
accessory;  m,  hypoglossal;  2,  trigonum  olfactorium; 
5,  anterior  perforate*!  substance;  4»  tuber  cinereuin  and 
infumlibulum;  4',  mamniillary  body;  6,  pyriform  lobe; 
G,  temporal  lobe;  7,  parietal  lobe;  S,  frontal  lobe;  9 
pons;  iO,  medulla  oblongata;  //,  cerebellum;  13,' 
bral  pcdxmcle;  75,  occipital  lobe.  (EUenberger-Baum 
Anat.  d.  Hundes.) 


Fig.  540.— Bra 


Stkm  of  Dog,  Dorsal  Vi 


a,  Spinal  cord;  />,  dorsal  median  groove;  c,  c\ 
funiculus  gracilis;  c",  clava;  d,  d' ,  funiculus  cuneatus;  d", 
tuberctilum  cuneatum;  e,  funiculus  lateralis;  e' ,  tuber- 
culum  Rolandi;  /.medulla oblongata;  /,//,///, floor  of 
fourth  ventricle  (fossa  rhomboidea) ;  y,  limiting  groove; 
h,  median  fissure;  i,  eminentia  medialis;  k,  ala  cinerea; 
/,  /'.pons;  m,  posterior  peduncle,  and  n,  middle  peduncle 
of  cerebellum  (cut);  o,  anterior  peduncle  of  cerebellum; 
;j,/y,corporaquadrigemina,  anterior  and  posterior;  q,</, 
peduncles  (brachia)  of  corpora  quadrigemina;  r,  thala- 
mus; s,  massa  intermedia;  /,  stria  medullaris;  »,  anterior 
tubercle  of  thalamus;  v,  pulvinar;  w,  corpus  geniculatum 
laterale;  r,  corpus  geniculatum  mediale.  (After  Ellen- 
berger,  in  Leisering's  Atlas.) 


The  lenf^th  of  the  cord  of  a  rather  large  dog  was  found  to  be  about  38  cm.;  of  this, 
the  cervical  part  was  11  cm.,  the  thoracic  17.4  cm.,  the  lumbar  about  7  (-m.,  and 
the  sacro-coccygeal  about  2.6  cm.  (Flatau-Jacobson). 

The  brain  weighs  about  60  to  70  g.  in  dogs  of  medium  size,  but  there  is,  of 
course,  a  wide  range  of  weight  in  the  different  breeds.     Thus  in  small  terriers  the 


THE  NERVOUS  SYSTEM  OF  THE  DOG 


725 


weight  is  30  g.  or  even  less,  while  in  very  large  clogs  it  may  exceed  150  g.  It  cor- 
responds much  more  closely  with  tlie  cranium  in  size  and  general  form  than  in  the 
animals  previously  described;  this  is  specially  true  of  the  small  breeds,  in  which  the 
bony  crests  and  frontal  sinuses  are  little  developed. 

The  medulla  is  broad  and  thick.  Its  ventral  surface  is  strongly  convex  from 
side  to  side.  The  pyramids  are  large  and  prominent  and  are  limited  l)y  distinct 
median  and  lateral  grooves.  The  olivary  eminence  is  a  well-defined  oval  elevation 
situated  between  the  pyramid  and  the  superficial  origin  of  the  hypoglossal  nerve. 
The  external  arcuate  fibers  form  a  wide  band  which  crosses  the  lateral  surface 
obliquely  upward  and  forward,  and  obscures  the  groove  which  limits  the  restiform 


Flv  — 


CAo 


Fig.  541. — Part  of  Cross-sf.ction  of  Brain  of  Dog,  Passing  through  Ganglion  Habentl.*:. 
Al,  Ansa  lenticularis  of  thalamic  radiation;  C  a  d,  dorsal  end  of  hippocampus;  C  a  v,  ventral  end  of  same; 
C  c,  corpus  callosum;  C  g  m,  corpus  geniculatuni  mediale;  C  m,  corpus  mammillare;  /''  (  d,  fimbria;  F  i  r,  ventral 
part  of  fimbria;  G  h,  ganglion  halaenulte;  M  B,  fasciculus  retroflexus;  P  p,  pes  ijedunculi;  T  h,  thalamus;  T  o, 
tractus  opticus;  T  /,  habenula;  V  A,  fasciculus  thalanio-mammillaris;  V  /■'.  fornix  ventralis;  //,  lateral  ven- 
tricle;   ///,  third  ventricle,      (.\fter  Probst.) 


body  externally.  The  cuneate  tubercle  is  distinct.  The  rhomboid  fossa  is  deep 
and  narrow. 

The  pons  is  relatively  small.  The  corpus  trapezoideum  is  very  wide  and  is 
divided  by  the  pyramids  into  two  lateral  parts.  The  cerebellum  is  very  broad,  but 
is  low  and  also  compressed  from  before  backward.  Rather  more  than  half  of  it  is 
overlap])ed  by  the  cerebral  hemispheres.  The  anterior  surface  is  accurately 
adapted  to  the  concave  tentorial  surfaces  of  the  hemispheres  and  to  the  posterior 
corpora  quadrigemina  and  their  commissure.  The  posterior  surface  is  almost 
vertical  and  is  convex  centrally  and  flattened  laterally.  The  vermis  is  prominent 
and  in  general  well  defined,  although  it  is  connected  in  its  middle  part  with  the 
hemispheres.  The  latter  are  three-sided  and  consist  of  four  lobules.  The  anterior 
peduncles  are  very  short. 

The  posterior  corpora  quadrigemina  are  large,  very  wide  apart,  and  prominent, 
and  are  connected  by  a  curved  commissure.     The  internal  geniculate  body  is  large. 


726 


THE  NERVOVS  SYSTEM  OF  THE  DOG 


In  the  deep  interpeduncular  fossa  are  two  small  hands  which  indicate  the  course  of 

the  fasciculi  retroflexi,  tracts  which  connect  the  halnnular  and  interpeduncular 

ganglia.     The  mammillary  body  is   double.     The 

tuber  cinereum  is  relatively  large.     The  pituitary 

body  is  circular  antl  rather  small. 

The  cerebral  hemispheres  are  very  broad 
behind  and  diminish  in  width  anteriorly;  there  is 
a  sudden  narrowing  at  the  frontal  poles,  which 
are  flattened  laterally.  The  tentorial  surfaces 
are  concave  and  form  a  deep  cavity  which  re- 
ceives the  anterior  part  of  the  cerebellum.  The 
arrangement  of  the  fissures  and  gyri  is  simpler 
than  in  the  animals  previoush'  examined.  The 
chief  fissures  are  as  follows: 

1 .  The  lateral  fissure  (of  Sylvius)  extends  up- 
ward and  backward  from  the  sulcus  rhinalis  a  little 
behind  the  middle  of  the  lateral  surface  of  the  hemi- 
sphere. 

2.  The  ectosylvian  fissure  has  approximately 
the  shape  of  an  inverted  u.  and  curves  over  the 
lateral  fissure.  It  is  regarded  as  consisting  of  three 
parts — anterior,  middle,  and  posterior  (F.  ectosylvia 
anterior,  media,  posterior). 

3.  The  suprasylvian  fissure  lies  above  and  ai> 
proxiniately  concentric  with  the  preceding.  It  also 
consists  of  three  parts — anterior,  middle,  and  pos- 
terior. 

4.  The  ectomarginal  or  collateral  fissure  runs 
forward  on   the  dorsal   aspect   of   the    hemis])here 

almost  parallel  with  the  dorso-medial  border.  A  little  in  front  of  the  middle  of 
the  surface  it  gives  oiT  a  short  ansate  fissure  (F.  ansata)  which  runs  obliciuely 
inward  and  forward,  and  is  continued  bv  the  coronal  fissure. 


Fig.  542. — CF.REBRtr.M  of  Dog,  Dorsal 

ViKW. 

a.  End  of  lateral  fissure  (of  S\l- 
vius);  6,  ectosylvian  fissure;  c,  c',  r", 
suprasyKnan  fissure:  d,  fissura  ansata 
minor;  e,  ectolateral  fissure;  /,  ectomar- 
ginal or  collateral  fissure;  o,  fissura  an- 
sata; h,  coronal  fissure;  /,  meflilateral 
fissure;  /:,  entomar^nal  fissure;  /.post- 
cruciate  fissure;  m,  cruciate  fissure;  o, 
presyhnan  fissure;  p.  fissura  prorea. 
(.\fler  Ellenherger,  in  I.eisering's  .\tlas.) 


Fig.  54.1.— Fisscrks  of  L.mf.r.m.  Sirf;\ck  or  Ckrk- 
BRU.M  OF  Dog,  Right  .Sidk, 
a,  Fissura  prorea;  b,  frontal  fissure;  c,  ol- 
factory fissure;  d,  d' ,  sulcus  rhinalis;  e,  presylvian 
fissure;  /.  precruciate  fissure;  g,  postcruciate  fissure; 
A,  cruciate  fissure;  i,  lateral  fis.<ure  (of  Sylvius); 
*i  *'.  *",  suprasylvian  fissure;  (,  /',  /*,  ectosylvian 
fissure;  m,  fissura  ansata  minor;  n,  ectomarginal  oi 
collateral  fissure;  n,  fissura  ansata;  p,  coronal  fissure; 
q,  cclol.-teral  fissure;  r,  mcdilateral  fissure;  s, 
entomarginal  fissure.  (After  EllenlwrRer,  in  Leiser- 
ing's  Atlas.) 


Fig.  544. — Richt  Cerf-brai,  Hkmisphf.re  of  Dog, 
Inner  Side. 
1.  Corpus  callosum;  1' .  genu,  1",  splenium  of 
corpus  callosum;  a.  genual  fissure;  b,  splenial  fissure; 
c,  suprasplenial  fissure;  d,  hippocainpal  fissure;  e, 
sulcus  corporis  callosi;  /,  postsplenial  fissure;  g,  lesser 
cruciate  fissure;  h,  cruciate  fissure.  (After  Ellen- 
berger,  in  Leisering's  Atlas.) 


5.  The  coronal  fissure  is  the  continuation  of  the  ectomarginal.  It  runs  forward 
and  dow-nwarri,  curvintr  around  the  cruciate  fissure,  and  ends  behind  the  middle 
of  the  presylvian  fissure. 


THE  NERVOUS  SYSTEM  OF  THE  DOG 


'27 


6.  The  ectolateral  fissure  lies  between  the  posterior  part  of  the  ectoniarginal 
fissure  and  tin-  sviprasyhian  fissure. 

7.  The  entomarginal  fissure  hes  between  the  anterior  part  of  the  ectoniarginal 
fissure  and  the  dorso-meilial  border.     It  is  often  indistinct  and  not  rarely  absent. 

8.  The  presylvian  fissure  begins  at  the  sulcus  rhinalis,  a  little  in  front  of  its 
middle,  and  curves  over  the  anterior  third  of  the  lateral  surface  of  the  hemisphere 
in  front  of  the  coronal  fissure. 

9.  The  cruciate  fissure  is  the  deepest  and  most  characteristic.  It  cuts  deeply 
into  the  anterior  third  of  the  dorso-medial  border  and  runs  almost  straight  outward. 
It  is  continuous  on  the  inner  surface  of  the  hemisphere  with  the  calloso-marginal 
or  splenial  fissure. 

10.  The  sulcus  rhinalis  is  continued  on  the  tentorial  surface  of  the  hemisphere 


Ftg.  545. — Deep  Dissection  of  Heao  of  Dog,  showing  Especially  Trigeminal  and  Hypoglossal  Xerves. 
a.  Hypoglossal  nerve;  6,  cenical  branch  of  a;  c,  mamlibular  division  of  trigeminus:  d,  lingual  ner\-e;  e, 
nerve  to  subma?dllary  gland;  /,  deep  temporal  ner\'e;  g,  pterygoid  nerve;  h,  buccinator  nerve  (cut);  z.  inferior 
alveolar  or  dental  ner\'e;  fc,  staphyline  branch  of  lingual  nerve;  /.  chorda  tympani;  m,  mylo-hyoid  ner\-e;  n, 
sphenopalatine  nerve:  o,  lesser  palatine  ner\-e:  p,  great  palatine  nerve;  (j,  infraorbital  ner\-es;  ^,  subcutaneus 
malte;  s,  branch  of  oculomotor  nerve  to  inferior  oblique  muscle;  t,  lacrimal  nerve;  u.  frontal  nerve;  i\  trochlear 
ner\-e;  w,  abducens;  /,  carotid  artery;  3,  lingual  artery:  d.  internal  maxillary  artery;  .{,  Ihyro-pharjngeus  muscle; 
S,  hyo-pharyngeus  muscle;  6.  thyro-hyoideus;  7,  sterno-hyoideus;  S,  baseo-glossus,  9.  genio-hyoideus;  10, 
genio-glossus;  /7,  stylo-glossus;  75,  pterj'goideus  internus;  i,^,  outline  of  submaxillary  gland  (dotted):  /4,  atlas; 
7-5,  bulba  ossea;  /5.  zygomatic  arch  (dotted);  J 7",  rectus  oculi  inferior;  /<S.  obliquus  oculi  inferior.  (Ellenberger- 
Baum,  .\nat.  d.  Hundes.) 


by  the  occipito-temporal  fissure.     Anteriorly  it  is  prolonged  as  the  olfactory  fis- 
sure, which  is  concealed  by  the  olfactory  l)ulb  and  tract. 

11.  The  calloso-marginal  or  splenial  fissure  is  parallel  with  the  splenium  and 
middle  part  of  the  corpus  callosum  on  the  inner  surface  of  the  hemisphere.  It  is 
continuous  in  front  with  the  cruciate  fissure  and  runs  do^\^lward  and  outward 
across  the  tentorial  surface  to  join  the  occipito-temporal  fissure  and  sulcus 
rhinalis.  It  gives  off  from  its  Wghest  part  the  short  lesser  or  accessory  cruciate 
fissure. 

12.  The  suprasplenial  fissure  runs  almost  parallel  with  the  posterior  part  of 
the  calloso-marginal  fissure  on  the  inner  and  tentorial  surfaces  of  the  hemisphere. 

The  olfactory  bulb  is  large  and  is  strongly  compressed  laterally;  its  anterior 
end  projects  beyond  the  frontal  pole  of  the  hemisphere.     The  tract  is  short  and  is 


728  THK  NEUVOUS  SYSTEM  OF  THE  DOG 

alsu  flattpiiecl  laterally.  Both  contain  a  narrow  cavity  which  communicates  with 
the  lateral  ventricle.     The  pyriform  lobe  is  large  and  rounded. 

The  cranial  nerves  ])re«'nt  tlie  following  special  features  which  are  worthy  of 
notice: 

The  ophthalmic  nerve  gives  oif  lacrimal,  frontal,  long  ciliary,  ethmoidal,  and 
infratrochlear  l)ranches.  The  lacrimal  nerve  arises  from  the  ophthalmic  at  its 
origin;'  its  recurrent  branch  emerges  at  tiie  orbital  ligament  and  concurs  with  the 
zygomatic  and  frontal  nerves  in  the  formation  of  the  anterior  auricular  plexus. 
The  frontal  nerve  emerges  from  the  orliit  in  front  of  the  upper  end  of  the  orbital 
ligament,  ramifies  in  the  upper  lid  and  the  adjacent  skin  of  the  forehead,  and  sends 
branches  backward  to  the  anterior  auricular  plexus.  The  long  ciliary  nerve  ac- 
companies the  optic  nerve  and  divides  into  several  branches  which  jiierce  the  pos- 
terior part  of  the  sclera.  The  ethmoidal  nerve  gives  off  internal  nasal  branches  and 
ends  in  th(>  nmzzle.     The  infratrochlear  nerve  runs  forward  between  the  internal 


Fic.  r)4fi. — Nerves  of  Fate  oi-  Dor,.  FAnoTin  fJt.ANn  is  Removed. 
a,  Facial  nerve;  b,  posterior  auricular  nerve;  c,  internal  auricular  nerve;  d,  digastric  nerve;  e,  inferior 
buccal  nerve;  /,  cervical  branch  of  facial;  ti,  auriculo-palpebral;  h,  superior  buccal  nerve;  /,  temporal  branch; 
k,  k',  k",  zygomatic  branch;  I,  auriculo-temporal;  m,  malar  branch  of  /,-  n,  buccinator  nerve;  o,  mylo-hyoiil 
branch;  p,  subcutaneu.s  malai;  q,  lacrimal  nerve;  r,  frontal  nerve;  s,  infratrochlear  nerve;  /.  infraorbit.il  nerve; 
1,  i>aramastoi(l  process;  2,  fligastricus  muscle;  S,  base  of  concha;  4,  masseter;  6,  zygomaticns;  (>,  scutularis; 
7,  zygomatic  arch;  S,  maxilla.     (Ellcnberger-Baum,  .\nat.  d.  Huntles.) 

straight  and  the  superior  oliliciue  muscles  of  the  eye  and  ramifies  on  the  face  in 
the  vicinity  (if  the  inner  canthu.s. 

Tlie  maxillary  nerve,  after  giving  off  the  zygomatic,  divides  into  infraorbital 
and  sphenopalatine  branches.  The  zygomatic  nerve  emerges  through  an  opening 
in  the  ui)per  part  of  the  orbital  ligiunent  and  ramifies  in  tlie  lower  lid  and  on  the 
adjaciMit  surface  of  the  face.  The  infraorbital  nerves,  two  in  number,  tlivide  within 
the  infra()rl)ital  canal  and  ;tfter  their  emergence  upon  the  face,  thus  forming  seviMi 
or  eight  external  nasal  and  superior  labial  branches.  The  sphenopalatine  nerve 
gives  off  lesser  ;uii!  greater  palatine  ami  posterior  nasal  nerves. 

Tlie  mandibular  nerve  jiasses  out  through  the  foramen  ovale.  The  superficial 
temporal  nerve  divides  into  auricular,  temporal,  and  malar  branches;  the  last- 
named  crosses  the  masseter  and  ramifies  with  the  buccal  nerves.  The  mylo-hyoid 
nerve  is  given  off  from  the  mandibular  nerve  almost  immediately  after  the  latter 
emerges  from  the  cranium;  it  innervates  the  mylo-hyoideus  and  digastricus  and 
gives  off  a  branch  which  turns  around  the  lower  jaw,  joins  the  inferior  buccal  nerve, 

'  The  origin  of  tlic  lurrimal  ncrvo  is  .sucli  that  Kllenberger-Baum  and  Martin  describe  it 
as  a  branch  of  tlie  maxillary  nerve. 


THE  NERVOUS  SYSTEM  OF  THE  DOG  729 

and  ramifies  on  the  lateral  surface  of  the  face.  The  inferior  alveolar  nerve  arises 
by  a  common  trunk  with  the  mylo-hyoid;  it  gives  oft'  dental  branches  and  term- 
inates in  mental  and  inferior  labial  branches.  The  lingual  nerve  supplies  vaso- 
dilator and  excito-secretory  filaments  to  the  submaxillary  and  sublingual  salivar}' 
glands;   these  fibers  are  derived  from  the  chorda  tympani. 

The  facial  nerve  divides  near  the  iiosterior  border  of  the  jaw  into  four  branches. 
The  upper  branch  is  the  auriculo-palpebral  nerve,  which  divides  after  a  very  short 
course  into  anterior  auricular  and  zygomatic  branches.  The  latter  curves  upward 
and  forward  across  the  zygomatic  arch  toward  the  eye,  and  divides  into  branches 
which  supply  the  eyelids  and  nasal  region  and  concur  with  the  frontal  and  lacrimal 
nerves  in  forming  the  anterior  auricular  plexus.  The  superior  buccal  nerve  ac- 
companies the  parotid  duct  across  the  masseter.  The  inferior  buccal  nerve  runs 
forward  along  the  lower  border  of  the  masseter  and  the  mandible.  The  two  nerves 
ramify  on  the  cheek  and  anastomose  with  each  other  and  the  infraorbital  nerves 
to  form  a  plexus  from  which  branches  go  to  the  muscles  of  the  lips  and  nostrils. 
The  cervical  branch  runs  downward  and  backward  over  the  submaxillary  gland 
and  ramifies  in  the  cervical  panniculus;  it  communicates  with  the  inferior  buccal 
nerve  and  sends  twigs  to  the  parotido-auricularis  muscle  and  the  submaxillary 
space. 

The  vagus  bears  a  jugular  ganglion  and  a  ganglion  nodosum.  The  latter  is 
situated  near  the  superior  cervical  ganglion  on  the  rectus  capitis  anterior  major 
and  dorsal  to  the  carotid  artery;  it  is  fusiform  and  may  lie  about  half  an  inch  (ca. 
1  to  1.0  cm.)  long  in  a  large  dog.  In  its  course  in  the  neck  the  nerve  is  inclosed  with 
the  sympathetic  trunk  in  a  common  sheath  and  is  related  ^-entrally  to  the  common 
carotid  artery.  The  formation  of  dorsal  and  ventral  oesophageal  trunks  by  the 
union  of  the  dorsal  and  ventral  divisions  of  the  two  nerves  takes  place  at  the  hiatus 
oesophageus.  The  dorsal  trunk  concurs  with  branches  of  the  solar  plexus  in  forming 
the  posterior  gastric  plexus  on  the  visceral  surface  of  the  stomach.  The  ventral 
trunk  ramifies  on  the  jiarietal  surface  of  the  .stomach,  forming  the  anterior  gastric 
plexus,  from  which  a  considerable  branch  passes  along  the  lesser  curvature  to  the 
pylorus.  Some  special  features  of  the  collateral  branches  are:  Two  pharyngeal 
branches  are  present.  The  superior  pharyngeal  branch  arises  from  the  vagus 
above  the  ganglion  nodosum.  It  passes  under  the  deep  face  of  the  carotid  artery 
and  descends  on  the  lateral  surface  of  the  jiharynx  to  end  in  the  crico-thyroid  muscle. 
It  furnishes  a  root  of  the  inferior  pharyngeal  branch,  and  comnmnicates  with  the 
pharyngeal  branch  of  the  ninth  and  with  the  superior  laryngeal  and  hypoglossal 
nerves.  The  inferior  pharyngeal  branch  is  formed  by  the  union  of  roots  derived 
from  the  superior  pharyngeal  nerve  and  the  ganglion  nodosum,  together  with  fila- 
ments from  the  superior  cervical  ganglion.  It  crosses  the  side  of  the  pharynx 
behind  the  superior  pharyngeal  and  ramifies  on  the  posterior  constrictor  of  the 
pharynx  and  the  origin  of  the  cesophagus.  It  contributes  filaments  to  the  pharyn- 
geal plexus,  communicates  with  the  recurrent  nerve,  and  supplies  twigs  to  the  thy- 
roid gland.  The  pharyngeal  plexus  is  formed  on  the  lateral  surface  of  the  pharynx 
by  branches  of  the  pharyngeal  nerves  and  the  communications  above  described; 
branches  from  it  innervate  the  muscles  and  mucous  meml)rane  of  the  pharynx. 
The  superior  laryngeal  nerve  arises  from  the  ganglion  nodosiun  and  descends  over 
the  side  of  the  phar\'nx.  crossing  beneath  the  carotid  artery  and  the  superior  laryn- 
geal nerve.  It  passes  through  the  thyroid  notch  and  ramifies  in  the  mucous  mem- 
brane of  the  larynx.  It  communicates  with  the  superior  cervical  ganglion  and  the 
superior  pharyngeal  branch  of  the  vagus,  and  gives  twigs  to  the  hyo-pharyngeus 
muscle.  Immediately  after  its  entrance  into  the  larynx  it  gives  off  a  large  branch 
which,  instead  of  uniting  with  the  recurrent  as  in  the  other  animals,  has  a  peculiar 
arrangement.  It  runs  back  near  the  dorsal  bortler  of  the  thyroid  cartilage,  gives  a 
branch  to  the  crico-arytenoideus  posterior  as  it  pa.sses  over  that  muscle,  and  con- 


730  THE  NERVOUS  SYSTEM  OF  THE  DOG 

tiiiue«  along  the  trachea  internal  to  the  recurrent  nerve.  At  the  thoracic  inlet  it 
communicates  with  the  inferior  cervical  ganglion  and  continues  backward  to  unite 
with  the  vagus  at  or  near  the  point  of  origin  of  the  recurrent  nerve.  Its  collateral 
filaments  supi)ly  the  trachea  and  concur  with  the  inferior  pharyngeal  branch  in 
forming  a  ]ilexus  on  the  cervical  ])art  of  the  cesophagus  which  innervates  that  tube.' 
The  depressor  nerve  is  a  very  delicate  filament  which  arises  usually  from  the  supe- 
rior laryngeal  nerve  and  accompanies  the  vago-s^^npathetic  trvudc  to  the  tliorax; 
its  fii)ers  reach  the  heart  through  the  cardiac  nerves.  The  pulmonary  and  pos- 
terior oesophageal  plexuses  are  highl.v  developed. 

The  hypoglossal  nerve  gives  off  a  long  branch  (R.  descendens)  which  rvms 
downward  and  backward  across  the  pharynx  and  larynx,  communicates  with  the 
ventral  branch  of  the  first  cervical  nerve,  and  supplies  the  thyro-hyoid,  sterno- 
hyoid, and  sterno-thyroid  muscles. 

The  spinal  nerves  number  thirty-six  or  thirty-seven  on  either  side,  and  com- 
prise eight  cervical,  thirteen  thoracic,  seven  lumbar,  and  five  or  six  coccygeal. 

The  brachial  plexus  (Fig.  487)  is  derived  from  the  ventral  branches  of  the  last 
four  cervical  anil  first  thoracic  nerves;  the  root  supplied  by  the  fifth  cervical  nerve 
is  very  small.  The  roots  unite  at  the  lower  border  of  the  scalenus.  The  more 
important  special  features  in  the  arrangement  of  the  nerves  which  emanate  from 
the  plexus  are  as  follows; 

The  musculo-cutaneous  nerve  passes  between  the  coraco-brachialis  and  the 
brachial  artery  and  descends  in  the  arm  in  front  of  the  artery.  At  the  shoulder 
joint  it  gives  off  branches  to  the  biceps  and  coraco-brachialis,  and  in  the  lower  third 
of  the  arm  is  connected  with  the  median  nerve  by  an  oblique  branch.  It  terminates 
near  the  elbow  by  dividing  into  a  branch  for  the  brachialis  and  a  small  cutaneous 
nerve  which  passes  down  over  the  inner  face  of  the  elbow  and,  inclining  a  little 
forward,  descends  over  the  deep  fascia  of  the  forearm  to  the  carpus. 

The  radial  nerve  descends  behind  the  ulnar  nerve,  gives  branches  to  the  ex- 
tensors of  tiie  eU)ow,  dips  in  between  the  internal  head  of  the  triceps  and  the  ac- 
cessory head  of  the  anconeus,  winds  around  the  arm,  and  divides  between  the  brach- 
ialis and  the  external  head  of  the  triceps  into  two  branches.  The  deep  branch 
(R.  profundus)  supplies  the  extensor  and  supinator  muscles  on  the  forearm.  The 
superficial  branch  (R.  superficialis)  emerges  upon  the  flexor  surface  of  the  elbow 
and  divides  into  two  liranches  which  terminate  by  supplying  two  dorsal  digital 
nerves  to  each  digit,  except  the  fifth,  which  receives  its  outer  dorsal  nerve  from  the 
ulnar.  The  inner  branch  descends  along  the  inner  side  of  the  cephalic  vein  to  the 
carjjus,  where  it  divides  into  dorsal  digital  nerves  for  the  first  digit  and  the  inner 
side  of  the  second.  The  outer  branch  is  much  larger.  It  runs  downward  on  the 
middle  of  the  front  of  the  forearm  and  supplies  the  remaining  dorsal  digital  nerves 
except  that  to  the  outer  side  of  the  fifth  digit. 

The  ulnar  nerve  is  as  large  as  or  larger  than  the  median,  with  which  it  is  united 
for  some  distance.  At  the  distal  third  of  the  arm  it  separates  from  the  median 
and  passes  over  the  internal  epicondyle  of  the  humerus.  At  the  proximal  part  of 
the  forearm  it  gives  off  the  dorsal  branch  (R.  dorsalis),  which  supplies  cutaneous 
twigs  to  the  dorso-lateral  surface  of  the  lower  part  of  the  forearm  and  carpus  and 
terminates  as  the  external  dorsal  digital  nerve  of  the  fifth  digit.  Descending  under 
cover  of  the  flexor  carpi  ulnaris,  the  ulnar  nerve  inclines  inward  under  the  tendon 
of  insertion  of  that  nniscle  and  divides  into  sui)erficial  antl  dee|)  branches.  The 
superficial  branch  (R.  superficialis)  runs  downward  along  the  outer  border  of  the 
flexor  tendons,  gives  off  the  external  volar  digital  nerve  of  the  fifth  digit  (X.  dig. 
vol.  lat.  dig.  V),  and  a  branch  (X.  met.  vol.  IV)  which  descends  in  the  space  between 
the  fourth  and  fifth  metacarpal  bones  and  unites  with  the  deep  l)ranch.     The  deep 

'  Lesbre  terms  this  the  tracheo-cesophagcal  branch,  and  considers  that  it  mu.st  bo  regarded 
as  an  accessory  or  internal  recurrent  nerve. 


THE  NERVOUS  SYSTEM  OF  THE  DOG 


731 


branch  (R.  profuiulus)  descends  in  the  carpal  canal  and  di\ides  under  the  deep 
Hexor  tentlon  into  its  terminal  Ijranchcs.  The  smaller  of  these  supply  the  volar 
metacariial  nmscles.  The  larger  terminals  are  the  three  volar  common  digital 
nerves  (Nn.  dig.  vol.  comm.  II,  III,  IV),  which  descend  along  the  second,  third, 
and  fourth  intermetacarpal  spaces,  sul)divide,  and  concur  with  the  volar  metacarpal 
branches  of  the  median  nerve  in  forming  the  volar  proper  digital  nerves  (Xn.  clig. 
vol.  proprii). 

The  median  nerve  descends  behind  the  brachial  arterj',  passes  over  the  internal 
epicondyle  of  the  humerus,  then  under  the  pronator  teres,  and  continues  in  the 
forearm  under  cover  of  the  flexor  carpi  radialis.     It  gives  l)ranches  below  the  elbow 


Branches  o/^tTl" 
radial  nerve 


Median  nerve 


Fig.  547. — Nkrvks  of  Distal  Part  of  Right  Fore 

Limb  of  Dog,  -\xterior  View  (Schematic). 

p,  Dorsal  proper  digital  nerves. 


Es  OF  Distal  Part  of  Right  Fore 
Dog,  Posterior  View  (Schematic). 
n,  \'olar  proper  digital  nerv'es. 


to  the  flexor  and  pronator  muscles,  and  lower  down  a  palmar  branch  to  the  skin 
on  the  inner  and  posterior  aspect  of  the  carpus,  and  terminates  between  the  super- 
ficial and  deep  flexor  tendons  by  dividing  into  three  volar  metacarpal  nerves 
(N.  met.  vol.  I,  II,  III).  These  descend  in  the  first,  second,  and  third  intermeta- 
carpal spaces  and  unite  with  the  volar  common  digital  nerves  in  forming  volar 
proper  digital  nerves.  The  arrangement  of  the  digital  nerves  is  indicated  in  the 
annexed  schematic  figures. 

The  lumbo-sacral  plexus  is  formed  from  the  ventral  branches  of  the  last  five 
lumbar  and  first  sacral  nerves.  The  more  important  special  facts  in  regard  to  the 
nerves  of  the  pelvic  limb  are  as  follows: 

The  saphenous  nerve  (Fig.  492)  is  relatively  large,  and,  in  fact,  might  be 


J32 


THE  NERVOUS  SYSTEM  OF  THE  DOG 


considered  as  the  eontimuition  of  the  femoral  nerve.  It  descends  at  first  in  front 
of  the  femoral  artery,  then  passes  over  the  lower  part  of  the  inner  surface  of  the 
thigh  with  the  saphenous  artery,  continues  down  the  leg  with  the  dorsal  branch  of 
that  vessel,  and  anastomoses  with  branches  of  the  superficial  peroneal  nerve.  It 
supplies  cutani'ous  twigs  from  the  stifle  to  the  metatarsus. 

The  peroneal  nerve  separates  from  the  tibial  above  the  origin  of  the  gastrocne- 
mius, runs  downward  and  forward  across  the  outer  head  of  that  muscle,  passes 
between  the  ileep  flexor  of  the  digit  and  the  peroneus  longus,  and  divides  into  super- 
ficial and  deep  branches.  The  superficial  peroneal  nerve  descends  the  leg  along 
the  peroneus  tertius  and  longus,  gives  off  a  dorsal  branch  to  the  first  digit  (N.  cutan- 
eus  dorsalis  inedialis),  and  divides  at  the  proximal  part  of  the  metatarsus  into  three 


Inlcrnal  idanlar 
nerve 


Dorsal  common  . 
digilal  nerves 


Plantar 
common 
digilal 


Fig.  549.— Nerves  of  Distal  Part  of  Right  Hin 

Limb  of  Doc,  .\nterior  View  (Schematic). 

p,  Dorsal  proper  digital  nerves. 


Fig.  550. — Nerves  of  Distal  Part  of  Right  Hixn 

Limb  of  Dog.  Posterior  View  (Schematic). 

V,  Plantar  projier  digital  nerves. 


dorsal  common  digital  nerves  (Nn.  dig.  pedis  dors.  comm.  II,  III,  IV).  These 
descend  with  the  superficial  dorsal  metatarsal  arteries  and  concur  with  branches 
of  the  deep  peroneal  n(>rve  in  forming  dorsal  proper  digital  nerves  (Nn.  dig.  ped. 
prop,  dorsales).  The  deep  peroneal  nerve  passes  down  the  leg  with  the  anterior 
tibial  vessels.  It  gives  twigs  to  the  hock  joint  and  the  extensor  brevis  muscle, 
and  divides  into  three  dorsal  metatarsal  nerves  (Nn.  met.  dors.  II,  III,  IV); 
these  descend  with  the  corresixjiiding  arteries  along  the  intermetatarsal  spaces 
ami  unite  with  the  dorsal  common  digital  nerves  in  supplying  the  dorsal  proper 
digital  nerves. 

The  tibial  nerve  divides  at  the  tarsus  into  two  plantar  branches.     The  internal 
plantar  nerve  descends  along  the  inner  border  of  the  superficial  flexor  tendon  and 


THE  NERVOUS  SYSTEM  OF  THE  DOG  733 

divides  near  tlie  iniildle  of  the  metatarsus  into  two  branches.  Of  these,  the  internal 
branch  constitutes  the  first  plantar  common  digital  nerve  (N.  dig.  comm.  plant.  I). 
The  outer  branch  descentis  cm  the  sujierfieial  flexor  tendon  and  divides  into  three 
plantar  metatarsal  nerves  (Xn.  met.  plant.  II.  Ill,  l\),  which  unite  with  the 
plantar  common  digital  nerves.  The  external  plantar  nerve  passes  down  between 
the  flexor  tendons,  sends  twigs  to  the  imi.-^cles  on  the  jilantar  surface  of  the  metatar- 
sus, and  divides  into  three  plantar  common  digital  nerves  (Xn.  dig.  comm.  plant.  II, 
III,  IV).  These  descend  with  the  deep  plantar  metatarsal  arteries  in  the  second, 
third,  and  fourth  intermetatarsal  spaces,  receive  the  plantar  metatarsal  nerves, 
and  divide  into  plantar  proper  digital  nerves,  which  pass  down  the  opposed  surfaces 
of  the  second  to  the  fifth  digits. 

The  sjmipathetic  system  presents  few  special  features  worthy  of  mention. 
The  superior  cervical  ganglion  lies  above  the  ganglion  nodosum  close  to  the  cranial 
base  and  internal  to  the  origin  of  the  internal  carotid  and  occipital  arteries.  It 
forms  connections  directly  or  through  the  carotid  plexus  with  the  last  seven  cranial 
and  first  cer\'ical  nerves.  The  cervical  trunk  unites  with  the  vagus  so  intimately 
as  to  form  a  vago-s\-mpathetic  trunk.  There  may  be  a  small  middle  cervical 
ganglion  in  front  of  the  inferior  cervical  ganglion.  The  latter  is  usually  distinct 
from  the  first  thoracic  ganglion,  which  is  stellate  and  lies  on  the  longus  colli  opposite 
the  second  rib  and  intercostal  space. 


/ESTHESIOLOGY 
THE  SENSE  ORGANS  AND  COMMON  INTEGUMENT 

The  organs  of  the  senses  (Organa  sensuum)  receive  external  stimuh  and  conduct' 
impulses  to  the  brain  which  result  in  sensations  of  sight,  hearing,  taste,  smell,  and 
touch.  They  consist  essentially  of  specially  differentiated  cells,  the  neuro-epithe- 
lium,  and  a  conduction  path  which  is  simple  in  the  more  generalized  sense  organs, 
elaborate  in  those  which  are  highly  specialized — the  eye  and  the  car. 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 
The  Eye 

The  eye  or  organ  of  vision  (Organon  visus)  in  the  broader  sense  of  the  term 
comprises  the  eyeball  or  globe  of  the  eye,  the  optic  nerve,  and  certain  accessory 

Upper  eyelid 
Third  eyelid     • 
Caruncula       \  j 

lacrimalis        \  i 


Inner  canthvs 


l^uirer  eyelid 
Fk;.  551. — Lkpt  Eye"  op  Horsk. 
9,  ZyKOiiiatic  arch;   10.  .supraorhKal  depression;   12.  supraorbital  procRss;  27.  facial  cresl.     (Afler  Ellenberger- 
Haum.  Anat.  fiir  Kiinstler.) 

organs  associated  therewith.  The  accessory  organs  (Organa  oculi  accessoria)  are 
the  orbital  fascia;  and  muscles,  the  eyelids  and  conjunctiva,  and  the  lacrimal 
apparatus.  These  structures  will  be  considered  in  the  order  in  which  they  may  be 
most  conveniently  examined,  taking  the  horse  as  a  type.  The  bony  walls  of  the 
orbit  have  been  described  in  connection  with  the  skull;  the  periorbita,  a  fibrous 
membrane  which  incloses  the  eyeball  together  with  its  muscles,  vessels,  and  nerves, 
may  be  appropriately  included  in  the  account  of  the  fascise. 

734 


THE  EYELIDS  AND  CONJUNCTIVA 


r35 


THE  EYELIDS  AND  CONJUNCTIVA 
The  eyelids,  uiiper  and  lower  (Paliiehra  sujierior  et  inferior),  are  movable 
folds  of  integument  situated  in  front  of  the  eyeball.  When  closed,  thej'  cover  the 
entrance  to  the  orbit  and  the  anterior  surface  of  the  eyeball.  The  upper  lid  is 
much  more  extensive  and  more  movable  than  the  lower  one,  and  its  free  edge  is 
more  concave.  The  interval  between  the  lids  is  termed  the  palpebral  fissure  (Rima 
palpelirarum).  When  the  ej'e  is  closed,  it  is  an  oblique  slit  about  two  inches  (ca. 
5  cm. )  in  length ;  when  open,  it  is  bicon- 
vex in  outline.  The  ends  of  the  fissure 
are  the  angles  or  canthi,  and  are  dis- 
tinguished as  internal  or  nasal,  and 
external  or  temporal  (Angulus  oculi 
medialis,  lateralis ) .  The  external  angle 
is  rounded  when  the  eye  is  open,  but 
the  internal  angle  is  narrowed  to  form 
a  ^  -shainMl  bay  or  recess,  termed  the 
lacrimal  lake  (Lacus  lacrimalis).  In 
this  there  is  a  rounded,  pigmented 
prominence  known  as  the  lacrimal 
canmcle  (C'aruncula  lacrimalis) ;  it  is 
about  the  size  of  a  small  pea  and  is 
covered  with  modified  skin,  connected 
with  that  of  the  inner  commissure, 
from  which  project  a  number  of  hairs 
'  provided  with  sebaceous  glands.  The 
lids  unite  on  either  side  and  form  the 
commissures,  internal  and  external 
(C'onunissiu'a  palpebrarum  medialis, 
lateralis).  The  anterior  surface  of 
the  lids  (Facies  anterior  palpebrarum) 
is  convex  and  presents  a  varialjle  num- 
ber of  long  tactile  hairs  in  addition  to 
the  ordinary  but  verj'  short  hairs.  A 
considerable  number  of  tactile  hairs 
are  scattered  over  the  lower  part  of 
the  lower  lid,  but  on  the  upper  lid 
they  are  very  scanty.  The  infrapal- 
pebral  depression  (Sulcus  infrapalpe- 
bralis)  indicates  somewhat  indistinctly 
the  limit  of  the  lower  lid.  The  upper 
lid  is  marked  by  tw'o  furrows  when 
raised.  The  posterior  svirface  (Facies 
posterior  palpebrarum)  is  adapted  to 
the  free  surface  of  the  eyeball  and  is 
covered  by  the  palpebral  conjunctiva.  The  free  border  of  the  lid  is  smooth  and 
usually  black.  It  has  a  well-defined  posterior  margin  (Limbus  palpebralis  pos- 
terior), along  which  the  ducts  of  the  tarsal  glands  open.  The  anterior  margin 
(Limbus  palpebralis  anterior)  bears  stiff  hairs  termed  the  cilia  or  eyelashes.  On 
the  upper  lid  the  cilia  are  long  and  numerous  except  at  its  inner  third,  where 
they  are  verj'  small  or  absent.  On  the  lower  lid  the  cilia  are  often  scarcely 
distinguishable  from  the  ordinary  hairs;  in  other  cases  they  may  be  clearly  seen 
except  near  the  external  canthus,  and  are  much  finer  and  shorter  than  those  of 
the    upper  lid.     The  edge  of  each  lid  is  pierced  near  the  internal  angle  by  a 


Fig. 


'7  3 

—Vertical   Section  of    Antehior    Part  of 

Eye  of  Horse,  with  Lids  Half  Closed. 

1,  Tarsal  gland  of  upper  lid;  2,  palpebral  con- 
junctiva; 3,  fornix  conjunctiva';  -J.  levator  palpebra* 
superioris;  5,  orbicularis  oculi;  6,  cornea;  7,  anterior 
chamber;  8,  iris;  9,  9\  granula  iridis,  10,  posterior 
chamber;  11,  ciliary  process;  12,  ciliary  muscle;  IS, 
ciliarj'  zone  or  suspensorj'  lig.  of  lens;  1^,  chorioid;  15^ 
sclera;  16,  lens;  17,  root  of  tactile  hair.  (After  Bayer, 
Augenheilkunde.) 


736  THE    SENSE    ORGANS    AND    SKIN    OF   THE    HORSE 

iniiiutc.   slit-like  ojioniiiK,   the  punctum  lacrimalis,  which  is  the  entrance  to  the 
lacrimal  duct  or  canaliculus. 

Structure  of  the  Eyelids. — The  skin  of  the  eyehds  is  thin  and  freely  movable, 
except  near  the  free  edge,  where  it  is  more  firmly  attached.  The  underlying 
subcutaneous  tissue  is  destitute  of  fat.  The  muscular  layer  consists  chieflj-  of  the 
elliptical  bundles  of  the  orbicularis  oculi,  with  which  are  associated  fibers  of  tlie 
corrugator  supercilii  in  the  upper  lid  and  the  malaris  in  the  lower  lid.  At  the  inner 
side  there  is  a  fibrous  band,  the  palpebral  ligament,  which  is  attached  to  the  lacrimal 
tubercle  and  furnishes  origin  to  some  fibers  of  the  orbicularis.  At  the  inner  com- 
missure a  bundle  detached  from  the  orbicularis  passes  inward  behind  the  lacrimal 
sac,  and  is  known  as  the  pars  lacrimalis  or  Horner's  muscle.  At  the  outer  side  an 
indistinct  i)alpebral  raphe  occurs  where  fibers  of  the  orbicularis  decussate.  The 
fibrous  layer  is  thicker  and  denser  along  the  free  edge  of  the  lid,  forming  here  the 
tarsus.  The  tarsus  furnishes  insertion  to  a  layer  of  unstriped  muscle  known  as  the 
tarsal  nniscle  (of  ]\liiller).  The  tarsal  glands  (CJlandulse  tarsales)  are  partly 
embedded  in  the  deep  face  of  the  tarsus,  and  are  visible  when  the  lid  is  everted  if 
the  conjunctiva  is  not  too  strongly  pigmented.  They  are  arranged  in  a  linear 
series,  close  together,  and  with  their  long  axes  perpendicular  to  the  free  edge  of 
each  lid.  In  the  upper  lid  they  number  forty-five  to  fifty;  in  the  lower,  thirty  to 
thirty-five.     Each  consists  of  a  tulnilar  duct  beset  with  numerous  alveoli,  in  which  a 


Fi<i.   55.3. — Piece  op  Upper  Eyelid,  Inner  Surface.       Fig.  554. — Cartilage  of  Third  Eyelid  of  Horse, 
/,  ('ili.i;    S.  limbus  palp,  posterior;    S,  tarsal  glaotls.  Convex  Surface. 

(.-Vfter  Ellenberger,  in  Leiseriiig's  .\llas.)  i,  Gland;    a,  fat   surrounding  deep    part   of  cartilage. 

(After  EUenberger,  in  Leisering's  Atlas.) 

fatty  substance,  the  palpebral  sebirni,  is  secreted.     The  palpebral  conjunctiva  lines 
the  ]i()sterior  surface  of  the  eyelids. 

The  conjunctiva  is  the  mucous  membrane  which  lines  the  lids  as  palpebral 
conjunctiva  (( ".  palpebrarum)  and  is  reflected  upon  the  anterior  part  of  the  eyeball 
as  bulbar  conjunctiva  (C.  bulbi);  the  line  of  reflection  is  termed  the  fornix  con- 
junctivae. The  palpeljral  part  is  closely  adherent  to  the  tarsus,  but  is  loosely  at- 
tached further  back.  It  is  papillated  and  is  covered  with  stratified  cylindrical 
epithelium  in  which  many  goblet-cells  are  present.  In  the  fornix  and  its  vicinity 
there  are  tubular  glands  (of  Henle).  Near  the  inner  angle  there  are  numerous 
lymph  nodules.  The  conjunctiva  of  the  outer  part  of  the  upper  lid  is  pierced  near 
the  fornix  by  the  orifices  of  the  excretory  ducts  of  the  lacrimal  gland.  The  bulbar 
conjunctiva  is  loosely  attached  to  the  anterior  part  of  the  sclera  and  is  pigmented 
in  the  vicinity  of  the  corneo-scleral  junction.  On  the  cornea  it  is  represented  by  a 
stratified  epithelium. 

When  the  lids  are  in  apposition,  the  conjunctiva  (including  the  epithelium  of  the  cornea) 
fonn.s  a  complete  conjunctival  sac,  as  the  capillary  space  between  the  lids  and  the  eyeball 
is  termed. 

The  third  eyelid  (Palpebra  tcrtia)  is  situated  at  the  inner  angle  of  the  eye 
(Figs.  5.51,  .").")()).  It  consists  of  a  semilunar  fold  of  the  conjunctiva,  known  as  the 
membrana  nictitans,  which  covers  and  partly  incloses  a  curved  plate  of  hyaline 
cartilage.     Its  marginal  part  is  thin  and  usually  more  or  less  pigmented.     The 


THE    LACRIMAL    APPARATUS  737 

cartilage  has  an  elongated  quadrilateral  outline.  The  part  of  it  which  lies  in  the 
membrana  is  wide  and  thin.  The  deep  part  is  narrower  and  thicker  and  is 
embedded  in  fat  at  the  inner  side  of  the  ej'eball.  Numerous  minute  lymph  nodules 
occur  in  the  membrana  nictitans,  anil  the  deep  part  of  the  cartilage  is  surrounded 
by  a  gland  which  resembles  the  lacrimal  gland  in  structure  (Glandula  superficialis 
palpebriE  tertise). 

Ordinarily  the  third  cychd  cxteiKls  very  httle  over  the  inner  end  of  the  cornea,  but  when  the 
evcl5all  is  strongly  retracteil  (a.s  in  tetanus)  tlie  membrana  is  protruded  over  it  so  as  to  measure 
about  an  inch  (ca.  2  to  3  cm.)  in  its  middle.  Tliis  effect  results  from  the  pressure  of  the  eyeball 
and  its  muscles  on  the  fat  which  surrounds  the  deep  part  of  the  cartilage. 

Vessels  and  Nerves. — The  arteries  which  chiefly  supply  the  eyelids  and  con- 
junctiva are  branches  of  the  ophthahnic  and  facial  arteries,  and  the  blood  is  drained 
away  by  corresponding  veins.  The  sensory  nerves  are  liranchcs  of  the  ophthalmic 
and  maxillary  divisions  of  the  trigeminus.  The  motor  nerves  to  the  orbicularis 
oculi,  corrugator  supercilii,  and  malaris  come  from  the  facial  nerve,  the  levator 
paljjebrae  superioris  is  innervated  by  the  oculomotor,  and  the  unstriped  muscle  of 
the  lids  by  the  sympathetic. 

THE  LACRIMAL  APPARATUS 

The  lacrimal  apparatus  (Apparatus  lacrimalis)  comprises:  (1)  the  lacrimal 
gland,  which  secretes  the  clear  lacrimal  fluid;  (2)  the  excretory  ducts  of  the  gland; 
(3)  the  two  lacrimal  ducts  or  canaliculi,  lacrimal  sac,  and  naso-lacrimal  duct,  which 
receive  the  fluid  and  convey  it  to  the  nostril. 

The  lacrimal  gland  (Glantlula  lacrimalis)  is  situated  between  the  supraorbital 
process  and  the  dorso-lateral  surface  of  the  eyeball  (Fig.  438).  It  is  flattened,  oval 
in  outline,  and  measures  about  two  inches  (ca.  5  cm.)  transversely  and  an  inch  or 
more  (2. .5  to  3  era.)  in  the  sagittal  direction.  Its  upper  face  is  convex  and  is  related 
to  the  concave  lower  surface  of  the  supraorbital  process.  The  lower  face  is  concave 
in  adaptation  to  the  eyeball,  from  which  it  is  separated  by  the  periorbita.  The 
excretory  ducts  (Ductuli  excretorii)  are  very  small  and  are  twelve  to  sixteen  in 
numi)er;  they  opeii  into  the  outer  part  of  the  conjunctival  sac  along  a  line  a  little 
in  front  of  the  fornix  conjunctiva  superior.  In  appearance  and  structure  the 
gland  resembles  the  parotid.  It  receives  its  blood-supply  chiefly  from  the  lacrimal 
artery.  The  sensory  nerve  is  the  lacrimal,  and  the  secretory  fibers  are  derived 
from  the  sympathetic. 

The  puncta  lacrimalia  are  the  entrances  to  the  two  lacrimal  ducts.  Each  is  a 
fine  slit-like  opening  (about  2  mm.  long),  situated  close  behind  the  free  edge  of  the 
lid  and  about  a  third  of  an  inch  (ca.  8  nun.)  from  the  internal  canthus.  The  lacri- 
mal ducts  (Ductus  lacrimales),  upper  and  lower,  begin  at  the  puncta  and  converge 
at  the  inner  commissure  to  open  into  the  lacrimal  sac.  The  latter  (Saccus  lacri- 
malis) may  be  regarded  as  the  dilated  origin  of  the  naso-lacrimal  duct.  It  occupies 
the  funnel-like  origin  of  the  bony  lacrimal  canal,  and  leads  to  the  naso-lacrimal  duct 
(Ductus  naso-lacrimalis),  which  passes  forward  and  a  little  dowTiward  along  the 
outer  wall  of  the  frontal  sinus  and  the  nasal  cavity  and  opens  near  the  lower  com- 
missure of  the  nostril.  Its  length  is  about  ten  to  twelve  inches  (ca.  25  to  30  cm.). 
In  the  first  part  of  its  course  it  is  inclosed  in  the  osseous  lacrimal  canal;  further 
forward  it  lies  in  the  lacrimal  groove  of  the  maxilla,  covered  at  first  by  a  plate  of 
cartilage  and  then  by  the  mucous  membrane  of  the  middle  meatus.  The  terminal 
part  lies  in  the  inferior  turbinal  fold  and  opens  on  the  skin  of  the  floor  of  the  nostril 
near  the  transition  to  mucous  membrane.  Accessory  openings  may  occur  a  little 
further  back. 

The  first  part  of  the  duct,  about  6  to  7  mm.  in  diameter,  extends  in  a  gentle  curve,  convex 
dorsally,  from  the  internal  commissure  toward  a  point  just  above  the  level  of  the  infraorbital 
forajiien.     The  second  part  (isthmus)  is  narrower  (ca.  3  to  4  mm.) ;   it  extends  forward  and  a 
47 


738  THE    SENSE    ORCANS    AND    .SKIN    OK   THE    HORSE 

little  vontrally  jihout  to  a  transverse  plane  through  the  first  cheek  tooth  and  lies  in  the  groove 
above  the  inferior  turbinal  crest.  Beyond  this  the  duct  inclines  upwani  and  widens  very  con- 
siderably, crosses  the  nasal  process  of  the  premaxilla  obliquely,  and  contracts  at  its  termination. 
Tlie  mucous  membrane  may  present  valvular  folds,  the  most  distinct  of  which  is  situated  at  tlie 
origin. 

THE  PERIORBITA 
The  periorbita  or  ocular  sheath  is  a  conical  fibrous  membrane  which  incloses 
the  eyeball  witii  its  muscles,  vessels,  nerves,  etc.  Its  apex  is  attached  around  the 
optic  and  lacerated  forainina,  and  its  base  is  in  part  attached  to  the  bony  rim  of 
the  orl)it,  in  part  continuous  with  the  filjrous  layer  of  the  lids.  Its  inner  part, 
which  is  in  contact  with  the  orbital  wall,  is  thin;  incorporated  with  it  beneath  the 
root  of  the  sujiraorbital  process  is  the  bar  of  cartilage  around  which  the  superior 
otjlique  nuLscle  is  reflected.  The  outer  part  is  thicker,  and  is  strengthened  by  an 
elastic  band  which  is  attached  to  the  pterygoid  crest  and  furnishes  origin  to  the 
thin  unstriped  orl)ital  muscle.  A  quantity  of  fat  (Corpus  adiposum  extraorbitale) 
lies  about  tiie  periorbita,  and  within  it  is  the  intraorbital  adipose  tissue  (Corpus 
adiposum  intraorbitale)  which  fills  the  interstices  lietween  the  eyeball,  muscles,  etc. 

THE  ORBITAL  FASCIA  AND  OCULAR  MUSCLES  (Figs.  438,  439,  555) 

The  straight  muscles  of  the  eyeball  and  the  oblique  muscles  in  part  are  inclosed 
in  fibrous  sheaths  (Fasciae  musculares),  formed  by  superficial  and  deep  layers  of 
fascia,  which  arc  united  by  intermuscular  septa  in  the  interstices  between  the 
muscles.  The  superficial  fascia  is  thin;  it  blends  in  front  with  the  fibrous  layer  of 
the  eyelids  and  is  attached  behind  around  the  optic  foramen.  The  deep  fascia 
consists  anteriorly  of  two  layers,  one  of  which  is  continuous  with  the  fibrous  tissue 
of  the  lids,  while  the  other  is  attached  at  the  corneo-scleral  jimction. 

The  posterior  part  of  the  eyeiiall  is  covered  by  the  bulbar  fascia  or  capsule  of 
Tenon  (Fascia  bulbi),  so  that  between  them  a  lymph  space  (Spatium  interfasciale) 
is  inclosed  which  communicates  with  the  subdural  space  along  the  course  of  the 
optic  nerve. 

The  levator  palpebrae  superioris  muscle  '  is  a  thin  band  about  half  an  inch  in 
width  which  lies  above  the  rectus  superior.  It  is  narrow  at  its  origin  above  and 
behind  the  ethmoidal  foramen  and  ends  l)y  an  expanded  tendoti  in  the  u]i])er  lid. 
Its  action  is  to  raise  the  upper  lid. 

The  recti  oculi  (Mm.  recti  bulbi)  are  fom-  in  numlier  and  are  designated  ac- 
cording to  tlieir  positions  as  superior,  inferior,  internal,  and  external.  They  are  all 
band-like,  arise  close  together  around  the  ojitic  foramen,  and  diverge  as  they  pass 
forward  to  the  eyeball.  On  reaching  the  latter  they  end  in  thin  tendons  which  are 
inserted  into  the  sclera  in  front  of  the  equator  of  the  ej'eball. 

Tlie  retractor  oculi  (M.  retractor  bultii)  siurounds  the  o]itic  nerve,  and  is 
incompletely  divided  into  four  parts  wliich  alternate  with  the  recti.  They  arise 
around  the  o|)tic  nerve  and  arc  inserted  into  the  sclera  liehind  the  recti. 

The  obliquus  oculi  superior  (M.  oblicnuis  bulbi  dorsahs  s. superior)  is  the  longest 
and  narrowest  of  the  ocular  muscles.  It  arises  near  the  ethmoidal  foramen  and 
passes  forward  internal  to  the  rectus  internus.  Under  the  root  of  the  supraorbital 
process  it  is  reflected  almost  at  a  right  angle  around  a  cartilaginous  jKilley  (trochlea), 
which  is  attached  to  the  anterior  i)art  of  the  inner  wall  of  the  orbit,  a  bursa  lieing 
interposed  here.  Tlie  muscle  is  then  directed  outward  and  somewhat  forward,  and 
ends  in  a  thin  t(>ndon  which  pa.sses  between  the  rectus  superior  and  the  eyeball, 
and  is  inserted  into  the  sclera  between  the  superior  and  ext(>rnal  recti,  about  lialf 
an  inch  behind  the  margin  of  the  cornea. 

The  obliquus  oculi  inferior  (M.  oblicums  bulbi  ventralis  s.  inferior)  is  wide  and 
•  This  belongs  to  the  upper  eyelid,  but  is  described  here  on  account  of  its  position. 


THE    EYEBALL 


739 


much  shorter  than  tlio  recti.  It  arises  from  the  inner  wall  of  the  orbit  in  the  small 
depression  (Fossa  muscularis)  Ijehind  the  lacrimal  fossa.  It  curves  around  the  rectus 
inferior  and  is  inserted  into  the  sclera  near  and  partly  beneath  the  rectus  externus. 
Actions. — The  superior  and  inferior  recti  rotate  the  eyeball  about  a  transverse 
axis,  moving  the  vertex  of  the  cornea  upward  and  downward  respectively.  Simi- 
larly the  internal  and  external  recti  rotate  the  eyeball  al)Out  a  vertical  axis,  turning 
the  vertex  of  the  cornea  inward  and  outward  respectively.  The  oblique  muscles 
rotate  the  eyeball  about  a  longitudinal  axis;  the  superior  oblique  raises  the  outer 
end  of  the  pupil,  while  the  inferior  oblique  lowers  it.  The  retractor  as  a  whole 
draws  the  eyeball  backward,  and  its  parts  may  separately  reinforce  the  correspond- 
ing recti.     Also  the  four  recti  acting  together  will  retract  the  eyeball. 


v-&-»^;- 


Fig.  555. — Vertical  Axiai.  Section  of  Orbit  op  Horse. 
a.  Eyelids;  b,  bulbar  fascia  (Tenon's  capsule);  c.  c',  retractor  bulbi;  d,  rectus  oculi  inferior;  e.  obliquus 
oculi  inferior  (in  cross-section);  /,  rectus  oculi  superior;  g,  levator  palpebrie  superioris;  h,  obliquus  oculi  superior 
(in  cross-section);  i,  lacrimal  gland;  k.  k' ,  periorbita;  /,  superficial  fascia;  m.deep  fascia;  n.  akin;  o,  retrobulbar 
fat;  p,  extraorbital  fat;  (/,  temporalis  muscle;  r,  supraorbital  process;  s,  cranial  wall;  i,  cornea;  2,  sclera; 
3,  chorioidea;  4.  ciliary  muscle;  S,  iris;  6,  granula  iridis;  7,  retina;  7',  optic  papilla;  S,  optic  ner\'e;  9,  crys- 
talline lens;  10.  capsule  of  lens;  11.  ciliary  zone;  IS.  posterior  chamber;  IS  anterior  chamber;  14,  conjunctiva 
bulbi;  15,  vitreous  body.      (After  EUenberger,  in  Leisering's  Atlas.) 

The  actual  movements  of  the  eyeball  are  by  no  means  so  simple  as  might  be  inferred  from 
the  foregoing  general  statements.  Practically  all  movements  are  produced  by  the  coordinated 
actions  of  several  muscles,  involving  combinations  which  are  quite  comple.x  and  difficult  to  analyze 
accurately.  Further  complication  is  caused  by  the  fact  that  the  recti  are  not  inserted  at  equal 
distances  from  the  equator  and  the  axes  of  rotation  of  the  oblique  muscles  do  not  correspond  to 
the  longitudinal  axis  of  the  eyeball. 

Nerve-supply. — The  oculomotor  nerve  supplies  the  foregoing  muscles,  with 
the  exception  of  the  rectus  externus  and  obliquus  superior,  which  are  innervated  by 
the  abducens  and  trochlearis  respectively. 


THE  EYEBALL 
The  eyeball  (Bulbus  oculi)  is  situated  in  the  anterior  part  of  the  orbital  cavity, 
protected  in  front  by  the  eyelids  and  conjunctiva,  in  its  middle  by  the  complete 
orbital  ring,  and  related  behind  to  the  bulbar  fascia,  fat,  and  ocular  muscles. 


740  THE    SENSE    OUGANS    AND    SKIN    OF   THE    HORSE 

It  has  the  form  approximately  of  an  oblate  spheroid,  liut  is  composed  of  the 
segments  of  two  spheres  of  different  sizes.  The  anterior,  transparent,  corneal 
segment  has  a  radius  of  curvature  of  alwut  17  mm.,  and  the  po.sterior,  opaque, 
scleral  segment  a  radius  of  about  25  mm.  The  anterior  segment  therefore  projects 
more  strongly,  and  the  junction  of  the  two  segments  is  marked  externally  by  a 
broad,  shallow  groove,  the  sulcus  sclerse.  The  central  points  of  the  anterior  and 
posterior  curvatures  of  the  eyeball  are  termed  respectively  the  anterior  and  pos- 
terior poles  (Pohis  anterior,  posterior),  and  the  line  connecting  the  poles  is  the  optic 
axis  (Axis  oculi  externa).  The  angle  of  divergence  of  the  optic  axes  is  about 
137  degrees.  The  equator  (.'Equator)  is  an  imaginary  line  drawn  around  the  eye- 
ball midway  between  its  poles,  anil  meridians  (Meridiani)  are  lines  drawn  around  it 
through  the  poles. 

Thp  avorago  transverse  diameter  of  the  eyeball  is  about  .'J  cm.,  the  ^■ertical  about  4.5  cm., 
ami  the  axial  about  4.2.5  cm.  The  distance  from  the  anterior  pole  to  the  point  of  entrance  of  the 
optic  nerve  is  about  3  cm. 

Letis  seen  through  cornea 
Cornco-Kchrdl  junctioiu 


Third  cyclitl^ 

/  \ 
Caruncula  iacriinalis  ^ 

\ 


^^^A'^'^"'  \ 


"Pupil 


Fig.  5.56. — Left  Etebai.i.  of  Horse,  in  aim.  after  Removal  of  Upper  and  Lower  Lids. 
9.  Zygomatic  arch;    IS,  supraorbital  process;    19,  orbital  fat;    S7 .  facial  crest.     (After  Ellenberger-Baum,  Anat. 

fiir  Kiinstler.) 

The  eyeball  consists  of  three  concentric  tunics  or  coats,  within  which  three 
refractive  media  are  inclosed. 

The  Fibrous  Tunic 

The  fibrous  tunic  (Tunica  fibrosa  oculi)  is  the  external  coat  and  is  compo.sed 
of  a  posterior  oi)a(iue  part,  the  sclera,  and  a  transparent  anterior  part,  the  cornea. 

The  sclera,  popularly  termetl  the  "white  of  the  eye,"  is  a  dense  fibrous  mem- 
brane which  forms  about  four-fifths  of  the  fibrous  tunic.  Thickest  in  the  vicinity 
of  the  posterior  pole  (ca.  2  mm.),  it  thins  at  the  equator  (ca.  0.4  mm.),  and  increases 
in  thickness  toward  the  junction  with  the  cornea  (ca.  1.3  mm.).  It  is  in  general 
white,  but  may  have  a  bluish  tinge  in  its  thinnest  parts.  Its  external  surface 
furnishes  insertion  to  the  ocular  muscles  and  is  covered  by  the  conjunctiva  sclersB 
in  its  anterior  part.  The  episcleral  tissue,  which  is  richly  supplietl  with  vessels 
and  nerves,  attaches  the  conjunctiva  to  the  sclera;  it  is  abundant  and  loosely 
meshed  except  at  the  junction  with  the  cornea.  The  inner  surface  is  attached  to 
the  chorioid  coat  by  a  layer  of  delicate,  pigmented,  connective  tissue,  the  lamina 


THE    FIBROUS    TUNIC 


741 


fusca.  The  anterior  border  is  oval,  the  long  axis  being  transverse,  and  is  continuous 
with  the  cornea.  The  transition  from  the  opaque  scleral  tissue  to  the  transparent 
corneal  substance  occurs  in  such  manner  that  the  sclera  appears  to  form  a  groove 
(Rima  cornealis),  into  which  the  cornea  fits  somewhat  as  a  watch-glass  in  the  case. 
Near  the  corneo-scleral  junction  there  is  a  circular  venous  ple.xus,  the  plexus  s. 
sinus  venosus  sclerae,  formerly  called  the  canal  of  Schlemm.  The  optic  nerve 
passes  through  the  jiosterior  part  of  the  sclera  a  little  below  and  external  to  the 
posterior  pole.  The  ojiening  t\)r  the  nerve  is  crossed  by  interlacing  fibrous  strands, 
forming  the  lamina  cribrosa  sclerae. 

The  sclera  consists  of  interlacing  bundles  of  white  fibrous  tissue,  associated 
with  which  there  are  a  few  elastic  fibers.  The  bundles  are  arranged  chiefly  in 
meridional  and  equatorial  laj-ers.  The  very  limited  blood-supply  is  derived  from 
the  ciliary  arteries,  and  the  veins  open  into  the  vense  vorticosse  and  ciliarj-  veins. 


Sclera 


Reflection  of  conjunctiva 
Iris 

Granula  iridis 

Cornea 


Lens 
Anterior  cha^nber 


Rectus  oculi  inferior 


Ciliary  processes 


— \'ertical  Sectiox  of  Eyeball  of  Horse,  about  ?. 
The  contour  of  the  crystalline  lens  is  dotted. 


The  lymphatics  are  represented  by  intercommunicating  cell  spaces.  The  nerves 
are  derived  from  the  ciliary  nerves. 

The  cornea  forms  the  anterior  fifth  of  the  fibrous  tunic.  It  is  transparent, 
colorless,  and  non-vascular.  Viewed  from  in  front  it  is  oval  in  outline,  the  long 
axis  being  transverse  and  the  broad  end  internal;  it  appears  more  nearly  circular 
when  viewed  from  behind.  Its  anterior  surface  (Facies  anterior)  is  convex  and  is 
more  strongly  curved  than  the  sclera:  its  central  part  is  termed  the  vertex  corneae. 
The  posterior  surface  (Facies  posterior)  is  concave;  it  forms  the  anterior  boundary 
of  the  anterior  cliamber,  and  is  in  contact  with  the  aqueous  humor.  The  margin 
(limbus  cornea>)  joins  the  sclera;  the  latter  overlaps  the  cornea  more  in  front  than 
behind,  and  more  above  and  below  than  at  the  sides,  thus  explaining  the  difference 
in  outline  of  the  two  surfaces.     The  cornea  is  thinnest  at  the  vertex. 

The  cornea  consists,  from  before  backward,  of  the  following  laj^rs:  (1)  The 
epithelium  corneae  is  continuous  with  that  of  the  conjunctiva  sclera?,  and  is  of  the 
stratified  squamous  type.     (2)   The  lamina  limitans  anterior  is  merely  a  condensa- 


742 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


tioii  of  the  next  layer.  (3)  Tlie  substantia  propria  forms  the  bulk  of  the  cornea 
and  is  conii)osed  of  interlacing  bundles  of  connective  tissue,  arranged  in  part  in 
lamellae  disposed  parallel  with  the  surface.  In  the  amorphous  cement  substance 
l)etween  the  lamella;  are  fiatteneil  connective-tissue  cells,  the  corneal  corpuscles. 
These  have  branching  processes  which  unite  with  those  of  other  cells,  thus  form- 
ing a  protoplasmic  network.'  (4)  The  lamina  elastica  posterior,  also  termed  the 
membrane  of  Descemet  or  Demours,  is  a  thin  and  iiractiially  homogeneous  mem- 
brane which  is  less  intimately  attached  to  the  sul)stantia  ]iro])ria  than  the  anterior 
lamina.  It  is  dear,  glistening,  and  elastic.  At  the  periphery  the  lamina  divides 
into  tliree  sets  of  fil)crs.  The  anterior  fibers  join  the  sclera,  the  middle  give  attach- 
iiiciit  to  tlie  ciiiaPN-  niusck-,  while  the  posterior  i)ass  into  the  iris  and  form  the 
ligamentum  pectinatum  iridis.  (.5)  The  endothelium  (camerae  anterioris)  consists 
of  a  layer  of  flattened  i)()lygonal  cells,  and  is  reflected  on  to  the  anterior  surface  of 
the  iris. 

The  cornea  is  without  blood-vessels  except  at  its  periphery,  where  the  terminal 
twigs  of  the  vessels  of  the  sclera  and  conjunctiva  terminate  in  loops.  The  nerves 
are  derived  from  the  ciliary  nerves.  They  form  a  plexus  around  the  periphery 
(Pl(>xus  annularis),  from  which  fibers  pass  into  the  substantia  projiria,  become  non- 
medullated,  and  form  the  fundamental  or  stroma  plexus.  From  this  perforating 
branches  pass  through  the  anterior  linuting  layer  antl 
form  a  subepithelial  plexus,  from  which  filaments  ascend 
between  the  epithelial  cells.  Other  liranches  from  the 
plexuses  in  the  suljstantia  propria  end  as  fibrils  which  are 
in  close  relation  with  the  corneal  corpuscles. 


Fig.  5.^S. — Tapetum  of  Horse 
a,  Optic  papilla;  6,  lowei 
border  of  tapetum.    (After  Ellen- 
berger,  in  Leisering's  .\tlas.) 


The  Vascular  Tunic 
The  vascular  tunic  (Tunica  vasculosa  oculi)  lies  in- 
ternal to  the  fibrous  coat;  it  comprises  three  parts — the 
chorioid,  the  ciliary  body,  and  the  iris. 

1.  The  chorioid  (Chorioidea)  is  a  thin  membrane 
which  lies  between  the  sclera  and  retina.  It  is  in 
general  rather  loosely  attached  to  the  sclera  by  the 
lamina  fusca,  but  is  intimately  adherent  at  the  point 
of  entrance  of  the  oj)tic  nerve  and  less  closely  in 
))!aces  where  the  ciliary  vessels  and  nerves  pass  through.  The  inner  surface 
is  in  contact  with  the  layer  of  pigmented  cells  of  the  retina,  which  adhere  so 
closely  to  the  chorioid  that  they  were  formerly  regarded  as  a  part  of  the  latter. 
The  general  color  of  the  chorioid  is  dark  brown,  but  an  extensive  semilunar  area  a 
little  above  the  level  of  the  optic  paijilla  has  a  remarkable  metallic  luster,  and  is 
termed  the  tapetum  of  the  chorioid  (Tapetum  chorioidea").  The  apjiearance  here 
varies  in  different  individuals,  l)ut  the  jirevailing  colors  in  most  cases  are  iridescent 
blue  and  green  in  various  nuances  shading  into  yellow.  Posteriorly  the  chorioid  is 
perforated  by  the  o[)tic  nerve,  and  anteriorly  it  is  continuous  with  the  ciliary  body. 
The  chorioid  consists  of  four  layers,  which  from  without  inward  are  as  follows: 
(1 )  The  lamina  suprachorioidea  consists  of  interlacing  fine  lamelUe  of  filirous  tissue, 
each  containing  a  network  of  elastic  tissue.  Among  these  are  large-branched,  pig- 
mented, connective-tissue  cells.  The  spaces  l)etwe(>n  the  lamelhe  are  lined  with 
endothelium,  and  form  a  system  of  lymph-clefts  whirh  together  form  the  pericho- 
rioiil space  (Spatium  perichorioideale).     (2)  The  lamina  vasculosa  is  the  outer  part 

'  According  to  Piersol  the  sy.stom  of  spaces  and  ranaliculi  in  the  substMiitia  propria  is  com- 
|)letely  filled  by  the  cells  and  their  processes,  upon  which  tlie  nutrition  of  the  cornea  largely  de- 
pends. The  lamina  ehistica  anterior,  formerly  described  as  a  distinct  Laver  between  tlie  corneal 
epithelium  and  the  substantia  propria,  does  not  exi.st  a,s  such,  but  there  "is  a  condensation  of  the 
Bupcrfieial  part  of  the  latter,  which  Rollett  termed  the  anterior  limiting  Layer;   it  is  not  elastic. 


THE    VASCULAR   TUNIC 


743 


of  the  proper  tissue  of  the  chorioid.  It  contains  the  larger  blood-vessels,  which 
are  supported  by  connective-tissue  and  elastic  fibers.  (3)  The  lamina  chorio- 
capillaris  consists  of  an  extremely  rich  network  of  capillaries  embedded  in  an  almost 
homogeneous  matrix.  Between  it  and  the  lamina  vasculosa  is  a  layer  of  filjro- 
elastic  tissue,  the  tapetum  fibrosum,  which  causes  the  metallic  luster  mentioned 
above.  (4)  The  lamina  basalis  is  very  thin  and  transparent.  It  is  composed  of 
an  inner  homogeneous  part  and  an  outer  elastic  part. 

2.  The  ciliary  body  (Corpus  ciliare),  the  middle  part  of  the  vascular  coat,  con- 
nects the  chorioid  with  the  periphery  of  the  iris.  In  meridional  section  it  has  the 
form  of  a  narrow  triangle,  the  base  of  which  is  next  to  the  iris.  On  its  inner  side 
are  the  ciliary  processes  and  on  its  outer  side  the  ciliary  muscle.  It  consists  of 
three  parts — the  ciliary  ring,  ciliary  processes,  and  ciliary  muscle.  The  ciliary 
ring  (Orl)icularis  ciliaris)  is  the  posterior  zone,  which  is  distinguished  from  the  chor- 
ioid mainly  bj'  its  greater  thickness 
and  the  absence  of  the  chorio-capil- 
laris.  Its  inner  face  presents  numer- 
ous fine  meridional  ridges,  by  the 
union  of  which  the  ciliary  processes 
are  formed.  The  ciliary  processes 
(Processus  ciliares),  more  than  a 
hundred  in  number,  form  a  circle 
of  radial  folds  which  surround  the 
lens  and  furnish  attachment  to  the 
zonula  ciliaris  or  suspensory  liga- 
ment of  the  latter.  They  are  small 
at  their  origin  on  the  ciliary  ring 
and  become  much  thicker  and 
higher  toward  their  inner  ends. 
The  \\-idth  of  the  circle  formed  by 
them  is  narrower  at  the  inner  side 
than  elsew'here.  Their  bases  ex- 
tend forward  to  the  periphery  of 
the  iris,  and  their  inner  ends  are 
close  to  the  margin  of  the  lens. 
They  bear  numerous  secondary 
folds.  Their  inner  surface  is  cov- 
ered by  a  continuation  of  the 
lamina  basalis  of  the  chorioid,  on 
which  there  are  two  layers  of  epi- 
thelial cells  which  constitute  the 
pars  ciliaris  retinae.     Thej'   consist 

of  a  rich  network  of  tortuous  vessels  supported  in  pigmented  connective  tissue. 
The  ciliary  muscle  (:\I.  ciliaris)  (Figs.  552,  555,  559)  constitutes  the  outer  part  of 
the  ciliary  body,  and  lies  between  the  sclera  and  the  ciliary  processes.  It  forms 
a  circular  band  of  unstriped  muscle,  the  fibers  of  which  are  for  the  most  part 
directed  meridionally.  They  arise  from  the  inner  surface  of  the  sclera  and  from 
the  ligamentum  pectinatum  iridis  close  to  the  corneo-scleral  junction,  and  run 
backward  along  the  sclera  to  be  inserted  into  the  ciliary  processes  and  ring. 
When  the  muscle  contracts,  it  pulls  the  processes  and  ring  forward,  thus 
slackening  the  ciliary  zone  or  suspensory  ligament  of  the  lens,  and  allowing 
the  latter  to  become  more  convex.  This  is  the  mechanism  of  accommodation 
for  near  objects. 

In  man  the  muscle  ha.s  the  form  of  a  prismatic  ring  which  is  triangular  in  meridional  section, 
the  base  being  directed  toward  the  periphery  of  the  iris.     It  consists  chiefly  of  meridional  fabers. 


Fig.  559. — Vascul 


Horse,  Front 


The  cornea  is  removed  and  the  sclera  is  reflected  in 
flaps.  1,  Sclera;  /',  lamina  fusca;  2,  chorioidea;  2' ,  ciliary 
veins;  S,  ciliary  muscle;  4,  iris;  o,  S' ,  granula  iridis;  6.  pupil, 
through  which  the  lens  is  visible.  (After  EUenberger,  in 
Leisering's  Atlas.) 


744  THE    SENSE    ORGANS   AND    SKIN    OF   THE    HORSE 

but  a  ring  of  circular  fibers  forms  the  inner  angle  of  its  base.  In  the  horse  the  muscle  is  much 
less  developed,  and  has  the  form  of  a  flat  band;  it  does  not  contain  circular  fibers,  but  the  arrange- 
ment is  rendered  more  or  less  plexiform  by  the  existence  of  oblique  and  equatorial  fibers. 

3.  The  iris  (Figs.  552,  557,  559)  is  a  muscular  diaphragm  placed  in  front  of  the 
lens,  and  is  vif^ililc  through  the  cornea.  It  is  pierced  centrally  liy  an  elliptical 
opening,  the  pupil  (Pupilla),  which  varies  in  size  during  life  and  determines  the 
amount  of  light  admitted  to  act  on  the  retina.  In  strong  Hght  the  vertical  diameter 
of  the  pu])il  is  very  short,  but  the  opening  is  almost  circular  when  the  pupil  is  fully 
dilated.  The  ciliary  border  (Margo  ciliaris)  or  periphery  of  the  iris  is  continuous 
with  the  ciliary  body  and  is  connected  with  the  corneo-scleral  junction  by  the  liga- 
mentum  pectinatum  iridis.  The  ligament  consists  of  strands  of  connective  tissue 
which  are  attached  externally  to  the  corneo-scleral  junction.  Its  bundles  interlace 
and  inclose  spaces  (Spatia  anguli  iridis)  which  are  lined  with  endothelium  and  com- 
nnmicate  with  the  anterior  chamber.  The  pupillary  border  (Margo  ])ui)illaris) 
surrounds  the  pupil.  Its  u]i]ier  part  bears  in  its  middle  several  black  masses  of 
variable  size,  termed  the  granula  iridis  or  corpora  nigra;  similar,  l)ut  much  smaller, 
projections  may  be  seen  on  the  lower  margin  of  the  pupil.  The  anterior  surface 
(F^acics  anterior)  determines  the  color  of  the  eye,  which  is  dark  brown  usually.  It 
is  marked  by  delicate  concentric  lines  (Plicje  iridis),  which  fade  out  near  the  pupil. 
The  smooth,  narrow,  central  part  is  termed  the  pupillary  zone  or  annulus  iridis 
minor,  while  the  much  broader  plicated  part  is  the  ciliary  zone  or  annulus  iridis 
major.  The  posterior  surface  (Facies  posterior)  is  usually  black.  It  bears 
numerous  fine  radial  lines  except  at  the  pupillary  margin.  Its  central  part  is  in 
contact  with  the  anterior  surface  of  the  lens,  but  peripherally  the  two  are  separated 
by  a  narrow  space  termed  the  posterior  chamber.  The  iris  consists  chiefly  of  the 
stroma  iridis,  a  delicate  framework  of  connective  tissue,  which  supports  numerous 
blood-vessels,  and  contains  branched  pigmented  cells.  The  muscular  tissue 
(unstriped)  consists  of  a  .sjjhincter  and  a  dilator  of  the  pu]iil.  The  sphincter 
pupillae  lies  in  the  posterior  jiart  around  the  pupil,  with  which  the  fibers  are  largely 
concentric.  The  dilatator  pupillae  consists  of  fibers  which  radiate  outward  from 
the  sphincter  to  the  ciliary  border.  The  anterior  surface  of  the  iris  is  covered  by  a 
continuation  of  the  endothelium  of  the  cornea.  Beneath  this  is  a  condensation  of 
the  stroma,  in  which  the  cells  are  close  together  and  are  full  of  pigmented  granules.' 
There  appear  to  be  minute  clefts  here  by  which  the  lymph-spaces  of  the  stroma 
comnumicate  with  the  anterior  chamber.  The  posterior  surface  is  covered  bj-  a 
])ignicute(l  epithelium,  the  stratum  pigmenti  iridis,  which  is  a  continuation  of  that 
of  the  ciliary  body. 

The  arteries  of  the  vascular  tunic  come  from  the  ciliary  branches  of  the  oph- 
thalmic artery.  The  arteries  of  the  chorioidea  are  derived  chiefly  from  the  short 
post(>rior  ciliary  arteries.  These  perforate  the  sclera  around  the  posterior  pole, 
run  forward  in  the  lamina  vasculosa,  and  form  the  rich  capillary  network  of  the 
choriocapillaris.  The  two  long  ciliary  arteries  perforate  the  sclera  obliquely  near 
the  optic  nerve;  they  run  forward  in  the  lamina  suprachorioidea  in  the  horizontal 
meridian,  one  on  the  inner,  the  other  on  the  outer,  side  of  the  eyeball.  On  reaching 
the  ciliary  body  each  divides  into  diverging  branches;  the  subdivisions  of  these 
unite  with  each  other  and  with  twigs  of  the  anterior  ciliary  arteries  to  form  a  circular 
anastomosis,  th(>  circulus  arteriosus  major.  From  this  branches  go  to  the  ciliary 
muscle  and  processes  anil  to  the  iris.  The  two  anterior  ciliary  arteries,  dorsal  and 
ventral,  form  an  episcleral  plexus  around  the  corneo-scleral  junction,  and  give  off 
branches  which  perforate  the  sclera.  These  sup]ily  twigs  to  the  ciliary  muscle  and 
recurrent  branches  to  the  chorioid,  and  assist  in  forming  the  circulus  arteriosus 
major. 

The  blood  is  carried  away  from  the  vascular  tunic  chiefly  by  four  or  five  venous 
'  In  albinos  the  pigment  is  absent  here,  as  elsewhere,  and  the  iris  is  pinkish  in  color. 


THE    RETINA 


745 


trunks,  the  venae  vorticosae,  which  are  formed  by  the  convergence  in  whorls  of 
numerous  veins,  coming  not  only  from  the  chorioid,  but  also  from  the  ciliary  body 
and  iris.  The  vena>  vorticosa-  perforate  the  sclera  about  at  the  ecjuator  and  join 
the  veins  of  the  ocular  muscles. 

The  nerves  come  from  the  long  and  short  ciliary  nerves.  They  form  a  plexus 
in  the  lamina  suprachorioidea,  which  contains  ganglion  cells,  and  sends  numerous 
non-medullated  fibers  chiefly  to  the  blood-vessels  of  the  chorioid.  At  the  ciliary 
muscle  a  second  plexus  (P.  gangliosus  ciliaris)  is  formed,  which  supplies  the  muscle 
and  sends  fibers  to  the  iris.  The  sphincter  jDupillae  is  supplied  by  fibers  derived 
from  the  oculomotor  nerve,  while  the  dilatator  pupill»  is  innervated  by  the  sym- 
pathetic. 

THE  RETINA 
The  retina  or  nervous  tunic  of  the  eyeball  is  a  delicate  membrane  which  extends 
from  the  entrance  of  the  optic  nerve  to  the  margin  of  the  pupil.     It  consists  of 


'II 


6. 


Fig.  560. — Inner  SuRFArE  of  .\nterior  Part  of 
Eyeball  of  Horse  (Equatorial  Section). 
/,  Sclera;  3,  chorioidea;  S,  retina  (drawn  away 
from  chorioidea):  4^  ciliary  processes;  3,  crystalline 
lens,  through  which  the  pupil  (6)  is  seen,  (.\fter 
Elienberger,  in  Leisering's  .\tlas.) 


-Fundus 
TION   o 


Equatorial  Sec- 


Eyeball  of  Ho 


I,  Sclera;  S,  chorioidea;  3,  retii 
4,  tapetum;  3,  optic  papilla;  6,  optic  i 
Elienberger,  in  Leisering's  .^tlas.) 


three  parts.  The  large  posterior  part,  which  alone  contains  the  nervous  elements, 
including  the  s]3ecial  neuro-epithelium  and  the  optic  nerve-fibers,  is  termed  the 
pars  optica  retinae.  It  extends  forward  to  the  ciliary  body,  where  it  terminates  at 
an  irregular  line  called  the  era  serrata.  Here  the  retina  rapidly  loses  its  nervous 
elements,  becomes  much  thinner,  and  is  continued  over  the  ciliary  body  and  the 
posterior  surface  of  the  iris  liy  two  laj'ers  of  epithelial  cells.  In  the  pars  ciliaris 
retinae  the  inner  stratum  is  non-pigmented,  while  the  outer  layer  is  a  direct  con- 
tinuation of  the  stratum  pigmenti  of  the  pars  optica.  In  the  pars  iridica  retinae 
both  are  pigmented.  In  the  dead  subject  the  pars  optica  is  an  (ipa(|ue,  gray,  soft 
membrane  which  can  be  stripped  of  the  chorioid,  leaving  most  of  its  outer  pigmented 
layer  on  the  latter.  During  life  it  is  transparent,  except  as  to  its  pigmented  epi- 
thelium, and  the  reddish  appearance  of  the  fundus  as  viewed  by  the  ophthalmoscope 
is  caused  by  the  l)lood  in  the  network  of  the  choriocapillaris.  The  entrance  of  the 
optic  nerve  forms  a  sharply  defined,  oval,  light  area,  the  optic  papilla  (Papilla  nervi 
optici),  situated  about  15  mm.  below  the  horizontal  meridian  and  3  to  4  mm.  ex- 
ternal to  the  vertical  meridian.  The  central  part  of  the  papilla  is  slightly  depressed 
(Excavatio  papillfe  n.  optici). 


746  THE   SENSE   ORGANS   AND    SKIN    OF   THE    HORSE 

The  transverse  diameter  of  the  papilla  is  about  6  to  7  mm.,  and  the  vertical  about  4  to  5  mm. 
It  is  commonly  situated  a  little  below  the  margin  of  the  tapetum,  but  the  latter  may  extend  down 
somewhat  on  "either  side  of  the  papilla.  The  lower  margin  is  often  indented  a  httle.  In  inspec- 
tion of  the  fundus  with  the  ophthalmoscope  numeious  fine  branches  of  the  arteria  centralis  retina 
are  seen  radiating  from  the  periphery  of  the  papilla. 

The  optic  nerve  fibers  converge  from  all  iiarts  of  the  pars  optica  to  the  papilla, 
where  they  collect  into  bundles  which  traverse  the  lamina  cribrosa  of  the  chorioidea 
and  sclera,  and  constitute  the  optic  nerve.  The  area  centralis  retinae  is  a  round 
spot,  2  to  3  mm.  in  diameter,  situated  above  and  external  to  the  optic  papilla;  it 
corresponds  to  the  macula  lutea  of  man,  which  is  histologically  more  highly  differen- 
tiated than  th(>  rest  of  the  retina  and  is  the  area  of  most  acute  vision. 

The  structure  of  the  retina  is  very  complex.  It  consists  of  nervous  elements 
which  are  sujjported  in  a  peculiar  sustentacular  tissue,  and  are  covered  externally 
by  a  layer  of  pigmented  epithelium  (Stratum  pigmenti  retinse).  The  nervous  ele- 
ments comprise  a  highly  specialized  neuro-epithelium,  the  rods  and  cones;  ganglion- 
cells,  the  axones  of  which  form  the  optic  nerve;  and  intermediate  neurones.  Ten 
layers  may  be  recognized  in  sections  microscopically.' 

The  arteries  of  the  retina  are  derived  from  the  arteria  centralis  retinte  and 
anastomotic  branches  from  the  short  ciliar.y  arteries.  The  arteria  centralis  enters 
the  optic  nerve  a  short  distance  behind  the  eyel:)all  and  runs  in  the  axis  of  the  nerve. 
The  artery  divides  2  to  3  mm.  before  reaching  the  papilla,  and  gives  off  thirty  to 
forty  branches  which  radiate  in  the  posterior  part  of  the  retina  and  divide  dichoto- 
mously  into  end-arteries.  The  anterior  part  of  the  retina  is  non-vascular.  The 
veins  accomjiany  the  arteries  except  in  the  capillary  plexuses;  their  walls  consist 
merely  of  a  layer  of  endothelial  cells,  around  which  are  a  lymph-channel  and  sheath. 


CHAMBERS  OF  THE  EYE  AND  AQUEOUS  HUMOR 
The  anterior  chamber  of  the  eye  (Camera  oculi  anterior)  is  inclosed  in  front  by 
the  cornea  and  behind  by  the  iris  and  lens  (Figs.  552,  555,  557).  It  communicates 
through  the  ]iupil  with  the  posterior  chamber  (Camera  oculi  posterior);  this  is  a 
small  aimular  space,  triangular  in  cross-section,  which  is  bounded  in  front  by  the 
iris,  behind  by  the  peripheral  part  of  the  lens  and  its  ligami^nt,  and  externally  by 
the  ciliary  processes.  The  chambers  are  filled  by  the  aqueous  humor  (Humor 
aqueus),  a  clear  fluid  which  consi-sts  of  about  98  per  cent,  of  water,  with  a  little 
sodium  chlorid  and  traces  of  albumin  and  extractives.  It  is  carried  off  chiefly 
through  the  spaces  (of  Fontana)  in  the  zonula  ciliaris  or  suspensory  ligament  of  the 
lens  into  the  plexus  venosus  sclerae. 


REFRACTIVE  MEDIA  OF  THE  EYEBALL 

The  vitreous  body  (Corpus  vitreum)  is  a  semifluid  transparent  substance 
situated  between  the  crystalline  lens  and  the  retina.  In  front  it  presents  a  deep 
cavity,  the  fossa  hyaloidea,  which  receives  the  posterior  surface  of  the  lens.  It 
consists  of  a  framework  of  delicate  fibrils,  the  stroma  vitreum,  the  meshes  of  which 
are  filled  by  the  fluid  humor  vitreus.  The  surface  is  covered  by  a  condensation  of 
the  stroma  known  as  the  membrana  hyaloidea. 

The  crystalline  lens  (Lens  crystallina)  is  a  liiconvex,  transparent  body,  situated 
in  front  of  the  vitreous  body  and  in  ])artial  contact  with  the  posterior  surface  of  the 
iris.  Its  ])erii)hery,  the  aequator  lentis,  is  almost  circular  and  is  closely  surrounded 
by  the  ciliary  processes.  The  anterior  surface  (Facies  anterior)  is  convex;  it  is 
bathed  by  the  aqueous  hmnor  and  is  in  contact  with  the  iris  to  an  extent  which 
varies  with  the  state  of  the  pupil.     The  posterior  surface  (Facies  posterior)  is  much 

'  For  the  minute  structure  of  the  retina  reference  must  be  niatie  to  histological  works. 


THE    EXTERNAL    EAR  747 

more  strongly  curved  than  the  anterior.  It  rests  in  the  fossa  of  the  vitreous  body. 
The  central  points  of  the  surfaces  are  the  anterior  and  posterior  poles  (Polus 
anterior  et  posterior  lentis),  and  the  line  which  connects  them  is  the  axis  of  the 
lens  (Axis  Icntis). 

The  transverse  diameter  of  tlie  lens  is  about  2  cm.,  the  vertical  diameter  is  shghtly  smaller, 
and  the  axis  measures  about  13  mm.  The  radius  of  curvature  of  the  anterior  surface  is  13.5  mm., 
and  of  the  posterior  surface  9.5  to  10  mm.  But  the  curvatures  of  its  surfaces — especially  that  of 
the  anterior — vary  during  life  according  as  the  eye  is  accommodated  for  near  or  far  \-ision. 

The  zonula  ciliaris  (of  Zinn)  or  suspensory  ligament  of  the  lens  (Fig.  552) 
consists  of  delicate  fibers  (FibriE  zonulares)  which  pass  in  a  meridional  direction 
from  the  ciliary  processes  to  the  capsule  of  the  equator  of  the  lens.  Many  fibers 
cross  each  other,  and  the  spaces  between  the  fibers  (Spatia  zonularia)  are  filled 
with  aqueous  humor;  the}'  communicate  with  each  other  and  with  the  posterior 
chamber. 

The  substance  of  the  lens  (Substantia  lentis)  is  inclosed  by  a  structureless, 
highly  elastic  membrane,  the  capsule  of  the  lens  (Capsula  lentis),  and  consists  of  a 
softer  substantia  corticalis,  and  a  dense  central  part,  the  nucleus  lentis.  The  cap- 
sule is  thickest  on  the  anterior  surface,  and  here  it  is  lined  In'  a  layer  of  flat  poh'- 
gonal  cells,  the  epithelium  of  the  lens  capstile.  The  lens  substance,  when  hardened, 
is  seen  to  consist  of  concentric  laminae  arranged  somewhat  like  the  layers  of  an 
onion,  and  united  by  an  amorphous  cement  substance.  The  laminse  consist  of 
lens  fibers,  hexagonal  in  section,  and  of  very  different  lengths.  Faint  lines  radiate 
from  the  poles  and  indicate  the  edges  of  layers  of  cement  stibstance  which  unite 
the  groups  of  lens  fibers.  These  lines,  the  radii  lentis,  are  three  in  number  in  the 
foetus  and  new-born,  and  form  with  each  other  angles  of  120  degrees.  On  the 
anterior  surface  one  is  directed  upward  from  the  pole  and  the  other  two  diverge 
downward;  on  the  posterior  surface  one  is  directed  downward  and  the  others 
diverge  upward.     The  developed  lens  has  neither  vessels  nor  nerves. 

In  the  foetus  the  lens  is  nearly  globular,  and  is  soft  and  pinkish  in  color.  During  part  of 
foetal  life  it  is  surrounded  by  a  vascular  network,  the  tunica  vasculosa  lentis.  This  is  derived 
chief!}-  from  a  temporary  vessel,  the  hyaloid  artery,  which  is  a  continuation  forward  of  the  arteria 
centralis  retince  through  the  hyaloid  canal  that  traverses  the  \'itreous  body.  In  old  age  the  lens 
tends  to  lose  its  elasticity  and  transparency;  it  also  becomes  flatter  and  the  nucleus  especially 
grows  denser. 

The  Ear 

The  ear  or  organ  of  hearing  (Organon  auditus)  consists  of  three  natural 
divisions — external,  middle,  and  internal. 


THE  EXTERNAL  EAR 

The  external  ear  (Auris  externa)  comprises  (1)  the  auricula,  a  funnel-like 
organ  which  collects  the  sound  waves,  together  with  its  muscles,  and  (2)  the 
external  auditory  canal,  which  conveys  these  waves  to  the  tympanic  membrane, 
the  partition  which  separates  the  canal  from  the  cavity  of  the  middle  ear. 

The  auricula  or  pinna  is  attached  by  its  base  around  the  external  auditory 
canal  in  such  a  manner  as  to  be  freely  movable.  In  the  following  description  it  will 
be  assumed  that  the  opening  is  directed  outward  and  that  the  long  axis  is  practically 
vertical.  It  has  two  surfaces,  two  borders,  a  base,  and  an  apex.  The  convex 
surface  or  dorsum  (Dorsum  auriculae)  faces  inward  and  is  widest  in  its  middle  part ; 
its  lower  part  is  almost  circular  in  cur^'ature,  while  above  it  narrows  and  flattens. 
The  concave  surface  (Scapha)  is  the  reverse  of  the  dorsum;  it  presents  several 
ridges  which  subside  toward  the  apex.  The  anterior  border  is  sinuous;  it  is  largely 
convex,  but  becomes  concave  near  the  apex.     It  divides  below  into  two  diverging 


748 


THE  SENSE  ORGANS  AND  SKIN  OK  THE  HORSE 


parts  (crura  helicis).  The  posterior  border  is  eonvex.  The  apex  is  flattened, 
jjointed,  and  curved  a  little  forward.  The  base  is  strongly  convex.  It  is  attached 
to  the  external  auditory  process  of  the  petrous  tenii)oral  hone,  and  around  this  there 
is  a  quantity  of  fat.  The  parotid  gland  overlaps  it  below  and  externally.  The 
structure  of  the  external  ear  comprises  a  framework  of  cartilages  (which  are  chiefly 
elastic),  the  integument,  and  a  comiilicated  arrangement  of  muscles. 

The  conchal  or  auricular  cartilage  (( 'artilago  auricula")  determines  the  shape 
of  the  ear;  its  form  can  be  maile  out  without  dissection,  except  below,  where  it  is 
concealed  by  the  muscles  and  the  parotid  gland.  The  basal  part  is  coiled  to  form 
a  tube,  which  incloses  the  cavity  of  the  concha  (Cavum  conchce).  This  part  is 
funnel-shaped  and  curves  outward  and  a  little  backward.  Its  internal  (medial) 
siH'face  is  strongly  convex,  forming  a  prominence  termed  the  eminentia  conchae. 
The  lowest  part  of  the  internal  margin  bears  a  narrow,  jiointed  prolongation,  the 

styloid  process.  This  jirocess  is 
about  an  inch  long  and  projects 
downward  externally  over  the  an- 
nular cartilage;  the  guttural  pouch 
is  attached  to  its  free  end.  Behind 
its  base  there  is  a  foramen  through 
S  which  the  auricular  branch  of  the 

vagus  passes. 

The  liasal  part  of  tlir  posterior  border 
is  cut  into  liy  a  notch,  whicli  wpanilcs  two  . 
irregular  quadrilateral  plates.  The  upper 
plate  (Tragus)  is  overlapped  by  the  an- 
terior border,  and  is  separated  fz-om  the 
ad.iacent  part  of  the  posterior  border 
(Antitragus)  by  a  notch  (Incisura  inter- 
tragica).  The  lower  plate  is  curved  to 
form  a  half  ring  and  partly  o\'erlaps  the 
anterior  border  and  the  annular  cartilage, 
Behind  the  notch  there  is  a  foramen, 
which  transmits  the  internal  auricular 
artery  and  internal  auricular  branch  of 
the  facial  nerve. 


Fio.  562. — Conchal  and  Annular  Cartilages  of  Ear  of 
HousF.,  E,\tkrnal  Vikw. 
i,  Base  of  concha:  5,  posterior  border,  ,^,  anterior  bor- 
der of  concha;  4,  intertrapc  notch;  5,  eminentia  concha; 
ff,  styloid  process;  7,  annular  cartilage;  9,  zygomatic  arch. 
(After  EllenberKer-Havim,  Anat.  fiir  Kiinstler.) 


The  annular  cartilage  (Cartil- 
ago  annularis)  is  a  quadrilateral 
plate,  curved  to  form  about  three- 
fourths  of  a  ring;  its  ends  are  a 
little  less  than  half  an  inch  (ca. 
1  cm.)  apart  internally  and  are 
united  by  elastic  tissue.  It  em- 
braces the  external  auditory  jirocess  and  forms  with  the  lower  part  of  the  conchal 
cartilage  the  cartilaginous  part  of  the  external  auditory  canal. 

The  scutiform  cartilage  (Cartilago  scutiformis  s.  scutulum)  is  an  irregular 
quadrilateral  plate  which  lies  on  the  temporal  muscle  in  front  of  the  base  of  the 
conchal  cartilage.  Its  sui)erficial  face  is  slightly  convex  from  side  to  side  and  its 
deep  face  is  correspondingly  concave.  The  anterior  end  is  thin  and  rounded;  the 
posterior  part  or  base  is  wider  and  thicker,  and  its  inner  angle  is  prolonged  by  a 
pointed  process  half  an  inch  or  more  in  length.  The  cartilage  moves  very  freely 
over  th:-  underlying  parts. 

The  external  auditory  canal  or  meatus  leads  from  the  cavum  concha;  to  the 
tympanic  menihrane.  It  does  not  contimie  the  general  direction  of  the  cavity  of 
the  concha,  but  extends  inward,  downwaril,  and  slightly  forward.  It  consists  of  a 
cartilaginous  part  formed  by  the  lower  part  of  the  conchal  cartilage  and  the  annular 
cartilage,  and  an  osseous  part  formed  by  the  external  auditory  process  of  the  tem- 


THE    AURICULAR   MUSCLES  749 

poral  t)one.  Those  are  unitetl  liy  elastic  membranes  to  form  a  complete  tube.  Its 
caliber  diminishes  from  \vithout  inward,  so  that  the  lumen  of  tlie  inner  end  is  al)out 
half  of  that  of  the  outer  end. 

The  skin  on  the  convex  surface  of  the  concha  presents  no  special  features;  it 
is  attached  to  the  cartilage  liy  a  considerable  amount  of  subcutaneous  tissue  except 
at  the  ajiex.  The  integument  which  lines  the  concave  surface  is  intimately  ad- 
herent to  the  cartilage  and  is  relatively  dark  in  color.  There  are  three  or  four 
cutaneous  ridges  which  run  about  parallel  with  the  borders  of  the  conchal  cartilage, 
but  do  not  extend  to  the  apex  or  the  cavum  conchae.  The  upper  and  marginal 
parts  and  the  ridges  are  covered  with  long  hairs,  but  between  the  ridges  and  below 
it  is  thin,  covered  sparsely  with  very  fine  hairs,  and  supplied  with  numerous 
sebaceous  glands.  In  the  external  auditory  canal  the  skin  becomes  thinner;  in 
the  cartilaginous  part  it  is  supplied  with  numerous  large,  coiled,  ceruminous  glands 
((ilandulse  ceruminosae)  and  is  sparsely  covered  with  very  fine  hairs;  in  the  osseous 
part  the  glands  are  small  and  few  or  absent  and  there  are  no  hairs. 


THE  AURICULAR  MUSCLES 

The  auricular  muscles  may  be  sulxlivided  into  two  sets,  viz.,  (a)  extrinsic 
muscles,  which  arise  on  the  head  and  adjacent  part  of  the  neck,  and  move  the  ex- 
ternal ear  as  a  whole,  and  {b)  intrinsic  muscles,  which  are  confined  to  the  auricula. 
In  this  connection  the  scutiform  cartilage  may  be  regarded  as  a  sesamoid  cartilage 
intercalated  in  the  course  of  some  of  the  muscles. 

The  extrinsic  muscles  are  as  follows; 

1.  The  scutularis  is  a  thin  muscular  sheet  situated  subcutancously  over  the 
temporalis  muscle.  Its  fibers  arise  from  the  zygomatic  arch  and  the  frontal  and 
sagittal  crests,  and  converge  to  the  scutiform  cartilage.     It  consists  of  three  parts. 

(a)  The  fronto-scutularis  comprises  temporal  and  frontal  parts,  w^hich  arise 
from  the  zygomatic  arch  and  the  frontal  crest,  and  arc  inserted  into  the  outer  and 
anterior  borders  of  the  scutiform  cartilage  respectively. 

(h)  The  interscutularis  arises  from  the  sagittal  crest,  over  which  it  is  in  part 
continuous  with  the  nuiscle  of  the  opposite  side.  Its  fibers  converge  to  the  inner 
border  of  the  scutiform  cartilage. 

(c)  The  cervico-scutularis  is  not  well  defined  from  the  preceding  muscle.  It 
arises  from  the  occipital  crest  and  is  inserted  into  the  inner  border  of  the  scutiform 
cartilage. 

2.  The  anterior  auricular  muscles  (Mm.  auriculares  nasales)  are  four  in  number. 
(a)  The  zygomatico-auricularis  arises  from  the  zygomatic  arch  and  the  parotid 

fascia,  and  is  inserted  into  the  outer  face  of  the  l)ase  of  the  conchal  cartilage  under 
cover  of  the  parotido-auricularis. 

(5)  The  scutulo-auricularis  superficialis  inferior  arises  on  the  outer  part  of 
the  superficial  face  of  the  scutiform  cartilage  and  ends  on  the  base  of  the  conchal 
cartilage  with  the  preceding  muscle. 

(c)  The  scutulo-auricularis  superficialis  medius  arises  from  the  posterior  part 
of  the  deep  surface  of  the  scutiform  cartilage  and  is  inserted  into  the  dorsum  of  the 
conchal  cartilage,  close  to  the  lower  part  of  its  anterior  border  and  above  and  behind 
the  preceding  muscle.     It  receives  a  slip  from  the  cervico-scutularis. 

(d)  The  scutulo-auricularis  superficialis  superior  is  a  thin  slip  w-hich  is  de- 
tached from  the  interscutularis  over  the  inner  border  of  the  scutiform  cartilage. 
It  ends  on  the  anterior  aspect  of  the  lower  jiart  of  the  dorsum  of  the  conchal  car- 
tilage. 

3.  The  superior  auricular  muscles  (Mm.  auriculares  dorsales)  are  two  in 
number. 

(a)  The  scutulo-auricularis  superficialis  accessorius  is  a  narrow  band  which  is 


750  THE    SENSE    ORGANS    AND    SKIN    OF   THE    HORSE 

largely  covored  by  the  proeeding  muscle.  It  arises  from  the  posterior  prolongation 
and  the  adjacent  part  of  the  superficial  face  of  the  scutiform  cartilage,  and  is 
inserted  into  the  conv'ex  surface  of  the  conchal  cartilage  internal  to  the  preceding 
muscle,  the  two  crossing  each  other  at  an  acute  angle. 

(6)  The  parieto-auricularis  is  flat  and  triangular;  it  arises  from  the  sagittal 
crest  under  cover  of  the  cer\ico-scutularis,  runs  outward  and  a  little  backward, 
and  is  inserted  liy  a  flat  tendon  into  the  lower  part  of  the  convex  surface  of  the 
concha  untler  cover  of  the  cervico-auricularis  superficialis. 

4.  The  posterior  auricular  muscles  (Mm.  auriculares  caudales)  are  three  in 
number. 

(a)  The  cervico-auricularis  superficialis  is  a  thin  triangular  sheet.  It  is  witle 
at  its  origin  from  the  occipital  crest  and  the  adjacent  part  of  the  ligamentum  nuchse. 


Fig.  563. — External  E.\r  op  Horsk  and  it.s  Muscles,  L.^teral  View. 
2,  Posterior  border,  3,  anterior  border  of  auricula:  8,  scutiform  cartilage;  5,  zygomatic  arch;  n,  parotido- 
auricularis;  o,  zygomatico-auricularis;  o',  scutulo-auricularis  superficialis  inferior;  o" ,  scutulo-auricularis  super- 
ficialis raedius  et  superior;  p,  interscutularis;  p',  fronto-.scutularis  (pars  temporalis):  q,  cervico-auricularis 
profundus  major;  «.  small  (or  anterior)  oblique  muscle  of  head;  (,  splenius;  ?/.  tendon  of  majstoido-humerulis; 
c,  mastoido-humeralis;   x,  wing  of  atlas.     (.■Vfter  Ellenberger-Baum,  Anat.  fijr  Kiinstler.) 

and  becomes  narrower  as  it  jxissos  outward  to  be  inserted  into  the  inner  side  of 
the  convex  surfac(>  of  the  concha. 

(6)  The  cervico-auricularis  profundus  major  arises  from  the  ligamentum 
nuchje,  partly  beneatli  antl  partly  beliind  the  preceding  muscle.  It  is  directeil 
outward  and  is  inserted  into  the  postero-external  aspect  of  the  base  of  the  ear, 
partly  under  cover  of  the  ])arotido-auricularis. 

(c)  The  cervico-auricularis  profundus  minor  arises  under  the  preceding 
muscle  and  passes  downward  and  outward  to  be  inserted  into  the  lowest  part  of 
the  convex  surface  of  the  conclia,  partly  under  cover  of  the  parotid  gland. 

5.  The  parotido-auricularis  (s.  M.  auricularis  inferior)  is  a  ribbon-like  muscle 
which  lies  on  the  ])ar()tid  gland.  It  is  thin  ami  wide  at  its  origin  from  the  fascia  on 
the  lower  ])art  of  tlie  parotid  gland  and  becomes  somewhat  narrower  and  thicker 
as  it  passes  upward.  It  is  inserted  into  the  conchal  cartilage  just  lielow  the  angle 
of  junction  of  its  borders. 


THE    AURICULAR    MUSCLES 


751 


G.  The  deep  auricular  ur  rotator  muscles  (M.  auriculares  profundi  s.  rotatores 
auricula-),  two  in  nuinlier,  are  situated  under  the  scutiform  cartilage  and  the  base 
of  the  concha  and  cross  eacli  other. 

(a)  The  scutulo-auricularis  profundus  major  is  the  strongest  of  tlie  auricular 
muscles.  It  is  flat  and  is  about  an  inch  wide.  It  arises  from  the  deep  face  of  the 
scutiform  cartilage  and  passes  liackward  to  end  on  and  below  the  most  ])rominent 
part  of  the  base  of  the  concha  (cniinentia  conclue). 

(6)  The  scutulo-auricularis  profundus  minor  lies  between  the  base  of  tlie  con- 
cha and  the  preceding  muscle,  and  is  best  seen  when  the  latter  is  cut  and  reflected. 


Fig.  564. — Muscles  of  Externai.  Ear  of  Horse,  Viewed  from  Above. 
On  the  riglit  si(ie  parts  of  the  superficial  muscles  have  been  removed  and  the  scutiform  cartilage  turned  back 
to  di.spiay  the  deeper  muscle.s.  a,  Frontal  part,  a',  temporal  part  of  fronto-scutularis;  b,  interscutularis;  c, 
cervico-scutularis;  rf,  e,  scutulo-auricularis  superficialis  superior  and  medius;  /,  zygomatico-auricularis;  3,  scutulo- 
auricularis  superficialis  acce-ssorius;  o,  cervico-auricularis  superficialis;  q,  scutulo-auricularis  superficialis  inferior; 
(,  scutiform  cartilage;  «,  parieto-auricular!.«:  v,  cervico-auricularis  profundus  major;  u\  cervico-auricularis  prof, 
minor;  j,  x',  scutulo-auricularis  prof,  major  et  minor;   y,  temporalis.      (Ellenberger-Baum,  .\nat.  d.  Hau^tiere.) 


It  is  flat  and  about  an  inch  in  length.  It  arises  from  the  posterior  part  of  the  deep 
face  of  the  scutiform  cartilage  and  from  the  cervico-scutularis,  and  passes  down- 
ward, backward,  and  outward  to  be  inserted  into  the  base  of  the  concha  under 
cover  of  the  preceding  muscle. 

7.  The  tragicus  or  mastoido-auricularis  is  a  small  muscle  which  arises  from 
the  temporal  bone  just  behind  the  external  auditory  process  and  from  the  annular 
cartilage;  it  passes  upward  to  be  inserted  into  the  lower  part  of  the  anterior  border 
of  the  conchal  cartilage. 

The  intrinsic  muscles  are  very  small  and  of  little  importance.  They  arc  as 
follows : 

1.  The  antitragicus  consists  of  a  few  bundles  which  are  attached  to  the  conchal 


752  THE    SENSE    ORGANS    AND    SKIN    OF   THE    HORSE 

cartilage  behind  tlie  junction  of  its  two  borders,  and  are  partially  l)lended  with  the 
insertion  of  the  parotido-auriciilaris. 

2.  The  helicis  is  a  small  muscle  attached  in  a  position  opposite  to  the  preceding 
on  the  anterior  hordiT  of  the  conchal  cartilage;  it  extends  also  into  the  depression 
between  the  two  divisions  of  the  border.  It  is  in  part  continuous  with  the  insertion 
of  the  parotido-auricularis. 

3.  The  verticalis  auriculae'  is  a  thin  stratum  of  muscular  and  tendinous  fillers 
which  extends  upward  on  the  posterior  surface  of  the  concha  from  the  eminentia 
conchae. 

Actions. — The  base  of  the  concha  is  rounded  and  rests  in  a  pad  of  fat  (Corpus 
adi])osum  auricula;),  so  that  the  movements  of  the  external  ear  resemble  those  of 
a  ball-and-socket  joint.  It  is  noticeable  that  movements  about  the  longitudinal 
and  transverse  axes  are  accompanied  by  rotation.  When  the  ear  is  vertical  or 
drawn  forward  ("pricked  up"),  the  opening  is  usually  directed  forward;  conversely, 
when  the  ears  are  "laid  back,"  the  opening  faces  backward.  These  movements 
evidently  result  from  the  coordinated  actions  of  several  muscles  which  are  verj' 
complex  and  cannot  be  discussed  in  detail  here.  The  scutularis  acting  as  a  whole 
fixes  the  scutiform  cartilage,  so  that  the  muscles  which  arise  on  the  latter  act 
efficiently  on  the  concha.  The  anterior  aiu'icular  muscles  in  general  erect  the  ear 
and  turn  the  opening  forward.  The  interseutularis  concurs  in  this  action,  causing 
adduction  and  a  symmetrical  position  of  the  ears;  it  also  acts  directl.y  on  the 
conchal  cartilage,  .since  the  scutulo-auricularis  superficialis  superior  is  in  reality  a 
conchal  insertion  of  the  interseutularis.  The  scutulo-auricularis  superficialis 
accessorius  draws  the  concha  forward  and  turns  the  opening  outward.  The  parieto- 
auricularis  adducts  the  concha  and  inclines  it  forward.  The  cervico-auricularis 
superficialis  is  chiefly  an  adductor  of  the  conchal  cartilage,  and  directs  the  opening 
outward.  The  cervico-auricularis  profundus  major  turns  the  opening  outward  and, 
acting  with  the  parotido-auricularis,  inclines  the  ear  toward  the  poll.  The  cervico- 
auricularis  profunrlus  minor  tends  to  direct  the  opening  downward  and  outward. 
The  parotido-auricidaris  draws  the  ear  downward  and  backward,  and  acts  with  the 
cervico-auricularis  i)rofuntlus  major  in  "laying  back  the  ears";  the  deep  auricular 
muscles  concur  in  these  actions.  The  tragicus  shortens  the  external  auditory  canal. 
The  actions  of  the  intrinsic  muscles  are  inappreciable. 

The  arteries  of  the  external  ear  are  derived  from  the  anterior  auricular  branch 
of  the  superficial  temporal,  the  posterior  or  great  auricular  branch  of  the  internal 
maxillary,  and  the  anterior  branch  of  the  occipital  artery. 

The  motor  nerves  to  the  muscles  come  from  the  auricular  and  auriculo-palpe- 
bral  branches  of  the  facial  nerve  and  from  the  first  and  second  cervical  nerves. 
The  sensory  nerves  are  supplied  by  the  superficial  temporal  branch  of  the  mandibu- 
lar nerve  and  the  auricular  branch  of  the  vagus. 


THE  MIDDLE  EAR 

The  middle  ear  (Auris  media)  or  tympanic  cavity  (Cavum  tympani)  is  a  space 
in  the  tympanic  and  petrous  parts  of  the  temjioral  Ijone  situated  between  the  mem- 
brana  tympani  and  the  internal  ear.  It  is  a  pneumatic  cavity,  which  is  lined  by 
mucous  membrane,  and  communicates  with  the  pharynx  and  the  guttural  pouch 
by  the  Eustachian  tube.  It  contains  a  chain  of  auditory  ossicles  by  which  the 
vibrations  of  the  membrana  tympani  are  transmitted  to  the  internal  ear. 

The  cavity  consists  of:  (1)  A  main  part  or  atrium,  which  lies  immediately  to 
the  inner  side  of  the  membrana  tympani;  (2)  the  recessus  epitympanicus,  situated 
above  the  level  of  the  membrane  and  containing  the  upper  part  of  the  malleus 

'EUenberger  and  Raum  regard  this  as  the  honiologue  of  !lie  transversus  and  obliquus 
auriculte  of  man. 


THE    MIDDLE    EAR 


753 


and  the  greater  part  of  the  incus;    (3)  a  relatively  large  ventral   recess  in  the 
bulla  ossea. 

The  external  wall  (Paries  menibranacea)  is  formed  largely  by  the  thin  mem- 
brana  tympani,  which  closes  the  inner  end  of  the  external  auditory  canal,  and  thus 
forms  the  septum  between  the  external  anil  middle  parts  of  the  ear.  The  membrane 
is  an  oval  tlisc,  which  slopes  obliquely  downward  and  inward  at  an  angle  of  about 
30  degrees  with  the  lower  wall  of  the  external  auditory  canal.  The  circumference 
is  attached  in  a  groove  (Sulcus  tj'mpanicus)  in  the  thin  ring  of  bone  (Annulus 
tympanicus)  which  almost  completely  surrounds  it.  The  handle  of  the  malleus 
(the  outermost  of  the  auditory  ossicles)  is  attached  to  the  inner  surface  of  the 
membrane  and  draws  the  central  part  inward,  prodvicing  a  slight  concavity  of  the 
outer  surface.  The  periphery  is  thickened,  forming  the  annulus  fibrosus.  The 
membrana  tympani  consists  of  three  layers.  The  external  cutaneous  layer 
(Stratum  cutaneum)  is  a  prolongation  of  the  lining  of  the  external  auditory 
meatus.     The  middle  fibrous  layer  or  membrana  propria  includes  two  chief  sets 


Fig.  565. — Right  PcTRors  Tempor.^l  Bone  of  Horse, 
Antero-internal  View. 
/,  External  auditory  meatus;  2,  annulus  tym- 
panicus; S,  lamina?  radiating  from  2;  4,  niembrana 
timpani;  5,  malleus;  6,  incus;  7,  stapes;  S,  fenestra 
cochlea;  (s.  rotundum);  9,  facial  canal;  II,  It",  semicir- 
cular canals;  //',  vestibule;  12  cochlea.  (After 
Ellenberger.  in  Leisering's  Atlas  ) 


Fig.  566. — Right  Auditory  Ossicleg  and  Mem- 
BRAN.v  TvMP.\Ni.  Enlarged  and  Viewed  erom 
Inner  Side  and  Below. 

J,  Malleus;  2,  incus;  2',  2",  short  and  long 
processes  of  2;  3,  stapes;  4.  tensor  tympani;  5, 
ligament  attaching  long  process  of  malleus;  6,  stape- 
dius muscle;  7,  fenestra  cochlete  (s.  rotundum). 
(.\fter  Ellenberger.  in  Leisering's  .\tlas.) 


of  fibers;  the  outer  stratum  (Stratum  radiatum)  consists  of  fibers  which  radiate 
from  the  handle  of  the  malleus,  while  the  inner  stratum  (Stratum  circulare)  is  com- 
posed of  circular  fibers  which  are  best  developed  peripherally.  There  are  also 
branched  or  dendritic  fibers  in  part  of  the  membrane.  The  internal  mucous  layer 
(Stratum  mucosum)  is  a  part  of  the  general  mucous  membrane  which  lines  the 
tympanic  cavity 

The  internal  wall  of  the  tympanic  cavity  (Paries  labyrinthica)  separates  it 
from  the  internal  ear;  it  presents  a  number  of  special  features.  The  promontory 
(Promontorium)  is  a  distinct  eminence  near  the  center  which  corresponds  to  the 
first  coil  of  the  cochlea,  and  is  marked  by  a  faint  groove  for  the  superficial  petrosal 
nerve.  Above  this  is  the  fenestra  vestibuli  (s.  ovalis),  a  reniform  opening  which  is 
closed  by  the  foot-plate  of  the  stapes  and  its  annular  ligament.  The  fenestra 
cochleae  (s.  rotundum)  is  situated  below  and  behind  the  preceding;  it  is  an  irregu- 
larly oval  opening  and  is  closed  by  a  thin  membrane  (Membrana  tympani  secund- 
aria), which  separates  the  tympanic  cavity  from  the  scala  tympani  of  the  cochlea. 

The  anterior  wall  (Paries  tubaria)  is  narrow,  and  is  pierced  by  the  slit-like 
48 


754 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HOKSE 


tympanic  o]ieiiing  of  llic  luistat'hian  tulic.  Ahovo  this  and  incompletely  separated 
from  it  by  a  tliin  ])iatc  of  hone  is  tlic  semicanal  for  the  tensor  tympani  muscle. 

The  superior  wall  or  roof  (Paries  tcgmentalis)  is  crossed  in  its  inner  part  by 
the  facial  nerxc:  liere  the  facial  canal  is  more  or  less  deficient  ventrally,  and  the 
nerve  is  covered  b}'  the  nmcous  membrane  of  the  tj'mpanum. 

The  posterior  wall  (Paries  mastoidea)  presents  nothing  of  importance;  a 
tympanic  antrum  and  mastoid  cells,  such  as  are  found  behind  the  tympanic  cavity 
proi)er  in  man  and  many  animals,  are  not  present  in  the  horse. 

The  inferior  wall  or  floor  (Paries  tympanica)  is  concave  and  thin.  It  is  crossed 
by  delicate  curved  ridges,  which  radiate  from  the  greater  part  of  the  annulus 
tympanicus. 

Tlie  auditory  ossicles  (Ossicula  auditus)  form  a  cliain  which  extends  from  the 
outer  to  tile  inner  wall  of  tlie  cavity.  They  are  named,  from  without  inward,  the 
malleus,  tlie  incus,  the  os  lenticulare,  and  the  stapes.  The  first  is  attached  to  the 
inner  surface  of  the  tyni]ianic  membrane  and  tlie  last  is  fixed  in  the  fenestra 
vestibuli. 

The  malleus  or  hammer,  the  largest  of  the  ossicles,  consists  of  a  head,  neck, 
handle,  and  two  processes.  The  head  (("apitulum  mallei)  is  situated  in  the 
epitynii)anic  recess.      It  is  smooth  and  convex  above  and  in  front,  and   presents 


Fig.    567. — .\L-mTORY    Ossicles    and    Membrani 

TyMPAXI,    I.NNER    ViEW,    ENLARGED. 

^,.\nnulu3  tympanicus;  ;2,  niembrana  tym- 
pani; 3,  malleus;  4.  incus;  S,  stapes,  (.\fter  Ellen- 
berger,  in  Leisering's  .\tlas.) 


Fi<;.  .'ifiS. — Ric;ht  .-VuDiTORY  Ossicles,  Enlarged  as  In- 
iiir,\Ti'.i>  HY  Li.N-Es  Giving  their  Actual  Length. 
a,  Malleus;  /,  head;  2,  neck;  3,  handle;  4,  long  pro- 
cess; 5,  muscular  process,  b,  Incus;  I,  body;  S.  short 
branch;  5,  long  branch;  c,  os  lenticulare.  c.  Stapes;  i.head; 
£,  crus;  3,  base;  4.  attachment  of  stapedius,  (.\fter  Ellen- 
berger,  in  Leisering's  .\tlas.) 


on  its  postero-internal  aspect  a  concave  facet  for  articulation  with  the  body  of  the 
incus.  The  neck  (( -ollum  mallei)  is  the  constricted  part  below  the  head;  its  inner 
surface  is  crossed  by  the  chorda  tympani.  The  handle  (Manubrium  mallei)  is 
directed  downward,  inward,  and  a  little  forward  from  the  neck,  and  is  attached  along 
its  entire  length  to  the  membrana  tympani.  On  its  inner  surface,  near  the  upper 
end,  there  is  a  slight  projection  to  which  the  tendon  of  the  tensor  tympani  muscle  is 
attached.  The  long  process  (Processus  longus)  is  a  pointed  spicule  which  projects 
forward  from  the  neck  toward  the  petro-tympanic  fissure.  The  short  process 
(Processus  brevis)  is  a  slight  projection  of  the  outer  side  of  the  neck,  and  is  attached 
to  the  upper  part  of  the  membrana  tympani. 

The  incus  or  anvil  is  situatcfl  chiefly  in  the  epitympanic  recess.  It  may  be 
said  to  resemble  a  bicuspid  tooth  with  two  divergent  roots,  and  consists  of  a  body 
and  two  processes.  The  body  (Corpus  incudis)  articulates  with  the  head  of  the 
hammer.  The  long  process  (I'rus  longum)  projects  downward  from  the  body  and 
then  curves  inwanl;  its  extremity  has  attached  to  it  a  small  nodule  of  bone,  the  os 
lenticulare,  which  articulates  with  the  head  of  the  stapes.  The  short  process 
(Crus  breve)  projects  chiefly  liackward,  and  is  attached  to  the  wall  of  the  recess  by 
a  small  ligament. 

The  stapes  or  stirrup  consists  of  a  heail,  two  crura,  and  a  base.     The  head 


THE    EUSTACHIAN    TUBE  755 

(Capitiilum  stapedis)  is  directed  outward  and  articulates  with  the  os  lenticulare. 
The  crura,  anterior  and  posterior  (Crus  anterius,  posterius),  are  directed  inward 
from  the  head,  and  join  the  ends  of  the  base.  The  base  or  foot-plate  (Basis 
stapedis)  oecujiies  the  fenestra  vestil)uli,  to  which  it  is  attached.  The  space  be- 
tween the  crura  and  tlic  base  is  closed  l)y  a  membrane. 

The  articulations  and  ligaments  of  the  auditory  ossicles  comprise:  (1)  A 
diarthrodial  joint  between  the  heail  of  the  malleus  and  the  body  of  the  incus  (Articu- 
latio  incudonialleolaris),  inclosed  by  a  capsule.  (2)  An  enarthrosis  between  the  os 
lenticulare  and  the  head  of  the  stapes  (Articulatio  incudostapedia),  also  surrounded 
by  a  capsule.  (3)  The  base  of  the  stapes  is  attached  to  the  margin  of  the  fenestra 
vestibuli  by  a  ring  of  elastic  fibers  (Lig.  annulare  baseos  stapedis).  (4)  Small 
ligaments  attach  the  head  of  the  malleus  and  the  short  crus  of  the  incus  to  the  roof 
of  the  epitympanic  recess,  ("i)  The  axial  ligament  (of  Helmholtz)  attaches  the 
neck  of  the  malleus  to  a  small  projection  (Spina  tympanica  anterior)  above  and  in 
front  of  the  annulus  tympanicus. 

The  muscles  of  the  auditory  ossicles  are  two  in  number,  viz.,  the  tensor  tjTn- 
pani  and  the  stapedius.  The  tensor  tympani  arises  from  the  upper  wall  of  the 
osseous  Eustachian  tube,  and  ends  in  a  delicate  tendon  which  bends  outward  and 
is  inserted  into  the  handle  of  the  malleus  near  its  upper  end.  When  it  contracts, 
it  draws  the  handle  of  the  malleus  inward  and  tenses  the  membrana  tjTnjiani;  it 
probably  also  rotates  the  malleus  around  its  long  axis.  It  is  innervated  by  the 
motor  part  of  the  trigeminus  through  the  otic  ganglion.  The  stapedius  arises  from 
a  small  prominence  (Eminentia  pyramidalis)  of  the  ]iosterior  wall  of  the  tympanum, 
runs  forward  on  the  facial  nerve,  and  is  inserted  into  the  neck  of  the  stapes.  Its 
action  is  to  draw  the  head  of  the  stapes  backward  and  rotate  the  anterior  end  of  the 
base  outward,  thus  tensing  the  annular  ligament.  It  is  innervated  by  the  facial 
nerve. 

The  tympanic  mucous  membrane  (Tunica  mucosa  tympanica)  is  continuous 
with  that  of  the  pharynx  and  the  guttural  pouch  through  the  Eustachian  tube. 
It  is  thin,  closely  united  with  the  underlying  periosteum,  and  is  reflected  over  the 
ossicles,  ligaments,  and  muscles,  the  chorda  tympani,  and  the  facial  nerve  in  the 
open  jjart  of  the  facial  canal.  It  contains  minute  lymph  nodules  and  small  mucous 
glands  (Glandulce  tympanicse).  The  epithelium  is  in  general  colunmar  ciliated, 
but  over  the  membrana  tympani,  ossicles,  and  promontory  it  is  flattened. 

The  artery  of  the  tympanum  is  the  stylo-mastoid,  a  small  vessel  which  arises 
from  the  posterior  auricular  branch  of  the  internal  maxillary  artery.  It  enters  the 
tympanum  through  the  stylomastoid  foramen,  and  forms  a  circle  around  the  tym- 
panic membrane.  The  nerves  of  the  mucous  membrane  come  from  the  tymjianic 
plexus. 

The  Eustachian  Tube 
The  Eustachian  or  auditory  tube  (Tuba  auditiva  [Eustachii])  extends  from  the 
tympanic  cavity  t(j  the  ])harynx;  it  transmits  air  to  the  former  and  equalizes  the 
pressure  on  the  two  surfaces  of  the  membrana  tympani.  It  is  directed  forward, 
downward,  and  slightly  inward,  and  is  four  to  five  inches  (ca.  10  to  12  cm.)  in  length. 
Its  posterior  extremity  lies  at  the  inner  side  of  the  root  of  the  muscular  process  of 
the  petrous  temporal,  and  comnnmicates  with  the  anterior  part  of  the  tympanic 
cavity  by  the  small  slit-like  tympanic  opening  (Ostium  tympanicum  tubse  auditive). 
For  a  distance  of  about  a  quarter  of  an  inch  (ca.  G  to  7  mm.)  in  front  of  this  opening 
it  is  a  complete  tube,  with  a  curved  lumen  which  is  little  more  than  a  capillary  space. 
Further  forward  it  has  the  form  of  a  plate  which  widens  anteriorly  and  is  curved  to 
inclose  a  narrow  groove,  that  opens  ventrally  into  an  extensive  diverticulum  termed 
the  guttural  pouch.  The  pharyngeal  opening  (Ostium  pharyngeum  tubff  audi- 
tivse)  is  situated  on  the  postero-superior  part  of  the  lateral  wall  of  the  pharjiix  just 


75G  THE    SENSE    ORGANS    AND    SKIN    OF   THE    HORSE 

below  the  level  of  the  jjosterior  iiares.  It  is  a  slit,  an  iiicli  or  more  (ca.  3  cm.) 
in  length,  which  slopes  downward  and  backward.  It  is  bounded  internally  by  the 
thin  free  edge  of  the  tube,  from  tli(>  lower  part  of  w^hich  a  fold  of  mucous  membrane 
(Plica  salpingo-pharyngea)  extends  in  the  same  direction  on  the  lateral  wall  of 
the  pharynx  for  a  distance  of  a  little  more  than  an  inch  usually.  The  outer  boun- 
dary of  the  opening  is  the  lateral  wall  of  the  pharynx.  The  liasis  of  the  tube  is  a 
plate  of  fibro-cartilage  (Cartilago  tuba'  auditivte)  wliich  is  firmly  attached  dorsally 
to  the  fibrous  tissue  which  closes  the  foramen  laccrum  basis  cranii,  the  temporal 
wing  of  the  sphenoid,  and  the  pterygoid  bone.'  On  cross-section  the  cartilage 
(except  at  its  tympanic  end)  is  seen  to  consist  of  two  laminae  which  are  continuous 
witli  each  other  above.  The  internal  lamina  (Lamina  medialis)  gradually  W'idens 
toward  the  pharyngeal  end,  where  it  forms  a  broad  valvular  flap.  This  is  convex 
internall}',  and  its  thin  anterior  edge  forms  the  inner  margin  of  the  pharyngeal 
opening.  Behind  this  the  lamina  has  a  thick  free  edge  which  projects  vcntrally 
from  the  roof  of  the  guttural  pouch.  The  external  lamina  (Lamina  lateralis)  is 
narrow  and  thin,  and  is  related  externally  to  the  levator  and  tensor  ])alati  muscles, 
which  are  in  part  attached  to  it;  it  does  not  exist  at  the  pharyngeal  entl  of  the  tube. 
The  mucous  memtjrane  of  the  tube  is  continuous  behind  with  that  of  the  tympanum 
and  in  front  with  that  of  the  pharj-nx.  On  either  side  it  is  reflected  to  form  a  large 
diverticulum,  the  guttural  pouch.  It  is  covered  with  ciliated  e]iithelium,  and  con- 
tains mucous  glands  and  lymph  nodules. 

The  pharyngeal  opening  appears  to  be  closed  ortlinarilv,  but  the  tube  opens  during  degluti- 
tion. This  action  is  apparently  produced  by  tlie  part  of  tlie  palato-pharyngeus  muscle  which 
is  attached  to  the  tube. 

The  Guttural  Pouches 
The  guttural  pouches,  right  and  left  (Figs.  255,  256,  569),  are  large  mucous 
sacs,  each  of  which  is  a  ventral  diverticulum  of  the  Eustachian  tube  (Diverticulum 
tubse  auditivse);  they  are  not  present  in  the  domesticated  animals  other  than  the 
equida;.  They  are  situated  between  the  base  of  the  cranium  and  the  atlas  above 
and  the  pharynx  below.  Medially  they  are  in  apposition  in  great  part,  but  are  to 
some  extent  separated  by  the  intervening  ventral  straight  muscles  of  the  head. 
The  anterior  end  is  a  small  cul-de-sac  which  lies  below  the  body  of  the  presi^henoid 
between  the  Eustachian  tube  and  the  median  recess  of  the  pharynx.  The  posterior 
extremity  lies  near  or  below  the  atlantal  attachment  of  the  longus  colli.  The  pouch 
is  related  dorsally  to  the  l)ase  of  the  cranium,  the  atlanto-occipital  joint  capsule, 
and  the  ventral  straight  muscles.  Ventrally  it  lies  on  the  pharynx  and  the  origin 
of  the  oesophagus.  Laterally  the  relations  are  numerous  and  coni])lex.  They 
comprise  the  pterygoid,  levator  palati,  tensor  palati,  stylo-hyoideus,  and  digastricus 
muscles;  the  parotid  and  submaxillary  glands;  the  external  carotid,  internal 
maxillary,  and  external  maxillary  arteries;  the  internal  maxillary  and  jugular  veins; 
the  pharyngeal  or  guttural  lymph  glands;  the  glosso-pharyngeal,  hyjioglossal,  and 
sujierior  laryngeal  nerves.  The  vagus,  accessory,  and  sympathetic  nerves,  the 
superior  cervical  ganglion,  the  internal  carotid  artery,  and  the  inferior  cerebral  vein 
are  situated  in  a  fold  of  the  upper  wall  of  the  pouch.  The  pouch  is  reflected  around 
the  anterior  border  of  the  great  cornu  of  the  hyoid  bone  so  as  to  clothe  both  surfaces 
of  the  upper  part  of  the  latter.  It  thus  forms  an  outer  compartment,  which  extends 
backward  external  to  the  great  cornu  and  the  occipito-hyoideus  muscle;  it  is 
related  externally  to  th(>  parotid  gland,  the  articulation  of  the  jaw,  the  ascending 
part  of  the  internal  maxillary  artery,  the  superficial  temporal  artery,  and  the  facial 
nerve;  dorsally  it  covers  the  mandibular  nerve  and  its  chief  branches,  and  is  at- 
tached to  the  styloid  process  of  the  conchal  cartilage. 

'  There  is,  strictly  speaking,  no  osseous  part  of  the  tube  such  as  occurs  in  man.  In  I  lie  horse 
the  cartilage  extends  to  the  tympanic  orifice. 


THE  GUTTURAL  POUCHES 


757 


Each  pouch  communicates  witli  the  ]iharynx  through  the  pharyngeal  orifice 
of  the  Eustachian  tube,  and  is  in  direct  continuity  with  the  mucous  memhrane  of 
the  latter. 

The  wall  of  the  ])ouch  is  a  delicate  nuicous  membrane  which  is  in  general 
rather  loosely  attached  to  the  surrounding  structures.  It  is  covered  with 
ciliated  epithelium  and  is  supplied  with  mucous  glands. 


Scutifiirm  airliUuje, 
posterior  process 


('Li)ichal  cartilage 

Mastoido-humcralis 
tendon 

Nerves  IX,  X,  XI 


Inferior  cerebral  rein 
Internal  carotid  artery 

Guttural  pouch 
Occijnto-h  yoideus 
inuscle 

ugular  vein 


Int.  maxillary  artery 
Ext.  maxillary  artery 

Pharyngeal  lymph  glands 
Stylo-maxillaris  muscle 

Sterno-ccphalicus  tendon 

■S^ibniiixillnry  gland 
Thyroid  cartilage 
Ext.  maxillary  rein 


Omo-hyoidei 


Fig.  569. — Cross-section  of  He.\d  of  Horse. 
The  section  passes  through  the  base  of  the  external  ear  and  just  behind  the  posterior  border  of  the  lower 
jaw.     /,  Rectus  capitis  anterior  minor;    2.  rectus  capitis  anterior  major;    S.  inner  walls  of  guttural  pouches  in  .,n- 
position;  4,  4.  arytenoid  cartilage,  upper  piece  apex; 
ventricle  of  larynx;   .9,  tr 


.  posterior  pillar  of  soft  palate;  6.  false  vocal  cord; 
;  vocal  cord;   9.  vocal  muscle;    10.  thyro-hyoideus  muscle. 


.  lateral 


It  is  worthy  of  note  that  the  pharyngeal  orifire  of  the  Eustachian  tube  is  at  such  u  level  as 
to  provide  (in  the  ordinary  position  of  the  head)  only  an  overflow  outlet  for  the  escape  ot  tluul 
which  may  accumulate  in  the  pouch.  The  two  pouches  are  often  unequal  in  size,  and  variations 
in  regard  to  the  distance  which  thev  extend  backward  are  not  uncommon  In  one  case  a  small 
aged  horse,  the  right  pouch  extended  along  the  oesophagus  about  five  inches  (ca.  1_  cm.)  behind 
the  ventral  tubercle  of  the  atlas,  and  the  left  one  a  little  more  than  two  inches  (ca.  *>  cm.).  iNo 
pathological  changes  were  apparent,  and  the  condition  was  not  recognizable  externally.  Lases 
of  extreme  size— so-called  tympanites— of  the  pouches  occur,  antl  are  apparently  congemtal 
defects  In  a  case  in  a  yearling  colt,  the  head  of  which  was  24  inches  long,  the  left  pouch  extended 
about  12  inches  (ca.  30  cm.)  behind  the  tubercle  of  the  atlas,  and  had  a  capacity  of  six  quarts. 


758  THE    SENSE    ORGANS    AND    SKIN    OF   THE    HORSE 

The  anterior  end  formed  a  cul-de-sac  about  two  inches  (ca.  5  cm.)  long  between  the  Eustachian 
tube  and  levator  palati  internally  and  the  internal  pterygoid  muscle  externally. 


THE  INTERNAL  EAR 
The  internal  ear  or  labyrinth  (Auri.s  intprna  s.  Laliyrinthus)  oonsists  of  two 
parts,  viz.:  (1)  a  complex  membranous  sac,  which  supports  the  auditory  cells  and 
the  peripheral  ramifications  of  the  auditory  nerve;  (2)  a  series  of  cavities  in  the 
petrous  teniixiral  Ihhic,  which  inclose  the  membranous  ]iart.  The  first  is  called 
the  membranous  labyrinth,  and  contains  a  fluid,  the  endolymph.  The  second  is 
the  osseous  labyrinth.  The  two  are  se]iarated  by  the  perilymphatic  space,  which  is 
occupieil  by  a  fluid  termed  the  perilymph. 

The  Osseous  Labyrinth 
The  osseous  labyrinth  (I^abyrintlius  osseus)   (Fig.  565)  is  excavated  in  the 
petrous  tein|ioral  Ixjuc  to  the  inner  side  of  the  tympanic  cavity.     It  consists  of 
three  divisions:    (1)  a  middle  part,  the  vestibule;    (2)  an  anterior  one,  the  cochlea; 
and  (3)  a  posterior  one,  the  semicircular  canals. 

1.  The  vestibule  (Vestil)uluin)  is  the  central  part  of  the  osseous  laljyrinth, 
and  communicates  in  front  with  the  cochlea,  behind  with  the  semicircular  canals. 
It  is  a  small,  irregularly  ovoid  cavity,  which  is  about  5  to  6  mm.  in  length.  Its 
outer  wall  separates  it  from  the  tympanic  cavity,  and  in  it  is  tlie  fenestra  vestibuli, 
which  is  occupied  by  the  base  of  the  stapes.  The  inner  wall  corrcsjionds  to  the 
fundus  of  the  internal  auditory  meatus.  It  is  crossed  by  an  oblique  ridge,  the 
crista  vestibuli,  which  separates  two  recesses.  The  anterior  and  smaller  of  these  is 
the  recessus  sphaericus,  which  lodges  the  saccule  of  the  membranous  labyrinth. 
In  its  lower  jtart  there  are  about  a  dozen  minute  foramina  which  transmit  filaments 
of  the  vestiliular  nerve  to  the  saccule.  The  posterior  and  larger  depression  is  the 
recessus  ellipticus,  which  lodges  the  utricle  of  the  membranous  labyrinth.  The 
crista  vestiljuli  divides  below  into  two  divergent  branches,  wliich  include  between 
them  the  small  recessus  cochlearis ;  this  is  perforated  by  small  foramina,  through 
which  nerve-bundles  reach  the  ductus  cochlearis.  Similar  foramina  in  the  recessus 
ellipticus  and  the  crista  vestibuli  tran.sinit  nerve  filaments  to  the  utricle  and  the 
ampulliB  of  the  superior  and  external  semicircular  ducts.  The  anterior  wall  is 
pierced  by  an  opening  which  leads  into  the  scala  vestibuli  of  the  cochlea.  The 
posterior  part  of  the  vestibule  presents  the  four  openings  of  the  semicircular  canals. 
The  inner  opening  of  the  aquseductus  vestibuli  is  a  small  slit  behind  the  lower  part 
of  the  crista  vestibuli.  The  afiuicductus  ])asses  backward  in  the  jietrous  temporal 
bone,  and  opens  on  the  inner  surface  of  tlie  latter  near  the  middle  of  its  posterior 
border;   it  contains  the  ductus  endolyiujihaticus. 

2.  The  osseous  semicircular  canals  (Canales  seniicirculares  ossei),  three  in 
number,  are  situated  behind  and  a]10^'e  the  vc^stibule.  They  are  at  right  angles  to 
each  other,  and  arc  designated  according  to  their  positions  as  superior,  posterior, 
and  external.  They  communicate  with  the  vestibule  by  four  openings  only,  since 
the  inner  end  of  the  superior  and  the  upper  end  of  the  posterior  canal  unite  to  form 
a  common  canal  (Crus  commune),  and  the  ampullate  ends  of  the  superior  and  ex- 
ternal canals  have  a  common  orifice.  Each  canal  forms  aliout  two-thirds  of  a 
circle,  one  end  of  which  is  (>nlarged  and  termed  the  ampulla.  The  superior  canal 
(Canalis  semicircularis  superior)  is  nearly  vertical  and  is  placed  obliquely  with 
regard  to  a  sagittal  plane,  so  that  its  outer  limb  is  further  forward  than  the  inner 
one.  The  antero-external  end  is  the  ain]nilla  and  ojx'iis  into  the  vestibule  with 
that  of  the  external  canal.  The  opposite  non-dilated  end  joins  the  adjacent  end  of 
the  posterior  canal  to  form  the  crus  cdininune,  which  opens  into  the  supero-internal 
part  of  the  vestibule.     The  posterior  canal  (Canalis  semicircularis  posterior)  is 


THE    MEMBRANOUS    LABYRINTH  759 

also  nearly  vertical.  Its  ampulla  is  below,  and  opens  into  the  vestilnilc  (liroctly, 
while  the  non-dilated  end  joins  that  of  the  superior  canal.  The  external  canal 
(Canalis  semicircularis  lateralis)  is  nearlj'  horizontal.  Its  ampulla  is  external  and 
opens  into  the  vestibule  with  that  of  the  superior  canal. 

3.  The  cochlea  is  the  anterior  part  of  the  bony  labyrinth.  It  has  the  form  of  a 
short  Ijlunt  cone,  the  base  of  which  (Basis  cochleae)  corresponds  to  the  anterior 
part  of  the  fundus  of  the  internal  auditory  meatus,  while  the  apex  or  cupola  (Cupula) 
is  directed  outward,  forward,  and  downward.  It  measures  about  7  nun.  acToss  the 
base  and  about  4  mm.  from  base  to  apex.  It  consists  of  a  spiral  canal  (Canalis 
sjiiralis  cochlea'),  which  forms  two  and  a  half  turns  around  a  central  cohunn  termed 
the  modiolus.  The  modiolus  diminishes  rajiidly  in  diameter  from  base  to  apex. 
Its  l)ase  (Basis  modioli)  corresponds  to  the  area  cochlea  of  the  fundus  of  the  internal 
auditory  meatus,  and  its  apex  extends  nearly  to  the  cupola.  Projecting  from  the 
modiolus  like  the  thread  of  a  screw  is  a  thin  plate  of  bone,  the  lamina  spiralis  ossea. 
This  begins  between  the  two  fenestrse  and  ends  near  the  cujiola  as  a  hook-like 
process  (Hamulus  lamina>  spiralis).  The  lamina  extends  about  half-way  to  the 
periphery  of  the  cochlea  and  partially  divides  the  cavity  into  two  passages;  of 
these,  the  upper  one  is  termed  the  scala  vestibuli,  and  the  lower  the  scala  tympani. 
The  membrana  basilaris  extends  from  the  free  margin  of  the  lamina  to  tlic  outer  wall 
of  the  cochlea  and  completes  the  sejjtum  between  the  two  scala-,  but  the_y  com- 
municate through  the  opening  (Helicotrema)  at  the  cupola.  The  modiolus  is 
traversed  by  an  axial  canal  which  transmits  the  nerves  to  the  apical  coil,  and  by  a 
spiral  canal  (canalis  spiralis  modioli),  which  follows  the  attached  border  of  the 
lamina  spiralis,  and  contains  the  spiral  ganglion  and  vein.  Close  to  the  beginning 
of  the  scala  t\nnpani  is  the  inner  orifice  of  the  aquaeductus  cochleae,  a  small  canal 
which  opens  behind  the  internal  auditory  meatus,  and  establi.^hes  a  conniiunication 
between  the  scala  tympani  and  the  subarachnoid  space. 

The  internal  auditory  meatus  has  been  described  in  part  {vide  Osteologj')- 
The  fundus  of  the  meatus  is  divided  by  a  ridge  (Crista  transversa)  into  upper  and 
lower  parts.  The  anterior  part  of  the  upper  depression  (Area  n.  facialis)  presents 
the  cranial  opening  of  the  facial  canal;  and  the  posterior  part  (Area  vestibularis 
superior)  is  perforated  by  foramina  for  the  jjassage  of  nerves  to  the  utricle  and 
the  ampulUe  of  the  superior  and  external  membranous  semicircular  canals.  The 
anterior  part  of  the  inferior  depression  (Area  cochleje)  presents  a  central  foramen 
and  a  spiral  tract  of  minute  foramina  (Tractus  spiralis  foraminosus)  for  the  passage 
of  nerves  to  the  cochlea.  Behind  these  is  an  area  of  small  openings  which  transmit 
nerves  to  the  saccule  (Area  vestibularis  inferior),  and  a  single  foramen  (F.  singulare) 
for  the  passage  of  a  nerve  to  the  ampulla  of  the  posterior  semicircular  canal. 

The  Membranous  Labyrinth 
The  membranous  labyrinth  (Labyrinthus  membranaceus)  lies  within,  but 
does  not  fill,  the  osseous  labyrinth.  It  is  attached  to  the  latter  by  delicate  tra- 
beculte  which  traverse  the  perilymphatic  space.  It  conforms  more  or  less  closely 
to  the  bony  labyrinth,  but  consists  of  four  divisions,  since  the  vestibule  contains 
two  membranous  sacs — the  utricle  and  saccule. 

1.  The  utricle  (Utriculus),  the  larger  of  the  two  sacs,  lies  in  the  postero- 
superior  part  of  the  vestiljule,  largely  in  the  recessus  ellipticus.  It  receives  the 
openings  of  the  membranous  semicircular  canals,  and  the  small  ductus  utriculo- 
saccularis  leatls  from  its  lower  part  to  the  ductus  endol3'mphaticus. 

2.  The  saccule  (Sacculus)  is  situated  in  the  recessus  sphsericus  of  the  vestibule. 
From  its  lower  part  the  ductus  rexmiens  proceeds  to  open  into  the  ductus  cochlearis, 
a  little  in  front  of  the  blind  end  of  the  latter.  A  second  narrow  tube,  the  ductus 
endolymphaticus,  passes  from  the  posterior  part  of  the  saccule,  and  is  joined  by  the 
ductus  utriculo-saccularis;   it  then  traverses  the  aquaeductus  vestibuli,  and  term- 


760 


THE    SENSE    ORGANS    AND    SKIN    OF   THK    HORSE 


inatcs  uiulor  tlie  duni  inatcr  on  the  jiDstcrior  part  of  the  internal  surface  of  tlie 
petrous  teniiioral  lionc  in  a  dilated  lilind  end,  the  saccus  endolymphatieus. 

3.  The  membranous  semicircular  canals  (Ductus  semicirculares)  correspond 
in  general  to  the  osseous  canals  alreaily  described,  but  it  may  be  noted  that  while 
the  ampuUiP  of  the  membranous  canals  nearly  fill  those  of  the  osseous  canals,  the 
other  parts  of  the  membranous  canals  only  occupy  about  one-fourth  of  the  bony 
cavities. 

4.  The  cochlear  duct  (Ductus  cochlearis)  is  a  spiral  tube  situated  within  the 
cochlea.  It  begins  by  a  blind  end  (Cscum  vestibulare)  in  the  cochlear  recess  of 
the  vestibule,  and  ends  by  a  second  blind  end  (Cscum  cupulare),  which  is  attached 
to  the  cupola  of  the  cochlea.  The  vestibular  part  is  connected  with  the  saccule 
by  the  ductus  reuniens.  The  duct  is  triangular  in  cross-section,  and  it  is  usual  to 
regard  it  as  having  three  walls.  The  vestibular  wall  or  roof,  which  separates  the 
cochlear  duct  from  the  scala  vestibuli,  is  formed  by  the  very  delicate  membrana 
vestibularis  (of  Keissner),  which  extends  obliquely  from  the  lamina  spiralis  ossca 
to  the  outer  wall  of  the  cochlea.  The  tympanic  wall  or  floor  intervenes  between 
the  cochl(>ar  duct  and  the  scala  tympani;  it  is  formed  by  the  periosteum  of  the  mar- 
ginal part  of  the  lamina  spiralis  and  the  membrana  basilaris,  which  stretches  be- 


Fio.     570. — Left     Membranovs     Labyrinth     (Es- 

I.ARGHD). 

/.  Cochlea;  2,  fenestra  vestibuli;  J,  fenestra 
cochlea;;  4.  ductus,  endolymphatieus;  6,  superior, 
6,  external,  7,  inferior  semicircular  canal,  (.\fter 
Ellenberger.   in  Leisering's  Atlas.) 


Fig.  57!. — Schem.atic  Sectional  View  of  L.vbyrinth 
(Enlarged). 
1,  2,  S,  Superior,  external,  and  inferior  semi- 
circular canals:  4<  utricle:  6,  saccule:  6,  cochlea: 
7,  auditory  nerve.  (After  EllenberRer,  in  Leisering's 
Atlas.) 


tween  the  fre(>  edge  of  tlie  lamina  and  the  outer  wall  of  the  cochlea.  The  outer 
wall  consists  of  tlie  fibrous  lining  of  the  cochlea,  which  is  greatly  thickened  to  form 
the  ligamentum  spirale  cochleae. 

Structure.' — The  membranous  labyrinth  consists  in  general  of  an  outer  thin 
fibrous  layer,  a  middle  transparent  tunic,  and  an  internal  epithelium,  composed  of 
flattened  cells.  But  in  certain  situations  s]iecial  and  remarkable  structures  occur, 
among  which  are  the  following:  (1)  The  maculae  acusticae  ajipcar  as  small  whitish 
thickenings  of  the  inner  walls  of  the  saccule  and  utricle.  The  epithelium  here 
consists  of  two  kinds  of  cells,  viz.,  supporting  cells  and  hair  cells.  The  latter  are 
flask-shaped  and  are  surrounded  by  the  fusiform  supporting  cells.  The  free  end 
of  each  hair  cell  bears  a  stiff,  hair-like  process  composed  of  a  bundle  of  cilia.  Fibers 
of  the  saccular  and  utricular  branches  of  the  vestibular  nerve  form  arborizations 
about  the  basal  parts  of  the  hair  cells.  Adherent  to  the  surface  of  the  maculae 
are  fine  crystals  of  lime  salts,  embedded  in  a  mucoid  substance,  and  termed  otoconia. 

(2)  The  cristae  acusticae  are  linear  thickenings  of  the  w-all  of  each  ampulla  of  the 
membranous  semicircular  canals.     Their  structure  is  similar  to  that  of  the  macule. 

(3)  The  spiral  organ  of  Corti  (Organon  spirale)  is  an  epithelial  elevation  which  is 
situated  upon  the  inner  part  of  the  membrana  basilaris,  and  extends  the  entire 
length  of  the  ductus  cochlearis.     It  is  very  complicated  in  structure,  but  consists 

'  For  the  finer  structure  reference  is  to  be  made  to  the  histological  literature. 


THE    SKIN  7G1 

essentially  of  remarkable  supporting  cells  and  hair  cells.     Fibers  of  the  cochlear 
nerve  ramify  about  the  Itasal  parts  of  the  hair  cells. 

Vessels  and  Nerves. — The  artery  of  the  internal  ear  is  the  internal  auditory 
artery,  a  very  small  vessel  which  usually  arises  from  the  posterior  cerebellar  artery, 
and  enters  the  internal  auditory  meatus.  The  veins  go  to  the  inferior  petrosal 
sinus.  The  vestibular  nerve  is  distributetl  to  the  utricle,  saccule,  and  membranous 
semicircular  canals,  and  mediati's  eiiuilibration.  The  cochlear  nerve  gives  a  branch 
to  the  saccule  and  enters  the  central  canal  of  the  modiolus.  Along  its  course  it 
gives  off  fibers  which  radiate  outward  between  the  two  plates  of  the  lamina  s]iiralis 
ossea,  and  ramify  about  the  hair  cells  of  the  organ  of  Corti.  The  ganglion  spirale 
or  ganglion  of  Corti  is  situated  in  the  spiral  canal  of  the  modiolus  near  the  fixed 
border  of  the  lamina  spiralis.     The  cochlear  nerve  mediates  the  sense  of  hearing. 


The  Skin 

The  skin  or  common  integument  (Integumentum  commime)  is  the  jirotective 
covering  of  the  liody,  and  is  continuous  at  the  natural  openings  with  the  mucous 
membranes  of  the  digestive,  respiratory,  and  urogenital  tracts.  It  contains  per- 
ipheral ramifications  of  the  sensory  nerves,  and  is  thus  an  important  sense  organ. 
It  is  the  principal  factor  in  the  regulation  of  the  temperature  of  the  body,  and  by 
means  of  its  glands  it  plays  an  important  part  in  secretion  and  excretion.  Some 
of  its  special  horny  modifications  or  appendages  are  used  as  organs  of  prehension  or 
as  weapons. 

The  thickness  of  the  skin  varies  in  the  different  species,  on  different  parts  of 
tht>  body  of  the  same  animal,  and  also  with  the  breed,  sex,  and  age.  The  color 
also  varies  greatly,  l)ut  this  is  masked  in  most  places  by  the  covering  of  hair  or  wool. 
The  skin  is  in  general  highly  elastic  and  resistant. 

Permanent  folds  of  the  skin  (Plica^  cutis)  occur  in  certain  situations,  and  in 
some  places  there  are  cutaneous  pouches  or  diverticula  (Sinus  cutis). 

The  skin  is  attached  to  the  underlying  parts  liy  the  subcutis  or  superficial 
fascia  (Tela  subcutanea).  This  consists  of  connective  tissue  containing  elastic 
fibers  and  fat.  When  the  fat  forms  a  layer  of  considerable  thickness,  it  is  termed 
the  panniculus  adiposus.  Over  a  consideralile  part  of  the  body  the  subcutis  con- 
tains striped  nuiscle,  the  panniculus  camosus  (M.  cutaneus);  in  some  regions  the 
fibers  of  the  muscle  are  inserted  into  the  skin,  and  their  contraction  twitches  the 
skin  or  produces  temporary  folds. ^  The  amount  of  subcutaneous  tissue  varies 
widely;  in  some  places  it  is  abundant,  so  that  the  skin  can  be  raised  consideralily; 
in  other  situations  it  is  practically  absent  and  the  skin  is  closely  adherent  to  the 
subjacent  structures.  Subcutaneous  bursae  often  develop  over  prominent  parts 
of  the  skeleton  where  there  is  much  pressure  or  friction. 

Structure. — The  integument  consists  of  the  cutis  or  skin  proper  and  its  epider- 
mal appendages,  e.  g.,  hairs,  hoofs,  claws,  horns,  etc.  The  cutis  consists  of  two 
distinct  strata,  viz.,  a  superficial  epithelial  layer,  the  epidermis,  and  a  deep  connec- 
tive-tissue layer,  the  coriimi. 

The  epidermis  is  a  non-vascular,  stratified  epithelium  of  varying  thickness.  It 
presents  the  openings  of  the  cutaneous  glands  and  the  hair-follicles,  and  its  deep 
surface  is  adapted  to  the  corium.-  It  is  divisible  into  a  superficial,  harder,  drier 
part,  the  stratum  comeum,  and  a  deeper,  softer,  moister  part,  the  stratum  germin- 
ativum.  The  cells  of  the  latter  contain  pigment,  and  liy  their  proliferation  com- 
pensate the  loss  bj'  desquamation  of  the  superficial  ]5art  of  the  stratum  corneum. 

'  This  muscle  has  been  described  in  the  Myology. 

^  To  prevent  a  possible  misapprehension,  it  may  be  stated  that  the  epidermis  primarily 
molds  the  corium,  and  that  tlie  glands  and  hair-follicles  are  invaginations  of  the  epidermis. 


762  THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 

In  many  i)laccs  further  subdivision  into  strata  is  evident   on  properly  jirepared 
cross-sections. 

The  coriiun  consists  essentially  of  a  feltwork  of  connective-tissue  and  elastic 
fibers.  It  is  well  supplied  with  vessels  and  nerves,  and  contains  the  cutaneous 
glands,  the  hair-follicles,  and  unstriped  muscle.  The  deeper  part  of  the  corium, 
the  tunica  propria,  consists  of  a  relatively  loose  network  of  coarse  bundles  of  fibers, 
and  in  most  places  there  is  no  clear  line  of  demarcation  between  it  and  the  subcutis. 
The  superficial  part,  the  corpus  papillare,  is  of  finer  texture  and  is  free  from  fat. 
Its  superficial  face  is  thickly  beset  with  blunt  conical  prominences,  the  papillae, 
which  are  received  into  corresponding  depressions  of  the  epidermis.  They  contain 
vascular  loops  and  nerves,  or,  in  certain  situations,  special  nerve-endings. 

The  papilla;  are  host  developed  where  the  epidermis  i.s  thick  and  hairs  are  small  or  absent. 
On  thickly-haired  regions  they  are  small  or  even  absent.  On  certain  parts  of  the  body  (anus, 
vulva,  prepuce,  scrotum,  eyelids,  etc.)  the  corium  contains  pigment  in  its  connective-tissue  cells. 

The  glands  of  the  skin  (Glandulae  cutis)  are  chiefly  of  two  kinds,  sudoriferous 
and  sebaceous. 

The  sudoriferous  or  sweat  glands  (Glandule  sudorifera?)  consist  of  a  tube,  the 
lower,  secretory  part  of  which  is  coiled  in  the  deep  part  of  the  corium  or  in  the  sub- 
cutis to  form  a  round  or  oval  ball  (Corpus  glanduUe  sudoriferEe).  The  excretory 
duct  (Ductus  sudoriferus)  passes  almost  straight  up  through  the  corium,  but  pur- 
sues a  more  or  less  flexuous  course  through  the  epidermis,  and  opens  into  a  hair- 
follicle  or  by  a  fininel-shaped  pore  (Porus  sudoriferus)  on  tlie  surface  of  the  skin. 

The  sebaceous  glands  (Glandulae  sebaceae)  are  in  great  part  associated  with 
the  hairs,  into  the  follicles  of  which  they  open.  Their  size  varies  widely,  and  is 
in  general  in  inverse  ratio  to  that  of  the  hair.  The  larger  ones  are  easily  seen  with 
the  naked  eye,  and  appear  as  small,  pale  yellow  or  brownish  Ijodies.  In  certain 
situations  {c.  cj.,  the  labia  vulvae,  anus,  prepuce)  they  are  independent  of  the  hairs 
and  are  well  developed.  In  form  they  may  be  branched  alveolar,  simple  alveolar, 
or  even  tubular  in  type.  They  secrete  a  fatty  substance,  the  sebum  cutaneum, 
which  serves  as  a  protective  against  moisture,  and  may  also  (l)y  its  aromatic 
constituents)  play  an  important  part  in  the  sexual  life  of  animals. 

The  two  kinds  of  glands  described  above  are  those  which  are  most  widely  distributed,  but 
many  sprcial  type-s  occur.  Some  of  these  are  to  be  regarded  as  modified  sweat  glands,  e.  g.,  the 
nasd-laliial  glands  of  the  ox,  the  glands  of  the  snout  of  the  pig,  and  the  glands  of  the  plantar 
cushion  of  the  horse.  Others,  c.  3.,  the  tarsal  (or  Meibomian)  glands  of  the  eyelids,  are  modified 
sebaceous.  Still  others  are  not  yet  d.-issilicd  satisfactorily.  Some  of  these  .spi^cial  types  have 
been  referred  to  in  previous  chai)tiis,  and  dtlieis  will  receive  attention  in  the  special  descriptions 
which  follow.  The  mammary  glands  arc  liiglily  modihed  cutaneous  glands,  which  are  intimately 
associated  in  function  with  the  genital  organs,  and  have  been  described  with  the  latter. 

Vessels  and  Nerves. — The  arteries  of  the  skin  enter  from  the  subcutis,  where 
they  communicate  freely.  In  the  deeper  part  of  the  corium  they  form  a  plexus, 
and  another  network  is  formed  under  the  papillse.  Small  vessels  from  the  deep 
plexus  go  to  the  fat  and  sweat  glands,  and  the  subpapillary  plexus  sends  fine 
branches  to  the  papillae,  hair-follicles,  and  sebaceous  glands.  The  veins  form  two 
plexuses,  one  beneath  the  jiapillte,  and  another  at  the  junction  of  the  corium  and 
subcutis.     The  lymph  vessels  form  subpapillary  and  subcutaneotis  plexuses. 

The  nerves  vary  widely  in  number  in  different  parts  of  the  skin.  The  terminal 
fibers  either  (>nd  free  in  the  epidermis  and  in  certain  parts  of  the  coritnn,  or  form 
special  microscopic  corpuscles  of  several  kinds. 


THE    APPENDAGES   OF  THE   SKIN 
The  appendages  of  the  skin  are  modifications  of  the  epidermis,  and  comprise 
the  hairs,  hoofs,  claws,  horns,  etc. 

The  hairs  (Pili)  cover  almost  the  entire  surface  of  the  body  in  the  domesticated 


THE  APPENDAGES  OF  THE  SKIN 


7G3 


inanimals,  and  some  parts  which  appear  at  first  sight  to  be  l)are  are  found  on  close 
inspection  to  be  provided  with  sparse  and  very  fine  liair.  The  hairs  are  constantly 
being  shed  and  replaced,  but  at  certain  periods  in  the  horse,  for  example,  they  fall 
out  in  great  numbers,  constituting  the  shedding  of  the  coat.  It  is  customary  to 
distinguish  the  ordinary  hairs  (the  coat),  which  determine  the  color  of  the  animal, 
from  the  special  varieties  found  in  certain  places.  Among  the  latter  are  the  long 
tactile  hairs  about  the  lips,  nostrils,  and  eyes;  the  eyelashes  or  cilia;  the  tragi  of 
the  external  ear:  and  the  vibrissae  of  the  nostrils.  Other  special  features  will  be 
noted  in  the  discussion  of  the  skin  of  the  various  species.  The  hairs  are  directed 
in  such  a  way  as  to  form  more  or  less  definite  hair-streams  (Plumina  pilorum), 
and  at  certain  points  these  converge  to  form  vortices  (Vortices  pilorum). 

The  part  of  the  hair  above  the  surface  of  the  skin  is  the  shaft  (Scapus  pili), 
while  the  root  (Radix  pili)  is  embedded  in  a  depression  termed  the  hair-foUicle 


(After  EIlenberger-Baum,  .^iiat. 


(Folliculus  pili).  A  vascular  papilla  (Papilla  pili)  projects  up  in  the  fundus  of  the 
follicle  and  is  capped  by  the  expanded  end  of  the  root,  the  bulb  of  the  hair  (Bulbus 
pili).  The  hair-follicles  extend  obliquely  into  the  corium  to  a  varying  depth;  in 
the  case  of  the  long  tactile  hairs  they  reach  to  the  underlying  muscle.  Most  of  the 
follicles  have  attached  to  them  small  unstriped  muscles  known  as  the  arrectores 
pilorum ;  these  are  attached  at  an  acute  angle  to  the  under  side  of  the  deep  part 
of  the  follicle,  and  their  contraction  causes  erection  of  the  hair  and  compression  of 
the  sebaceous  glands,  one  or  more  of  which  open  into  the  follicle. 

The  hairs  are  composed  of  epidermal  cells,  and  consist  from  without  inward  of 
three  parts.  The  cuticle  is  composed  of  horny,  scale-like  cells  which  overlap  like 
slates  on  a  roof.     The  cortex  consists  of  horny  fusiform  cells  which  are  packed  close 


704  THE  SENSE  OKGANS  AND  SKIN  OF  THE  HORSE 

together  and  contain  ])igment.  The  medulla  is  the  central  core  of  softer,  cubical 
or  polyhedral  cells;   it  contains  some  ])igment  and  air-spaces. 

The  hair-follicles,  being  invaginations  of  the  skin,  are  composed  of  a  central 
epidermal  part,  and  a  peripheral  layer  which  corresponds  in  structure  to  the  corium. 
The  follicles  of  the  tactile  hairs  have  remarkably  thick  walls  which  contain  blood- 
sinuses  lietween  their  outer  and  inner  layers;  in  ungulates  the  sinuses  are  crossefl 
by  trabeculae  and  assume  the  character  of  cavernous  or  erectile  tissue. 

The  hoofs,  claws,  horns,  and  other  horny  structures  consist  of  closely  packed 
epidermal  cells  which  have  undergone  cornification.  In  structure  they  might  be 
comi)arcd  to  hairs  matted  together  liy  intervening  epidermal  cells.  They  cover  a 
specialized  corium  known  as  their  matrix,  from  which  the  stratum  germinativum 
derives  its  nutrition. 

THE  SKIN  OF  THE  HORSE 

The  thickness  of  the  skin  of  the  horse  varies  from  1  to  5  mm.  in  different  regions, 
and  is  greatest  at  the  attachment  of  the  mane  and  the  ventral  surface  of  the  tail. 

The  glands  are  numerous  and  are  larger  than  those  of  the  other  domesticated 
animals.  The  sebaceous  glands  are  si^eciallj-  developed  on  the  lips,  the  prepuce, 
mammarj-  glands,  perineum,  and  labia  of  the  vulva.  The  sweat  glands  are  yellow 
or  brown  in  color.  They  occur  in  almost  all  parts  of  the  skin,  L'ut  are  largest  and 
most  numerous  on  the  outer  wing  of  the  nostril,  the  flank,  mammary  glands, 
and  free  part  of  the  penis. 

In  addition  to  the  ordinary  and  tactile  hairs  certain  regions  present  coarse 
hairs  of  great  length.  The  mane  (Juba)  sj^rings  from  the  dorsal  border  of  the  neck 
and  the  adjacent  part  of  the  withers;  its  anterior  part,  which  covers  the  forehead 
to  a  varialile  extent,  is  termed  the  foretop  (Cirrus  capitis).  The  tail,  with  the 
excejition  of  its  ventral  surface,  bears  verj'  large  and  long  hairs  (Cirrus  caudae). 
The  tuft  of  long  hairs  on  the  flexion  surface  of  the  fetlock  (Cirrus  pedis)  gave  rise  to 
the  popular  name  of  this  region. 

The  development  of  these  .special  hairs  varies  wiilfly,  and  is  in  general  much  greater  in  the 
draft  breed.s  than  in  others.  In  Shire  and  <  IxdcxLilc  Ih.ix-,  for  instance,  the  hair  on  the  volar 
aspect  of  the  metacarpus  and  metatarsus  and  I'ltlnck  In  (ilicii  so  long  and  abundant  as  to  account 
for  the  term  "feather,"  which  is  commonly  aiiphnl  tu  ii  I'V  hur.scmen. 

THE   HOOF 

The  hoof  (Unguis)  is  the  horny  covering  of  the  distal  end  of  the  digit.  It  is 
convenient  to  tlivide  it  for  description  into  three  parts,  termed  the  wall,  sole,  and  frog. 

1.  The  wall  is  defined  as  the  jiart  of  the  hoof  which  is  visible  when  the  foot  is 
placed  on  the  ground.-  It  covers  the  front  and  sides  of  the  foot,  and  is  reflected 
posteriorly  at  an  acute  angle  to  form  the  bars.  The  latter  (Pars  inflcxa  medialis, 
lateralis)  appear  on  the  ground  surface  of  the  hoof  as  convergent  ridges,  which  sub- 
side in  front  and  are  fused  with  the  sole;  they  are  united  with  each  other  by  the  frog. 
For  topographic  purposes  the  wall  may  be  divided  into  an  anterior  part  or  "toe" 
(Pars  ungulaj  dorsalis),  lateral  parts  or  "quarters"  (Pars  ungula»  medialis,  later- 
alis), and  the  angles  or  "heels"  (Pars  ungularis  medialis,  laterales).  It  presents 
two  surfaces  and  two  borders. 

The  outer  surface  is  convex  from  side  to  side  and  slopes  obli<iuely  from  edge 
to  edge.  In  front  the  angle  of  inclination  on  the  ground  plane  is  about  50°  for  the 
fore  limb,  55°  for  the  hind  limb;  on  the  sides  the  angle  gradually  increases  and  is 
100°  at  the  angles.     The  curve  of  the  wall  is  wider  on  the  external  than  on  the 

'  The  hoof  may  be  loosened  and  removed  intact  by  allowing  the  foot  to  macerate  or  by 
boiling  it. 

^  The  term  foot  i.s  used  here  in  the  popular  sense,  i.  c,  to  designate  the  hoof  and  the  structures 
inclosed  within  it. 


THE    HOOF  765 

internal  side,  and  the  external  quarter  is  more  oVilique  than  the  internal  one.  The 
surface  is  smooth  and  is  crossed  by  more  or  less  distinct  ridges,  which  are  parallel 
with  tile  coronary  laorder  and  indicate  variations  in  the  activity  of  the  growth  of 
the  houf.  It  is  also  marked  by  fine  parallel  striae,  which  extend  from  border  to 
border  in  an  almost  rectilinear  manner. 

Tlie  slope  of  the  wall  varies  consiilerably  in  apparently  normal  hoofs.  Lungwitz  found 
by  careful  measurements  of  50  fore  and  30  hind  feet  the  following  average  angles: 

Fore  Foot  Hind  Foot 

Toe 47.26°  54.1° 

Inner  angle 101.57°  96.50° 

Outer  angle 101.37°  96.1° 

The  wall  of  the  fore  foot  may  even  be  more  upright  than  that  of  the  hind,  and  may  have  an 
angle  of  60°.  The  length  of  the  wall  at  the  toe,  quarters,  and  heels  is  in  the  ratio  of  about 
3  :  2  :  1  in  the  fore  foot  and  aliout  2  :  13  2  :  1  in  the  hind  hoof. 

The  inner  surface  is  concave  from  side  to  side,  and  bears  about  six  liundred 
thin   primary  laminae  (Crista  ungulse),  which  ex- 
tend  from  the   coronary  groove   to   the   junction         V  j 
of  wall  and  sole.     Each  bears  a  hundred  or  more        ^jU 
secondary  laminae   on   its    surfaces,   so  that   the 
ai'rangcment   is  pennate  on  cross-section.     These         ^_  , 
horny  laminse  are  continued  on  the  inner  surface  of 
the  bars,  and  alternate  with  corresponding  laminaj     ;i' 
of  the  matrix.                                                                       '\~ 

The  proximal  or  coronary  border  (Margo  oc-        '^' 
cultus)  is  thin.     Its  outer  aspect   is  covered  by  a 

layer  of  soft  horn  known  as  the  periople;   this  Ji^-il'  \.1\  -J 

appears    as    a    ring-like   prominence    above    and  .^,.     v     -'^     B      a 

gradually  fades  out  below;   at  the  angle  it  forms  ^  "■ ' 

a  wide  cap  or  bulb  and  blends  centrally  with  the 

frog.     The  inner  aspect  of  the  border  is  excavated    £  cf         ■        x^l^'-^ 

to  form  the  coronary  groove  (Sulcus  coronalis  ^llfc^^i.  l^V'-l-'^ 
ungulse),  which  contains  the  thick  coronary  ma- 
trix. The  groove  is  deepest  in  front,  narrows 
on  the  sides,  and  is  wide  and  shallow  at  the 
heels.'  It  is  perforated  by  innumerable  small, 
funnel-like  openings  which  are  occupied  Ijy  the  „  sys—Dinrr  of  Horsf 
papillffi    of    the    coronarj-    matrix    in    the  natural  surface  Relatiox.s  of  Boxes 

state  AND  Joi.xTS.    The  Lateral  Car- 

The  distal  or  ground  border  (Margo  liber)  of  tilage  is    xposed. 

°  .  -11  "■  First  phalanx;  b,  second  phal- 

the  unshod  hoot  comes  m  contact  with  the  anx;  c,  third  phalanx;  d,  lateral  carti- 
grOUnd.       Its     thickness,  is     greatest     in    front    and        lage;  f,  third  sesamoid  or  navicular  bone; 

decreases  considerably  from  before  backward  on     {^roTVairof  ZTl'-T'i'milt 

the     sides,     but    there     is     a    slight    increase    at    the        matrix,     (.\fter  Ellenberger,  in  Lelser- 

angles.     Its   inner    face    is    united   with   the   per-     '"s's  .\tias.) 

iphery  of  the  sole   by  horn  of  lighter  color  and 

softer  texture,  which  appears  on  the  ground  surface  of  the  hoof  as  the  white  line. 

In  the  case  of  horses  at  liberty  the  wall  is  usually  worn  off  to  the  level  of  the  adjacent  sole, 
but  if  the  ground  is  too  .soft  the  wall  is  likely  to  become  unduly  long  and  split  or  break  or  undergo 
deformation.  On  very  hard  or  rough  ground,  on  the  other  hand,  the  wear  may  be  in  excess  of 
the  growth.  In  the  case  of  shod  horses  it  is  necessary  to  remove  the  excess  of  growth  of  the  wall 
at  each  shoeing.  The  thickness  of  the  wall  at  the  toe,  quarters,  and  heels  is  about  in  the  ratio 
of  4:3:2  for  the  fore  foot  and  about  3  :  2J/2  :  2  for  the  hind  foot. 

2.  The  sole  (8olea  ungulae)  forms  the  greater  part  of  the  ground  surface  of 
the  hoof.  It  is  somewhat  crescentic  in  outline,  and  presents  two  surfaces  and  two 
borders. 

'  The  wide  groove  at  the  heels,  however,  contains  chiefly  the  matrix  of  the  periople. 


766 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


Tlic  superior  or  inner  surface  is  convex,  and  slopes  with  a  varying  degree  of 
obliquitv  downward  to  tiie  convex  border.  It  presents  numerous  small  funnel-liko 
openings  which  contain  the  papilla  of  the  sole  matrix  in  the  natural  state 


Wall 

Lamintc  oj  wall 

LamituiT  matrU 

Third  phalanx 

Plantar  cushion 

Bar 

Frog 

Space  between 
bar  and  frog 

Angle  of  heel 

Periople  of  heel 

Fig.  574.— Cro: 


Horse,  Cut  V 


[E  Coronary  Boroer 


The  inferior  or  ground  surface  is  the  converse  of  the  preceding.  It  is  normally 
arched — and  more  strongly  in  the  hind  than  in  the  fore  foot — but  the  curvature  is 
sul)ject  to  wide  variation;   in  heavy  draft  horses  the  sole  is  commonly  less  curved 


Periople  of  heel 


While  line       '5o'c 


Fin.   ST.i.— Ha 


OF  Horse,  Interna 


than  in  the  lighter  breeds  and  may  even  be  flat.     The  surface  is  usually  rou.gh, 
since  the  horn  exfoliates  here  in  irre,gular  flakes. 

The  convex  border  is  joined  to  the  wall  by  relatively  soft  horn,  previously 


THE    HOOF 


767 


referred  to  as  forming  the  white  line  on  the  ground  surface  of  the  hoof.  The  angle 
of  junction  is  roundeil  internally  and  presents  a  numl)er  of  low  ridges  and  sjiecially 
large  openings  for  the  papilUr  of  the  matrix.  There  is  frciiucntly  a  ridge  of  larger 
size  at  the  toe. 

The  concave  border  has  the  form  of  a  deep  angle  which  is  occupieil  by  the  bars 
and  frog.  By  its  junction  with  these  it  forms  two  pronounced  ridges  in  the  interior 
of  the  foot.  The  ]iarts  of  the  sole  between  the  wall  and  bars  may  be  termed  its 
angles. 

3.  Tlie  frog  (Furca  unguhe)  is  a  wedge-shaped  mass  which  occupies  the  angle 
between  the  bars  and  sole,  anil  extends  consitlerably  below  these  on  the  ground 
surface  of  the  foot.  It  may  be  described  as  having  four  surfaces,  a  base,  and  an 
apex. 

Perioplc  at  commirij  margin 
Coronary  ijroore 
Lamina: 


Fig.  576. — Internal  Srn 


Median  furrow 

Lateral  ridge 
'u  1      Spine  or  Jrug-sta y 


.\tlas  d.  .\nat.  d.  Pferdes.) 


The  superior  or  internal  surface  is  deeply  concave  from  side  to  side.  It  bears 
a  central  ridge,  the  spine  or  "frog-stay"  (Spina  furcae  ungulse),  which  is  high  pos- 
teriorly and  subsides  al)ruptly  in  front.  On  either  side  of  this  is  a  deep  depression, 
bounded  outwardly  by  the  rounded  ridge  formed  b>-  the  junction  of  the  frog  with 
the  bar  and  sole.  Tliis  surface  presents  fine  stria;  and  openings  for  the  papillae 
of  the  frog  matrix. 

The  inferior  or  ground  surface  presents  a  central  furrow  (Sulcus  intercruralis), 
which  is  bounded  by  two  ridges  or  crura  (Crura  furcse  ungula^) ;  these  converge 
and  form  the  apex. 

The  sides  (Facies  medialis  et  lateralis)  are  united  at  the  upper  part  with  the 
bars  and  sole,  but  are  free  below  and  form  the  central  wall  of  the  deep  lateral 
furrows  (Sulci  cruroparietales),  which  are  bounded  outwardly  by  the  bars. 

The  base  is  wide  and  high.     It  is  depressed  centrally  and  prominent  at  the 


7(58 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


sides,  where  it  unites  with  the  angles  of  the  walls;   the  junction  here  is  covered  by 
the  expiiniled  jjeriojile  and  constitutes  the  bull)  of  the  hoof. 


Fig.  577.— Hoof  ok  Horse,  Richt  Fore  Foot, 
Ohound  Surf.\ce. 
a?,  Inner  (juarter;  ^5,  outer  quarter;  iS9, 
ground  border  of  wall  (toe);  40,  white  line;  41, 
sole;  4S,  apex  of  froK;  4'^,  lateral  ridge  of  frog; 
44,  central  furrow  of  frog;  4i,  lateral  furrow  be- 
tween frog  and  bar;  46,  bar.  (After  Ellenberger- 
Baum,  .\nat.  fur  Kiinstler.) 


Fig.  .'J7S. — Horizontal  SErxioN  of  Hoof  of  Horse. 
The  section  i.s  cut  just  above  the  ridges  of  the  frog 
and  bars  and  parallel  with  the  ground  surface,  i.  Wall; 
^,  sole;  d,  median  ridge  of  frog;  4,  lateral  ridge  formed 
b,^■  junction  of  frog  and  bar;  5,  median  furrow  over  apex 
of  frog:   G,  lamina'  of  wall;    7,  lamina?  of  bar. 


The  apex  occupies  the  central  angle  of  the  concave  border  of  the  sole,  and 

forms  a  blunt,  round  prominence  a 
/•w,  little  in  front  of  the  middle  of  the 

ground  surface  of  the  hoof. 

Structure  of  the  Hoof. — The 
hoof  is  comjiosed  of  epithelial 
cell.s  wliich  are  more  or  less  com- 
jiletely  keratinized  except  in  its 
deepest  ]iart,  the  stratum  ger- 
minativum;  here  the  cells  have 
not  undergone  cornification,  and 
by  their  proliferation  maintain  the 
growth  of  the  hoof.  The  cells  are 
in  part  arranged  to  form  tubes 
which  are  united  by  intertulnilar 
epithelium,  and  inclose  medullary 
cells  and  air-spaces. 

The  wall  may  be  regarded  as 
consi.sting  of   three    layers.      The 
external  layer  consists  of  the  jieri- 
opl(!    and    the    stratum    vitreum. 
The    periople    is    composed   of   soft,    non-pigmented   tubular   horn.      It   is   con- 
tinuous with  the  epidermis  above,  and    extends  downward  a  variable  distance. 


Fig.  579.— Fhoxtai. 

I'.VUT 

/,  Wall;    S,  s 
frog;    0,  lateral 
lamina-  of  bar; 
periople  of  heel 


of  Horse 
Front. 


,  sole;    S,  bar;    .{,  frog; 
ige  formed  by  jtinction 


5,  median  ridge  of 
of  frog  and  bar;  7, 
ironary  groove:    /O, 


THE  MATRIX  OF  THE  HOOF  769 

Usually  it  forms  a  distinct  haiul  somewhat  less  than  an  inch  wide,  except 
at  the  heels,  where  it  is  much  wider,  ami  caps  the  angle  of  inflection  of 
the  wall  proper.  The  stratum  vitreum  is  a  thin  layer  of  horny  scales  which 
gives  the  wall  below  the  ])eri()])le  its  smooth,  glossy  ai)i)earance.  The  middle 
or  tubular  layer  forms  the  bulk  of  the  wall,  and  is  the  densest  part  of  the 
hoof.  Its  horn  tubes  run  in  a  straight  direction  from  the  coronary  to  the  ground 
border.  In  dark  hoofs  it  is  pigmented  except  in  its  deep  part.  The  internal  or 
laminar  layer  consists  of  the  primary  and  secondary  laminae  and  is  non-pigmented. 
The  laminse  are  narrow  and  thin  at  their  origin  at  the  lower  margin  of  the  coronary 
groove,  but  become  wider  and  thicker  below.  At  the  junction  of  the  wall  and  sole 
they  are  united  by  interlaminar  horn  to  form  the  white  line.  Only  the  central 
part  of  the  laminae  becomes  fully  keratinized.  They  are  composed  of  non-tubular 
horn  in  the  normal  state. 

The  sole  consists  of  tubular  and  intertubular  horn.  The  tutjes  run  parallel 
with  those  of  the  wall  and  vary  much  in  size. 

The  frog  is  composerl  of  relatively  soft  horn,  which  is  much  more  elastic  than 
that  of  the  wall  or  sole,  and  is  not  fully  keratinized.  The  horn  tubes  in  it  are 
slightly  flexuous. 

The  hoof  is  non-vascular  and  receives  its  nutrition  from  the  matrix.  It  is 
also  destitute  of  nerves. 

The  Matrix  of  the  Hoof 
The  matrix  of  the  hoof  (Matrix  ungula?)  is  the  specially  modified  and  highly 
vascular  part  of  the  corium  of  the  common  integument  which  furnishes  nutrition 
to  the  hoof.     It  is  convenient  to  divide  it  into  five  parts  which  nourish  correspond- 
ing parts  of  the  hoof. 

1.  The  perioplic  matrix  or  ring  (Margo  matricis  unguis)  is  a  band  5  to  6  mm. 
in  width  which  lies  in  a  groove  between  the  perioi^le  and  the  coronary  border  of 
the  wall.  It  is  continuous  above  with  the  corium  of  the  skin,  and  is  marked  off  by 
a  groove  from  the  coronary  matrix.  At  the  heels  it  widens  and  blends  with  the 
matrix  of  the  frog.  It  bears  very  fine,  short  papillae  which  curve  downward  and 
are  received  in  depressions  of  the  periople,  to  which  it  supplies  nutrition. 

2.  The  coronary  matrix  or  cushion  (Corona  matricis  ungulse)  is  the  thick  part 
of  the  corium  which  occupies  the  coronary  groove,  and  furnishes  nutrition  to  the 
bulk  of  the  wall.  It  diminishes  in  width  and  thickness  posteriorly,  and  along  the 
ujiper  border  of  the  bar  it  is  not  very  clearly  defined  from  the  matrix  of  the  frog. 
The  convex  superficial  surface  is  thickly  covered  with  papillie  4  to  ft  mm.  in  length, 
which  are  received  into  the  funnel-like  openings  of  the  coronary  groove.  At 
the  heels  and  along  the  bars  the  papillte  are  arranged  in  rows,  separated  by  fine 
furrows.  The  deep  surface  is  attached  to  the  extensor  tendon  and  the  lateral 
cartilages  by  an  abundant  subcutis  which  contains  many  elastic  fibers  and  a  rich 
venous  plexus. 

3.  The  laminar  matrix  (Latus  matricis  unguis) — also  termed  the  sensitive 
laminse — bears  primary  and  secondary  laminae  which  are  interleaved  with  the  horny 
laminae  of  the  wall  and  bars  in  the  natural  state.  It  is  attached  to  the  wall  surface 
of  the  third  phalanx  by  a  modified  periosteum  (Stratum  periosteale)  which  contains 
a  close-meshed  network  of  vessels,  and  to  the  lower  part  of  the  lateral  cartilages 
by  a  subcutis  which  contains  a  rich  venous  plexus.  The  laminae  are  small  at  their 
origin  above,  become  wider  below,  and  end  in  several  papillae  4  to  5  mm.  in  length. 
The  sensitive  laminae  supply  nutrition  to  the  horny  laminae  and  to  the  interlaminar 
horn  of  the  white  line. 

4.  The  sole  matrix  (Latus  volare  matricis  ungula>) — also  termed  the  sensitive 
sole — corresponds  to  the  horny  sole,  to  which  it  supplies  nutrition.  It  is  often 
more  or  less  pigmented  and  bears  long  papillae,  which  are  specially  large  along  the 


r70 


THE  SENSE  ORGANS  AND  SKIN  OF  THE  HORSE 


convex  border  and  at  the  angles.  Centrally  it  is  continuous  with  the  matrix  of 
the  frog  and  bars.  The  deep  surface  is  attached  to  the  sole  surface  of  the  third 
phalanx  bj-  a  modified  and  highly  vascular  periosteum. 


Cut  edge  of  skin 
Ptnophc  mull  1 1 


Cornnnri/  mnli  1 1  — -j 
Laminar  iiialri  t 


Outline  nf  hoof 


Fig.  5S0. — Lateral  View  of  Foot  of  Horse  after  Removal  of  Hoof  and  Part  of  Skin,     (.\fter  Schmaltz, 
Atlas  d.  Anat.  d.  Pferdes.) 

5.  The  frog  matrix  (Furca  matricis  unguis) — also  called  the  sensitive  frog — is 
moulded  on  the  deep  surface  of  the  frog  and  bears  small  papillae.     Its  deep  face  is 


Perioplic  matrix 
Coronary  matrix 

Laminar  matrix 

Frog  matrix 
Position  of  navicular  lionc 

Sole  matrix 

Aj)ex  of  frog 


White  line 
Ground  border  of  wall 
Fio.  581 . — Ground  Sl-rfack  of  Foot 


Pcriople  of  heel  or  hnlb 


TKK    KkMOVAT 

.\na(,  il.  Pfer.les.) 


HnoF.      (After  Schmtvltz,  Atlas  d. 


blended  with  the  plantar  cushion.     The  germinal  cells  of  the  frog  derive  their 
nutrition  from  this  part  of  the  matrix. 


THE    MATRIX    OF   THE    HOOF 


771 


Tho  digital  or  plantar  cushion  (Torus  digitalis)  is  an  important  part  of  the 
elastic  apparatus  of  the  foot.  It  is  a  wedge-shaped  mass  whieh  overlies  the  frog. 
It  presents  for  description  four  surfaces,  a  base,  and  an  apex.  The  superior  surface 
faces  upward  and  forward  and  is  connected  with  the  distal  fibrous  sheath  of  the; 
deep  flexor  tendon.  The  inferior  surface,  covered  by  the  matrix  of  the  frog,  is 
moulded  on  the  upper  face  of  the  frog.  The  lateral  surfaces  are  related  chiefly  to 
the  lateral  cartilages;  interiorly  the  cushion  is  closely  attached  to  the  cartilages, 
but  higher  up  a  rich  venous  jilexus  intervenes.  The  base,  situated  posteriorly,  is 
partly  sul)cutaneous,  and  is  divided  by  a  central  depression  into  two  rounded 
prominences  termed  the  bulbs  of  the  plantar  cushion.  The  apex  lies  under  the 
terminal  part  of  the  deep  flexor  tendon.  The  cushion  is  poorly  supplied  with  ves- 
sels. It  consists  of  a  feltwork  of  fibrous  trabecular  and  elastic  fibers,  in  the  meshes 
of  which  are  masses  of  fat.  The  bulbs  are  soft  and  loose  in  texture  and  contain  a 
relatively  large  amount  of  fat,  but  toward  the  apex  the  cushion  becomes  denser  and 
more  purely  white  fibrous  in  structure.  Branched  coil  glands  occur  chiefly  in  the 
part   of    the    cushion    which    overlies 

the  central  ridge  of  the  frog.     Their  ^ 

ducts  pursue  a  slightly  flexuous  course 
through  the  matrix  and  pass  in  a  spiral 
manner  through  the  frog.  Their  secre- 
tion contains  fat. 

Vessels  and  Nerves. — The  matrix 
is  richly  supplied  with  blood  by  the 
digital  arteries.  The  veins  are  valve- 
less,  and  form  remarkable  plexuses 
which  communicate  freely  with  each 
other  and  are  drained  by  the  digital 
veins.  The  lymph  vessels  form  sub- 
papillary  plexuses  in  the  matrix  of  the 
sole  and  frog,  and  a  wider-meshed 
plexus  at  the  base  of  the  plantar 
cushion.  A  considerable  lymph  vessel 
lies  in  the  attached  edge  of  each  of  the 
laminse.  The  nerves  are  branches  of 
the  digital  nerves ;  some  fibers  end  in 
lamellar  corpuscles  and  end-bulbs. 

The  ergot  is  a  small  mass  of  horn 
which  is  situated  in  the  tuft  of  hair  at 
the  flexion  surface  of  the  fetlock.     It 

is  the  vestige  of  the  second  and  fourth  digits  of  extinct  equida>,  and  hence  is  absent 
in  cases  in  which  these  digits  are  developed.  A  small  tendinous  band,  3  to  5  mm. 
in  width,  extends  downward  and  slightly  forward  from  the  fibrous  basis  of  the 
ergot  on  each  side,  crosses  over  the  digital  vessels  and  nerves  very  obliquely,  and 
blends  l)elow  with  the  digital  fascia  and  the  plantar  cushion.  It  is  known  as  the 
ligament  or  tendon  of  the  ergot. 

The  term  chestnut  is  applied  to  the  masses  of  horn  which  occur  on  the  inner 
surface  of  the  forearm  about  a  handbreadth  above  the  carpus,  and  on  the  lower 
part  of  the  inner  face  of  the  tarsus.  They  have  an  elongated  oval  form  and  are 
flattened.  They  are  regarded  usually  as  vestiges  of  the  first  digit.  That  of  the 
hind  limb  is  absent  in  the  donkey  and  very  small  in  the  mule. 

These  horny  vestiges  are  quite  variable  in  form  and  size  and  are  correlated  with  tho  finene.ss 
or  coarseness  of  the  integument  in  general.  The  supracarpal  chestnut  is  about  1 J  2  to  2 1 2  inches 
long,  oval  in  outline,  the  proximal  end  being  pointed;  it  overlies  the  flexor  carpi  internus  at  a 
quite  variable  distance  above  the  carpus,  and  hence  should  not  be  used  as  a  surgical  landmark. 
The  tarsal  chestnut  lies  at  a  point  behind  the  lower  part  of  the  internal  lateral  ligament  of  the 


Fig.  5S2. — Cross-section  of  Digit  op  Horse,  throit.h 
Dlstal  End  op  Second  Phalanx. 
a.  Second  phalanx;  b,  deep  flexor  tendon;  b' , 
digital  synovial  shealh;  c,  plantar  cushion;  d,  lateral 
cartilage;  e,  skin;  /,  hoof;  g,  anterior  extensor  tendon; 
h,  cavity  of  coffin  joint;  i,  suspensory  ligament  of  navi- 
cular bone;  k,  lateral  ligament  of  cotfin  joint;  /,  digital 
artery;  m.  digital  ner\-e.  (.\fter  Ellenberger,  in  Leiser- 
ing's  Atlas.) 


772  SENSE    ORGANS    AND    SKIN    OF   THE    OX 

hock.  When  well  developed  it  is  about  2  to  2>2  inches  long,  broad  below  and  produced  above 
to  form  a  long  pointed  end,  with  a  short  blunt  anterior  process.  The}'  are  composed  of  horn 
somewhat  like  that  of  the  frog. 

Organ  of  Smell 

The  peripheral  part  of  the  olfactor.y  apparatus  or  organ  of  smell  (Organon 
olfactus)  is  that  part  of  the  nasal  mucous  membrane  which  was  referred  to  in  the 
description  of  the  nasal  cavity  as  the  olfactory  region;  this  (Regio  olfactoria)  is 
limited  to  the  ethmo-turbinals  and  the  adjacent  part  of  the  superior  turbinal  and 
the  septum  nasi,  in  which  the  fibers  of  the  olfactorj'  nerve  ramify.  It  is  dis- 
tinguished by  its  yellow-brown  color,  thickness,  and  softness.  It  contains  charac- 
teristic tubular  olfactory  glands  (of  Bowinan),  which  arc  lined  by  a  single  layer  of 
pigmented  cells,  and  a  neuro-epithelium,  the  olfactory  cells,  the  central  processes 
of  which  extend  as  non-meduUated  fibers  to  the  olfactory  bulb. 

The  epitheUum  is  non-ciliated  and  is  covered  by  a  structureless  limiting  layer.  It  consists 
essentially  of  three  kinds  of  cells,  supporting,  basal,  and  olfactory.  The  supporting  cells  are  of 
long  columnar  form  above  and  contain  pigment  granules;  below  they  taper  and  often  liranch, 
and  their  central  processes  unite  with  those  of  adjacent  cells  to  form  a  protoplasmic  network. 
The  basal  cells  are  branched  and  lie  on  a  basement  membrane.  The  olfactory  cells  are  situated 
between  the  supporting  cells;  they  have  the  form  of  long  narrow  rods,  with  an  enlarged  lower 
part  which  is  occupied  by  the  nucleus.  The  peripheral  end  pierces  the  limiting  membrane  and 
bears  a  tuft  of  fine  hair-like  cilia  (olfactory  hairs).  A  central  process  extends  from  the  nucleated 
pole  of  the  cell  to  the  olfactory  bulb  as  a  non-medullated  olfactory  nerve-fiber. 

The  vomero-nasal  organ  (of  Jacobson)  lies  along  each  side  of  the  anterior  part 
of  the  lower  l)order  of  the  septum  nasi.  It  communicates  with  the  nasal  cavity 
through  the  naso-palatine  canal.  It  consists  of  a  tube  of  hyaline  cartilage  lined 
with  mucous  membrane;  a  small  part  of  the  latter  along  the  inner  side  is  olfactory 
in  character. 

The  Organ  of  Taste 

The  peripheral  part  of  the  gustatory  apparatus  (Organon  gustus)  is  formed  by 
the  microscopic  taste  buds  (Calyculi  gustatorii) ,  which  occur  especially  in  the  foliate, 
fungiform,  and  vallate  papilla?,  in  the  free  edge  and  anterior  pillars  of  the  soft 
palate,  and  the  oral  surface  of  the  epiglottis.  The  taste  buds  are  ovoid  masses, 
which  occupj'  corresponding  recesses  in  the  ordinary  epithelium;  each  presents  a 
minute  opening,  the  gustatory  pore.  The  buds  consist  of  fusiform  supporting  cells 
grouped  around  central  gustatory  cells.  The  latter  are  long  and  narrow;  the 
peripheral  end  of  each  bears  a  small  filament,  the  gustatory  hair,  which  projects  at 
tlie  gustatory  pore;  the  central  end  is  produced  to  form  a  fine  process  which  is  often 
branched.  The  taste  buds  are  innervated  by  fit)ers  of  the  glosso-pharj^ngeal 
nerve  and  the  lingual  branch  of  the  trigeminus. 


SENSE  ORGANS  AND  SKIN  OF  THE  OX 
THE  EYE 
The  eyelids  are  thick,  prominent,  and  less  pliable  than  those  of  the  horse. 
The  lower  lid  bears  a  considerable  number  of  cilia,  which  are,  however,  finer  than 
those  of  the  upper  lid.  The  tarsal  glands  are  more  deeply  embedded  and  therefore 
not  so  evident.  The  conjunctiva  of  the  lower  lid  presents  folds  or  ridges,  and  one 
or  two  prominences  which  contain  numerous  leukocytes;  the  conjunctival 
epithelium  is  transitional  in  tjTDe.  The  superficial  part  of  the  cartilage  of  the 
third  eyelid  is  leaf  or  shovel-shaped  and  thicker  than  in  the  horse;  the  edge  Ijears 
a  narrower  process,  on  which  there  is  a  transverse  bar,  giving  the  arrangement 


THE    EYE  773 

some  resemblance  to  an  anchor.  The  gland  of  the  thinl  eyelid  is  very  large — an 
inch  or  more  in  length — anil  may  he  divided  into  two  parts.  The  deep  part  is 
pink  and  consists  of  loose  lobules,  but  the  much  larger  superficial  part  is  more  com- 
pact. There  are  two  large  and  several  smaller  cxcretorj-  ducts.  The  subconjunc- 
tival tissue  of  the  third  eyelid  contains  lymph  nodules,  which  are  specially  numer- 
ous on  the  bulbar  side. 


Upper  eyelid^ 


Third  eyelid 
Caruuculn  lacrimalis. 
Internal  canth 


Lower  eyelid 
Fig.  .583.— Eye  of  Ox.       (.\fter  EllenberKer-Baum,  .\nat.  fiir  KUnsller.) 

The  lacrimal  gland  is  thick  and  di.stinctly  loliulated.  It  is  more  or  less  clearly 
divided  into  a  thick  upper  and  a  thinner  lower  part  (Glandula  lacrimalis  superior, 
inferior't.  Tliere  are  six  to  eight  larger  excretory  ducts  and  several  smaller  ones. 
The  naso-lacrimal  duct  is  shorter  than  in  the  horse,  and  is  almost  straight.  Its 
terminal  part  is  inclosed  between  two  plates  of  cartilage,  and  it  opens  near  the  nostril 
on  the  outer  wall;  the  orifice  is  placed  on  the  inner  side  of  the  alar  fold  of  the  inferior 
turbinal,  and  is  therefore  not  easilv  found. 


Conjunctim  bulbi 


Third  eyelid 
Caruncula  Incrimali^ 


Cornea 


Pupil 
Fig.  584. — Left  Eyeball  of  Ox  m  situ,  Exterx.\l  View. 
19,  Orbital  fat.     (.\fter  Ellenberger-Baum,  .\nat.  fiir  Kunstler.i 

The  eyeball  resembles  that  of  the  horse  in  sha])e,  but  is  considerably  smaller. 

The  average  transverse  diameter  is  about  42  mm.,  the  vertical  diameter  41  mm.,  and  the 
axis  36  mm.     The  angle  between  the  axes  is  about  119°. 

The  sclera  is  often  more  or  less  pigmented:  where  non-pigmented  it  may  have 
a  bluish  tinge.  The  point  of  entrance  of  the  optic  nerve  is  about  2  mm.  external 
to  the  vertical  meridian,  and  about  7  mm.  below  the  horizontal  meridian. 

The  thickne.ss  of  the  sclera  is  about  2  mm.  at  the  posterior  pole,  1  mm.  at  the  equator,  and 
1.2  to  1.5  mm.  near  the  cornea. 


774  SENSE    ORGANS    AND    SKIN    OF   THE    OX 

The  cornea  is  thicker  than  that  of  the  horse. 

The  tapetum  of  the  chorioidea  is  extensive  at  the  outer  side,  but  is  a  narrow 
strip  internally.  It  has  a  metallic  luster,  shading  from  a  brilliant  green  to  a  deep 
blue;   centrally  it  has  a  reddish  sheen. 

The  iris  is  usually  very  dark  colored.  The  granula  form  a  continuous  series 
of  small  nodules  along  the  upper  margin  of  the  pupil  and  are  most  prominent 
centrally:    they  are  very  small  on  the  lower  margin. 

The  optic  papilla  is  much  smaller  and  is  not  so  sharply  defined  on  ophthal- 
moscopic examination  as  that  of  the  horse.  Several  relatively  large  retinal  arteries 
radiate  from  the  center  of  the  papilla  to  the  periphery  of  the  retina.  They  may  be 
seen  to  wind  spirally  around  the  veins,  which  are  very  large. 

The  artcria  centralis  retina?  arises  from  a  posterior  ciliary  artery  and  divides  close  to  the 
optic  papilla  into  three  brandies  usually;  of  these  the  upper  is  larger  than  the  two  lateral  branches. 
The  retina  is  more  vascular  than  that  of  the  horse;  it  has  a  round  area  centralis  at  the  inner  side, 
which  is  continued  outward  by  a  narrow  strip  of  a  similar  histological  structure. 

The  vitreous  body  is  less  fiuid  than  that  of  the  horse. 


THE  EAR 
The  external  ear  is  inclined  outward.  The  middle  part  is  much  wider  and  less 
curved  than  in  the  horse.  The  apex  is  also  wide  and  does  not  curve  forward. 
The  lower  part  of  the  anterior  border  is  bent  backward  and  bears  long  hairs.  The 
posterior  border  is  thin  and  is  regularly  convex,  except  below,  where  it  is  indented. 
The  opening  is  wide  and  the  concave  surface  presents  four  ridges;  the  convex 
surface  presents  corresponding  depressions.  The  styloid  process  of  the  conchal 
cartilage  is  .short  and  blunt.  The  edges  of  the  annular  cartilage  are  in  contact  at 
the  inner  side  and  the  upper  border  is  notched  externally.  The  scutiform  cartilage 
is  a  very  irregular  ciuadrilateral  plate;  it  is  situated  on  the  lateral  aspect  of  the 
cranium  with  its  concave  surface  in  contact  with  the  fat  and  temporalis  muscle. 
The  osseous  external  auditory  meatus  is  directed  practically  straight  inward;  .it  is 
about  twice  as  long  as  that  of  the  horse,  and  tapers  ver>-  gradually  from  without 
inward.  The  chief  special  characters  of  the  auricular  muscles  are  as  follows: 
(1)  The  scutularis  blends  with  the  frontalis  muscle.  The  interscutularis  arises 
from  the  base  of  the  processus  cornu  (or  the  corresponding  area  in  polled  cattle) 
and  from  the  frontal  crest.  (2)  The  cervico-scutuhiris  arises  from  the  posterior 
surface  of  the  cranium  below  the  frontal  eminence,  and  receives  slips  from  the 
parieto-auricularis  and  cervico-auricularis  supcrficialis.  (3)  The  zygomatico- 
auricularis  and  scutulo-auricularis  supcrficialis  inferior  are  fused.  (4)  The  scutulo- 
auricularis  superficialis  superior  is  distinct  from  the  interscutularis;  it  arises  from 
the  superficial  face  of  the  scutiform  cartilage.  (5)  The  cervico-auricularis  supcr- 
ficialis arises  from  the  ligamentum  nuchas  and  ends  on  the  convex  surface  of  the 
conchal  cartilage.  (6)  The  parieto-auricularis  arises  from  the  nuchal  surface  of 
the  frontal  bone,  the  adjacent  part  of  the  parietal  bone,  and  the  ligamentimi  nucha; 
it  is  inserted  below  the  preceding  muscle.  (7)  The  scutulo-auricularis  superficialis 
accessorius  arises  from  the  superficial  face  of  the  scutiform  cartilage  and  is  inserted 
by  a  round  tendon  into  the  anterior  part  of  the  convex  surface  of  the  conchal  car- 
tilage. (8)  The  cervico-auricularis  profundus  minor  consists  of  two  fasciculi;  the 
inner,  narrow  part  is  deep  red  in  color,  and  arises  from  the  fascia  of  the  cervical 
muscles  external  to  the  occipital  attachment  of  the  ligamentum  nuchse;  the  outer, 
wider  part  is  pale,  and  arises  beneath  the  cervico-auricularis  sui)erficialis,  indirectly 
from  the  scutiform  cartilage.  The  two  unite  and  are  inserted  into  the  lower  aspect 
of  the  base  of  the  conchal  cartilage.  (9)  The  scutulo-auricularis  profundus  minor 
arises  from  the  temporal  crest  above  the  external  auditory  meatus  and  is  inserted 
into  the  anterior  part  of  the  deep  face  of  the  scutiform  cartilage. 


COMMON    INTEGUMENT 


775 


The  cavum  tympani  is  small;  it  communicates  ventrally  with  the  air-cells  of 
the  bulla  ossea.  The  tympanic  membrane  is  nearly  circular  and  is  not  so  oblique 
as  in  the  horse.  The  auditory  ossicles  are  smaller  than  those  of  the  horse;  the 
malleus  is  more  curved,  the  body  of  the  incus  is  longer,  and  there  is  a  small  promi- 
nence on  the  front  of  the  head  of  the  stapes  for  the  attachment  of  the  stapedius 
muscle. 

The  Eustachian  tube  is  small  and  is  only  about  two  inches  long.  The  pharyn- 
geal opening  is  small  and  is  situated  on  the  side  of  the  fornix  of  the  pharynx  close 
to  the  base  of  the  cranium.  There  is  no  flap-like  expansion  of  the  cartilage,  but 
the  inner  border  of  the  orifice  is  formed  by  a  fold  of  mucous  membrane. 

The  internal  ear  has  essentially  the  same  arrangement  as  in  the  horse. 


COMMON  INTEGUMENT 

The  thickness  of  the  skin  of  the  ox  is  greater  than  that  of  any  of  the  other 
domesticated  animals;  in  general  it  is  about  3  to  4  mm.,  but  at  the  root  of  the  tail 
and  the  point  of  the  hock  it  is  about  5  mm.  and  on  the 
brisket  6  to  7  mm.  The  variably  developed  prominence 
at  the  anterior  part  of  the  pectoral  region  known  as  the 
brisket  consists  of  a  fold  of  skin  (Plica  colli  ventralis 
longitudinalis),  which  contains  posteriorly  a  mass  com- 
posed of  coarse  fibrous  trabcculse  and  fat. 

The  cutaneous  glands  arc  fewer  and  less  developed 
than  in  the  horse.  Except  about  the  natural  openings,  at 
the  point  of  tlie  hock,  and  the  flexion  surface  of  the  fet- 
lock, the  sweat  glands  do  not  form  a  coil,  but  are  enlarged 
at  the  deep  end  and  are  variably  flexuous.  The  sebaceous 
glands  are  best  developed  about  the  natural  openings  and 
on  the  udder,  but  there  are  none  on  the  teats.  The 
naso-labial  glands  form  a  thick  laj-er  under  the  bare  skin 
of  the  muzzle.  They  are  compound  tubular  glands  and 
are  lined  with  cubical  epithelium.  The  openings  of  their 
excretory  ducts  are  easily  seen. 

The  hairs  are  extremely  variable  in  color  and  size  in 
the  different  breeds  and  in  different  individuals.  The  hair 
of  the  frontal  region  is  often  curly,  especially  in  the  bull. 
There  is  no  mane,  and  the  long  hairs  of  the  tail  occur  only 
at  the  end,  where  they  form  the  "brush"  (Cirrus  caudse). 

The  claws,  four  in  number  on  each  limb,  cover  the  ends  of  the  digits.  Those 
of  the  chief  digits  conform  in  a  general  way  to  the  shape  of  the  third  phalanges, 
and  each  may  be  regarded  as  having  three  surfaces.  The  abaxial  or  outer  surface 
is  convex  from  side  to  side,  and  is  marked  by  ridges  parallel  with  the  coronary 
border.  Its  anterior  part  is  concave  from  edge  to  edge,  and  the  angle  which  it 
forms  with  the  ground  is  about  30°.  The  interdigital  or  inner  surface  is  con- 
cave and  grooved;  it  touches  the  opposite  claw  only  at  its  ends.  The  inferior  or 
ground  surface  consists  of  two  parts,  viz.,  a  slightly  concave  sole,  which  is  pointed 
in  front  and  widens  behind,  and  a  prominent  bulb  of  soft  thin  horn,  which  is  con- 
tinuous above  with  the  skin.  The  claw  may  be  regarded  as  consisting  of  three 
parts — periople,  wall,  and  sole.  The  periople  surrounds  the  coronary  border  in 
the  form  of  a  flat  band,  which  is  about  half  an  inch  wide,  except  at  the  heels,  where 
it  widens  to  cover  the  entire  surface.  The  wall  forms  most  of  the  abaxial  or  outer 
part  of  the  claw  and  is  reflected  in  front  upon  the  interdigital  surface.  It  thins  out 
toward  the  bulb  or  heel,  which  appears,  as  stated  above,  to  consist  of  the  thin 
expansion  of  the  periople.     The  sole  occupies  the  angle  of  inflection  of  the  wall; 


5S5. — Claws  of  Ox, 
Volar  Aspect,  (.\fter 
Ellenberger-Baum, 
Anat.  fiir  Kunstler.) 


776 


SENSE  ORGANS  AND  SKIN  OF  THE  OX 


it  is  continuous  without  demarcation  with  the  periople  of  the  Ijull).  The  periophc 
matrix  bears  relatively  long  papilla-.  The  coronary  matrix  is  much  less  developed 
than  in  the  horse  and  its  papillae  are  short.  The  sensitive  laminae  are  much  nar- 
rower and  are  more  numerous  than  in  the  horse;  secondary  laminae  are  not  jiresent. 
The  matrix  of  the  sole  is  not  marked  off  behind  from  that  of  the  perio]ile;  its 
papillae  are  very  small  and  close  together.  The  matrix  of  the  bulbs  is  separated 
from  the  flexor  tendon  by  a  mass  of  elastic,  fatty  tissue,  which  is  analogous  with 
the  plantar  cushion  of  the  horse.  The  papillae  here  arc  long  and  often  compound. 
The  accessory  digits  hea.T  short  conical  horn  capsules  which  resemble  in  a 
general  way  those  of  the  chief  digits,  and  have  a  similar  matrix,  which  covers  one 
or  two  nodular  vestigial  phalanges.      From  these  a  fibrous  band  descends  obliciuely 


Lateral  extensor  tendon 
Metacarpal  bone 


^I et  war po- phalangeal  articulation 
First  phalanx 
Lateral  extensor  tendon 
Common  extensor  tendon 
Proximal  interphalangeal  join 
Second  phalanx 

Perioph 
Coronary  matrix 
Third  phalanx 
Wall  of  hoo. 


Annular  liijament 

5: ^Plantar  cushion 

I  /'/"'"  pouch  of  capsule 

nf  distal  inter  phalangeal 

J,  nut 
— A'lineular  hone 


on  tlie  volar  asjiect  of  each  chief  digit  and  is  attached  below  t(i  the  distal  iihalanx 
and  sesamoid  bones,  sending  fibers  also  to  the  clastic  pail  of  the  heel. 

The  horns  (C'ornua)  inclose  the  horn  processes  of  the  frontal  bones  (except  in 
the  polled  breeds).  They  vary  very  greatly  in  size,  form,  and  curvature.  Tlie  root 
or  base  of  the  horn  (Radix  eornus)  has  a  thin  edge  which  is  continuous  with  the 
epidermis.  It  is  covered  by  a  thin  layer  of  .soft  horn  similar  to  the  periople  of  the 
hoof  of  the  hor.se.  Near  the  root  the  horn  is  encircled  by  variable  rings.  Toward 
the  apex  (Apex  eornus)  the  thickness  of  the  horn  increa,ses  till  it  becomes  jiractically 
a  solid  mass.  The  horn  consists  mainly  of  tubes  which  are  very  close  together, 
except  at  the  rings,  where  there  is  more  intertubular  horn.  The  matrix  of  the  horn 
(Matrix  eornus)  is  united  to  the  horn  process  by  periosteum  which  is  traversed  by 
numerous  blood-vessels.     The  matrix  at  the  root  of  the  horn  is  thick  and  bears 


SENSE    ORGANS    AND    INTEGUMENT    OF   THE    PIG  777 

long,  slencU'r  iia]iilla';  in  the  body  of  tlio  horn  it  becomes  thin  and  tli(>  papillae 
are  smaller,  bvit  increase  in  size  apically.  Rudimentary  papillated  laminae  also 
occur. 

The  skin  of  the  sheep  varies  in  thickness  from  0.5  to  3  nun.,  liut  differs  greatly 
in  fineness  and  in  other  respects  in  various  breeds.  In  Merinos  considerable 
folds  occur  on  the  neck.  Cutaneous  pouches  (Sinus  cutis)  are  constantly  present 
in  certain  situations.  The  infraorbital  or  lacrimal  pouch  (Sinus  cutaneus  infra- 
orbitalis)  is  an  invagination  about  half  an  inch  in  tlepth,  which  is  situated  in 
front  of  the  inner  angle  of  the  eye.  It  bears  scattered  fine  hairs,  into  the  follicles 
of  which  large  compound  sebaceous  glands  o])en;  coil  glands  are  also  present.  The 
secretion  of  the  glands  is  fatty  anil  forms  a  yellow  sticky  covering  on  the  skin  when 
dry.  The  inguinal  (or  mammary)  pouch  (Sinus  cutaneus  inguinalis)  is  much  more 
extensive,  anil  is  situated  in  the  inguinal  region  in  both  sexes.  The  skin  of  the 
pouch  bears  scattered  fine  hairs  and  contains  well-develoiied  sebaceous  glands  and 
exceedingly  large  coil  glands.  Tlie  interdigital  pouch  (Sinus  cutaneus  interdigi- 
talis)  is  a  peculiar  tubular  invagination  of  the  integument  which  opens  at  the  an- 
terior part  of  the  interdigital  cleft.  On  sagittal  section  it  appears  as  a  bent  tube, 
an  inch  or  more  (ca.  2.5  to  3  cm.)  in  length,  and  about  a  fourth  of  an  inch  (ca.  6 
to  7  mm.)  in  diameter.  The  pouch  extends  downward  and  liackward,  and  then 
curves  sharply  upward  between  the  distal  ends  of  the  proximal  phalanges.  Its 
deep  blind  end  is  somewhat  ampullate.  The  subcutis  forms  a  capsule  around  it. 
The  skin  of  the  pouch  is  thin  and  pale;  it  bears  fine  colorless  hairs,  the  follicles  of 
which  receive  the  secretion  of  several  sebaceous  gands.  The  coil  glands  here  are 
compound  and  very  large;  they  open  into  the  hair-follicles  or  directly  into  the  pouch. 
The  secretion  of  the  glands  is  a  colorless  fatty  substance.  The  skin  is  covered  in 
great  part  by  wool,  which  is  similar  in  structure  to  hair,  but  is  finer,  curly,  and 
usually  contains  no  medullary  cells.  The  follicles  of  the  wool  are  curved,  and  are 
arranged  more  or  less  distinctly  in  groups  of  ten  or  a  dozen,  several  of  which  open 
in  common  on  the  surface.  A  considerable  part  of  the  face  and  the  limbs  is  covered 
with  short,  stiff  hair,  and  long  hairs  occur  more  or  less  interspersed  among  the  wool. 
The  claws  resemble  those  of  the  ox.  The  horns,  when  present,  are  more  or  less 
prismatic,  distinctly  ringed,  and  vary  in  length  and  curvature  in  different  breeds. 
Their  structure  is  similar  to  those  of  the  ox. 

The  olfactory  and  gustatory  organs  resemble  in  general  those  of  the  horse. 


SENSE  ORGANS  AND  INTEGUMENT  OF  THE  PIG 
THE   EYE 

The  posterior  part  of  the  orbital  margin  is  formeil  chiefly  by  the  orbital  liga- 
ment, which  extends  from  the  extremely  short  supraorbital  process  to  the  small 
eminence  at  the  junction  of  the  malar  and  the  zygomatic  process  of  the  temporal. 

Cilia  occur  only  on  the  upper  eyelid.  The  inner  canthus  is  prolonged  by  a 
groove  on  the  infraorbital  region.  The  tarsal  glands  are  very  short  and  curved. 
The  conjunctival  epithelium  is  of  the  transitional  type  with  many  goblet  cells. 

The  deep  part  of  the  cartilage  of  the  third  eyelid  is  broad  and  spoon-like,  the 
superficial  part  somewhat  anchor-shaped.  In  addition  to  the  gland  which  sur- 
rounds the  deep  part  of  the  cartilage,  there  is  a  deeper  gland  of  Harder  (Glandula 
palpebrse  tertia;  profunda),  which  is  surrounded  by  a  distinct  capsule  and  a  blood- 
sinus.  This  gland  is  brownish  or  yellowish-gray  in  color,  elliptical  in  outline,  and 
about  an  inch  (2  to  3  cm.)  in  length.  It  is  situated  deeply  below  the  attachment  of 
the  inferior  oblique  muscle. 


778  SENSE    ORGANS   AND    INTEGUMENT   OF   THE    PIG 

The  canmcula  lacrimalis  has  the  form  of  a  ritlgo;  it  (Uvides  into  two  branches 
which  join  the  skin  at  the  inner  commissure.  It  is  red  in  color  and  contains 
numerous  large  coil  glands. 

The  lacrimal  gland  is  mucous  in  type.  There  is  no  lacrimal  sac,  and  the  two 
lacrimal  ducts  i)ass  through  sejiarate  ojienings  at  the  infraorbital  margin.  The 
naso-lacrimal  iluct  is  usually  short  and  opens  into  the  inferior  meatus  at  the  pos- 
terior end  of  the  inferior  turbinal.' 

The  eyeball  appears  small,  partly  on  account  of  the  narrowness  of  the  palpebral 
opening;  it  closely  approaches  the  spherical  form.  The  cornea,  although  in  reality 
almost  circular,  appears  oval  when  viewed  from  the  front,  the  inner  end  being  much 
the  broader.  The  chorioid  has  no  tapetum.  The  iris  is  usually  dark  grajash- 
brown  or  yellowish-brown,  but  sometimes  has  a  blue  tinge.  The  pupil  is  a  trans- 
verse oval  in  ordinary  light,  but  almost  circular  when  dilated;  granula  are  not 
present.  The  optic  papilla  is  nearer  the  posterior  pole  than  in  the  horse  and  ox, 
and  has  a  distinct  central  arterv  and  vein. 


THE   EAR 

The  external  ear  differs  considerably  in  size,  thickness,  and  position.  It  may 
be  carried  vertically,  inclined  inward,  or  hang  downward.  It  is  relatively  wide  and 
is  little  curved  except  at  the  base.  The  concave  surface  presents  several  cutaneous 
ridges  which  correspond  approximately  with  the  long  axis  of  the  ear.  The  anterior 
border  of  the  concha  is  strongly  recurved  in  its  lower  jiart,  and  divides  into  two 
branches,  one  of  which  passes  almost  horizontally  backward  in  the  cavum  concha;, 
while  the  other  continues  the  general  direction  of  the  border.  The  posterior  border 
is  slightly  concave  above,  strongly  convex  below,  forming  a  prominence  somewhat 
analogous  to  the  lobule  of  the  human  ear.  The  osseous  external  auditory  meatus 
is  very  long  and  is  directed  downward  and  inward.  The  tympanic  membrane  is 
almost  circular. 

The  tympanic  cavitj'  proper  is  small,  but  it  is  continuous  with  the  numerous 
cells  of  the  large  bulla  ossea.  The  Eustachian  tube  is  short;  its  pharyngeal  opening 
is  situated  in  the  upper  part  of  the  wall  of  the  pharynx  immediately  l)ehin(l  the 
posterior  nares.  It  is  somewhat  infundibular,  and  is  bounded  internally  l\v  a  thick 
fold  of  mucous  membrane  (Torus  tubarius). 


THE   SKIN  AND  APPENDAGES 

The  thickness  of  the  skin  in  improved  breeds  is  1  to  2  mm.  Fat  usually  ac- 
cumulates in  the  subcutis  and  forms  a  distinct  and  often  extremely  thick  panniculus 
adiposus  over  the  greater  part  of  the  body. 

The  sebaceous  glands  are  in  general  small  and  much  fewer  than  in  the  other 
animals.  The  sweat  glands,  on  the  other  hand,  are  large,  yellow  or  brownish  in 
color,  and  are  in  many  places  visible  to  the  naked  eye.  At  the  inner  side  of  the 
carpus  there  are  small  cutaneous  diverticula,  the  so-called  carpal  glands,  into  which 
numerous  compound  coil  glands  open.  Large  glands  also  occur  in  the  skin  of  the 
digits  and  interdigital  space.  Compound  tubular  glands  are  present  in  the  skin  of 
the  snout.  Large  sebaceous  and  sweat  glands  are  found  at  the  entrance  to  the  pre- 
putial diverticulum. 

The  hairs  are  sparsely  scattereil  in  improved  breeds — indeed,  in  some  cases 
the  skin  is  almost  bare.     The  long  hairs  or  bristles  are  arranged  usually  in  groups 

'The  lowrr  punplvim  hiorimalp  is  frpqupiitly  absent  and  the  corro.'iponding  duct  therefore 
bhnd.  There  is  often  a  duct  or  its  remnant  wliich  opens  below  the  inferior  turbinal  foki,  but  is 
not  connected  beliind  with  the  functional  duct. 


SENSE    ORGANS    AND    INTEGUAIENT    OF   THE    DOG  779 

of  three.     They  are  most  developed  on  the  neck  and  back.     The  liristles  about  the 
snout  and  the  chin  are  sinus  hairs. 

The  claws  and  their  matrix  resemble  those  of  the  ox,  but  the  bulbs  are  more 
prominent  and  form  a  greater  part  of  the  ground  surface;  they  are  also  better 
defined  from  the  sole,  which  is  small.  The  claws  of  the  accessory  digits  are  more 
developed  and  their  parts  lietter  differentiated  than  those  of  the  ox. 

The  olfactory  region  is  extensive  in  correlation  with  the  large  size  of  the 
olfactory  bulbs;    the  mucous  membrane  here  is  brown  in  color. 


SENSE  ORGANS  AND  INTEGUMENT  OF  THE  DOG 
THE  EYE 

The  posterior  margin  of  the  orbit  is  formed  by  the  orbital  ligament,  as  in  the 
pig.  The  orbital  axes  if  produced  backward  would  include  an  angle  of  about  79°, 
the  optic  axes  an  angle  of  about  92.5°  (Koschel). 

The  lower  eyelid  has  no  distinct  cilia.  The  inner  angle  is  wide,  the  lacus 
lacrimalis  shallow,  and  the  caruncula  lacrimalis  small  and  yellowish-brown.  The 
conjunctival  epithelium  is  cylindrical,  with  many  goblet  cells.  The  gland  which 
surrounds  the  deep  end  of  the  cartilage  of  the  third  eyelid  is  large  and  pink;  it  is  a 
mixed  gland. 

The  lacrimal  gland  is  flat  and  lies  chiefly  under  the  orbital  ligament.  It  is 
pink  in  color  and  mixed  in  structure.  The  naso-lacrimal  duct  is  variable  in  arrange- 
ment and  may  differ  on  the  two  sides.  It  may  open  into  the  inferior  meatus  im- 
mediately after  its  emergence  from  the  osseous  lacrimal  canal;  thence  it  continues 
forward  and  opens  on  the  lateral  wall  of  the  nostril  below  the  inferior  turbinal  fold. 

The  eyeball  is  almost  spherical  and  is  relatively  large,  especially  in  the  small 
breeds.  The  sclera  is  thick  in  the  ciliary  region,  where  it  contains  a  well-developed 
venous  plexus;  in  the  vicinity  of  the  equator  it  is  thin,  and  the  chorioid  shows 
through  it.  The  cornea  is  almost  circular.  The  chorioid  is  richly  pigmented, 
and  presents  a  well-defined  tapetum  cellulosum ;  this  is  somewhat  triangular  in 
outline  and  has  a  metallic  luster.  Its  color  is  often  golden  green,  shading  to  blue 
peripherally,  but  the  blue  tone  may  predominate,  and  in  other  cases  it  is  mainly 
golden  yellow  or  reddish-yellow.  The  appearance  is  due  to  several  layers  of  peculiar 
flattened  polygonal  cells.  The  ciliary  muscle  is  more  developed  than  in  the  other 
species.  The  iris  is  commonly  light  or  yellow  brown,  but  not  rarely  has  a  blue 
tinge;  the  color  often  differs  in  the  two  eyes.  The  pupil  is  round;  its  edge  is 
either  smooth  or  bears  minute  round  prominences.  The  retina  presents  a  round 
area  centralis  external  to  the  optic  papilla.  The  latter  is  variable  in  outline; 
commonly  it  has  the  form  of  a  triangle  with  the  angles  rounded  off,  but  is  often 
round  or  oval.  Branches  of  the  central  vessels  of  the  retina  radiate  from  the 
middle  of  the  papilla.  The  surfaces  of  the  lens  are  not  so  strongly  curved  as  in 
the  other  domestic  animals,  and  there  is  little  difference  in  the  radius  of  curvature 
of  the  two  surfaces. 

THE  EAR 

The  external  ear  differs  greatly  in  size  and  form  in  the  various  breeds ;  in  most  it 
is  relatively  wide  and  thin  and  the  greater  part  of  it  hangs  down  over  the  opening. 
The  anterior  border  has  a  prominence  (Spina  helicis)  at  its  lower  part,  and  below 
this  it  divides  into  two  branches  (Crura  helicis).  One  of  these  continues  down  to  a 
blunt  point,  while  the  other  turns  in  to  the  cavity  of  the  concha.     The  posterior 


780  SENSE    ORGAN'S    AND    INTEGUMENT    OF   THE    DOG 

border  forms  a  pouch  below  its  middle,  and  is  thick  and  rounded  in  its  basal  part. 
Here  the  conchal  cartilage  bears  a  jiointcd  process  (Processus  uncinatus),  which  pro- 
jects upward  and  backward.  The  outer  wall  of  the  cavuni  conchse  is  supported 
by  a  quadrilateral  plate  (Tragus)  above  and  a  somiannular  cartilage  below.  The 
concave  surface  presents  several  cutaneous  folds,  and  in  the  cavum  conchse  there 
arc  ridges  and  irregular  prominences.  There  are  long  hairs  on  the  borders,  apex, 
and  the  folds  of  the  concave  surface,  but  the  skin  of  the  cavum  conchte  is  bare. 
The  annular  cartilage  is  a  complete  ring.  The  osseous  external  auditory  meatus 
is  wide  and  extremely  short. 

The  auricular  muscles  are  thin.  The  scutularis  is  extensive  and  is  ilivisible 
into  interscutularis  and  fronto-scutularis.  It  partly  covers  the  occipitalis  muscle, 
which  is  oval  and  unpaired  and  ends  in  the  fascia  of  the  frontal  region.  The 
scutulo-auriculares  superficiales,  inferior  et  accessorius,  and  the  cervico-scutularis 
are  not  differentiated  as  separate  muscles.  The  cervico-auricularis  superficialis 
and  the  parieto-auricularis  both  bifurcate  and  are  inserted  into  the  base  of  the 
concha  and  the  scutiform  cartilage.  The  parotiilo-auricularis  is  narrow  and  almost 
long  enough  to  meet  the  opposite  muscle.  The  tragicus  consists  of  two  parts;  of 
these  the  lateral  one  is  long  and  arises  from  the  border  of  the  mantlible  above  the 
angular  process.     The  helicis  and  the  verticalis  auricula?  are  well  developed. 

The  tympanic  cavity  is  very  roomy,  extending  ventrally  into  the  large  but 
simple  cavity  of  the  bulla  ossea.  The  tj'mpanic  membrane  is  extensive  and  oval. 
The  promontory  is  verj'  pronounced.  The  auditorj'  ossicles  are  large.  The 
Eustachian  tube  is  short,  and  has  a  fibrous  outer  wall.  Its  pharyngeal  opening  is 
an  oblique  slit  situated  on  the  lateral  wall  of  the  naso-pharyngeal  meatus,  and  is 
margined  internally  by  a  thick  mucous  fold. 

The  cochlea  has  three  and  a  half  turns  and  is  more  sharply  pointed  than  in  the 
ungulates. 

THE  SKIN  AND  APPENDAGES 

The  skin  varies  greatly  in  thickness  in  tliffcrent  breeils.  It  is  remarkably 
loose  on  the  dorsal  aspect  of  the  neck  and  trunk,  where  it  can  be  raised  in  extensive 
folds.  The  coat  is  also  subject  to  extreme  variation  in  length,  thickness,  color,  etc. 
The  hairs  are  arranged  in  groups  of  three  to  a  large  extent.  The  sebaceous  glands 
are  best  developed  in  the  short  and  rough  haired  breeds.  They  are  largest  and 
most  nmnerous  at  the  lips,  anus,  dorsal  surface  of  the  trunk,  and  sternal  region. 
The  sweat  glands  are  relatively  better  developed  in  the  long  and  fine  haired  breeds. 
The  largest  are  found  in  the  digital  pads.  Coil  glands  occur  in  the  skin  of  the 
muzzle,  the  i)erincinn,  and  the  paranal  pouches. 

On  the  flexion  surface  of  the  carpus  and  digit  there  are  hairless,  cushion-like 
pads.  The  carpal  pad  (Torus  carpalis)  is  situated  medial  anil  distal  to  the  accessory 
carpal  bone.  The  metacarpal  and  metatarsal  pads  (Torus  metacarpalis,  meta- 
tarsalis)  are  the  largest  and  are  situated  Ijehind  the  distal  ends  of  the  metacarpal 
or  metatarsal  bones  and  the  greater  part  of  the  first  phalanges.  They  are  somewhat 
heart-shaped,  with  two  uneciual  lateral  lobes,  and  the  apex  distal.  The  metapodio- 
phalangeal  joints  rest  on  them  wh(>n  the  paw  supports  the  weight.  The  digital 
pads  (Tori  digitales)  are  oval  and  are  much  smaller;  they  similarly  support  the 
second  digital  joints.  That  of  the  first  digit  is  small  on  the  fore  limb,  and  usually 
absent  from  the  hind  limb.  Each  receives  two  suspensory  bands  from  the  tubercles 
at  the  distal  end  of  the  corresponding  second  phalanx.  The  pads  have  a  basis  of 
fibro-elastic  tissue  and  fat,  which  is  intimately  adherent  to  the  skin  and  is  connected 
by  trabeculic  with  the  bones  and  tendons.  The  epidermis  is  thick  and  largely 
keratinized,  and  is  studded  with  numerous  rounded  papilla  which  are  readily  seen 
with  the  naked  eye.  The  coritnn  has  large  papillae,  and  contains  sweat  glands  and 
lamellar  corpuscles. 


OLFACTORY    AND    CU.STATOKY    ORGANS 


rsi 


The  claws  (Ungues)  correspond  in  form  to  the  ungual  part  of  the  distal  pha- 
langes which  they  inclose.  The  horn  of  the  claw  consists  of  a  body  or  wall  anil  a 
sole.  The  former  is  strongly  curved  in  both  directions,  and  is  compressed  laterally. 
Its  root  or  coronary  border  fits  into  the  depression  under  the  bony  collar  or  ungual 
crest  of  the  third  phalan.\  and  is  covered  by  skin.  The  lateral  borders  converge 
and  inclose  the  sole  anteriorly.  The  matrix  presents  a  coronary  part  which  bears 
papillse  only  near  the  coronary  Ixirder.  On  the  dorsal  surface  it  is  thickened 
to  form  a  ridge,  and  the  corresponding  part  of  the  horny  covering  is  thick  and 
maintains  the  pointed  character  of  the  claw.  The  matri.x  of  the  sides  of  the  wall 
bears  small  lamina^  which  converge  to  the  matrix  of  the  sole.  The  latter  is  papil- 
lated.     When  the  flexor  muscles  are  inactive,  the  distal  phalanges  and  the  claws  are 


Fig.  587.— Pads  of  Paw  of  Dog. 

,  Cari>al  pad;    b,  metacarpal  pad;    c^-c^,  digital  pads 

(From  Leisering's  .\tlas.) 


Fig.  588. — Half  of  Cl.aw  of  Dog,  Inner  Surface. 
a,  a'.  Coronary  part,  fc,  volar  part  of  wall; 
c,  sole;  d,  section  of  c;  e,  section  of  wall;  1 ,  coronary 
border;  2,  apex;  S,  dorsal  surface.  (From  Leisering's 
Atlas.) 


maintained  in  dorsal  flexion  by  two  elastic  ligaments.  These  arise  from  the 
tubercles  at  the  proximal  end  of  the  second  phalanx  and  converge  to  the  dorsal 
aspect  of  the  ungual  crest  of  the  third  iihalanx. 


OLFACTORY  AND  GUSTATORY  ORGANS 

The  olfactory  region  lies  above  the  lamina  transversa,  which  separates  it  from 
the  naso-pharyng(>al  meatus.  The  mucous  membrane  is  distinguished  by  its 
thickness  and  yellow  color,  and  is  very  extensive.  It  covers  about  half  of  the  large 
ethmoturbinals,  and  one-third  to  one-half  of  the  septum  nasi.  The  ethmoturbinal 
which  projects  into  the  frontal  sinus  and  the  adjacent  inner  wall  of  the  sinus  is 
olfactory  in  character.  Olfactory  nerve-fibers  ramify  in  the  vomero-nasal  organ 
(of  Jacobson). 

The  gustatory  apparatus  presents  no  special  features  of  importance. 


^ 


NDEX 


Abdomen,  muscles  of,  245 
of  dog,  326 
of  pig,  313 

muscles  of,  301,  313 
Abdominal  aorta,  536 
branches  of,  566 
of  dog,  638 
artery,  anterior,  541 
posterior,  579 
subcutaneous,  .580 
cavity  of  horse,  352 

of  ox,  390 
fascia  of  horse,  245 
muscles  of  dog,  326 
of  horse,  245 
of  pig,  301,  313 
panniculus,  245 
plexuses,  713 
tunic  of  horse,  245 

of  pig.  313 
veins,  59S 
Abducent  nerve,  683 
Abduction  of  joints,  172 
Abductor  cruris  posterior  mus- 
cle, 327 
digiti    quinti    muscle,    324, 

329 
hallucis  muscle,  329 
pollicis  brevis  et   opponens 
poUicis  muscle,  324 
Abomasum  of  ox,  390,  392 
cavity  of,  396 
of  sheep,  409 
Accelerator  urinte,  499 
Accessory  carpal  bone,  84 
fibro-cartilage  of  patella,  105 
organs,  330 
pancreatic  duct  of  dog,  431 

of  horse,  373 
pillars  of  rumen,  .393 
spleens  of  horse,  379 
thyroids  of  dog,  468 
of  horse,  458 
of  ox,  464 
Acetabular  angle,  94,  96 
fossa,  96 
notch,  96 
Acetabulum  of  dog,  167 
of  horse,  96 
of  ox,  131 
of  pig,  148 
Acromion  of  dog,  162 

of  ox,  127 
Adduction  of  joints,  172 
Adductor    brevis     muscle    of 
horse,  282 
digiti  quinti  muscle  of  dog. 
324 
secunda  muscle  of  dog,  324 
hallucis  muscle  of  dog,  329 
longus  muscle  of  horse,  282 
magnus  muscle  of  horse,  282 


Adductor  muscle  of  dog,  328 
of  horse,  282 
of  ox,  308 
of  pig,  316 
parvus  muscle  of  horse,  282 
pollicis  muscle  of  dog,  324 
Aditus  laryngis  of  horse,  447 
Adrenal  bodies  of  dog,  484 
of  horse,  477 

structure  of,  478 
of  ox,  481 
of  sheep,  481 
plexus,  714 
Adventitia  of  seminal  vesicles, 
492 
of  vas  deferens,  489 
^■Equator  lentis,  746 
iEsthesiology,  734 
Air-cells  of  lungs,  457 
Ala;  nasi,  436 
Alar  canal,  51 
cartilage,  437 

of  ox,  459 
fold,  437 
foramen,  68 
Alimentary  canal,  330 
Alveolar  arch,  superior,  69 
artery,  inferior,  552 
of  dog,  635 
of  pig,  627 
border  of  mandible,  64 
ducts  of  lungs,  457 
nerve  of  dog,  729 

of  horse,  681,  682 
periosteum  of  teeth,  339 
tuberosity  of  horse,  69 
vein,  589 
inferior,  .5.87 
Alveoli  of  horse,  58 
of  lungs  of  horse,  457 
of   thyroid   gland   of  horse, 
458 
Alveus,  669 
Amphiarthroses,  172 
Ampulla     ductus     deferentis, 
489 
of  semicircular  canals,  758 
of  uterus  of  bitch,  523 
recti  of  horse,  370 
Amygdaloid  nucleus,  676 
Anal  glands  of  dog.  432 
lymph  glands,  605 
of  ox,  626 
of  pig,  632 
sacs  of  dog,  432 
Anastomosis  of  arteries,  524 
Anatomy.  17 
gross,  17 
macroscopic,  17 
microscopic,  17 
philosophical,  17 
special,  17 

7S3 


Anatomy,  systematic,  17,  18 
topographic,  17,  18 
veterinary,  17 
Anconeus  muscle,  262 

of  pig,  315 
Angiology,  524 

Angle,  duodenal,  of  horse,  372 
of  mandible,  64 
splenic,  372 
Angular  artery  of  eye,  550 
of  ox,  611 
movements  of  joints,  171 
process  of  mandible  of  dog, 
159 
Annular  cartilage  of  ear,  748 
ligament,  212 

anterior,  of  horse,  263 
of  manus  of  horse,  263 
of   pelvic   limb   of   horse, 

274 
posterior,    of    carpus    of 
horse,  263 
Annulus  tympanicus,  753 
Ansate  fis.sure  of  dog,  726 
Anterior  angle  of  pancreas,  372 
of  scapula,  76 
annular  ligament  of  horse, 

263 
aorta,  .537 
aperture  of  thoracic  cavity, 

450 
fossa  of  skull,  70 
nares,  436 
Antero  -  external      angle      of 

ischium,  95 
Antero  -  internal      angle      of 

ischium,  95 
Antibrachial  artery  of  dog,  635 
Anticlinal  vertebra?  of  horse,  42 
Antitragicus  muscle,  751 
Antitragus,  748 
Antrum  pylori,  358 
Anus  of  horse,  371 

of  ox,  400 
Aorta,  .535 

abdominal,  536 
branches  of,  566 
of  dog,  638 
anterior,  .537 
arch  of,  535 
of  ox,  609 
of  pig,  627 
thoracic,  536 
branches  of,  565 
Aortic  orifice  of  heart  of  horse, 
533 
plexus,  712 
Aperture,  anterior,  of  thoracic 
cavity,  450 
of  abdominal  ca%ity,  353 
pharyngeal,  of  horse,  447 
Apex  ca?ci,  364 


784 


INDEX 


Apical  lobe  of  lungs  of  ox,  462, 

463 
Aponeuroses,  211 
Aponeurosis    of    external    ob- 
lique muscle,  246 
of  internal  oblique  muscle, 

248 
of     transversus     abdominis 

nuiscle,  249 
pharyngeal,  350 
Appendages  of  skin,  762 
Appendix  testis,  485 

ventrieuli  larjTigis,  447 
Aquanluctus  cochlea?,  759 

vestibuli,  758 
A(nieihK't  of  cerebrum,  664 

of  Sylvius,  664 
Aqueous  humor,  746 
Arachnoid  granulations,  047 
Arachnoidea,  646 

spinal,  647 
Arch,    alveolar,    superior,    of 
horse,  69 
of  aorta,  .535 
of  cricoid  cartilage,  441 
plantar,  581 
venous,  595 
zygomatic,  56,  67 
Arciforin  ligaments,  182 
Arcuate  fibers,  external,  657, 
658 
internal,  658 
of  cerebellum,  661 
Arcus  terminalis,  564 
venosus  plantaris,  599 
volaris,  595 
Area  acustica,  662 
of  ox,  715 
centralis  retinae,  746 
ccclilea-,  759 
pardU'actoria,  671 
radicularis  ventralis,  649 
tentorial,  668 
vestibularis  superior,  759 
Arm,  bones  of,  28 
muscles  of,  259 
of  ox,  muscles  of,  302 
of  pig,  muscles  of,  314 
Arrectores  pilorum,  763 
Arterial  circle  of  Willis,  546 
jilantaris  lateralis  of  ox,  620 
reticularis  of  ox,  615 
Arteries  or  artery,  534,  535 
abdominal,  anterior,  541 

posterior,  579 
alveolar,  552 
of  dog,  635 
of  pig,  627 
anastomosis  of,  524 
angular,  of  eye,  550 

of  ox,  611 
antibraehial,  of  dog,  635 
asternal,  .541 
auricular,  5.50 
of  dog,  635 
of  ox,  611 
of  pig,  627 
posterior,  550 
axillary,  5.56 
basilar,  546 
bicipital,  of  dog,  635 
brachial,  .538,  556 
deep,  559 
of  dog,  633,  635 


Arteries,  brachial,  of  ox,  609, 
612 

of  pig,  627 
brachiocephalic,  538 

of  dog,  633 

of  pig,  627 
bronchial,  457,  565 

of  ox,  614 

of  pig,  627 
broncho-oesophageal,  565 
buccinator,  555 

of  pig,  627 
cscal,  570 

carotid,  common,  541 
of  dog,  634 
right,  .542 

external,  547 
of  ox,  611 

internal,  546 

of  dog,  633,  634 

of  ox,  610 

of  pig,  627 
central,  of  retina,  554 
cephalic,  541 
cerebral,  546 

posterior,  546 
cerebrospinal,  545 

of  dog,  634 
cerN-ieal,  deep,  540 

inferior,  541 

of  dog,  633 

of  ox,  609 

of  pig,  627 

superior,  540 
ciliary,  554 
circumflex,  anterior,  558 

external,  577 
of  ox,  619 

of  dog,  635 

of  ox,  612 

of  scapula,  556 

posterior,  556 
coccygeal,  lateral,  577 

middle,  575 

of  dog,  641 

of  ox,  618 
eoeliac,  566 

of  dog,  638 

of  ox,  614 

of  pig,  627 
colic,  570 
communicating       posterior, 

546 
condyloid,  545 

of  dog,  634 

of  ox,  611 
coronary,  535,  537 

of  dog,  632 

of  ox,  609 
cremasteric,  578 
dental,  .552 

inferior,  555 
digital,  564 

common,  563 
of  ox,  621 

external,  of  ox,  614,  620 

of  dog,  637,  641 

of  pig,  629,  630 
dorsal,  538 

of  dog,  633 

of  ox,  609 
dorso-intereostal,  538 
end,  524 
ethmoid,  5.54 


Arteries,  external  coat,  525 
facial,  547 

of  dog,  635 

transverse,  550 
femoral,  579 

anterior,  580 

deep,  580 

of  dog,  639 

of  ox,  619 

of  pig,  630 

posterior,  580 
femoro-popliteal,  580 
frontal,  553 
gastric,  .506 

of  dog,  638 
gastro-duodenal,  569 
gastro-epiploic,  569,  570 
gastrohepatic,  of  pig,  627 
gastrosplenic,  of  dog,  638 
gluteal,  anterior,  577 

of  dog,  641 

of  ox,  619 

posterior,  575 
ha>morrhoidal,  594 

of  dog,  641 
hepatic,  377,  567 

of  dog,  638 

of  ox,  614 
hypogastric,  573 
ideal,  570 
ileocEecal,  570 
ileo-ca>co-colic,  of  ox,  617 
iliac,  circumflex,  578 
of  dog,  639 

external,  578 
of  ox,  619 

internal,  573 

of  ox,  618 

iliaco-femoral,  577 

of  ox,  619 
ilio-lumbar,  577 

of  dog,  641 

of  ox,  619 

of  pig,  630 
incisor,  552 
infraorbital,  555 

of  dog,  635 

of  pig,  627 
intercostal,  565 

of  ox,  614 

of  pig,  627 
internal  coat  of,  525 
interosseous,  common,  561 

dorsal,  562 

of  dog,  635 

of  ox,  612 

recurrent,  561 
intestinal,  570 
intima  of,  525 
ischiatic,  575 

of  ox,  619 
labial,  549 

of  ox,  611 

superior,  550 
lacrimal,  553 
laryngeal,  of  ox,  610 
lingual,  548 

of  dog,  634 

of  ox,  611 
lumbar,  571,  573 

of  ox,  618 

of  pig,  629 
malar,  555 
mammary,  580 


785 


Arteries,  mammary,  of  ox,  619 
masseteric,  inferior,  547 

of  ox,  612 
mastoid,  545 
maxillary,  external,  547 

internal,  551 
of  ox,  612 

of  dog,  635 

of  ox,  611 

of  pis,  627 
maxillo-musoular,  547 
median,  559 

of  ox,  612 
meningeal,  anterior,  546 

middle,  552 

of  dog,  634 

posterior,  545 
mental,  552 
mesenteric,  great,  570 

of  dog,  638 

of  ox,  615 

of  pig,  62S,  629 

posterior,  of  ox,  618 

small,  571 
metacarpal,  dorsal,  562 

external  volar,  562 

internal  volar,  562 

large,  563 

of  dog,  635,  636,  637 

of  ox,  614 

of  pig,  629 

palmar,  563 
metatarsal,  581 

dorsal,  585 
of  ox,  620 

great,  585 

internal   superficial   plan- 
tar, 619 

of  dog,  640,  641 

of  pig,  630 
middle  coat  of,  525 
nasal,  550 

of  ox,  611 
nutrient,  of  femur,  580 

of  humerus,  559 

of  tibia,  581 
obturator,  577 

of  ox,  619 
occipital,  544 

of  dog,  634 

of  ox,  611 

of  pig,  627 
oesophageal,  565,  567 

of  ox,  614 

of  pig,  627 
of  adrenal  bodies  of  horse, 

478 
of  articulations,  171 
of  bladder  of  horse,  477 
of  bulb,  575 
of  cUtoris,  575 
of  conjunctiva,  737 
of  corpus  callosum,  546 
of  dog,  633 
of  external  ear,  752 
of  eyeUds,  737 
of  Fallopian  tubes  of  mare, 

511 
of  first  phalanx,  564 
of  hoof,  771 
of  internal  ear,  761 
of  ox,  609 

of  pehdc  limb  of  ox,  619 
of  penis,  496 
50 


Arteries  of  penis,  dorsal,  580 
of  pig,  627 

of  plantar  cushion,  564 
of  rete  carpi  volare,  562 
of  retina,  746 
of  second  phalanx,  564 
of  skin,  762 
of  small  intestine,  570 
of  third  phalanx,  564 
of  tympanum,  755 
of  uterus,  513 
of  vagina,  514 
of  vascular  tunic  of  eye,  744 
omaso-abomasal,  of  ox,  615 
ophthalmic,  553 

of  dog,  635 

of  ox,  612 
orbital,  555 
ovarian,  571 

of  mare,  510 
palatine,  555 

of  pig,  627 
palato-labial,  555 
pancreatic,  569 
pancreatico-duodenal,  569 
parotid,  .543 

of  pig,  627 
perineal,  574 

of  dog,  641 
peroneal,  585 
perpendicular,  564 
pharyngeal,  548 

of  ox,  611 
phrenic,  565 

of  ox,  614 
phrenico-abdominal,  of  dog, 
639 

of  pig,  628 
plantar,  581 

of  dog,  640 

of  ox,  619 
popUteal,  581 

of  ox,  619 

of  pig,  630 
preplantar,  564 
prepubic,  579 
prevertebral,  545 
pterygoid,  552 
pudic,  external,  580 

internal,  573 

of  pig,  630 
pulmonary,  457,  524,  535 
pyloric,  569 
radial,  anterior,  559 

of  dog,  635 

of  ox,  613 

posterior,  559 
of  ox,  612 
renal,  475,  571 

of  dog,  639 

of  ox,  618 

of  pig,  628 
reticular,  of  ox,  615 
ruminal,  of  ox,  615 
sacral,  lateral,  575 

middle,  of  ox,  618 

of  ox,  619 
saphenous,  580 

of  dog,  640 

of  ox,  619 

of  pig,  630 
sheath  of,  525 
spermatic,  487,  489,  571 

of  dog,  639 


Arteries,  spermatic,  of  ox,  618 

of  pig,  627 
sphenopalatine,  555 
splenic,  569 

of  dog,  638 

of  ox,  615 

of  pig,  628 
staphyline,  555 
structure  of,  .525 
stylomastoid,  550 
subcostal,  539 

of  dog,  633 

of  ox,  609 
sublingual,  548 

of  dog,  635 
submaxillary,  547 
submental,  .549 
subscapular,  556 

of  dog,  635 

of  ox,  612 
supraorbital,  553 
suprascapular,  556 
systemic,  524 
tarsal,  external,  581 

of  pig,  630 

perforating,  585 
temporal,  anterior  deep,  553 

of  dog,  635 

of  ox,  612 

posterior,  deep,  552 

superficial,  550 
terminal,  524 
thoracic,  external,  541 

internal,  540 

of  dog,  633 

of  ox,  609 

of  pig,  627 
thoracico-dorsal,  556 
thyroid,  accessory,  543 

of  ox,  610 

of  pig,  627 
thjTO-laryngeal,  543 
tibial,  anterior,  583 

of  dog,  641 

of  ox,  620 

of  pig,  630 

posterior,  581 

recurrent,  581 
tympanic,  552 
ulnar,  559 

of  dog,  637 

of  ox,  613 

superior  collateral,  of  ox, 
612 
umbiUcal.  574,  606 

of  ox,  619 
uterine,  571 

middle,  578 

of  dog,  641 

of  ox,  619 

posterior,  574 
utero-ovarian,  571 

of  dog,  639 

of  ox,  618 
vertebral,  540 

of  dog,  633 

of  ox,  609 
vesical,  574 
vesicoprostatic,  574 
volar,  deep,  562 

of  second  phalanx,  564 
Arthrodia,  172 
Arthrology,  169 
comparative,  203 


786 


Articular  cartilage,  170 

discs,  171 
Articularis  genu  muscle  of  ox, 

307 
Articulatio     carpi    of     horse, 

183 
Articulations,  169,  172 
abduction  of,  172 
adduction  of,  172 
angular  movements,  171 
arteries  of,  171 
atlanto-axial,  176 
atlanto-occipital,  170 
biisi-cornual,  ISO 
capsule,  170 
carpal,  183 

of  dog,  205 

of  ox,  205 

of  pig,  205 
carpo-mctacarpal,  183 
cavity  of.  170 
chondro-sternal,  17S 
circumduction  of,  171 
classification  of,  169 
coccvgeal,  175 
coffin,  189 
costo-central,  177 
costo-chondral,  178 
costo-transverse,  177 
cost  o- vertebral,  177 
crico-arytenoid,  4-14 
crico-thyroitl,  444 
dorsal  flexion  of,  171 
elbow,  ISl 

of  dog,  205 

of  ox,  205 

of  pig,  205 
extension  of,  171 
femoro-patellar,  194 
femoro-tibial,  196 
fetlock,  185 
flexion  of,  171 
folds  of,  170 

gliding  movements  of,  171 
hip,  192 

of  dog,  209 

of  ox,  209 

of  pig,  209 
hock,  199 

of  dog,  210 

of  ox,  210 

of  pig,  210 
hyoidean,  180 
intercarpal,  183 
interccntnil,  173 
intercornual,  180 
intermetacarpal,      of      dog, 
206 

of  ox,  206 

of  pig,  206 
JntcnK'ural,  173 
inten)lia!angeal,  distal,   1S9 

of  dog,  209 

of  ox,  208 

of  pig,  208 

proximal,  188 
intertransverse,  175 
knee,  i83 
metacarpo-phalangeal,  185 

of  dog,  2()S 

of  ox,  206 

of  pig,  208 
movable,  170 
movements  of,  171 


Articulations,  nerves  of,  171 
of  larynx,  444 
of  pelvic  limb,  190 
of  dog.  209 
of  ox.  209 
of  pig,  209 
of  ribs,  177 
of  skull,  179 
of  thoracic  limb,  180 
of  dog,  205 
of  ox,  205 
of  pig,  205 
of  thorax,  177 
of  dog,  204 
of  ox,  204 
of  pig,  204 
overextended,  171 
pastern,  188 
plantar  flexion  of,  171 
radio-carpal,  183 
radio-ulnar,  182 
rotation  of,  172 
sacral,  175 
sacro-iliac,  190 
of  dog,  209 
of  ox,  209 
of  pig.  209 
shoulder,  180 
of  dog,  205 
of  ox,  205 
of  pig,  205 
sternal,  178 
stifle,  194 
of  dog,  209 
of  ox,  209 
of  pig,  209 
surfaces  of,  170 
.synovial  layer  of,  170 
temporo-liyoid,  180 
temporo-inandibular,  179 
of  dog,  204 
of  ox,  204 
of  pig,  204 
thyro-liyoid,  444 
tibio-fibular,  199 
of  dog,  210 
of  ox,  209 
of  pig,  210 
tibio-tarsal,  199 
true,  170 
veins  of,  171 
vertebral  column,  172 
of  dog,  204 
of  ox,  203 
of  pig,  204 
\-illi  of,  170 
volar  flexion  of,  171 
Arytenoid  cartilages  of  larynx, 
443 
of  dog,  467 
of  ox,  4.59 
of  pig,  465 
ligament,  transverse,  of  lar- 
ynx, 444 
Arytenoideus  transversus  mus- 
cle of  larynx  of  horse,  446 
Asternal  artery,  541 
ribs,  25 

of  horse,  43 
Astragalo-calcaneal  ligaments, 

202 
Astragalo-scaphoid  ligaments, 

202 
Atlanta!  gland  of  ox,  623 


Atlanto-axial    articulation    of 
horse,  176 
ligament,  inferior,  176 
superior,  176 
Atlanto-occipital  articulation, 
176 
membrane,  inferior,  176 
superior,  176 
Atlas,  33,  34 
of  dog,  150 
of  ox,  112 
of  pig,  147 
Atrio-ventricular     groove     of 
heart,  .527 
opening  in  left  atrium,  530 
in  right  atrium.  530 
left,  of  ventricle,  533 
right,  of  ventricle,  531 
Atrium  of  heart,  .529 
left,  530 
right,  .529 

openings  in,  .529 
sinus  of,  .529 
ventricuH  of  ox,  393 
Auditory  canal,  external,  747, 
748 
meatus,  external,  56,  748 

internal,  56,  7.59 
nerve,  686 
ossicles,  7.54 

process,  external,  56,  67 
tube,  7.55 
Auricle  of  horse,  747 
Auricular  artery,  anterior,  550 
of  dog,  635 
of  pig,  627 
posterior,  .5.50 
of  ox,  611 
I'jranch  of  vagus,  687 
cartilage,  748 
lympli  gland  of  dog,  643 
muscles,  749 
of  dog,  780 
of  ox,  774 
nerve,  685 

posterior,  695 
vein,  588 
Auriculopalpebral  nerve,  685 
of  dog,  729 
of  ox,  717 
Axillary  artery.  556 

ligament  of  Helniholtz,  755 

lymph  glands,  605 

of  dog,  643 

of  ox,  625 

of  pig,  631 

nerve  of  horse,  697 

Axis,  34 

development  of,  3.5 
lentis,  747 
of  dog,  1.50 
of  ox,  112 
of  pelvis,  97 
of  ox,  133 
of  pig,  137 
optic,  740 
Azygos  uvula',  muscle  of,  333 


Back,  fascia-  of,  235 
superficial,  235 
muscles  of,  235 
of  dog,  muscles  of,  .325 
of  ox,  muscles  of,  300 


INDEX 


787 


Back  of  pig,  muscles  of,  313 
Ball-and-socket  joint,  172 
Bands,  longitudinal,  of  c;pcum, 
364 
muscular,  of  great  colon,  368 
Bars  of  hoof,  764 
Bartholin's  ducts  of  mare,  515 

glands  of  cow,  519 
Basi-cornual  articulation,   180 
Basihyoid  bone,  64 
Basilar  artery,  546 
plexus,  592 

venous,  592 
process,  48 

of  third  phalanx,  91 
Basis  pedunculi.  6154 
Belly  of  muscle,  212 
Biceps  brachii,  259 
of  dog,  322 
of  pig,  314 
femoris  muscle,  278 
of  dog,  326 
of  ox,  306 
of  pig,  316 
rotator  tibiaUs,  280 
of  ox,  302 
Bicipital  artery  of  dog,  635 
bursa  of  horse,  259 
groove  of  humerus,  79 
tuberosity  of  radius,  81 
of  scapula,  77 
Bicuspid  valve,  533 
Bifurcation  of  trachea,  449 
Bile-duct,  common,  of  sheep, 
410 
of  dog,  431 
of  ox,  398 
of  pig,  419,  422 
Bipennate  muscle,  212 
Biventer    cervicis    muscle    of 

dog,  325 
Bladder,  469,  475 
arteries  of,  477 
blood-supply  of,  477 
fixation  of,  476 
lateral  ligaments  of,  476 
lymph  vessels  of,  477 
middle  ligament  of,  476 
mucous  coat  of,  476 
muscular  coat  of,  476 
neck  of,  416 
nerves  of,  477 
of  dog,  484 
of  ox,  480 
of  pig,  483 
relations  of,  476 
round  ligament  of,  476 
serous  coat  of,  476 
sphincter  of,  476 
structure  of,  476 
trigoniim  of,  476 
veins  of,  477 
vertex  of,  476 
Blind  sacs  of  rumen  of  ox,  392 
Blood-vascular    system,    524, 
525 
of  dog,  632 
of  ox,  608 
Blood-vessels,  524 

of  cornea,  742 

Body,  ciliary,  743 

geniculate,  665 

of  dog,  725 

of  ox,  716 


Body,  mammillary,  665 

of  dog,  726 
pineal,  665 

of  ox,  716 
pituitary,  664,  665 

of  dog,  726 

of  ox,  716 
restiform,  656 
vitreous,  746 

of  ox,  774 
Bone  or  bones,  acetabulum,  of 

pig,  148 
acromion,  of  dog,  162 
air-spaces,  21 
arteries,  21 
atlas,  33 

of  dog,  150 

of  ox,  112 

of  pig,  137 
axis,  34 

of  dog,  150 

of  ox,  112 

of  pig,  137 
basihyoid,  64 
carpal,  28,  83 

of  dog,  164 

of  ox,  129 

of  pig,  147 
cartilage,  22 
ca\'ities,  23 

chemical  composition,  23 
chevron,  of  dog,  152 
clavicle,  27 

of  dog,  162 
compact  substance,  20 
coracoid,  27 
cranial,  27,  47 

of  dog,  154 

of  ox,  115 

of  pig,  139 
depressions,  23 
descriptive  terms,  23 
development  and  growth,  22 
digital,  28,  30 
diploe,  21 
eminences,  23 
ethmoid,  52 

of  dog,  157 

of  ox,  116 

of  pig,  142 
facial,  27,  57 

of  dog,  157 

of  ox,  120 

of  pig,  142 
femur,  29,  97 

of  dog,  167 

of  ox,  133 

of  pig,  148 
fibula,  29,  104 

of  dog,  168 

of  ox,  134 

of  pig,  149 
flat,  19 
frontal,  55 

of  dog,  155 

of  ox,  118 

of  pig,  141 
hock,  105 

of  ox,  134 

of  pig,  149 
humerus,  28,  77 

of  dog,  162 

of  ox,  127 

of  pig,  146 


Bone,  hvoid,  64 

of  (log,  1.59 

of  ox,  122 

of  pig,  144 
ilium,  29,  93 

of  dog,  165 

of  ox,  131 

of  pig,  148 
interparietal,  53 

of  dog,  155 

of  ox,  116 

of  pig,  140 
irregular,  19 
ischium,  29,  95 

of  dog,  165 

of  ox,  131 

of  pig,  148 
lacrimal,  61 

of  dog,  158 

of  ox,  121 

of  pig,  143 
long,  19 

lymph-vessels,  21 
malar,  62 

of  dog,  158 

of  ox,  121 

of  pig,  143 
mandible,  63 

of  dog,  158 

of  ox,  122 

of  pig,  143 
marrow,  21 
maxilla,  58 

of  dog,  157 

of  ox,  120 

of  pig,  142 
medullary  arteries,  21 

cavity,  20 
membrane,  22 
metacarpal,  28,  87 

of  dog,  164 

of  ox,  130 

of  pig,  147 
metatarsal,  30,  110 

of  dog,  168 

of  ox,  135 

of  pig,  149 
nasal,  61 

of  dog,  158 

of  ox,  121 

of  pig,  143 
navicular,  92,  111 
nerves,  21 
number,  19 
occipital,  47 

of  dog,  154 

of  ox,  115 

of  pig,  139 
of  arm,  28 
of  face,  27 
of  forearm,  28 
of  forefoot,  28 
of  hand,  28 
of  leg,  29 

of  pelvic  limb,  29,  92 

of  dog,  165 

of  ox,  131 

of  pig,  148 

of  skull,  27,  47 

of  dog,  153 

of  ox,  115 

of  pig,  139 
of  thoracic  Umb,  27,  74 
of  dog,  162 


788 


Bones,  of  thoracic  limb  of  ox, 
127 
of  pig,  146 
of  thorax,  27,  47 
of  dog,  153 
of  ox,  115 
of  pig,  139 
OS  coxa?,  29,  92 

of  pig,  148 
palatine,  60 
of  ox,  120 
of  pig,  142 
parietal,  54 
of  ilog,  155 
of  ox,  117 
of  Dig,  140 
patella,  29,  104 
of  dog,  168 
of  ox,  134 
of  pig,  149 
pelvic,  93 
of  dog,  167 
of  ox,  132 
of  pig,  148 
perforations,  23 
periosteal  arteries,  21 
periosteum,  21 
pliacoid,  of  cat,  164 
phalanges,  29,  89,  HI 
of  dog,  165 
of  ox,  130,  136 
of  pig,  148,  150 
physical  properties,  23 
premaxilla,  59 
of  dog,  157 
of  ox,  120 
of  pig,  142 
prenasal,  of  pig,  143 
prominences,  23 
pterygoid,  60 
of  dog,  158 
of  ox,  121 
of  pig,  143 
pubic,  29,  95 
of  dog,  167 
of  ox,  131 
of  pig,  148 
radius,  25,  80 
of  dog,  163 
of  ox,  127 
of  pig,  147 
red  marrow,  21 
ribs,  25,  43 
of  dog,  153 
of  ox,  114 
of  pig,  138 
rostri,  of  pig,  143 
sacrum,  39 
of  dog,  151 
of  ox,  114 
of  pig,  138 
scapula,  27,  74 
of  dog,  162 
of  ox,  127 
of  pig,  146 
sesamoid,  29,  92,  111 

developing  in  tendon  tis- 
sue, 211 
distal,  29 
of  dog,  165 
of  ox,  131,  136 
of  pig,  148 
proximal,  29 
short,  19 


Bone,  sinuses,  21 
sphenoid,  50 
of  dog,  156 
of  ox,  115 
of  pig,  141 
spongy  substance,  20,  21 
sternum,  26,  45 
of  dog,  153 
of  ox,  115 
of  pig,  139 
structure  of,  20 
tarsal,  29,  105 
of  dog,  168 
of  ox,  134 
of  pig,  149 
temporal,  55 
of  dog,  156 
of  ox,  120 
of  pig,  141 
thigh,  29 
thorax,  47 
of  dog,  153 
of  ox,  115 
of  pig,  139 
tibia,  29,  100 
of  dog,  167 
of  ox,  134 
of  pig,  149 
tibial,  29 
tissue,  20 
tubula  vitrea,  21 
turbinal,  62,  438 
of  dog,  158 
of  ox,  122 
of  pig,  143,  465 
ulna,  28,  82 
of  dog,  163 
of  ox,  128 
of  pig,  147 
veins,  21 
vertebra;,  24,  31 
anticlinal,  42 
caudal,  24 
cervical,  24 
coccygeal,  24,  41 
diaphragmatic,  42 
knnbar,  24,  38 
of  dog,  150 
of  ox,  112 
of  pig,  136 
sacral,  24 
thoracic,  24,  35 
vessels,  21 
vomer,  63 
of  dog,  1.58 
of  ox,  122 
of  pig,  143 
yellow  marrow,  21 
zygomatic,  of  horse,  62 
Brachia  conjunctiva,  661 
Brachial  artery,  538,  556 
deep,  5.59 
of  dog,  633,  635 
of  ox,  609,  612 
of  pig,  627 
plexus,  696 
of  dog,  730 
of  ox,  717 
of  pig,  723 
triceps,  260 
vein,  593 
of  dog,  642 
Brachialis  anticus,  260 
muscle,  260 


Brachialis  muscle  of  dog,  322 

of  pig,  315 
Brachiocephalic  artery,  538 
of  dog,  633 
of  pig,  627 
trunk  of  aorta,  537 
veins  of  dog,  641 
Brachio-radialis  muscle  of  dog, 

322 
Brachium  pontis,  659 
Brachycephalic  breed  of  dogs, 

159 
Brain,  development  of,  655 
of  dog,  724 
of  horse,  652 
of  ox,  715 
of  pig,  720 
veins  of,  .592 
Bristles  of  pig,  778 
Broad  ligaments  of  uterus,  356 
of  bitch,  .523 
of  cow,  518 
of  mare,  513 
Broca's  parolfactory  area,  671 
Bronchi,  interlobular,  457 
of  dog,  468 
of  horse,  450,  456 

structure  of,  456 
of  ox,  460 
of  pig,  466 
Bronchial  artery,  457,  565 
of  ox,  614 
of  pig,  627 
branches  of  lungs,  456 

of  vagus,  690 
lymph  glands,  457,  603 
of  dog,  643 
of  pig,  631 
vein,  587 
Bronchioles,  lobular,  457 

respiratory,  457 
Broncho-oesophageal    artery, 

565 
Brush  of  ox,  775 
Buccal  fascia,  213 
glands,  332 
of  ox,  383 
of  pig,  410 
nerve,  685 
of  dog,  729 
of  ox,  717 
of  pig,  722 
Buccinator  artery,  555 
of  pig,  627 
muscle,  216 
of  dog,  318 
of  ox,  295 
nerve  of  horse,  681 
vein,  .590 
of  pig,  630 
Bulb  of  hair,  763 
olfactory,  671 
of  dog,  727 
of  ox,  717 
of  pig,  721 
Bulbar  conjunctiva,  736 

fascia  of  horse,  738 
Bulbi  vestibuli  of  mare,  515 

olfactorius,  671 
Bulbo-cavernosus    muscle    of 
penis  of  ox,  .503 
of  urethra  of  horse,  499 
Bulbo-urethral  glands  of  dog, 
506 


789 


Bulbo  -  urethral      glands      of 
horse,  VXi 
structure  of,  49-i 
of  ox,  503 
of  pig,  505 
Bulbus  aortse,  536 

oculi,  739 
Bulla,  lacrimal,  of  ox,  121 

ossea,  57 
Burdach's  column,  1552 
Bursa,  bicipital,  259 
na\'icular,    of    deep    digital 

flexor  muscle,  272 
of    biceps    femoris    muscle, 

279,  280 
of    flexor    pedis    perforatus 

muscle,  293 
of  gastrocn('niiu>  nuiscle,  290 
of  rectus  fen inri>  n nitric,  284 
of    semiteniliiiDsus    muscle, 

280 
ovarica  of  mare,  511 
ovarii  of  bitch,  522 
podotroclilearis,  272 
supra-atloid,  174 
supra-spinous,  of  horse,  175 
of  anterior  digital  exten- 
sor muscle,  265 
synovial,    of    infraspinatus 
muscle,  256 
of  lateral  digital  extensor 

muscle,  266 
of  teres  minor  muscle,  257 
Bursal     synovial     membrane, 
211 


Cecal  artery,  570 

lymph  glands  of  pig,  632 
Cseco-colic  fold,  367 

orifice,  364 
Ca'cum,  363 

of  dog,  431 

of  ox,  398 

of  pig,  420 

of  sheep,  409 

cupulare,  760 

vestibulare,  760 
Caleaneo-cuboid       ligaments, 

202 
Calcaneo-cunean      ligaments, 

202 
Calcaneo-metatarsal  ligament, 

201 
Calcaneo-scaphoid      ligament, 

202 
Caliber  of  great  colon  of  horse, 

367 
Callosal  sulcus,  669 
C'allosomarginal  fissure,  660 
of  dog,  727 
of  ox,  716 
of  pig,  721 
Calyces  majores,  480 

minoras,  480 
Camera  oculi,  746 
Canal,  alar,  51 

auditory,  external,  748 

carotid,  156 

carpal,  86 

cervical,  of  cow,  518 
of  mare,  512 

condyloid,  of  ox,  115 

dental,  inferior,  of  horse,  64 


Canal,     dental,     superior,     of 
horse,  59 
facial,  of  horse,  56 
femoral,  of  horse,  282 
for    naso-lacrimal    duct    of 

horse,  71 
infraorbital,  of  horse,  59 
inguinal,  of  horse,  249 
lacrimal,  osseous,  of  horse, 

61 
mandibular,  of  horse,  64 
medullary,  of  metacarpus  of 

ox,  130 
naso-palatine,  of  ox,  384 
of  Gartner,  519 
of  tarsus  of  horse,  109 
of  temporal  l)one  of  dog,  156 
palatine,  of  horse,  58 
parieto-temporal,    of   horse, 

54,  57 
petro-basilar,  of  dog,  156 
pterygoid,  of  horse,  51,  61 
sacral,  of  horse,  41 
semicircular,     membranous, 
760 
osseous,  758 
semilunar,  91 
spiral,  of  cochlea,  759 
subsphenoidal,  of  horse,  51 
supraorbital,  of  ox,  119 
vertebral,  of  horse,  42 
Vidian,  of  horse,  51,  61 
Canalis  centralis,  650 
Canine  teeth,  338,  341,  346 
of  dog,  425 
of  ox,  386 
of  pig,  412 
Canthi  of  eye,  735 
Capillaries,  524 
Capped  hock,  293 
Capsular  ligament,  170 
Capsularis     muscle     of     dog, 
328 
of  horse,  258,  286 
of  ox,  307 
of  pig,  314,  317^ 
Capsule,  external,  675 
fibrous,  of  liver,  376 
internal,  676 
joint,  170 

of  horse,  174 
of  articulation.  176 
of  carpal  joints,  183 
of  coffin  joint,  189 
of  elbow  joint,  181 
of  femoro-patellar  articula- 
tion, 194 
of     femoro-tibial     articula- 
tion, 197 
of  fetlock  joint,  185 
of  hip  joint,  192 
of  hock  joint,  200 
of  lens,  747 
of  pastern  joint,  188 
of    sacro-iliac    articulation, 

190 
of  shoulder  joint,  180 
of   temporo-mandibular   ar- 
ticulation, 179 
of  tenon,  738 
of  tibio-fibular  articulation, 

199 
splenic,  379 
Caput  laterale  tricipitis,  261 


Caput  longum  tricipitis,  261 

medialc  tricipitis,  261 
Cartliac    bronchus    of    \agus, 
690 
glands  of  stomach  of  liorse, 

360 
impression  of  lungs  of  horse, 

454 
lobe  of  lungs  of  ox,  463 
muscle,  211 
nerves,  712 

notch  of  lungs  of  horse,  456 
plexus,  712 

sphincter  of  horse,  3.59 
veins,  586 
Cariniform  cartilage,  46 
Carnassial  teeth  of  dog,  426 
Carotid  artery,  common,  541 
h'ft,  543 
of  dog,  634 
of  ox,  610 
right,  542 
external,  547 
internal,  546 
of  dog,  633,  634 
of  ox,  611 
of  pig,  627 
canal  of  dog,  1.56 
foramen  of  dog,  156 
notch  of  horse,  51 
plexus,  711 
Carpal     articular    surface    of 
radius  of  horse,  82 
bones,  28 

accessory,  84 
canal  of  horse,  86 
fascia  of  horse,  263 
glands,  778 
groove  of  horse,  86 
joints  of  dog,  205 
of  horse,  183 
of  ox,  205 
of  pig,  205 
pads  of  dog,  780 
sheath  of  deep  digital  flexor 
muscle,  272 
of  superficial  digital  flexor 
muscle,  271 
Carpo  -  metacarpal     joint     of 
horse,  183 
sac  of  horse,  183 
Carpus,  28 
of  dog,  164 
of  horse,  83 

development  of,  86 
of  ox,  129 
of  pig,  147 
Cartilage,  or  cartilages,  alar,  of 
horse,  437 
of  ox,  459 
annular,  of  cow,  74S 
articular,  170 
arytenoid,  of  larynx,  443 
of  dog,  467 
of  ox,  459 
of  pig,  465 
auricular,  748 
bones,  22 
cariniform,  46 
conchal,  748 
costal,  25,  26 
of  horse,  45 
cricoid,  of  dog,  467 
of  horse,  441 


790 


Cartilage,  cricoid,  of  ox,  459 

of  pig,  4(j5 
eiisiform,  of  liorsc,  46 
epiglottic',  of  dog,  467 

of  horse,  442 

of  ox,  459_ 

of  pis,  465 
epipliyseal,  22 
iiitcnirytonoid,  of  dog,  467 

of  pig,  465 
liitcnil,  of  third  phalanx  of 

liorsp,  1)1 
marginal,  171 
of  larynx  of  horse,  441 
of   nasal   septum   of   horse, 

437 
of  nost  rils  of  ox,  459 
parietal,  of  nasal  cavity   of 

horse,  437 
scapular,  of  horse,  75 
scutiform,  74S 
semilunar,  of  horse,  196 
thyroid,  of  dog,  467 

of  horse,  442 

of  ox,  459 

of  pig,  465 
xiphoid,  26 

of  horse,  46 
Cartilagines       tracheales      of 

horse,  450 
Caruncle,  lacrimal,  735 
Caruncula  lacrimalis,  735 

of  dog,  779 

of  pig,  778 
sublingualis  of  horse,  334 
Cauda  equina  of  horse,  648 
Caudate   ligament    of    horse, 

375 
lobe  of  liver,  433 

of  ox,  402 

of  pig,  421 
nucleus,  675 
Cavernous  plexus,  711 

sinus,  542 
Cavity,  abdominal,  of  ox,  390 
cranial,  of  dog,  161 

of  horse,  69 

of  ox,  124 

of  pig,  145 
gleiioitl,  of  horse,  67,  68,  76 
joint,  170 
nasal,  of  dog,  161,  466,  467 

of  horse,  71,  436 

of  ox,  125,  458 

of  pig,  145,  464 
of  abomasum  of  ox,  396 
of  larynx  of  horse,  447 
of  riiouth  of  horse,  330 
of  onuusum  of  ox,  395 
of  rumen  of  ox,  393 
of  tunica  vaginalis  of  horse, 

490 
of  uterus  of  mare,  513 
pelvic,  of  horse,  97 

of  ox,  133,  390 
sigmoid,  of  ulna  of  horse,  82 
thoracic,  of  horse,  450- 

of  ox,  461 

Cavura  concha;  of  dog,  780 

epidurale,  646 

subdurale,  646 

tympani,  752 

of  dog,  780 

of  ox,  775 


Cavum  tjmpani  of  pig,  778 
Cells,  air,  of  lungs  of  horse,  457 
ethmoidal,  of  horse,  52 
gustatory,  772 
Cement  of  "teeth,  339 
Center,     tendinous,     of     dia- 
phragm of  horse,  243 
Central  artery  of  retina,  554 
canal  of  cord,  650 
tarsal  bone  of  horse,  107 
of  ox,  134 
Cephalic  artery,  541 
index  of  dog,  159 
part  of  sympathetic  system, 

711 
vein,  591,  593 
of  dog,  642 
of  ox,  622 
Cerebellar  peduncles,  661 
middle,  659 
tract,  direct,  661 
veins,  592 
Cerebello-olivary      fasciculus, 

658 
Cerebellospinal  fasciculus,  661 
Cerebellum  of  dog,  725 
of  horse,  660 
of  ox,  716 
of  pig,  720 
Cerebral  arteries,  546 
posterior,  546 
fissures  of  horse,  668 

of  ox,  716 
gyri  of  horse,  668 
hemispheres,  667 
of  dog,  726 
of  ox,  716 
of  pig,  721 
nerves  of  horse,  676 
peduncles,  664 
of  ox,  716 
of  pig,  720 
vein,  588,  592 
of  ox,  621 
Cerebrospinal  artery,  545 
of  dog,  634 
fasciculi,  660 
Ceruminous  glands,  749 
Cervical  artery,  deep,  540 
inferior,  541 
of  dog,  633 
of  ox,  609 
of  pig,  627 
superior,  540 
branch  of  facial  nerve,  685 
canal  of  cow,  518 

of  mare,  513 
enlargement  of  horse,  648 
ganglia,  711 
of  dog,  733 
of  ox,  720 
of  pig,  724 
Ivniph  glands,  601 
of  dog,  643 
of  pig,  631 
nerves  of  horse,  694 
part  of  sympathetic  nervous 

system,  711 

plexus,  694 

vein,  deep,  586 

inferior,  591 

vertebra;,  24 

of  (log,  1.50 

of  horse,  32 


Cervical  vertebrte  of  ox,  112 

of  pig,  136 
Cervicahs    ascendens    muscle, 

225 
CerV'ico-auricularis,  750 
of  dog,  780 
of  ox,  784 
Cervico-scutularis,  749 
of  dog,  780 
of  ox,  774 
Cervix  uteri  of  cow,  517 
of  mare,  513 
of  sow,  522 
Chambers  of  eye,  746 
Check    ligament,    inferior,    of 
carpal  joints,  183 
of     deep     digital     flexor 

muscle,  272 
of  hock  joint,  200 
superior,     of     superficial 
digital     flexor     muscle, 
270 
Cheek  teeth,  338,  342 

deciduous,  of  horse,  346 
of  dog,  425 
of  ox,  386 
of  pig,  412 
of  sheep,  405 
Cheeks  of  dog,  423 
of  horse,  332 

muscles  of,  213 
of  ox,  382 
of  pig,  410 
of  sheep,  405 
Chestnut,  771 
Chevron  bones  of  dog,  152 
Chiasma  opticum,  666 
Choana^,  posterior,  of  horse,  68 
Chondro  -  pharyngeus  muscle 

of  horse,  350 
Chondro-sternal    articulations 

of  horse,  178 
Chorda  tympani,  683,  684 
Chorda"  tendineie,  531,  533 
Chorioid,  742 
fissure,  670 
of  dog,  779 
of  pig,  778 

plexus   of   fourth   ventricle, 
657,  663 
of  lateral  ventricle,   670, 

675 
of  third  ventricle,  666 
Cilia,  735 

Ciliary  arteries,  554 
body,  743 
border  of  iris,  744 
ganglion,  679,  711 

of  ox,  717 
muscle,  743 
nerve  of  dog,  728 

of  horse,  679 
processes,  743 
ring,  743 
Circle,  coronary,  564 

of  Willis,  .546 
Circulation,  fa?tal,  606 

pulmonary,  607 
Circulatory  system  of  dog,  632 
of  ox,  608 
of  pig,  626 
Circulus  arteriosus  major,  744 
Circumanal  glands  of  dog,  432 
Circumduction  of  joints,  171 


791 


Circumflex    artery,    anterior, 
558 
external,  577 
of  ox,  019 
of  coronary  cushion,  564 
of  dog,  635 
of  ox,  612 
of  scapula,  556 
posterior,  556 
iliac  artery,  578 
nerve  of  horse,  697 
vein,  external.  598 
Cistern,  milk,  of  cow,  521 
Cisterna  chyli,  600 

of  dog,  643 
Cisternse  suharachnoidales,  6-46 
Clarke's  column,  651 
Claustrum,  675 
Clavicle,  27 

of  dog,  102 
Claws  of  dog,  781 
of  ox,  775 
of  pig,  779 
Cleft,   palatine,   of  horse,   60, 
69,  71 
\'ulvar,  of  mare,  514 
Cleido-cervicaiis     muscle     of 

dog,  320 
Cleido-mastoideus    muscle    of 
dog,  320 
of  horse,  252 
of  pig,  314 
Cleido-occipitalis     muscle     of 

pig,  314 
Cleido-transversarius     muscle 

of  horse,  252 
Clinoid   process    of   sphenoid 
bone  of  dog,  156 
of  pig,  142 
Clitoris,  artery  of,  575 
of  bitch,  52"3 
of  cow,  glans  of,  519 
of  mare,  515 

prepuce  of,  515 
of  sow,  522 
Coccygeal  artery,  lateral,  577 
middle,  575 
of  dog,  641 
of  ox,  618 
fascia  of  horse,  238 
gangUon,  713 
nerves  of  horse,  710 
vertebrae,  24 
of  dog,  152 
of  horse,  41 
of  ox,  114 
of  pig,  138 
Coccygeus  muscle  of  dog,  325 
of  horse,  238 
ventraUs  lateralis  muscle  of 
horse,  240 
Cochlea,  759 
of  dog,  780 
Cochlear  nerve,  686,  761 
Ca'liac  arterv,  566 
of  dog,  638 
of  ox,  614 
of  pig,  627 
Ij'mph  gland  of  ox,  626 
plexus,  714 
CceUaco-mesenteric      ganglia, 

714 
Coffin  bone  of  horse,  90 
joint,  189 


Cofliin  joint,  capsule  of,  189 
lateral  hgaments  of,  189 
movements  of,  190 
Colic  arteries,  570 

lymph  glands  of  pig,  632 
mesentery  of  horse,  354,  369 
Collateral  fissure  of  dog,  726 

vessel,  524 
Colliculus  facialis,  662 
seminahs  of  horse,  499 
of  ox,  504 
Colon,  great,  of  horse,  365 
of  dog,  432 
of  ox,  398 
of  pig,  420 
of  sheep,  409 
small,  of  horse,  369 
tsni;p  of,  370 
Column  of  Burclach,  652 
of  GoU,  652 
of  spinal  cord,  651 
renal,  of  horse,  473 
Columna  grisea  of  cord,  650 
Columnar  fornieis,  673 
Comma-shaped  tract,  652 
Commissura  grisea,  650 

hypothalamiea,  665 
Commissure,        hippocampal, 
670 
of  nostrils  of  horse,  436 
of  spinal  cord,  650 
of  vulva  of  mare,  515 
optic,  666 
Common   bile-duct   of   sheep, 

410 
Communicating    artery,    pos- 
terior, 546 
Compact   substance  of   bone, 

20 
Complexus  muscle  of  dog,  325 
of  horse,  231 
of  pig,  312 
Compressor  coccvgis  muscle  of 

horse,  238 
Concha  of  pig,  778 
Conchal  cartilage,  748 
Condyle,  external,  of  humerus 
of  horse,  80 
internal,     of     humerus     of 

horse,  79 
occipital,  of  horse,  48,  68,  69 
of  femur  of  horse,  99 
of  mandible  of  liorse,  64 
of  temporal  bone  of  horse, 

55 
of  tibia  of  horse,  101 
Condyloid  artery,  545 
of  dog,  634 
of  ox,  611 
canal  of  ox,  115 
fossa  of  horse,  48,  68 
vein,  588 
Conjugal    Ugament   of   horse, 

177 
Conjugate  diameter  of  pehns 
of  horse,  97 
of  ox,  132 
Conjunctiva,  736 

of  ox,  772 
Conjunctival  sac,  736 
Constrictor  vestibuli  muscle  of 
mare,  515 
vuh'se  of  mare,  515 
Conus  arteriosus  of  horse,  530 


Conus  medullaris  of  horse,  648, 
649 
vasculosus  of  epididymis  of 
horse,  487 
Coraco-brachialis    muscle    of 
dog,  322 
of  horse,  258 
of  ox,  302 
of  pig,  314 
Coracoid,  27 

process  of  horse,  77 
Coraco-radialis      muscle      of 

horse,  259 
Cord,  spinal,  of  dog,  724 
of  horse,  648 
of  ox,  715 
of  pig,  720 
Cores,  horn-,  of  ox,  118 
Corium,  762 
of  dog,  780 
Cornea  of  dog,  779 
of  horse,  741 
of  ox,  774 
of  pig,  778 
Cornu  ammonis,  669 

anterior,     of     thyroid     car- 
tilage of  horse,  442 
of  nostrils  of  horse,  437 
posterior,    of    thyroid    car- 
tilage of  horse,  442 
Cornua,  great,  of  horse,  65 
middle,  of  horse,  65 
small,  of  horse,  65 
thyroid,  of  horse,  65 
uteri  of  cow,  517 
of  mare,  511 
Corona    glandis  of    penis    of 
horse,  495 
radiata,  676 
Coronal  border  of  hoof,  765 
fissure  of  dog,  726 
of  ox,  716 
of  pig,  721 
Coronarv  arteries,  535,  537 
of  dog,  632 
of  ox,  609 
circle,  564 

groove  of  heart,  527 
of  hoof,  765 
of  rumen  of  ox,  392 
ligament  of  horse,  374 
matrix,  769 

pillars  of  rumen  of  ox,  393 
plexus,  595 
sinus,  585 

of  horse,  opening  of,  529 
veins,  535,  586 
Coronoid  fossa  of  humerus  of 
horse,  80 
process  of  mandible  of  horse, 
64 
of  radius  of  horse,  80 
Corpora  quadrigemina,  663 

of  dog,  725 
Corpus  adiposum  of  eye,  738 
albicans  of  mare,  510 
callosum,  672 

of  ox,  716 
cavernosum  penis  of  horse, 

495 
fornieis,  673 

geniculatum  mediale,  665 
luteura  of  mare,  510 
Luvsi,  665 


792 


INDEX 


Corpus   mctUillarc   of   cprchcl- 
luin,  661 
|):i|)ill:ir(',  762 
Mihniin  of  maif,  .510 
s|)()iitjii)suin  of  horse,  495 
striatiiin,  675 
irapi'zoideum,  655 
of  .loK,  725 
of  ox,  715 
of  pig,  720 
vitreuin,  746 
Corpuscles,     Malpighian,     of 
horse,  379,  473 
renal,  of  horse,  473,  474 
Corrugator    superoilii    muscle 

of  horse,  2 IS 
Cortex    of    thymus    gland    of 

horse,  45S 
Corticopontile  fibers,  (MiO 
Costal  arcli,  23 
<-urtiIag<'s,  25,  26 

(if  hurse.  45 
facets  (if  tlioracic  vertelira', 

36,  37 
groove,  26 
pleura  of  horse,  451 
Costo-centnil  articulations  of 

horse,  177 
Costo-eiiondral      articulations 

of  horse,  178 
Costo-sternal  ligament,   supe- 
rior, of  horse,  178 
Costo-transverse  articulations 

of  horse,  177 
Costo-\ertebral     articulations 

of  horse,  177 
Cotyledons,   uterine,    of   cow, 

518 
Cotyloid    ligament    of    horse, 

192 
Cowper's  glands  of  horse,  493, 
506 
of  ox,  503 
of  pig,  505 
Coxal  angle  of  ilium  of  horse, 

94 
Cranial  bones,  27 
of  dog,  154 
of  horse,  47 
of  ox,  115 
of  pig,  1.39 
cavity  of  dog,  161 
of  horse,  69 
of  ox,  124 
of  pig,  145 
nerves  of  clog,  728 
of  horse,  676 
of  ox,  717 
of  pig,  722 
roots  of,  6.56 

superKcial  origins  of,  653 
region  of  lior.se,  67,  68 
sutures  of  horse,  179 
Cranio-faoial  index  of  dog,  1,59 
CreiTiaster,  external,  of  horse, 
249,  490 
of  ox,  .500 
of  pig,  313 

of  testicle  of  pig,  504 
Creiniusteric  artery,  578 
Crest,  facial,  of  horse,  58,  62, 
68 
frontal,  of  horse.  55,  66 
na.sal,  of  horse,  71 


Crest,   occipital,  of  horse,  .50, 
69 
of  fcmiu-  of  horse,  99 
of  ilium  of  horse,  94 
of  sacrum  of  ox,  114 
parietal,  of  ox,  117 
petrosal  of  horse,  57,  70 
pterygoid,  of  horse,  51 
renal,  of  liorse,  473 
sagittal,  of  horse,  54,  6(i 
seniihinar,  of  third  phalanx 

of  horse,  91 
splicno-occipital,    of    horse, 

51 
sublingual,  of  horse,  348 
suiiracondyloid,  of  femur  of 

liorse,  97 
tiliial,  of  horse,  100 
turbinal,  inferior,  of  horse, 
58 
superior,    of   nasal   bones 
of  horse,  61 
urethral,  of  male  horse,  499 
zygomatic,  of  horse,  58,  62 
Cribriform   plate   of   ethmoid 

of  horse,  52 
Crico-arvtenoid        joints        of 

hor.se, '444 
Crico-arytcnoideus        lateralis 

muscle  of  horse,  445,  446 
Cricoid  cartilage  of  dog,  467 
of  horse,  441 
of  ox,  4.59 
of  pig,  465 
Crico-pharyngeus    muscle    of 

horse,  350 
Crico-thyroid  joints  of  liorse, 
444 
membrane  of  liorse,  444 
Crico-thyroi(^leus     muscle     of 

horse,  445 
Crico-tracheal    membrane    of 

horse,  445 
Crista  galli  of  horse,  52,  70 
terminales  of  horse,  530 
vestibuli,  7.58 
Cristas  a('ustica>,  760 

unguhe,  765 
Crown  of  tooth,  339 
Crucial  fissure  of  ox,  717 
ligaments    of    femoro-tibial 
articulation  of  hor.se,  198 
Cruciate  fissure  of  dog,  727 

of  pig,  721 
Crura  cerebri,  664 
fornicis,  673 
helicis,  74S 

of  dog.  779 
of  diaphragm  of  hor.sc,  243 
Crural  fascia  of  hor,se,  274 
nerve,  anterior,  of  horse,  706 
triceps  muscle  of  horse,  284 
Crureus  muscle  of  horse,  286 
Crystalline  lens,  746 
Cubital  Ivniph  glands,  606 

of  dog,  t;43 
Cuboido-cunean   ligaments  of 

horse,  202 
Cuboido-seaplioid  ligament  of 

horse,  202 
Cuneate  tubercle  of  pig,  720 
Cuneiform  cartilage  of  larynx 

of  dog,  467 
Cupola,  759 


Curvator   coccygis   muscle   of 

liorse,  239 
Cushion  of  hoof,  769 

plantar,  771 
Cutaneous  glands  of  ox,  775 

nerve  of  leg  of  horse,  70S 
of  neck,  695 
Cutaneus      maximus      muscle 
of  abdomen.  245 

scapula'   et    humeri    muscle, 

Cuticular    ridge    of    stomach, 

360 
Cystic  duct  of  ox.  403 


Dartos  of  scrotuni  of  horse, 

488 
Deciduous  canine  teeth,  .346 
cheek  teeth,  346 
incisor  teeth,  .346 

of  ox,  386 
teeth,  346 
Decusisalio  lemniscorum.  6.58 
Deeus.saliciii  of  fillet,  6.5S 
of  iiyramids,  655 
of     superior      peduncle     of 

cerebellum,  661 
pyramidal,  6.5s 
Deep  abdominal  fascia,  245 
digital  flexor  muscle,  271 
of  dog,  323,  329 
of  leg,  293 
of  ox,  305 
of  pig,  316,  317 
fascia,  212 

of  forearm.  262 
of  head  of  liorse,  213 
of  neck  of  horse,  224 
of  shoulder  of  horse,  255 
fle.xor  imiscle  of  ox,  311 
gluteus  muscle,  278 
pectoral  muscle,  253   254 
of  dog,  320 
of  ox,  302 
of  pig,  314 
se,samoidean  ligament,  188 
Deferential    fold    of    testicles, 

491 
Deltoid  muscle,  255 
of  dog,  320 
of  ox,  302 
of  pig,  314 
tuberosity  of  horse,  78 
Dental  artery,  552 
superior,  555 
canal,  inferior,  64 

superior,  .59 
nerve,  6S1,  682 
plate  of  ox,  384 
vein,  587 
Dentine,  339 

Depressor  coccygis  muscle,  240 
labii  inferioris  muscle,  216 
of  dog,  318 
of  ox,  295 
of  pig.  311 
superioris    muscle    of    ox, 
295 
nerve  of  dog,  730 
rostri  muscle  of  pig,  311 
Descemet,  membrane  of,  742 
Descent  of  testicles,  490 
Descriptive  terms,  18 


793 


Diagonal  fissure  of  ox,  716 

of  pig,  721 
Diameter,  conjugate,  of  pelvis, 
97 
of  ox.  132 
sacro-pubic,  of  pelvis,  97 
transverse,  of  pelvis,  97 
Diaphragm  of  dog,  325 
of  horse,  243 
of  ox,  300 
of  pig,  313 
Diapliragma  sellir,  6-16 
Diaphragmatic  flexure,  366 
lobe  of  lung  of  ox,  463 
pleura,  451 
vertebra,  42 
Diarthroses,  170 
Diencephalon,  664 
Digastric  muscles,  213 

ner\-e,  6S5 
Digastricus  muscle,  222 
of  dog,  319 
of  ox,  297 
of  pig,  311 
Digestive  svstem,  330 
of  dog,"  423 
of  ox,  3S2 
of  pig,  410 
of  sheep,  405 
Digit  or  digits,  2S 
of  dog,  165,  780 

extensor  muscles  of,  322, 
328 
of  horse,  fascia  of,  263 

muscles  of,  295 
of  ox,  130,  775 
of  pig,  muscles  of,  315 
Digital  artery,  564 
common,  563 

of  ox,  620 
external,  of  ox,  614,  920 
of  dog,  641,  637 
of  pig,  629,  630 
volar,  of  ox,  614 
bones,  28,  30 
cushion,  771 

extensor  muscle,  anterior,  of 
dog,  328 
of  ox,  304,  309 
of  pig,  317 
common,  of  dog.  322 
of  ox,  304 
of  pig,  315 
internal,  of  ox,  304,  309 
lateral,  of  dog,  322,  328 
of  ox,  304.  309 
of  pig,  315,  317 
of  ox,  304,  309 
of  pig,  315 
fascia,  274 

flexor  muscle,  deep,  of  dog, 
323,  329 
of  ox,  305 
of  pig,  316 
superficial,  of  dog,  323, 
329 
of  ox,  305 
of  pig,  316 
fossa  of  epididymis,  485 
nerves  of  dog.  730,  732 
of  horse,  701 
of  ox,  718,  719 
of  pig,  723 
pads,  780 


Digital  veins,  595 
of  dog,  642,  643 
of  ox,  621,  623 
Dilatator  naris  apicalis  muscle 
of  ox,  296 
inferior  muscle  of  horse, 
218 
of  ox,  296 
lateralis  muscle  of  horse, 
217 
of  ox,  295 
of  pig,  311 
superior  muscle  of  horse, 
218 
of  ox,  296 
transversus      muscle      of 
horse,  217 
of  pig,  311 
pupilla^,  744 
Diploe,  21 
Diploic  veins,  593 
Discs,  articular,  171 

of     temporo  -  mandibular 
articulation,  179 
Distal  interphalangeal  joint  of 
horse,  189 
sesamoid  bones  of  ox,  131 
Diverticulum  duodeni  of  horse, 
362 
nasi  of  horse,  436 
preputial,  of  pig,  .506 
suburethral,  of  cow,  519 

of  sow,  522 
tuba;  auditivEe,  756 
ventriculi  of  stomach  of  pig, 
418 
Dolichocephalic  breed  of  dogs, 

1.59 
Dorsal  artery,  538 
of  dog,  633 
of  ox,  609 
of  penis,  580 
of  pig,  627 
columns  of  spinal  cord,  651 
common  ligament  of  carpal 

joints,  183 
flexion  of  joints,  171 
groove  of  third  phalanx,  91 
ligaments  of  hock  joint,  201 
of  interphalangeal   joints 
of  dog,  209 
plexus,  595 

sacro-iliac  ligament,  190 
sesamoids  of  dog,  165 
vein,  .586 
Dorso-intercostal  artery,  538 
Dorso-scapular     ligament    of 

horse,  235 
Dorsum  of  tongue  of  horse,  335 
Duct    or    duets,    alveolar,    of 
lungs,  457 
Barthohn's,  of  mare,  515 
bile,  common,  of  sheep,  410 
of  ox,  398 
of  pig,  419,  422 
cystic,  of  ox,  403 
ejaculatory,  488,  492,  499 
hepatic,  376 
lacrimal,  737 
lactiferous,  of  cow,  521 

of  mare,  516 
lymphatic,  right,  601 
naso-lacrimal,  436,  737 
of  ox,  773 


Ductsofbulbo-iucthral  glands, 

494,  499 
of  epididymis,  487 
of     mammary     glands     of 

mare,  516 
of  pancreas,  372 
of  prostate,  493 
orbital,  of  dog,  427 
pancreatic,  accessory,  of  dog, 
431 
of  horse,  373 

of  dog,  431,  434 

of  horse,  372 

of  ox,  398 

of  pig,  419,  423 
parotid,  of  dog,  423,  427 

of  horse.  347 

of  pig,  411,  414 
prostatic,  of  horse,  499 

of  ox,  502 
Santorini's,  of  horse,  373 
sublingual,  of  dog,  427 

of  horse,  348 
submaxillary,  of  dog,  427 

of  horse,  348 
thoracic,  of  dog,  643 

of  horse,  600 

of  pig,  630 
tracheal,  603 
Wirsung's,  of  liorse,  372 
Ductus  arteriosus,  535,  607 
endolympliaticus.  759 
reuniens,  759 

sublingualis  major,   of   pig, 
416 

minores,  of  pig,  416 
utriculo-saccularis,  759 
venosus,  607 

of  ox,  403 
Duodenal  angle  of  horse,  372 

glands  of  liorse,  363 
Duodenum  of  horse,  360 

of  ox,  398 
Dura  mater,  645 

spinal,  646 

Ear,  external,  of  horse,  747 
internal,  of  horse,  758 
middle,  of  horse,  752 
of  dog,  779 
of  horse,  747 
of  ox,  774 
of  pig,  778 
Ectolateral  fissure  of  dog,  727 
Ectomarginal  fissure,  669 
of  dog,  726 
of  ox,  716 
of  pig,  721 
Eotosyhian  fissure  of  dog.  726 
Ectoturbinals   of   ethmoid   of 

liorse,  52 
Eighth  nerve,  686 
Ejaculatorv   ducts,   488,   492, 

499 
Elastic  membrane  of  trachea, 

449 
Elbow  joint  of  dog,  205 
of  horse,  181 
of  ox.  205 
of  pig,  205 
Eleventh  nerve.  690 
Embryology,  17 
Eminence,  frontal,  of  ox,  118 


794 


INDEX 


Eminence,     iliopectineal, 
puljis,  95 

intcrcondyloid,  of  tibia, 

olivary,  of  dog,  72.') 
Eminent  ia  fonclia>,  748 

medialis,  662 

pyrainidalis,  755 
Emissary  \cins,  591 
Enaniel'of  teeth,  339 
Enarthrosis,  172 
Enceplialon  of  horse,  652 
End  arteries,  524 
End-brain,  667 
Endocardium,  530,  534 
Endothoracic  fascia,  450 
Endoturbiiuils  of  ethmoid, 
Ensiforra  cartilage,  46 
Entomarsjinal   fissure  of  ( 


Of!. 


of  horse,  689 
of  o\,  716 
of  pig,  721 
Epicardium,  525,  534 
Epicondvle,  external,  of  femur, 
100 
of  humerus,  80 
internal,  of  femur,  100 
of  humerus,  80 
Epidermis,  761 

of  dog,  780 
Epididymis  of  dog,  506 
of  horse,  485 

structure  of,  485 
of  ox,  500 
of  pig,  504 
Epidural  space,  646 
Epigastric  zone  of  horse,  353 
Epiglottis  of  dog,  467 
of  horse,  442 
of  ox,  459 
of  pig,  411,  465 
Epihyoids  of  horse,  65 
Epiphyseal  cartilage,  22 
Epiphysis,  665 
Epiploic  foramen,  379 

of  ox,  396 
Epithelium,  corneae,  741 
germinal,  of  ovary,  510 
of  Fallopian  tubes,  511 
Equator  of  eye,  740 
Erectile  tissue  of  urethra,  499 
Erector  clitoridis  muscle,  515 

penis  muscle,  496 
Ergot,  771 

Esophageal  membrane,  360 
Esophagus.     SeeCEsopluKjiis. 
Ethmoid  artery,  554 
bone  of  dog,  1.57 
of  horse,  52 

development  of,  52 
of  ox,  116 
of  pig,  142 
sinus,  74 
Ethmoidal  cells,  52 
foramen,  51,  52,  67,  70 
fossa,  52,  70 
meatuses,  52 

of  njusal  cavity,  440 
nerve,  678 
of  dog,  728 
Ethmo-turbinals,  52 
Eustachian  tube,  348,  755 
of  dog,  780 
of  ox,  775 


Eustachian  tube  of  pig,  778 

osseous,  57 
Excavatio  pupilla?  nervi  optici, 

745 
Excretory  ducts,  737 
Exoskeleton,  19 
Extension  of  joints,  171 
Extensor  brevis  muscle  of  ox, 
310 
carpi  muscle  of  dog,  322 
obliquus  muscle,  of  dog, 
322 
of  horse,  267 
of  ox,  304 
of  pig,  315 
radialis  brevis  muscle  of 
dog,  322 
longus   muscle  of  dog, 

322 
muscle  of  horse,  263 
of  ox,  304 
of  pig,  315 
ulnaris     muscle    of    dog, 
323 
of  horse,  268 
digitalis    brevis    muscle    of 
dog,  328 
of  pig,  317 
communis  muscle  of  dog, 
322 
of  horse,  263 
lateralis    muscle   of   dog, 
322 
of  horse,  265 
of  leg  of  horse,  288 
longus   muscle   of   leg   of 
horse,  288 
digit!  quinti  muscle  of  dog, 
323 
tertii  et  quarti  muscle  of 
dog,  323 
fossa  of  femur  of  horse,  100 
hallucis    longus    muscle    of 
dog,  328 
of  pig,  317 
indicis    proprius   muscle   of 

pig,  315 
metacarpi   obliquus   muscle 

of  horse,  267 
muscle  of  digits  of  dog,  322, 

328 
pedis  brevis  muscle  of  horse, 
295 
muscle  of  horse,  264,  288 
External  angle  of  ilium,  94 
of  pubis,  96 
auditory  meatus,  56 

process,  56,  67 
condyle  of  humerus,  80 
cremaster  muscle,  249,  490 
epicoiulyle  of  femur,  100 

of  himierus,  80 
frontal  crest,  55 
inguinal  ring,  246,  250 
intercostal  muscles  of  dog, 
325 
of  horse,  240 
of  pig,  313 
interosseous  muscle  of  horse, 

273 
lateral    ligament    of    carpal 
joints,  183 
of  coffin  joint,  189 
of  elbow  joint,  182  ' 


External    lateral    ligament   of 
femoro-tibial    articu- 
lation, 197 
of  fetlock  joint,  1S5 
of  hock  joint,  200 
of  pastern  joint,  188 
ligament    of    temporo-man- 

dibular  articulation,  179 
malleolus  of  tibia,  101 
metatarsal  bone.  111 
oblif|ue  muscle  of  abdomen, 

246 
occipital  protuberance,  50 
patellar  Ugament,  195 
pterygoideus  muscle,  220 
sagittal  crest,  54,  66 
supracondyloid  crest  of  hu- 
merus, SO 
trochanter  of  femur,  99 
tuberosity  of  humerus,  78 

of  radius,  81 
urethral  orifice  of  cow,  519 
of  horse,  499 
of  mare,  515 
of  ox,  503 
Eye  of  dog,  779 
of  horse,  734 
of  ox,  772 
of  pig,  777 
Eyeball  of  dog,  779 
of  horse,  739 
of  ox,  773 
of  pig,  778 
Eyelashes,  735 

of  pig,  777 
Eyelid  of  dog,  779 
of  horse,  735 

muscles  of,  218 
of  ox,  772 
of  pig,  777 
structure  of,  736 
third,  736 
of  ox,  772 
of  pig,  777 


Face,  bones  of,  of  dog,  157 

of  horse,  57 

of  ox,  120 

of  pig,  142 
of  dog,  muscles  of,  318 
of  ox,  muscles  of,  295 
Facets,  anterior,  of  larynx,  441 
costal,  of  thoracic  vertebra;, 

36,  37 
of  tibia,  102 
of  ulna,  83 

posterior,  of  larynx,  441 
Facial  artery,  547 

of  dog,  635 

transverse,  550 
bones,  27 
canal,  .50 
crest,  58,  62,  68 
nerve,  684 

of  dog,  729 

of  ox,  717 
nucleus,  684 
paimiculus  of  pig,  311 
tuberosity  of  ox,  120 
veins,  5.SS 

of  pig,  630 
Facies  articulares  aryta>noidea;, 
441 


INDEX 


795 


Facies  articulares  thyreoide®, 

441 
cost  alls,  454 
diaphragraatica,  456 
mediastinalis,  454 
Falciform  ligament,  374 
Fallopian  tubes  of  bitch,  522 

of  cow,  517 

of  mare,  511 

structure  of,  511 

of  sow,  522 
False  nostril  of  horse,  436 
ribs,  25.  4  i 
vertebra",  24 
vocal  cords  of  dog,  467 
of  horse,  447 
Falx  cerebri,  645 
Fascia,  211,  212 

abdominal,  deep,  245 

superficial,  245 
buccal,  213 
carpal,  263 
coccygeal,  238 
common,  of  leg,  274 
criu-al,  274 
deep,  212 

of  head,  213 
digital,  274 

endothoracic,  of  horse,  450 
femoral,  internal,  274 
gluteal,  273 
iliac,  273 

lata  of  gluteal  region,  273 
lumbo-dorsal,  235 
metatarsal,  274 
of  back,  235 
of  forearm,  262 
of  head,  213 
of  horse,  213 
of  loins,  235 

of  mammary  glands,  516 
of  manus,  262 
of  metacarpus,  263 
of  neck,  224 
of  pelvic  limb,  273 
of  shoulder  of  horse,  255 
of  tail,  238 
orbital,  738 
pectoral,  2.52 
pelvic,  273 
pharyngeal,  213 
propria  of  neck,  224 
scrotal,  488 
superficial,  212 

of  gluteal  region,  273 

of  head,  213 
tarsal,  274 
temporal,  213 
transversalis,  249 
Fasciculus,     cerebello-olivary, 

658 
cerebellospinal,  681 
cerebrospinal,  660 
cuneatus,  652 
dorsal      longitudinal,      658, 

660 
gracilis,  652 
intracommissuralis  ventralis, 

6.52 
nucleo-cerebellar,  661 
pedunculo-mammillaris,  665 
pyramidal,  660 
thalamo-mammillaris,  665 
Faucial  tonsil,  333 


Femoral  artery,  579 
anterior,  580 
deep,  580 
of  dog,  639 
of  ox,  619 
of  pig,  630 
posterior,  580 
canal,  282 
fascia,  internal,  274 
layer    of    external    oblique 

muscle,  246 
nerve  of  horse,  706 
vein,  598 
of  dog,  642 
Femoro-patellar    articulation, 
194 
ligaments,  lateral,  195 
Femoro-popliteal  artery,  580 

vein,  59S 
Feraoro-tiliial  articulation,  196 
Femur,  29,  97 

development  of,  100 
of  dog,  167 
of  ox,  1.33 
of  pig,  148 
Fenestra  cochlea,  7.53 
ovalis,  753 
rotundum,  753 
vestibuU,  7,53,  758 
Ferrein's  pvramid,  473 
Fetlock  joint,  185,  764 
Fibers  of  heart,  534 

of  stomach,  359 
Fibrse  arcuata;  externa,  657 

zonvilares,  747 
Fibro-cartilagp,    accessory,    of 
patella,  105 
intervertebral,  173 
Fibrous  capsule  of  liver,   376 
layer  of  articulations,  170 

of  pericardium,  525 
ring  of  heart,  534 

of     intervertebral     fibro- 
cartilages,  173 
tunic  of  eve,  740 
Fibula,  29 
of  dog,  168 
of  horse,  104 

development,  of  104 
of  ox,  134 
of  pig,  149 
Fibular  tarsal  bone,  106 
ligaments  of,  202 
of  ox,  134 
sustentaculum    tali    of, 

106 
tuber  calcis  of,  106 
Fifth  nerve  of  horse,  677 

spinal  root  of,  658 
Fila  lateralis  pontis,  661 

radicularia,  651 
Filiform  papillse  of  tongue  of 

horse,  336 
Fillet,  658 
lateral,  660 
medial,  660 

terminale  of  horse,  648,  649 
Fimbria  of  brain,  669 
of  Fallopian  tubes,  511 
ovaricae  of  mare,  511 
First  carpal  bone,  85 
intertarsal  sac,  200 
nerve  of  horse,  676 
phalanges  of  dog,  165 


First  phalanges  of  horse,  89, 1 1 1 
development  of,  89 

of  ox,  130 
tarsal  bone,  109 
of  ox,  135 
Fissura  callosn-marginalis,  669 
ectouKUfiiiKilis,  (i()9 
entoinarginulis,  (i69 
lateralis  .Sylvii,  668 
marginalis,  669 
mediana  ventralis,  649 
sublimbica,  669 
thyreoidea  of  dog,  467 
transvensa,  669 
Fissure,  ansate,  of  dog,  726 
callosomarginal,  669 

of  dog,  727 

of  ox,  716 

of  pig,  721 
central,  of  dog,  726 

of  horse,  668 

of  ox,  716 
chorioid,  670 
collateral,  of  dog,  726 
coronal,  of  dog,  726 

of  ox,  716 

of  pig,  721 
crucial,  of  ox,  717 
cruciate,  of  dog,  727 

of  pig,  721 
diagonal,  of  ox,  716 

of  pig,  721 
ectolateral,  of  dog,  727 
ectomarginal,  669,  721 

of  dog,  726 

of  ox,  716 
ectosylvian,  of  dog,  726 
entomarginal,  of  dog,  727 

of  horse,  669 

of  ox,  716 

of  pig,  721 
genual,  of  ox,  717 

of  pig,  721 
Glaserian,  of  horse,  57 
lateral,  of  cerebrimi,  667 

of  dog,  726 

of  horse,  668 

of  ox,  716 

of  pig,  721 
longitudinal,  of  brain,  667 
marginal,  of  horse,  669 

of  ox,  716 

of  ]5ig,  721 
naso-maxillarv,  of  horse,  73, 

439 
of  lungs  of  ox,  462 
of  Sylvius,  667,  668 

of  dog,  726 

of  ox,  716 

of  pig,  721 
orbital,  51 
petro-tj'mpanic,  57 
portal,  of  dog,  433 

of  horse,  373 

of  ox,  402 
prsesylvian,  669 

of  dog,  727 

of  horse,  669 

of  pig,  721 
splenial,  of  pig,  721 
subUmbic,  669 
suprasplenial,  of  dog,  727 
suprasylvian,  of  dog,  726 

of  horse,  668 


796 


INDEX 


Fissure,    suprasvlviaii.   of   ox, 
716 
of  pig,  721 
transverse,  669 

of  ox,  71(5 
uinl)ilic;il.  37-i 
ventral  iiicdiari,  249 
P^ixcil  vfrteljnr.  24 
Flat  nmsclcs,  211 
Flexion  of  joints,  171 
Flexor  brachii  muscle  of  liorse, 
259 
carpi    externus    muscle    of 
horse,  268 
of  pig,  316 
internus   muscle   of   dog, 
323 
of  horse,  267 
of  pig,  315 
medius  muscle  of  dog,  323 
of  horse,  268 
of  pig,  315 
digitalis  pedis  muscle  of  dog, 

329 
digiti  quinti  muscle  of  dog, 

321 
hallucis  brevis  muscle,  329 

longus  muscle.  329 
musi-lc,  deep,  of  ox,  311 
suiK-rticial,  of  ox,  311 
of  carpus  of  ox,  305 
pel  lis   [jcrforatus   muscle   of 

horse,  271,  292,  293 
perforans  muscle,  271 
perforatus  muscle,  269 
pollicis  brovis  muscle,  324 
Flexure,  diaphragmatic,  366 
gastro-hepatic,  366 
pelvic,  366 
sigmoid,  .503 
sternal,  366 
Floating  ribs,  25 
Floccular    fossa    of    temporal 

bone  of  dog,  156 
Floor  of  mouth  of  horse,  334 
Fnetal  circulfUion,  606 

lung  of  horse,  454 
Fold,  alar,  437 
cicco-colic,  367 
deferential,  of  testicles,  491 
gastro-pancreatic,  3.5S 
of  articulations,  170 
ruiniiiii-icticular,  393 
■sagittal,  of  pleura,  4.52 
turbinal,  inferior,  440 

superior,  440 
urogenital,  355 
vahular,  of  c.erum,  365 
Folia  cerebelU,  (ill! 
Foliate  papdUe  of  tongue,  336 
Follicle,  (Jraafian,  of  mare,  510 
hair,  763 
lymph,  600 

of  small  intestine  of  horse, 
363 
of  thyroid  gland  of  horse,  4.5S 
Foot  of  horse,  muscles  of,  287 
of  ox,  muscles  of,  309 
of  pig,  muscles  of,  317 
Foramen,  alar,  68 
alare,  34 

ca;cum  of  medulla,  655 
carotid,  of  dog,  1.56 
ethmoidal,  51,  52,  67,  70 


Foramen,   hypoglossal,  48,  68, 
71 
incisix'e.  .59,  69 
infraorbital,  .5S,  OS 
interxentricular,  (i67,  674 
intervertebral,   of  horse,   33 

of  ox,  112 
lacerum  basis  cranii,  57,  68, 
71 
of  horse,  49 

orbitale  of  horse,  51,  67 
niagmnn  of  horse,  48,  68 
mandibular,  64 
maxillary,  58,  67 
mental,  63 

mitrient,  of  femur,  97 
of  humerus,  78 
of  ilium.  94 
of  metacarpus,  88 
of  tibia,  100 
obturator,  of  dog,  167 
of  horse,  96 
of  ox,  132 
of  Monro,  667,  674 
optic,  of  horse,  50,  51.  67.  70 
orbital,  internal,  67,  70 
ovale,  607 
of  horse,  530 
of  ox,  115 
palatine,  posterior,  58,  68 
pathetic,  67 
pterygoid,  51,  68 
rotundum,  51,  67 
sacral,  40 

inferior,  of  ox,  114 
sciatic,  great,  of  horse,  94 
singulare,  759 
sinistrum,  244 
sphenopalatine,  58,  60,  67,  71 
stylo-mast  oid,  57 
supraorbital,  of  horse,  55,  66 

of  ox,  119 
supratrochlear,   of  humerus 

of  dog,  163 
temporal,  of  hor.se,  51,  67 
thyreoideum,  442 
transversarium  of  axis  of  ox, 

112 

venic  cav;p,  of  horse,  245 

volar,  of  third  phalanx,  91 

Winslow's,  of  horse,  379 

of  ox,  396 

Foramina  papilloma  of  kidnev 

of  ox,  480 
Forearm,  bones  of,  28  i 

of  horse,  fascia"  of,  262  I 

deep,  262  j 

superficial,  262 
muscles  of,  262 
of  ox,  muscles  of,  304 
of  pig,  muscles  of,  315 
Forefoot,  bones  of,  28 
Foretop,  764 

Formatio  reticularis.  651,  6()0 
Fornix,  673 

conjunctiva',  73() 
vagina;  of  mare,  514 
Fossa,  acetabular,  96 

anterior,  of  skull,  70  j 

atlantis  of,  34 
condyloid,  of  horse,  48,  68 
coronoid,  of  honse,  80 
digital,  of  epididymis,  485 
ethmoidal,  52,  70 


Fossa,  extensor,  of  femur,  100 
floccular,  of  temporal  bone 

of  dog,  156 
glandis  of  penis,  495 
glenoid,  .56 
hyaloidea.  746 
hypophy.seal.  .50 
infraspinous,  75 
infratemporal,  68 
intercondyloid,   anterior,  of 
tibia,'  102 
of  femur,  99 
posterior,  of  tibia,  102 
interi;eduncularis,  664 
ma.sscteric,   of  mandible   of 

dog,  1.59 
middle,  of  skull,  71 
ovulation,  of  mare,  509 
ovalis,  607 

of  horse,  530 
of  Sylvius.  667 
olecranon.  SO 
olfactory.  52.  70 
pituitary.  50 
post<'riiir,  of  skull,  71 
post-glenoid,  ,56 
pterygo-palatine.  60.  ()7 
.subscai}ular,  75 
su])raci)ndyloid.  of  fenuir  of 

horse,  99 
supraspinous,  75 
synovial,     of    tibial     tarsal 

bone,  105 
temporal,  67 
transverse,  658 
trochanteric,  of  femur.  99 
synovial,  170 
vagina'  of  mare,  514 
Fourth  carpal  bone  of  horse, 
86 
metatarsal   bone    of   horse, 

111 
nerve  of  horse,  677 
tarsal  bone  of  horse.  109 

of  ox,  134 
ventricle  of  horse,  662 
Fovea    capitis    of    femur    of 
horse,  99 
nasalis.  662 
trochlearis  of  horse,  55 
Fraenula  labii  of  horse,  331 
Frenum  linguie  of  horse,  334, 
335 
of  pig,  411 
preputial,  of  horse,  497 
Frog  matrix,  770 
of  hoof,  767 
sen.sitive.  770 
structure  of,  769 
Frog-stai,-,  767 
Frontal  artery,  553 
bone  of  dog,  1,55 
of  horse,  55 
of  ox,  lis 
of  pig,  141 
crest  of  horse,  55,  66 
eminence  of  ox,  118 
nerve  of  dog,  728 
of  horse,  678 
of  ox,  717 
process  of  dog,  157 
region  of  skull  of  horse,  66 
sinus  of  dog,  161 
of  horse,  55,  73 


797 


Frontal  sinus  of  ox,  125 
of  pig,  145 

surface  of  skull  of  horse,  65 
of  ox,  123 

suture  of  horse.  55 

vein  of  ox,  621 
Frontalis  muscle  of  ox,  295 
Fronto-lacrimal      sutures      of 

horse,  55 
Fronto-maxillary    opening    of 

liorse,  73 
Fronto-scutularis,  749 
Fundus  glands  of  stomach  of 

horse,  360 
Fungiform  papilla;  of  tongue 

of  horse,  336 
Funiculi  dorsales,  651 

ventrales,  651 
Furoa  ungula?,  767 


Gall-bladder  of  dog,  434 
of  ox,  403 
of  pig,  422 
Ganglia,  cervical,  of  ox,  720 
ca'liaco-mesenteric,  714 
definition  of,  644 
sacral,  of  ox,  720 
thoracic,  of  ox,  720 
GangHon,  cervical,  711 
of  dog,  733 
of  pig,  724 
ciUary,  679,  711 

of  ox,  717 
coccygeal,  713 
Gasserian,  678 
impar,  713 
jugular,  687 
of  dog,  729 
of  ox,  717 
'      of  pig,  722 
lumbar,  713 
mesenteric,  714 
nodosum  of  dog,  729 
of  ox,  717 
of  pig,  722 
otic,  681,  711 
of  ox,  717 
petrous,  686 
semilunar,  678 
sphenopalatine,  711 
spinal,  692 
spirale,  761 
thoracic,  712 
vestibular,  686 
Gartner,  canals  of,  of  vagina 

of  cow,  519 
Gasserian  ganglion,  678 
Gastric  artery,  506 
of  dog,  63S 
lymph  glands,  604 
of  ox,  626 
of  pig,  632 
plexus,  714 

of  dog,  729 
vein,  597 
Gastrocnemius  muscle  of  dog, 
329 
of  horse,  290 
of  ox,  311 
of  pig,  317 
Gastro-coiic       omentum       of 

horse,  358 
Gastro-duodenal  artery,  569 


Gastro-duodenal  vein,  597 
(jastro-epiploic  artery,  569, 570 
Gastro-hepatic  artery  of  pig, 
627 
flexure  of  liorse,  366 
omentum  of  horse,  354  358 
Gastro-pancreatic       fold       of 

horse,  358 
Gastro-phrenic     ligament     of 

horse,  358 
Gastro-splenic  artery  of   dog, 
638 
omentum  of  horse,  354,  358, 
379 
Gemellus  muscle  of  horse,  284 
of  ox,  308 
of  pig,  317 
Geniculate  body,  internal,  665 
of  dog,  725 
of  ox,  716 
Genio-glossus  muscle  of  horse, 

338 
Genio-hyoideus  muscle  of  ox, 

298 
Genital  organs,  469 
female,  508 
male,  485 
of  dog,  506 
of  horse,  485 
of  ox,  500 
of  pig,  504 
of  bitch,  522 
of  cow,  517 
of  mare,  508 
of  sow,  521 
Genito-hyoideus     muscle     of 

horse,  223 
Genu  of  corpus  callosum,  672 
Genual  fissure  of  ox,  717 

of  pig,  721 
Germinal  epithelium  of  ovary 

of  mare,  510 

Ginglymus,  172 

Girdle,  pelvic,  29 

of  horse,  92 

shoulder,  27 

of  horse,  muscles  of,  250 
of  ox,  muscles  of,  302 
of  pig,  muscles  of,  314 
Glands  or  gland,  anal,  of  dog, 
432 
buccal,  of  horse,  332 
of  ox,  383 
of  pig,  410 
bulbo-urethral,  of  dog,  506 
of  horse,  493 
of  ox,  503 
of  pig,  505 
cardiac,  of  stomach  of  horse, 

360 
carpal,  778 
ceruminous,  749 
circumanal,  of  dog,  432 
Cowper's,  of  dog,  506 
of  horse,  493 
of  ox,  503 
of  pig,  505 
duodenal,  of  liorse,  363 
fundus,  of  stomach  of  horse, 

360 
hsemolymph,  600 
labial,  of  horse,  332 
lacrimal,  of  dog,  779 
of  horse,  737 


Glands,  lacrimal,  of  ox,  773 
lingual,  of  horse,  336 
Ivmph,  599 

bn.ncl.ial,  of  horse,  457 

of  ox,  623 

1)1'  pig,  630 
mammary,  of  bitcli,  523 

of  cow,  519 

of  mare,  516 

of  sow,  522 
molar,  of  ox,  383 
mucous,  of  larynx  of  horse, 
448 

of  trachea  of  horse,  450 
nasal,  of  horse,  440 
of  Bartholin  of  cow,  519 
of  Bowman,  772 
of  Henle,  736 
of  rectum  of  horse,  370 
of  skin,  762 
of  small  intestine  of  liorse, 

362 
of  uterus  of  cow,  518 
olfactory,  of  horse,  440 
orbital,  of  dog,  427 
palatine,  of  horse,  333 
parathyroid,  of  dog,  468 

of  horse,  458 

of  ox,  464 
parotid,  of  dog,  427 

of  horse,  346 

of  ox,  388 

of  pig,  414 
preputial,  of  horse,  497 
prostate,  of  dog,  506 

of  horse,  493 

of  ox,  502 

of  pig,  505 
pyloric,  of  stomach  of  horse, 

360 
salivary,  of  dog,  427 

of  horse,  346 

of  ox,  388 

of  sheep,  407 
sebaceous,  762 

of  dog,  780 

of  ox,  775 

of  pig,  778 
solitary,  of  rectum  of  horse, 
370 

of  small  intestine  of  horse, 
363 
of  pig,  420 
sublingual,  of  dog,  427 

of  horse,  348 

of  ox,  388 

of  pig,  415 
submaxillary,  of  dog,  427 

of  horse,  347 

of  ox,  388 

of  pig,  415 
sudoriferous,  762 
suprarenal,  of  horse,  477 
sweat,  762 

of  dog,  780 

of  ox,  775 

of  pig,  778 
tarsal,  735 
thymus,  of  dog,  468 

of  horse,  458 

of  ox,  464 

of  pig,  466 
thyroid,  of  dog,  468 

of  horse,  457 


798 


INDEX 


Glands,  thyroid,  of  ox,  464 
of  pig,  4G6 
urotliral,  of  horse,  499 
uterine,  of  cow,  518 

of  mure,  513 
zygomatic,  of  dog,  427 
Glandula    laryngeal   of    liorse, 
4-18 
palpeljrx    tertia;    profunda, 

779 
tympanica",  755 
vestibulares  majores  of  cow, 
519 
of  mare,  515 
minores  of  mare,  515 
Ghins  clitoridis  of  dog,  519 
of  mare,  515 
penis  of  dog,  506 
of  horse,  495 
of  ox,  503 
Glasserian  fissure  of  horse,  57 
Glenoid  cav-ity  of  horse,  67,  68, 
76 
fossa  of  horse,  56 
notch  of  horse,  76 
Ghding  joint,  172 

movement  of  joints,  171 
Glomerulus  of  kidney  of  horse, 

474 
Glossopliaryngeal  nerve,  686 
Glottis  of  liorse,  447 

vocalis  of  horse,  448 
Gluteal  artery,  anterior,  577 
of  dog,  641 
of  ox,  619 
posterior,  575 
fascia  of  liorse,  273 
line  of  horse,  93 
nerve  of  horse,  706 
Gluteo-biceps  muscle  of  horse, 

278 
Gluteus  accessorius  muscle  of 
horse,  278 
medius  muscle  of  dog,  326 
of  horse,  277 
of  ox,  306 
of  pig,  316 
profunilus    muscle    of    dog, 
326 
of  horse,  278 
of  ox,  306 
of  pig,  316 
superficialis  muscle  of  dog, 
326 
of  horse,  277 
of  ox,  306 
of  pig,  316 
Goll's  column,  652 
Gompluisis,  169 
Ciraahan  follicles  of  mare,  510 
Gracilis  muscle  of  dog,  328 
of  horse,  2S1 
of  ox,  308 
of  pig,  316 
Granula  iridis,  744 
Gray  commissure  of  cord  of 
horse,  650 
matter  of  nervous  system, 
644 
Great    colon    of    horse,    365. 
See  also  Colon,  great. 
cornua  of  horse,  65 
mesentery    of     horse,     354, 
362 


Great   oblique  muscle  of  ab- 
domen of  horse,  246 
omentum  of  horse,  354,  358 

of  ox,  396 
sciatic  foramen  of  horse,  94 
trochanter     of     femur     of 
horse,  99 
Ciroove,  bicipital,  of  humerus 
of  horse,  79 
carpal,  of  horse,  S6 
coronarv,  of  heart  of  horse, 
527 
of  rumen  of  ox,  392 
dorsal     median,     in     horse, 
649 
of  tliird  phalanx  of  horse, 
91 
dorsolateral,  in  horse,  649 
lacrimal,  of  horse,  58 
longitudinal,    of     heart     of 

horse,  528 
musculo-spiral,  of  horse,  77 
oesophageal,  of  ox,  394 

of  sheep,  408 
of  heart  of  horse,  527 
of  radius  of  horse,  82 
of  sacrum  of  ox,  114 
of  tibia  of  horse,  102 
optic,  of  horse,  50 
palatine,  of  horse,  59,  69 
sagittal,  of  horse,  54 
subpubic,  of  horse,  95 
supraorbital,  of  ox,  119 
lU'ethral,  of  horse,  495 
vertebral,  of  horse,  42 
Gross  anatomy,  17 
Gubernaculum  testis  of  horse, 

491 
Gudden's  commissure,  666 
Gums  of  horse,  332 
Gustatory  cells,  772 
hair,  772 

organs  of  dog,  781 
pore,  772 
Guttural  pouches,  756 

region  of  horse,  68 

Gyri,  cerebellar,  661 

cerebral,  668 

of  ox,  716 

of  pig,  721 

>Gyrus  dentatus,  669 

subcallosal,  671 


H^MAL   arches   of    coccygeal 
vertebra;  of  dog,  152 
spine,  25 
Hxmolymph  glands,  600 
Ha'inorrhoidal  artery,  574 
of  dog,  641 
nerve  of  horse,  710 
Hair,  gustatory,  772 
Hair-follicle,  762 
Hairs,  762 
of  horse,  764 
of  ox,  775 
of  pig,  77S 
tactile,  763 
Hamulus  of  horse,  61 
Hand.     See  Manna. 
Hard  palate  of  dog,  423 
of  horse,  69,  332 
of  ox,  383 
of  pig,  411 


Hard  palate  of  sheep,  405 
Harder's  gland,  777 
Head  of  horse,  fascia;  of,  213 
muscles  of,  213 
of  pig,  muscles  of,  311 
Heart,  524 
of  dog,  632 
of  horse,  526 

structure  of,  534 
of  ox,  60S 
of  pig,  62(j 
veins  of,  585 
Heels,  764 
Hehcis  muscle,  752 
HeUcotrema,  759 
Hemispheres,  cerebellar,  660 
cerebral,  667 
of  dog,  726 
of  ox,  716 
of  pig,  721 
Henle,  glands  of,  736 
Hepatic  artery,  567 
of  dog,  638 
of  hor.se,  377 
of  ox,  614 
duct  of  horse,  376 
lymph  glands,  605 
of  ox,  626 
of  pig,  632 
plexus,  714 

of  horse,  377 
veins,  596 
of  horse,  377 
Hepato-renal    ligament     of 

horse,  375 
Hiatus  aorticus  of  horse,  244 

cesophageus  of  horse,  244 
Hilus  of  lungs  of  horse,  454 
of  ovary  of  mare,  510 
of  spleen  of  horse,  378 
renalis,  of  horse,  470 
Hinge-joint,  172 
Hip-joint  of  horse,  192 
of  ox,  209 
of  pig,  209 
Hippocampal  commissure, 

670 
Hippocampus,  669 
Histologv,  17 
Hock,  29 
capped,  293 
joint  of  dog,  210 
of  horse,  199 
of  ox,  210 
of  pig,  210 
of  horse,  105 
of  ox,  134 
of  pig,  149 
Hoof  of  horse,  764 
matrix  of,  769 
structure  of,  76S 
Horn-cores  of  ox,  118 
Horner's  muscle,  736 
Horns  of  lateral  ventricle,  674 

of  ox,  776 
Humefalis  obliquus  muscle  of 

horse,    260 

Humerus,  28 

of  dog,  162 

of  horse.  77 

development  of,  SO 
of  ox,  127 
of  pig.  146 
Humor,  aqueous,  746 


Humor,  vitreous,  746 
Hydatid  of  Morgagni  of  Fal- 
lopian   tubes   of   mare, 
511 
of  testicles  of  horse,  485 
Hymen  of  mare,  514 
Hyo-epislottic  ligament,  444 
Hyo-epitilot til-US  muscle,  44c 
Hyo-glossus  muscle,    338 
Hyoid  bone  of  dog,  159 
of  horse,  64 
of  ox,   122 
of  pig,  144 
muscle  of  dog,  319 
of  horse,  222 
of  ox,  297 
process  of  horse,  57 
Hyoidean  articulations,  180 
Hyoideus  transversus  muscle, 
224 
of  ox,  298 
Hyo-pharyngeus  muscle,  350 
Hyo-thyreoitleus  muscle,  445 
Hyperdactylism,  29 
Hypogastric  arteries,  573 
plexus,    715 
vein,  597 
zone,  353 
Hypoglossal  foramen,  48,  68, 
71 
nerve,  692 
of  dog,  730 
of  ox,  717 
of  pig,  722 
nucleus,  692 
Hypophyseal  fossa  of  horse,  50 
Hypophysis,  653,  665 


Ileal  artery,   570 
Ileo-csecal  artery,  570 
orifice,  364 
value  of  dog,  431 
of  horse,  362,  364 
Ileo-ca-co-coUc    artery    of    ox, 

617 
Ileum,  361 

Iliac  artery,  circumflex,  578 
of  dog,  639 
external,  578 
of  ox,  619 
internal,   573 
of  ox,  618 
fascia,  273 
layer  of  oblique    muscle  of 

abdomen,  246 
lymph  glands,  604 
of  dog,  643 
of  ox,  625 
of  pig,  631 
vein,  common,  597 
external,  597 
internal,  597 
of  dog,  642 
Iliaco-femoral  artery,  577 
of  ox,  619 
vein,  598 
Iliacus  muscle  of  dog,  326 
of  horse,  275 
of  ox,  306 
Ilio-costalis     cervicis     muscle 
of  horse,  227 
muscle  of  horse,  236 
of  ox,  300 


INDEX 

Iliohvpogastric  nerve  of  horse, 

704 
Ilio-inguinal    nerve   of    horse, 

704 
Ilio-lumbar  artery,  577 
of  dog,  641 
of  ox,  619 
of  pig,  630 
ligament  of  horse,  191 
vein,   597 
Ilio-pectineal  line  of  horse,  93 
lUo-psoas  muscle  of  horse,  275 
Iliopectineal  eminence  of  pubis, 

95 
Ilium,  29 
of  dog,   165 
of  horse,  93 
of  ox,  131 
of  pig,  148 
Impression,  cardiac,  of  lungs, 

454 
Incisive  foramen,  59 
Incisivus    inferior    muscle    of 
horse,   216 
of  ox,  295 
superior  muscle,  216 
Incisor  artery,  552 
teeth,  338,"  341 

deciduous,  of  ox,  386 
of  dog,  425 
of  ox,   3S6 
of  pig,  412 
of  sheep,  405 
Incisura  intertragica,  748 

thyreoidea  caudalis,   442 
Incus,  754 

Index,  cephahc,  of  dog,  159 
cranio-facial,  of  dog,  159 
Inferior  angle  of  scapula,  76 
atlanto-axial  ligament,   176 
atlanto-occipital  membrane, 

176 
border  of  mandible,  64 
check    ligament    of    carpal 
joints,  183 
of    deep    digital    flexor 
muscle,  272 
conmiissure  of  vulva,  515 
common  vertebral  ligament, 

173 
dental  canal,  64 
dilatator  naris  muscle,  218 
incisivus  muscle,  216 
interdigital  ligaments  of  ox, 

208 
ischiatic  spine,   95 
maxiUary  foramen,  64 

sinus,  73 
meatus  of  nasal  cavity  of 
dog,  467 
of  horse,  439 
of  pig,  465 
of  nose,  62,  72 
navicular  hgament,  190 
sacral  foramen  of  ox,  114 
sacro-coccygeus  muscle,  240 
sesamoidean  ligaments,  188 
thyro- arytenoid     ligament, 

444 
turbinal  bone  of  dog,  158 
of  horse,  62 
of  ox,   122 
crest,  58 
fold  of  horse,  440 


799 

Infraorbital  artery,  555 
of  dog,  635 
of  pig,  627 
canal,  59 
foramen,  58,  68 
nerve  of  dog,  728 
of  horse,  6S1 
of  pig,  722 
poucli,    777 
vein,    589 
Infraspinatus  muscle   of  dog, 
321 
of  horse,  256 
of  ox,  302 
of  pig,  314 
Infraspinous  fossa,  75 
Infratemporal  fossa,  68 
Infratrochlear   nerve  of    dog, 
728 
of  horse,  679 
Infundibular  recess,  667 
Infundibulum,  653 
of  Fallopian  tubes,  511 
of  incisor  teeth,  341 
Inguinal  canal,  249 
ligament,    246 
lymph  glands,  604 
of  dog,  643 
of  ox,  625 
of  pig,  632 
pouch  of  sheep,  777 
ring,  external,  246,  250 
internal,  248,  249 
Inlet  of  pelvis  of  dog,  167 
of  horse,  96 
of  ox,   132 
of  pig,  148 
of  thoracic  cavity,  450 
Inscriptiones  tendinea-  of  rec- 
tus abdominis  of  horse,  248 
Insertion  of  muscles,  212 
Interalveolar  septa,  58 

space,  58,  69 
Interarytenoid  cartilage  of 
larynx  of  dog,  467 
of  pig,  465 
Interbrain,   664 
Intercarpal  joint,   183 

sac,  183 
Intercentral    articulations    of 

vertebrae,  173 
Interchondral  ligaments,  178 
Intercondyloid  fossa,  anterior, 
of  tibia,  102 
eminence  of  tibia,  101 
fossa  of  femur,  99 

posterior,  of  tibia,   102 
Intercornual     articulation     of 

horse,    180 
Intercostal  arteries,  565 
of  ox,   614 
of  pig,  627 
lymph  glands,  603 
muscles,  external,  of  dog,  325 
of  horse,  240 
of  pig,  313 
internal,  of  horse,  242 
of  pig,  313 
nerves  of  horse.  702 
spaces,  25 
veins,  587 
Interdental  space  of  horse,  58 
Interdigital  ligaments,  inferior, 
of  ox,  208 


800 


Interdigital    ligaments,    suiio- 
rior,  of  ox,  20G 
pouch,  777 
Intcrlolmhir  bronchi  of  liorsc, 
457 
tissue  of  lungs,  4o7 
Intcrniccliate   carpal    bone   of 
iiorsc,    83 
zone  of  kidney,  473 
Intermetacarpal  joints  of  dog, 
•JOt) 
of  ox,  200 
of  pig,  206 
Intermuscular  septa,  212 
of  forearm,  262 
of  gluteal  region,  273,  274 
of  leg,  274 
of  shoulder,  255 
Internal  angle  of  ilimn,  94 
of  pubis,  95 
auditory  meatus,  56 
capsule,  065,  676 
condyle     of     humerus     of 

horse,  79 
digital    extensor   muscle   of 

ox,  304,  309 
ear  of  horse,  758 
epicondyle  of  femur,  100 

of  humerus,  80 
femoral  fascia,  274 
flexor  muscle,  267 
inguinal  ring,  248,  249 
intercostal  muscles,  242 

of  pig,  313 
interosseous  muscle,  273 
lateral    ligament    of    carpal 
joints,   1S4 
of  cotfin  joint,  189 
of  elbow  joint,  181 
of  femoro-tibial  articu- 
lation, 197 
of  fetlock  joint,  185 
of  hock  joint,  201 
of  pastern  joint,   188 
malleolus  of  tibia,  103 
metatarsal  bone,  111 
musclesof  thighofox,  308 
oblique  muscle  of  abdomen, 

247 
occipital  protuberance,  54 
orbital  foramen,  67,  70 
patellar  ligament,  196 
pterygoiileus  muscle,  219 
sagittal  crest,  54 
trochanter  of  femur,  97 
tubercle  of  humerus,  78 
tuberosity  of  humerus,  79 

of  radius,  81 
urethral  orifice  of  horse,  477 
of  mare,  499 
Intcrneural     articulations     of 

vertebra;,  173 
Interosseous  artery,  common, 
.561 
dorsal,    562 
of  dog,  ()35 
of  ox,  012 
recurrent,  561 
ligami'nt  of  radio-ulnar  ar- 
ticulation, 1,S2 
medius  muscle  of  ox,  305 
membrane    of    tibio-fibular 

articulation,  199 
muscles  of  dog,  324,  329 


Interosseous  muscles  of  horse, 
273,  295 
plexus,  595 
space  of  forearm,  80 

of  leg,  29 
vein,  .595 
Interparietal  bone  of  dog,  155 
of  horse,  53 
of  ox,  116 
of  pig,  140 
suture  of  horse,  54 
Interpeduncular  space,  664 
Interphalangeal     articulation, 
distal,  1,89 
proximal,  188 
joints  of  dog,  209 
of  ox,  208 
of  pig,  208  ^ 
Interscutularis,  749 
of  dog,   780 
of  ox,  774 
Intersesamoidean       ligament, 

1S7 
Interspinales  muscles  of  dog, 
325 
of  ox,  300 
of  pig,  313 
Interspinous   1  i  g  a  m  e  n  t  s   of 

horse,  175,  176 
Interstitial  tissue  of  mammary 

glands,    516 
Intertarsal  sac,  first,  200 

second,  200 
Inter!  nrisvrrsales  caudff,  239 
colli  iniis,-l<.,  228 
luniboruni  muscle,  2.38,  276 
muscle  of  dog,  324,  325 
of  ox,  300 
of  pig,  312,  313 
Intertransverse    articulations, 
175 
ligaments,  175 
Intertubercular  groove  of  hu- 
merus, 79 
Interventricular  foramen,  667, 
674 
grooves  of  heart,  528 
septum  of  left  ventricle,  .534 
Inter\ertebral  fibro-cartilages, 
173 
foramen,  33 
of  ox,  112 
foramina,   25 
Intestinal  arteries,  570 
Intestine,  large,  of  dog,  433 
of  horse,  363 
of  ox,  398 
of  pig,  420 
of  dog,  430 
of  ox,  397 
of  pig,  410 
of  sheep,  409 
small,  of  dog,  430 
of  horse,  360 
of  ox,  398 
of  pig,  419 
of  sheep,  409 
Intima  of  arteries,  525 

of  veins,  525 
Intraarticular  ligaments,    171 
Intumescontia     cervicalis     of 
horse,    648 
lumbalis,    648 
Iris  of  dog,  779 


Iris  of  horse,  744 
of  ox,  774 
of  pig,  778 
Ischiatic  artery,  575 
of  ox,  019" 
lymph  glands,  604 
of  ox,  020 
of  pig,  632 
spine,  inferior,  of  horse,  95 
superior,  of  horse,  94,  95 
Ischio-cavernosus    muscle    of 
clitoris,  515 
of  penis,  490 
of  ox,   503 
Ischio-coccygois  muscle,  238 
Ischio-femoralis  muscle,  283 
Iscluo-urethr;d    muscles   of 

horse,    499 
Ischium,  29 
of  dog,  105 
of  horse,  95 
of  ox,  131 
of  pig,  148 
Isthmus     faucium    of     horse, 
335,  348 
of  ox,  385 
oesophagi  of  dog,  428 
of  prostate,  493 
of  thvroid  gland,  457 

of  dog,  408 
of  urethra  masculina,  498 
pharyngeal,  350 


Jacobson's  organ  of  horse,  440 
Jejuno-ileum,  361 
Jejunum,  361 
Joint,  109.     See  also  Arliculu- 

lions. 
Jugular  ganglion,  087 

of  dog,  729 

of  ox,  717 

of  pig,  722 
veins,  587 

of  dog,  042 

of  ox,  621 

of  pig,  630 
Jugulomandibularis      muscle, 
222 


Kerato-hyoideus  muscle,  223 

of  ox,  298 
Kerato-hyoids  of  horse,  65 
Kerato-pharyngeus  muscle  of 

horse,  3.50 
Kidneys,  409 
of  dog,  483 
of  horse,  469 
arteries  of,  475 
blood-supply  of,  475 
cortical  substance  of,  473 
fibrous  capsule  of,  473 

coat  of,  474 
fixation  of,  472 
glomerulus  of,  474 
intermediate  zone  of,  473 
left,  470 
lobules  of,  473 
lymph  vessels  of,  475 
Malpighian       corpuscles, 
473 
pyramid  of,  473 
medullary  substance,  473 


Kidnevs  of  horse,  mucous  coat 
"of,  474 

muscvihir  coat  of,  474 

papilla  of,  474 

pelvis  of,  473 

right,  409 

stroma  of,  475 

structure  of,  473 

tubules  of,  474 

veins  of,  47o 

vessels     and     nerves    of, 
754 

weight  and  size  of,  472 
of  ox,  478 
of  pig,  481 
of  sheep,  480 


Labia  of  vulva,  515 

\ocalis  of  horse,  448 
Labial  arterv,  549 

of  ox,  611 

superior,  550 
glands  of  horse,  332 
ner\-e  of  horse,  681 
veins,  589 

of  ox,  621 
Labyrinth,  membranous,  759 
of  ethmoid  bone,  52 
osseous,  758 
Lacrimal  apparatus,  737 
artery,  553 
bone  of  dog,  158 

of  horse,  61 

of  ox,  121 

of  pig,  143 
bulla  of  ox,  121 
canal,  osseous,  61 
caruncle,  735 
duct  of  horse,  737 
gland  of  dog,  779 

of  horse,  737 

of  ox,  773 
groove,  58 
lake,  735 
nerve  of  dog,  728 

of  horse,  678 

of  ox,  717 

of  pig,  722 
pouch,  777 
process  of  dog,  158 
sac  of  horse,  737 
sinus  of  ox,  126 
tubercle  of  horse,  61 
Lactiferous  ducts  of  cow,  521 

of  mare,  516 
sinus  of  cow,  521 
Lacus  lacrimalis,  735 
Lamina  basalis,  743 
choriocapillaris,  743 
cribrosa  sclene,  741 
elastica  posterior,  742 
fusca,  740 

limitans  anterior,  741 
of  hoof,  765 
of  nostrils,  437 
of  omasimi  of  ox,  305 
of  thyroid  cartilage.  442 
papyracea,  52 
spiralis  ossea,  759 
suprachorioidea,  742 
terminahs  of  third  ventricle, 

667 
51 


Lamina,  transverse,  of  ethmoid 
bone  of  dog,  157 
vasculosa,  742 
Laminar  matrix,  769 
Laryngeal  arterj'  of  ox,  610 
nerve  of  dog,  729 
recurrent,  689 
superior,  689 
orifice,  34S 
saccule,  447 
Larynx  of  dog,  arytenoid  car- 
tilage of,  467 
cricoid  cartilage  of,  467 
cuneiform  cartilage,  467 
interarytenoid      cartilage 
of,  467 
of  horse,  440 

arytenoid  cartilages,  443 
arytenoideus    transversus 

muscle  of,  446 
cartilages  of,  441 
cavity  of,  447 
crico- arytenoideus     dor- 
salis  muscle  of,  445 
laterahs  muscle  of,  446 
cricoid  cartilage  of,  441 
facets.  441 
joints  of.  444 
lateral  ventricle  of,  447 
ligaments  of,  444 
membranes  of,  444 
middle  ventricle  of,  447 
mucous  glands  of,  448 

membrane  of,  448 
muscles  of,  445 
transverse  arytenoid  liga- 
ment of,  444 
ventricular  Ugament,  444 
vessels    and     nerves     of, 

448 
vestibule  of,  447 
walls  of,  441 
of  ox,  459 
of  pig,  465 
Lateral  cartilages  of  phalanges, 
ligaments  of,  190 
of  third  phalanx,  91 
column  of  spinal  cord,  651 
digital   extensor   muscle   of 
dog,  322,  328 
of  horse,  265 
of  leg  of  horse,  288 
of  ox,  304,  309_ 
of  pig,  315,  317 
femoro-patellar  ligaments  of 

horse,  194 
fissure  of  cerebrum,  667 
of  dog,  726 
of  horse,  668 
of  ox,  716 
of  pig,  721 
ligament,  external,  ot  carpal 
joints,  183 
of  coffin  joint,  189 
of  elliow  joint,  182 
of  femoro-tibial  articu- 
lation, 197 
of  fetlock  joint,  185 
of  hock  joint,  200 
of  pastern  joint,  188 
internal,  of  carpal   joint, 
184 
of  coffin  joint,  189 
of  elbow  joint,  181 


801 

Lateral  ligament,  internal,  of 
femoro-tibial    articu- 
lation, 197 
of  fetlock  joint,  185 
of  hock  joint,  201 
of  pastern  joint,  188 
left,  of  fiver,  375 
of  atlanto-occipital  articu- 
lation, 177 
of  l)laddcr,  476 
of  liorse,  3.56 
right,  of  liver,  375 
ma.sses  of  ethmoid,  52 
muscles  of  neck,  229 
pterygoidcus  muscle,  220 
rectus  capitis,  228 
sacro-coccygcus  muscle,  239 
sacro-iliac  ligament,  190 
sesamoidciui  ligaments,  187 
surface  of  skull  of  dog,  160 
of  horse,  66 
of  ox,  123 
of  pig,  144 
\entricle,  674 

of  larj-nx  of  hor.se,  447 
of  ox,  459 
Laterahs     sterni     nuiscle     of 

horse,  242 
Latissimus  dorsi  muscle  of  dog, 
320 
of  horse,  251 
of  ox,  302 
of  pig,  314 
Layer,    femoral,    of    external 
oblique  muscle,  246 
fibrous,  of  articulations,  170 

of  pericardium,  525 
iUac,    of    external    oblique 

muscle,  246 
muscular,  of  trachea,  450 
serous,  of  pericardium,  525 
sjTiovial,    of     articulations, 

170 
\-isceral,  of  pericardium,  525 
Leg,  bones  of,  29 

of  horse,  muscles  of,  287 
anterior,  288 
posterior,  290 
of  ox,  muscles  of,  309 
of  pig,  muscles  of,  317 
Lemniscus,  6.58 
lateralis.  660 
medialis.  600 
Lens,  crystalline,  746 
Lenticular  nucleus,  675 
Levatores  costarum  muscle  of 
dog,  325 
of  horse,  240 
of  ox,  300 
of  pig,  313 
labii  superioris  proprius  of 
dog,  318 
of  horse,  215 
of  ox.  295 
of  pig,  311 
nasolabialis  muscle  of  dog, 
318 
of  horse,  214 
of  ox,  295 
of  pig,  311 
palati  muscle  of  hor.se,  333 
palpel)ra>  superioris,  219, 73S 
rostri  muscle  of  pig,  311 
scapula;  hominis,  254 


802 


Ligainont  or  ligaments,  annu- 
lar, 212 
anterior,  of  horse,  263 
of  manus  of  horse,  263 
of   pelvic  limb   of  horse, 

274 
posterior,    of    parpus    of 
horse,  263 
arciform,  of  radio-iilnar  ar- 
ticulation (if  horse,  182 
arytenoid,      transverse,      of 

larvnx  of  horse,  444 
astra(jalo-i-alr:ineal,  202 
ast ranalii-sraphoid,  202 
atlanto-axial,  inferior,  176 

superior,  176 
axillary,  of  Helmholtz,  755 
broad,   of   uterus  of  bitch, 
523 
of  cow,  518 
of  horse,  356 
of  mare,  513 
calcaneo-cuboid,  202 
calcaneo-cunean,  202 
ealeaneo-raetatarsal,  201 
ealeaneo-scaphoid,  202 
capsular,  170 
caudate,   of   liver,  375 
check,    inferior,    of    carpal 
joints  of  horse,  183 
of    deep    digital    flexor 
muscle  of  horse,  272 
of  hock  joint  of  horse,  200 
superior,     of     superficial 
digital  flexor  muscle  of 
horse,  270 
common  vertebral,  inferior, 
of  liorse,  173 
superior,  of  horse,  173 
conjugal,  of  horse,  177 
coronary,  of  horse,  374 
coslo-sternal,  superior,  178 
costo-trans\erse,      superior, 

177 
cotyloid,  of  horse,  192 
crucial,  of  femoro-tibial  ar- 
ticulation of  horse,  198 
cul)oido-cunean,  202 
cuboido-scaphoid,  202 
dorsal    common,    of    carpal 
joints  of  horse,  183 
of  hock  joint  of  horse,  201 
of   interphalangeal   joints 
of  dog,  209 
dorso-scapular,  of  horse,  235 
external    lateral,    of   carpal 
joints  of  horse,  183 
of  coffin  joint,  189 
of  elbow  joint,  182 
of  femoro-tibial  articu- 
lation of  horse,   197 
of  fetlock  joint,  185 
of  hock  joint,  200 
of  pastern  joint,  188 
of  t  emporo-niandiljular  ar- 
ticulation, 179 
falciform,  of  horse,  374 
femoro-natellar,  lateral,  195 
gastro-phrenic,  of  horse,  358 
hepa to-renal,  of  horse,  375 
hyo-epiglottic,  of  horse,  444 
ilio-lumbar,  of  horse,  191 
inguinal,  of  horse,  246 
intcrchondral,  of  horse,  178 


Ligament,    interdigital,     infe- 
rior, of  ox,  208 
superior,  of  ox,  206 
internal    lateral,    of    carpal 
joints  of  horse,  184 
of  coffin  joint,  189 
of  elbow  joint,  181 
of  femoro-tibial  articu- 
lation of  horse,  197 
of  fetlock  joint,  185 
of  hock  joint,  201 
of  pastern  joint,  188 
interosseous,  of  radio-ulnar 
articulation  of  horse,  182 
intersesamoidean.   187 
interspinous,  of  horse,  175, 

176 
intertransverse,  175 
intraarticular,  171 
lateral,  left,  of  liver  of  horse, 
375 
of     atlanto-occipital     ar- 
ticulation, 177 
of  bladder  of  horse,  476 
of  horse,  356 

right,  of  liver  of  horse,  375 
long,  of  hock  joint,  201 
middle  of  bladder,  476 

of  horse,  356 
navicular,  inferior,  190 

suspensory,  of  horse,  189 
odontoid,  of  horse,  176 
of  auditory  ossicles.  755 
of  fibular  tarsal  bone,  202 
of  larynx  of  horse,  444 
of  lateral  cartilages  of  phal- 
anges of  horse,  190 
of  liver  of  horse,  374 
of  lung  of  horse,  452 
of   neck   of    rib,   of   horse, 

177 
of  peritoneum  of  horse,  354 
of  scroliini  ..f  hiiVM'.  4SS 
of  tilii:il  I:iism1  Ihiiic,  202 
of  vcrtchnc  of  dog,  204 
of  horse,  172 
of  ox,  203 
of  pig,  204 
ovarian,  of  bitch,  ,522 

of  mare,  509 
l)alpebral,  736 
patellar,  of  horse,  195 
periarticular,  171 
plantar,  of  hock  joint,  201 
posterior,   of  pastern  joint, 
188 
of  temporo-mandibular  ar- 
ticulation,  179 
Poupart's,  of  horse,  246 
pulio-fcnioral,  193,  2.50 
radiate,  of  horse,  177 
round,  of  bladder,  476 
of  hip  joint  of  horse,  193 
of  horse,  356 
of  li\er  of  hor.se,  375 
of  uterus  of  bitch,  523 
of  cow,  518 
of  mare,  513 
sacro-iliac,  dorsal,  190 
sacro-iliac,  lateral,  190 

ventral,  190 
sacro-sciatic,  of  horse,  190 
.scaphoido-cunean,  202 
scrotal,  of  horse,  488 


Ligament,     sesamoidean,     of 
horse,  186,  187,  188 
of  ox,  207 
short,  of  hock  joint.  201 
sternal,  of  horse,  17S 
structure  of,  171 
subcarpal,  of  horse,  183 
subtarsal,  of  horse,  200 
supraspinous,  of  horse,  174 
suspensory,  of  penis,  494 
of  spleen  of  horse,  379 
tarso-metatarsal.  202 
thyro-arvtenoiil.        inferior, 
444" 
superior.  444 
tliyro-eiiiglottic.  444 
transverse,  of  carpus,  263 
of    hip    joint    of    horse, 

192 
of  radio-ulnar  articulation 
of  horse,  182 
umbilical,  of  bladder.  476 
vaginal,  212 

ventricular,  of  larynx,  444 
vocal,  of  horse,  444 
volar,  of  carpal  joints,  183 

of  pastern  joint,  188 
V-.shaped.  of'liorse.   ISS 
Y-.shapcd,  uf  horse,  ISS 
Ligament;!   annularia    of    tra- 
chea, 450 
fiava,  174 

sternopericardiaca     of     ox, 
608 
Liganientum  arteriosum,  535, 
607 
crico-thyreoideum,  444 
denticulatum,  647 
nucha',  174 
pectinatuin  iriilis,  742 
spiralc  cc>clilc:c,  760 
Limbus  palpeliralis,  735 
Line,     curved,     superior,     of 
skull,  69 
gluteal,  93 
ilio-pectineal,  93 
popliteal,  of  tiliia,  100 
terminal,  353 
Linea  alba,  246 
Lingu.al  artery,  548 
of  dog,  634 
of  ox,  611 
branch  of  ninth  nerve,  687 
glands,  336 
nerve,  683 

of  dog,  729 
process  of  horse,  65 
vein,  590 
dorsal,  587 
Lingula,  660 
Lips  of  dog,  423 
of  luorse,  330 

muscles  of,  213 
of  ox.  382 
of  pig,  410 
of  sheep,  405 
Liquor  folliculi  of  mare,  510 
pericardii  of  horse,  525 
pleura'  of  horse,  453 
Liver  of  dog,  432 
of  horse,  373 

structure  of,  376 
of  ox,  400 
of  pig,  421 


INDEX 


803 


Liver  of  shopp,  400 
Lobe,  apical,  of  lungs  of  ox, 
462,  463 
cardiac,  of  lungs  of  ox,  463 
caudate,  of  liver,  433 
of  ox,  402 
of  pig,  421 
cerebellar,  661 
diaphragmatic,   of    lung   of 

ox,  463 
iiu'diastinal,  of  lung  of  horse, 
456 
of  ox,  463 
of  liver  of  dog,  432 
of  horse,  374 
of  pig,  421 
of  lungs  of  dog,  46S 
of  horse,  456 
of  ox,  462,  463 
of  pig,  466 
of  mammary  glands,  516 
of  prostate  of  horse,  493 
of  thymus  gland  of  horse, 

458 
of  thyroid  gland  of  dog,  468 

of  horse,  457 
precardiac,  of  lung  of  horse, 

463 
pvriform,  66S 
'of  dog,  72S 
Lol>ular  bronchioles,  457 
Lobulation  of  lungs,  456 
of  ox,  463 
of  sheep,  464 
Lobules  of  epididymis,  487 
of  kidney  of  horse,  473 
of  liver  of  pig,  422 
of  lung  of  horse,  457 
of  mammary  glands,  516 
of  jjrostate  of  horse.  493 
of  testicles  of  horse,  4S6 
of  thymus  gland,  458 
of  thyroid  gland,  458 
Lobus  piriformis,  672 
Locus  perforatus  posticus,  664 
Loins  of  dog,  muscles  of,  325 
of  horse,  fascia;  of,  235 
.  muscles  of,  235 
of  ox,  muscles  of,  300 
of  pig,  muscles  of,  313 
Long  ligament  of  hock  joint, 
201 
muscles,  211 
Longissimus  capitis  et  atlantis 
muscle  of  horse,  229 
muscle  of  dog,  325 
of  horse,  237 
of  ox,  300 
Longitudinal  bands  of  caecum 
of  hor.se,  364 
fissure  of  cerebrum,  607 

of  brain,  654 
grooves  of  heart,   528 
sinus,  superior,  591 
Longus  capitis  muscle,  227 
colli  muscle  of  dog,  324 
of  horse,  228 
of  pig,  312 
Lower,  tubercle  of,  530 
Lumbar  arteries,  571,  573 
of  ox,  618 
of  pig,  629 
enlargement  of  horse,  648 
ganglia,  713 


Lumbar  lymph  glands,  604 
of  dog,  643 
of  ox,  625 
of  pig,  631 
nerves  of  horse,  702 
wins,  596,  597 
viTlcbra-,  24 
c.t  .log,  151 
of  liorse,  38 
of  ox,  112 
of  pig,  138 
Lumbo-dorsal  fascia,  235 
Lumbo-sacral   plexus  of  dog, 
731 
of  horse,  705 
of  o.x,  719 
of  pig,  723 
Lumbricales   muscles  of  dog, 
324,  329 
of  horae,  273,  295 
of  ox,  305 
of  pig,  316 
Lung,  foetal,  of  horse,  454 
of  dog,  468 

lobes  of,  468 
of  horse,  453 
air-cells  of,  457 
alveolar  duct.s  of,  457 
alveoli  of,  457 
apex  of,  456 
l)asal  border  of,  456 
base  of,  4.56 

bronchial  branches  of,  456 
carcUac  impression  of,  454 

notch  of,  456 
color  of,  454 
costal  surface  of,  454 
dorsal  border  of,  455 
form  of,  454 
hilus  of,  454 

interlobular  tissue  of,  457 
ligament  of,  451 
lolies  of,  4.56 
lobulation  of,  456 
IcjlHile  of,  457 
lymph  vessels  of,  456,  457 
liiediastinal  lobe  of,  456 

surface  of,  454 
precardiac  lobe  of,  463 
root  of,  456 
ventral  border  of,  4.54 
^■esscls  and  nerves  of,  457 
of  ox,  462 

apical  lobe  of,  462,  463 
cardiac  lobe  of,  463 
diaphragmatic  lolie,  463 
fissures  of,  462 
lobes  of,  462,  463 
lobulation  of,  463 
mediastinal  lobe  of,  463 
of  pig,  463 

lobes  of,  466 
of  sheep,  lobulation  of,  464 
Luvs's  bodv,  665 
Lvmph,  599,  600 
"follicles,  600 

of  small  intestine,  363 
glands,  599 
anal,  605 

of  pig,  632 
atlantal  of  ox,  623 
auricular,  of  dog,  643 
axillary,  605 
of  dog,  643 


Lymph  glands,  axillary,  of  ox, 
625 

of  pig,  631 
bronchial,  603 

of  horse,  457 

of  ox,  624 

of  pig,  631 
ca-cal,  of  pig,  632 
cervical,  601 

of  ilog,  643 

of  ox,  624 

of  pig,  631 
colic,  of  pig,  632 
cubital,  of  dog,  643 
gastric.  604 

of  pig,  632 
hepatic,  605 

of  pig,  632 
iliac,  6()4 

of  dog,  643 

of  ox,  625 

of  pig,  631 
inguinal,  604 

of  pig,  632 
intercostal,  603 
ischiatic,  604 

of  pig,  632 
lumbar,  604 

of  dog,  643 

of  ox,  625 

of  pig,  631 
mediastinal,  603 

of  dog,  643 
mesenteric,  605 

of  dog,  643 

of  jiig,  632 
of  ca'cum,  605 
of  colon,  ()05 
of  dog,  643 

of  Fallopian  tubes,  511 
of    mammary    glands    of 
cow,  521 
of  mare,  517 
of  ovaries  of  mare,  510 
of  ox,  623 
of  penis,  496 
of  pig,  630 
of  prepuce,  497 
of  spermatic  cord,  489 
of  uterus,  513 
of  vagina,  514 
orbital,  606 
pancreatic,  605 
parotid,  of  dog,  643 

of  pig,  630 
pectoral,  601 
pharyngeal,  602 

of  dog,  643 

of  ox,  623 

of  pig,  630 
popliteal,  606 

of  dog,  643 

of  pig,  632 
precrural,  606 

of  pig,  632 
prepectoral,  of  pig,  631 
prescapular,  602 

of  dog,  643 

of  ox,  624 

of  pig,  631 
renal,  of  ox,  625 
sacral,  604 
splenic,  605 

of  pig,  632 


804 


INDEX 


Lymph  glands,  sternal,  of  ox, 
624 
subiliac,  606 
submnxillarv,  601 
of  iloti.  643 
of  ox,  623 
of  pig,  630 
subparotid,  of  ox,  623 
thoracic,  of  pig,  631 
nodes,     599.     See     Lymph 

(/lands. 
no'diilps,  600 

of  siilccn  of  horse,  379 
spaces,  600 
Lymphatic  duct,  right,  (iOl 

system,  599 
Lymphocytes,  599,  600 
Lymjih-vessels,  524,  599 
of  adrenal  bodies,  478 
of  tlog,  643 
of  heart,  535 
of  kidneys  of  horse,  475 
of  lungs  of  horse,  456,  457 
of  ox,  623 
of  pig,  630 
Lyssa  of  dog,  424 


Macroscopic  anatomy,  17 
iSIacula-  acusticae,  760 
^Lalar  artery,  555 
bone  of  dog,  158 
of  horse,  67 
of  ox,  121 
of  pig,  143 
Malaris  muscle  of  horse,  218 

of  ox,  296 
Malleolus,   external,   of   tiljia, 
103 
internal,  of  tibia,  103 
Malleus,  754 

Malpighian  corpuscles,  379 
of  kidney,  473,  474 
pyramids  of  kidney,  473 
Mammary  artery,  580 
of  ox,  619 
glands  of  bitch,  523 
teats  of,  523 
of  cow,  519 
of  mare,  516 
of  sow,  522 
Ij'mph  glands,  604 
yein  of  ox,  (i22 
Mammillary  body,  653,  665 
of  ,!,,«.■  726 
processes,  25,  43 
Mandiljle  of  dog,  158 
of  horse,  63 
of  ox,  122 
of  pig,  143 
Mandibular  canal,  64 
foramen,  64 
nerve  of  dog,  728 
of  horse,  681 
of  ox,  717 
of  pig,  722 
teeth  of  horse,  344 
Mane,  764 
Mantle,  brain,  668 
Manubrium  mallei,  754 
sterni,  26 
of  horse,  46 
Manas,  bones  of,  28 
of  horse,  fascia>  of,  262 


Manus   of   horse,    muscles   of, 

262 
Marginal  cartilage,  171 
fissure  of  horse,  669 
of  ox,  716 
of  jiig,  721 
pole,  716 
Margo  ciliaris,  744 

pupillaris,  744 
Marrow  of  bone,  21 
Masseter  muscle  of  dog,  318 
of  horse,  219 
of  ox,  297 
Masseteric  artery,  inferior,  547 
of  ox,  612 
fossa  of  mandible  of  dog,  159 
nerve  of  horse,  681 
vein,  588 
Mastication,    muscles    of,    of 
dog,  318 
of  horse,  219 
of  ox,  297 
of  pig,  311 
Mastoid  artery,  545 

process  of  horse,  67 
Mastoido-humeralis  muscle  of 
dog,  320 
of  horse,  225,  252 
of  ox,  302 
of  pig,  314 
Matrix  of  horn,  776 

of  hoof,  769 
Maxilla  of  dog,  157 
of  horse,  58 

inferior,  63 
of  ox,  120 
of  pig,  142 
Maxillary  artery,  external,  547 
internal,  551,  612 
of  <log,  635 
of  ox,  611 
of  pig,  627 
foramen  of  horse,  58,  64,  67 
nerve  of  dog,  728 
of  horse,  679 
of  pig,  722 
process  of  dog,  158 
region  of  horse,  68 
sinus,  inferior,  of  horse,  73 
of  dog,  161 
of  horse,  72 
of  ox,  126 
of  pig,  146 
superior,  of  horse,  73 
teeth  of  horse,  .343 
tuberosity  of  hor.se,  58 
vein,  588 
internal,  587 
of  dog,  642 
Maxillo-niuscular  artery,  547 

vein,  588 
Maxillo-turbinal  bone,  62 
Meatus,     auditory,     external, 
56,  748,  759 
internal,  of  horse,  56 
common,    of   nasal    cavity, 

440 
ethmoidal,  of  nasal  cavity, 

440 
inferior,  of  nasal  cavity  of 
dog,  467 
of  horse,  439 
of  pig,  465 
of  nose  of  horse,  72 


Meatus,     middle,      of     nasal 
cavity  of  dog,  467 
of  horse,  438 
of  pig,  465 
of  nose  of  horse,  72,  71 
common,  62 
inferior,  62 
middle,  62 
superior,  62 
superior,  of  nasal  cavity  of 
horse,  438 
of  pig,  465 
of  nose  of  horse,  72 
Median  artery,  559 
of  ox,  612 
nerve,  696 
of  dog,  731 
of  horse,  699 
of  ox,  719 
of  pig,  723 
palatine  suture,  69 
Mediastinal   lobe   of   lung   of 
horse,  456 
of  ox,  463 
lymph  glands,  603 
of  dog,  643 
of  ox,  624 
pleura  of  horse,  451 
Mediastinum  of  horse,  450 

testis  of  horse,  486 
Medulla  oblongata  of  dog,  735 
of  horse,  655 
of  ox,  715 
of  pig,  720 
of  thymus  gland,  458 
Medullary  artery,  21 

canal  of  metacarpus  of  ox, 

130 
cavity,  19,  20 

substance  of  adrenal  bodies, 
47S 
of  kidney,  473 
velum,  660,  663 
Meissner,  plexus  of,  714 
Membrane,     atlanto-occipital, 
inferior,  of  horse,  176 
superior,  of  horse,  176 
basilaris,  760 
bones,  22 

crico-thyroid,  of  hor.se,  444 
crico-tracheal,  of  horse,  445 
elastic,  of  trachea,  449 
interosseous,  of  tibio-fibular 

articulation,  199 
obturator,  of  horse,  191 
asophageal,  of  horse,  360 
of  Descemct,  742 
of  larynx  of  horse,  444 
of  Kcissner,  760 
synovial,  211 
■  bursal,  211 
of     anterior    digital     ex- 
tensor muscle,  265 
of  caipal  j()int.s,  183 
of  elbow  joint,  181 
of  hip  joint,  193 
of  lateral  digital  extensor 

muscle,  265 
vaginal,  211 
Membrani  nictitans,  736 
tympani,  753 

secundaria,  753 
vestibularis,  760 
Membranous  labyrinth,  759 


805 


Meningeal     artery,     anterior, 
546 
middle,  552 
of  dog,  634 
posterior,  545 
veins,  592 
Meninges,  645 
Meniscus,  171 
Mental  artery,  552 

foramen,  63 
Men  talis  muscle,  216 
Mentum  of  horse,  331 
Meridians  of  eye,  740 
Mesaticephalic  breed  of  dogs, 

159 
Mesencephalon,  663 
Mesenteric  artery,  great,  570 
of  dog,  638  " 
of  ox,  615 
of  pig,  628,  629 
posterior,  of  ox,  618 
small,  571 
ganglia,  714 
lymph  glands,  605 
of  dog,  643 
of  ox,  626 
of  pig,  632 
plexus,  714 
vein,  597 
Mesentery,  colic,  354,  369 

great,  3.54.  .362 
Mescthmoid    of    ethmoid    of 

horse,  52 
Mesocolon  of  dog,  432 
Mesoduodenum,  361 
Mesogastric  zone  of  horse,  353 
Mesorchium,  489,  490 
Mesorectum,  355,  370 
Mesosalpinx  of  bitch,  522 

of  mare,  511 
Mesosternum,  26 
Mesotendon,  212 
Meso^-arium  of  mare,  509 
Metacarpal  artery,  dorsal,  562 
external  volar,  562 
internal  volar,  562 
large,  563 

of  dog,  635,  636,  637 
of  ox,  614 
of  pig,  629 
palmar,  563 
bones,  28 
large,  87 

of  ox,  130 
small,  of  horse,  88 
of  ox,  130 
muscles  of  horse,  273 

of  ox,  305 
nerves  of  dog,  731 

of  horse,  701 
tuberosity  of  horse,  88 
vein,  595 
of  dog,  642 
of  ox,  621 
Metacarpo-phalangeal     joints 
of  dog,  208 
of  horse,  185 
of  ox,  206 
of  pig,  208 
Metacarpus,  28 
of  dog,  164 
of  horse,  87 

development  of,  88 
fascia  of,  263 


Metacarpus  of  ox,  128 

of  pig,  147 
Metasternum,  26 
Metatarsal  arteries,  581 
dorsal,  585 

of  ox,  620 
internal  superficial   plan- 
tar, of  ox,  619 
great,  .585 
of  dog,  640,  641 
of  pig,  630 
bones,  30 

of  horse,  110,  111 
of  ox.  135 
fascia  of  horse,  274 
nerves  of  dog,  732 
veins,  .599 
of  dog,  643 
of  ox,  622 
Metatarsus  of  dog,  168 
of  horse.  110 

muscles  of,  295 
of  ox,  135 
of  pig,  149 
Meynert's  commissure,  666 
Microscopic  anatomy,  17 
Mid-brain,  663 
Middle  cornua  of  horse,  65 
ear  of  horse,  752 
fossa  of  skull  of  horse,  71 
gluteus  muscle  of  horse,  277 
ligament  of  bladder,  476 

of  horse,  356 
meatus  of  nasal   cavity   of 
dog,  467 
of  horse,  438 
of  pig,  465 
of  nose  of  horse,  62,  72 
patellar  ligament,  195 
sesamoidean     ligament     of 

horse,  188 
ventricle  of  larynx  of  horse, 
447 
Milk  cistern  of  cow,  .521 
teeth  of  horse,  346 

of  cow,  521 
vein,  301 
Mitral  valve  of  horse,  533 
Modiolus,  7.59 
Molar  glands  of  ox,  383 
Molars,  338,  342 
Monakow's  rubrospinal  tract, 

652 
Morgagni,  hj'datid  of,  of  Fal- 
lopian tubes,  511 
of  testicles,  485 
Morphology,  17 
Mouth  of  dog,  423 
of  horse,  330 
cavity  of,  330 
floor  of,  334 

mucous  membrane  of,  330 
of  ox,  382 
of  pig,  410 
Movable  joints,  170 

vertebra;,  24 
Movements  of  joint,  171 
Mucous  glands  of  larynx,  448 
of  trachea  of  horse,  450 
membrane,  nasal,  of  horse, 
440 
of  abomasum  of  ox,  397 
of  cxcum  of  dog,  432 
of  larj'nx  of  horse,  448 


Mucous   membrane  of    mam- 
mary gland  of  cow,  521 
of  mouth  of  horse,  330 
of    oesophagus   of    horse, 

352 
of  omiusum  of  ox,  397 
of  pharynx  of  hor.se,  350 
of  rectum  of  hor.se,  370 
of  reticulum  of  ox,  395 
of  stomacli  of  ox,  397 
of  nmien  of  ox,  394,  397 
of  seminal  vesicles,  492 
of  .small  intestine,  362 
of  stomach  of  dog,  430 
of  tongue  of  horse,  335 
of  trachea  of  horse,  4.50 
of  lu'eters  of  horse,  475 
of  urethra  of  marc,  516 

masculina  of  horse,  499 
of  uterus  of  cow,  518 

of  mare,  513 
of  yas  deferens,  489 
of  vulva  of  mare,  515 
M  tiller,  muscle  of,  736 
Multifidus  cervicis  muscle,  231 
dorsi  muscle  of  horse,  238 
muscle  of  pig,  313 
Muscles  or  muscle,  211 
abdominal,  of  horse,  245 

of  pig,  313 
abductor  cruris  posterior,  of 
dog,  327 
digit  i  quinti,  of  dog,  324, 

329 
hallucis,  of  dog,  329 
pollicis  brevis  et  opponens 
poUicis,  of  dog,  324 
accelerator  urinEe,  499 
action  of,  212 
adductor  bre\ns,  282 

digit!  quinti.  of  dog,  .324 

secundi,  of  dog,  324 
hallucis.  of  dog,  329 
longus,  of  horse,  282 
magnus,  of  horse,  282 
of  dog,  328,  329 
of  horse,  282 
of  ox,  308 
of  pig,  316 
parvus,  of  horse,  282 
pollicis,  of  dog,  324 
anconeus,  of  horse,  262 

of  pig,  315 
anterior  digital  extensor,  263 
of  leg  of  horse,  288 
of  ox,  304,  309 
extensor,  of  phalanges.  264 
of  thigh  of  ox,  307 
antitragicus,  751 
arrectores  piloruni,  763 
articularis  genu,  of  ox,  307 
arytenoideus  transyersus,  of 

larynx  of  horse.  44t) 
attachments  of.  211,  212 
auricular,  749 

of  ox,  774 
azygos  u%iila?,  of  hor.se,  333 
belly  of,  212 

biceps  brachii.  of  dog.  322 
of  horse,  259 
of  pig,  314 
femoris,  of  dog.  326 
of  horse.  27.8 
of  ox,  306 


806 


INDEX 


Muscle,    biceps     femoris,     of 
pig,  316 

of  ox,  302 
bipenniite,  212 
hi  veil  I  cr  cervicis,  of  dog,  32.5 
l)i:i<luiil  triceps,  of  horse,  260 
bracliialis.  of  dog,  322 

of  liorse,  260 

of  pig.  Mo 
bracliio-rudialis,  of  dog,  322 
bucciiiutDr,  of  dog,  31S 

of  horse,  216 

of  ox,  2'.)-, 
bulbo-caverno.su.s,    of    penis 
of  ox,  .503 

of  urethra  of  horse,  499 
capsularis,  of  dog,  328 

of  horse,  258,  286 

of  ox,  307 

of  pig,  314,  317 
cardiac,  211 
ccrvicaUs      ascendens,       of 

horse,  227 
cervico-aurieularis,  7o0 
eervico-scutularis,  749 

of  dog,  780 

of  ox,  774 
ehondro-pliaryngeus,  3.50 
cihary,  743 

clcidci-cervicalis,  of  dog,  320 
cl<'id()-inastoideus,    of    dog, 
320 

of  liorse,  2.52 

of  pig,  314 
cleido-occipitalis,     of      pig, 

314 
cleido-transversarius,  252 
coccygeiif,  nf  dog,  32.5 


vrnnMli^  lai 
comiiKiuiligit:! 


rahs,  240 
extensor,  263 
of  ox,  304 
complexus    major,    of   dog, 
325 
of  ilog,  325 
of  horse,  231 
of  pig,  312 
compressor     coccygis,       of 

liorse,  238 
constrictor      vestibuli,      of 
mare,  515 
vulva",  of  mare,  515 
coraco-brachiaUs,     of     dog, 
322 
of  horse,  258 
of  ox,  302 
of  pig,  314 
coraco-radialis,  of  horse,  259 
corrugator  supercilii,  218 
crema-ster,  external,  249,  490 
of  pig,  313 

of  testicles  of  ox,  500 
of  pig,  504 
crico-arytenoideus    dorsalis, 
of  larynx  of  horse,  445 
lateralis,  of  horse,  446 
crico-pharyngeus,  350 
cricfi-thyroideus,  445 
crural  triceps,  of  horse,  284 
crureus,  of  horse,  286 
curvator  coccygis,  239 
cutaneus   maximus,    of   ab- 
domen of  horse,  245 
scapula;  et  humeri,  255 


Muscle,    deep    digital   flexor, 
271 
of  leg  of  horse,  293 
of  ox,  305 
flexor,  of  ox,  311 
gluteus,  of  horse,  278 
jjectoral,  of  ox,  302 
deltoid,  of  dog,  320 
of  horse,  255 
of  ox,  302 
of  pig,  314 
depressor  coccygis,  240 
labii  inferioris,  of  dog,  318 
of  horse,  216 
of  ox,  295 
of  pig,  311 
superioris,  of  ox,  295 
rostri,  of  pig,  311 
diaphragm,  of  dog,  325 
of  horse,  243 
of  ox,  300 
of  pig,  313 
digastric,  213 
digastricus,  of  dog,  319 
of  horse,  222 
of  ox,  297 
of  pig,  311 
digital  extensor,  anterior,  of 
dog,  328 
of  pig,  317 
common,  of  dog,  322 

of  pig,  315 
lateral,  of  dog,  322,  328 

of  pig,  315,  317 
of  ox,  304,  309 
of  pig,  315 
flexor,  deep,  of  dog,  323, 
.329 
of  pig,  316,  317 
superficial,  of  dog,  323, 
329 
of  pig,  316,  317 
dilatator   naris  apicalis,    of 
ox,  296 
inferior,  of  horse,  218 

of  ox,  296 
lateralis,  of  horse,  217 
of  ox,  295 
of  pig,  311 
superior,  of  horse,  218 

of  ox,  296 
transversus,    of    horse, 
217 
of  pig,  311 
pupilhe,  744 
erector  clitoridis,    of    marc, 
515 
penis,  of  horse,  496 
extensor  brevis,  of  ox,  310 
carpi  obliqiius,  of  dog,  322 
of  horse,  267 
of  ox,  304 
of  pig,  315 
of  dog,  322 

radialis  bre\ds,  of  dog, 
322 
longus,  of  dog,  322 
of  horse,  263 
of  ox,  304 
of  pig,  315 
ul  naris,  of  dog,  323 
of  hor.se,  268 
digitalis    brevis,    of   dog, 
328 


Muscle,       extensor      digitalis 
brevis,  of  pig,  317 
communis,  of  horse,  263 
lateralis,  of  horse,  265 

of  leg  of  horse,  288 
longus,  of  leg  of  horse, 
288^ 
digiti  quinti,  of  dog,  323 
tertii  et  quarti,  of  dog, 
323 
hallucis   longus,    of   dog, 
328 
of  pig,  317 
indicis    proprius,    of    pig, 

315 
metacarpi     obliquus,     of 

horse,  267 
of  digits  of  dog,  322,  329 
of    second   digit    of    pig, 

315 
pedis  bre%is,  of  horse,  295 
of  horse,  264,  288 
flat,  211 

flexor  brachii,  of  hor.se,  259 
carpi  externus,  of  horse, 
268 
of  pig,  316 
internus,  of  dog,  323 
of  horse,  267 
of  pig,  315 
medius,  of  dog,  323 
of  horse,  268 
of  pig,  315 
digitalis  pedis,  of  dog,  329 
digiti  quinti,  of  dog,  324 
hallucis  brevis.  of  dog,  329 

loiifius,  of  dog,  329 
pedis  ])erforans,  of  horse, 

292, 293 
perforans,  of  horse,  271 
perforatus,  of  horse,  269 
pollicis  brevis,  of  dog,  324 
form  of,  211 
frontalis,  of  ox,  295 
fronto-scutularis,  749 
gastrocnemius,  of  dog,  329 
of  horse,  290 
of  ox,  311 
of  pig,  317 
gemellus,  of  horse,  284 
of  ox,  308 
of  pig,  317 
genio-glossus,  of  horse,  338 
gcnio-hyoideus,  of  ox,  298 
genito-hyoideus,  223 
gluteo-bieeps,  of  hor.se,  278 
gluteus  accessorius,  278 
medius,  of  dog,  326 
of  horse,  277 
of  ox,  306 
of  pig,  316 
profundus,  of  dog,  326 
of  horse,  278 
of  ox,  306 
of  pig,  316 
superficialis,  of  dog,  326 
of  liorse,  277 
of  ox,  306 
of  pig,  316 
gracilis,  of  dog,  328 
of  hor.se,  281 
of  ox,  308 
of  pig,  316 
head  of,  213 


807 


Muscle,  lielicis,  752 
Homer's,  736 
humeralis  obliquus,  200 
hyo-epiglotticus,  44o 
hyo-glossus,  of  horse,  33S 
hyoid,  of  dog,  319 
of  horse,  222 
of  ox,  297 
hvoideus  trans  versus,  224 

of  ox,  298 
hyo-pharyngeus,  350 
hyo-tliyreoideus,  445 
iliacus,  of  dog,  326 
of  horse,  275 
of  ox,  306 
iho-costaHs  cer\'icis,  227 
of  horse,  236 
of  ox,  300 
iho-psoas,  of  horse,  275 
mcisivus  inferior,  216 
of  ox,  295 
superior,  of  horse,  216 
infraspinatus,  of  dog,  321 
of  horse,  256 
of  ox,  302 
of  pig,  314 
insertion  of,  212 
intercostal,  external,  of  dog, 
325 
of  horse,  240 
of  pig,  313 
internal,  of  horse,  242 
of  pig,  313 
internal  digital  extensor,    of 
ox,  304,  309 
flexor,  of  metacarpus,  267 
of  thigh  of  ox,  308 
interossei,  of  dog,  324,  329 
of  horse,  273,  295 
of  ox,  305 
interscutularis,  749 
of  dog,  780 
of  ox,  774 
interspinales,  of  dog,  325 
of  ox,  300 
of  pig,  313 
intertransversales       cauds, 
239 
colli,  of  horse,  328 
lumborum.  238,  276 
of  dog,  324,  325 
of  ox,  300 
of  pig,  312,  313 
ischio-eavernosus.    of   clito- 
ris of  mare,  515 
of  penis  of  horse,  496 
of  ox,  503 
ischio-coccygeus,  238 
ischio-femoralis,  283 
ischio-iu-ethral,  499 
jugulomandibularis,  222 
kerato-hvoideiLs,  223 

of  ox,  298 
kerato-pharyngeus,  350 
lateral  digital  extensor,  265 
of  leg  of  horse,  288 
of  ox,  304,  309 
lateralis  sterni,  of  horse,  242 
latissimus  dorsi.  of  dog,  320 
of  horse,  251 
of  ox,  302 
of  pig.  314 
levator  labii  superioris  pro- 
prius,  of  dog,  318 


Muscle,   levator   labii  superi- 
oris proprius,  of 
horse,  215 
of  ox,  295 
of  pig,  311 
nasolabialis,  of  dog,  318 
of  horse,  214 
of  ox,  295 
of  pig,  311 
palati.  of  horse,  333 
palpebne  superioris,  219, 

738 
rostri,  of  pig,  311 
scapulae  hominis,  254 
levatores  costarum,  of  dog, 
325 
of  horse,  240 
of  ox,  300 
of  pig,  313 
long,  211 

longissimus  capitis  et  atlan- 
tis,  of  horse,  229 
of  dog,  325 
of  horse,  237 
of  ox.  300 
longus  capitis,  of  horse,  227 
colU,  of  dog,  324 
of  horse,  228 
of  pig,  312 
lumbricales,  of  dog,  324,  329 
of  horse,  273,  295 
of  ox,  305 
of  pig,  316 
malaris,  of  horse,  218 

of  ox,  296 
mn.*.--eler.  of  dog,  318 
of  horse,  219 
of  ox,  297 
mastoido-humerahs,  of  dog, 
320 
of  horse,  225,  252 
of  ox,  302 
of  pig.  314 
mentalis,  of  horse,  216 
metacarpal,  of  horse,  273 

of  ox,  305 
middle  gluteus,  of  horse,  277 
multifidus  cer^^cis,  231 
dorsi,  of  horse,  238 
of  pig,  313 
mylo-hyoideus,  of  dog,  319 
of  horse,  222 
of  ox,  297 
names  of,  212 
nasal,  of  dog,  318 
ner\'e-supply  of,  213 
non-striated,  211 
obUque  extensor,   of  meta- 
carpus of  horse,  267 
great,  of  abdomen,  246 
small,  of  abdomen,  247 
of  head  of  horse.  233 
obliquus    abdominis    exter- 
nus,  of  dog,  326 
of  horse,  246 
of  ox,  301 
of  pig,  313 
internus,  of  dog,  326 
of  horse,  247 
of  ox,  301 
of  pig,  313 
capitis  anterior,  233 
posterior,  of  horse,  233 
of  pig,  313 


Muscle,    obliquus    oculi    infe- 
rior, 738 
superior,  738 
obturator  extemus,  283 
of  ox,  308 
of  pig,  317 

internus,  of  horse,  283 
of  ox,  308 
of  pig,  317 
occipito-hvoideus,  223 

of  ox,  29S 
ocular,  of  horse,  738 
of  abdomen  of  dog,  326 

of  ox,  301 
of  anus  of  horse,  371 
of  arm  of  horse,  259 

of  ox,  302 

of  pig,  314 
of  auditory  ossicles,  755 
of  back  of  dog,  325 

of  horse,  235 

of  ox,  300 

of  pig,  313 
of  cheeks  of  horse,  213 
of  digit  of  horse,  295 

of  pig,  315 
of  dog,  318 

of  eyelids  of  horse,  218 
of  face  of  dog,  318 

of  ox,  295 
of  foot  of  horse,  287 

of  ox,  309_ 

of  pig,  317 
of  forearm  of  horse,  262 
extensor  division,  263 
flexor  division,  267 

of  ox,  304 

of  pig.  315 
of  head  of  horse,  213 

of  pig,  311 
of  hip,  external,  of  horse,  276 
of  ox,  306 

of  pig,  316 
of  horse,  213 
of  larvnx  of  horse,  445 
of  leg    of  horse,   287,   288, 
290 

of  ox,  309 

of  pig.  317 
of  hps  of  horse,  213 
of  loins  of  dog,  325 

of  horse,  235 

of  ox,  300 

of  pig,  313 
of  manus  of  horse,  262 
of  mastication  of  dog,  318 

of  horse,  219 

of  ox,  297 

of  pig,  311 
of  metatarsus  of  horse,  285 
of  Miiller.  736 
of  neck  of  dog,  324 

of  horse.  224,  229 

of  ox,  298 

of  pig.  311 
of  nostrils  of  horse,  217 
of  ox,  295 

of  pehic  limb  of  dog,  326 
of  horse.  274 
of  ox,  306 
of  pig.  316 
of  penis  of  horse,  496 
of  phan,-nx  of  horse,  348 
of  pig,  311 


808 


Muscle  of  shoulder    girdle  of 
horse,  250 
of  ox,  302 
of  pig,  314 
joint  of  horse,  181 
of  horse,  255 
of  ox,  302 
of  pig,  314 
of  tail  of  dog,  325 
of  horse,  23S 
of  ox,  300 
of  pig,  314 
of  thigh,  anterior,  284 
external,  of  horse,  276 

of  ox,  308 
internal,  of  horse,  281 
of  pig,  316 
of  thoracic  limb  of  dog,  319 
of  horse,  250 
of  ox,  302 
of  pig,  314 
of  tliorax  of  dog,  325 
of  liorse,  240 
of  ox,  300 
of  pig,  313 
of  tongue  of  horse,  337 
onio-hyoideus,  224,  226 
of  ox,  298 
of  pig,  312 
omo-transvcrsarius   of   dog, 
319 
of  ox,  302 
of  pig,  312,  314 
orljicular,  211 
orbicularis   ocuh,   218 
of  ox,  296 
oris  of  dog,  318 
of  horse,  213 
of  ox,  295 
of  pig,  311 
origin  of,  212 
palato-pharyngeus,  349 
palmaris  brevis,  of  dog,  324  I 
longus  accessorius,  of  dog, 
323 
palpebral,  of  dog,  318 
panniculus  carnosus,  of  dog, 
318 
of  pig,  311 
of  ox,  295 
of  pig,  311 
parainoro-biceps,  278 
parieto-auricularis,  750 
of  dog  780, 
of  ox,  774 
parol  ido-auricularis,  750 
peel  ineus,  of  dog,  328 
of  horse,  282 
of  ox,  308 
of  pig,  316 
pectoral,     anterior    superfi- 
cial, of  pig,  314 
deep,  of  dog,  320 
of  horse,  253 
of  pig,  314 
of  horse,  252 

posterior  deep,  of  pig,  314 
.sup(>rficial,  of  dog,  320 
of  horse,  253 
of  pig,  314 
peroneus  brevis,  of  dog,  328 
longus  of  dog,  328 

of  pig,  317 
of  horse,  288 


Muscle,    peroneus    tertius,   of 
dog,  328 
of  horse,  289 
of  ox,  310 
of  pig,  317 
plantar,  of  pig,  317 
popUteus,  of  dog,  329 
of  horse,  294 
of  pig,  317 
preputial,  of  ox,  503 
pronator  quadratus,  of  dog, 
324 
teres,  of  dog,  323 
of  horse,  268 
of  pig,  315 
protractor,  of  prepuce  of  ox, 

503 
psoiis  major,  of  dog,  326 
of  horse,  275 
of  ox,  306 
of  pig,  316 
minor,  of  dog,  326 
of  horse,  275 
of  ox,  306 
of  pig,  316 
pterygoideus  externus,  220 
internus,  of  horse,  219 
lateralis,  of  horse,  220 
of  ox,  297 
pterygo-pharyngeus,    of 

horse,  349 
pyriformis,  of  dog,  326 

of  horse,  284 
quadratus  femoris,   of  dog, 
328 
of  horse,  283 
of  ox,  308 
of  pig,  317 
lumborum,  of  dog,  326 
of  horse,  276 
of  ox,  306 
of  pig,  316 
plantar,  of  dog,  329 
quadriceps  femoris,  284 
of  ox,  307 
of  pig,  317 
radialis  volaris,  of  dog,  323 
rectus   abdominis   internus, 
of  pig,  313 
of  dog,  326 

of  horse,  248 
of  ox,  301 
of  pig,  313 
capitis  anterior  major,  of 
dog,  324 
of  horse,  227 
of  ox,  300 
minor,  of  horse,  227 
of  ox,  300 
dorsalis  major,  of  horse, 
234 
minor,  of  horse,  234 
lateralis,  of  horse,  228 

of  ox,  300 
of  pig,  313 

posterior      major,      of 
horse,  234 
minor,  of  horse,  234 
femoris,  of  dog,  327 

of  horse,  284 
lateralis,  of  dog,  324 
minor,  of  dog,  324 
oeuli,  738 
parvus,  of  horse,  286 


Muscle,    rectus     thoracis,    of 
horse,  242 
of  pig,  313 
relations  of,  213 
retractor  ani,  of  dog,  432 
of  horse,  371 
eosta>,  of  horse,  242 

of  pig,  313 
oculi,  73S 

of  prepuce  of  ox,  503 
penis,  of  horse,  496 
of  ox,  503 
rhomboideus  capitis,  of  dog, 
320 
cervicalis,  of  dog,  320 

of  horse,  251 
of  dog,  320 
of  horse,  251 
of  ox,  302 
of  pig,  314 

thonicalis,  of  dog,  320 
of  horse,  251 
ring-like,  21 1 
rotator,  757 

sacro-coecygei,  of  pig,  314 

sacro-coccygeus  accessorius, 

of  dog,  325 

inferior,  of  horse,  240 

lateralis,  of  horse,  239 

of  dog,  325 

superior,  of  horse,  238 
ventralis      lateralis,       of 
horse,  240 
sartorius,  of  dog,  328 
of  horse,  281 
of  ox,  308 
of  pig,  316 
scalenus  dorsalis,  of  dog,  324 
of  ox,  300 
of  horse,  227 
of  pig,  312 
ventralis,  of  dog,  324 
of  ox,  298 
of  pig,  312 
scansorius,  of  horse,  278 
scapulo-humeralis   posticus, 

of  horse,  258 
scapulo-ulnaris,  of  horse,  260 
scutularis,  749 
semimembranosus,    of    dog, 
327 
of  horse,  280 
of  ox,  306 
of  pig,  316 
.semispinalis  capitis,  of  horse, 
231 
colli,  of  horse,  231 
semitcndinosus,  of  dog,  327 
of  horse,  280 
of  ox,  30f) 
of  pig,  316 
serratus  anterior  hominis,  of 
horse,  254 
anticus,  of  dog,  325 
of  horse,  235 
of  ox,  300 
of  pig,  313 
cervicis,  of  horse,  254 
magnus,  of  dog,  320 
of  horse,  254 
of  ox,  302 
of  pig,  314 
posticus,  of  dog,  325 
of  horse,  236 


INDEX 


80!) 


Muscle,  serratus    posticus,  of 
ox,  300 

thoracis,  of  horse,  254 
vcntralis,  of  horse,  254 
shape  of,  212 
short,  211 
skeletal,  211 
small  posterior  straight,  of 

head  of  horse,  234 
soleus,  of  horse,  292 

of  ox,  311 

of  pig,  317 
sphincter,  211,  213 

ani  externus,  of  horse,  371 
internus,  of  horse,  371 

pupilte,  744 
spinalis  et   semispinalis,   of 
pig,  313 

of  horse,  233 
spinous,  transverse,  of  neck 

of  horse,  231 
splenius,  of  dog,  324 

of  horse,  229 

of  ox,  300 

of  pig,  312 
stapedius,  755 
sterno-cephalicus,     of    dog, 
324 

of  neck  of  horse,  225 

of  ox,  29S 

of  pig,  312 
sterno-mandibularis,  225 
sterno-maxillaris,  225 
sterno-thyro-hyoideus,       of 
dog,  319 

of  horse,  224,  226 

of  ox,  298 

of  pig,  312 
sterno-thyroideus  et  sterno- 

hyoideus,  of  horse,  226 
straight,    of    head    of    pig, 

312 
striated,  211 
structure  of,  212 
stylo-glossus,  of  horse,  337 
stylo-hyoideus,  of  dog,  319 

of  horse,  223 

of  ox,  297 
stvlo-mandibularis,  222 

"of  ox,  297 
stylo-niaxillaris,  222 
stylo-pharyngeus,  349 
sublumbar,  of  horse,  274 

of  ox,  306 

of  pig,  316 
subscapularis,  of  dog,  321 

of  horse,  257 

of  ox,  302 

of  pig,  314 
subscapulo-hyoideus,  226 
superficial  digital  flexor,  269 
of  leg  of  horse,  292 
of  ox,  305 

flexor,  of  ox,  311 

gluteus,  of  horse,  277 

pectoral,  of  ox,  302 
supinator,  of  dog,  323 

of  pig,  315 
supraspinatus,  of  dog,  321 

of  horse,  256 

of  ox,  302 

of  pig,  314 
tarsal,  736 
temporalis,  of  dog,  318 


Muscle,  temporalis,  of    horse, 
219 
of  ox,  297 
tendo  femorotarseus,  289 
tensor  fasciae  antibrachii,  of 
dog,  322 
of  horse,  260 
of  ox,  303 
of  pig,  315 
lata>,  of  dog,  326 
of  horse,  276 
of  ox,  306 
of  pig,  316 
palati,  of  horse,  333 
tyrnpani,  755 
teres  major,  of  dog,  322 
of  horse,  258 
of  ox,  302 
of  pig,  314 
minor,  of  dog,  321 
of  horse,  256 
of  ox,  302 
of  pig,  314 
th>To-arytenoideus,  446 
thyro-hyoideus,  445 
thjTO-pharyngeus,  350 
tibiaUs  anterior,  of  dog,  328 
of  horse,  290 
of  ox,  310 
of  pig,  317 

posterior,  of  dog,  329 
trachelo-mastoideus,  of  dog, 
325 
of  horse,  229 
of  pig,  312 
tragicus,  7.ol 

transversaUs    costarum,    of 
dog,  325 
of  horse,  236 
of  ox,  300 
of  pig,  313 
.    transversus    abdominis,     of 
dog,  326 
of  horse,  248 
of  ox,  .302 
of  pig,  313 
costarum,  of  horse,  242 
thoracis,  of  horse,  242 

of  pig,  313 
trapezius     cerv'icalis,     of 
horse,  250 
of  dog,  319 
of  horse,  250 
of  ox,  302 
of  pig,  314 

thoracalis  of  horse,  251 
triangularis  sterni,  242 
triceps  brachii,  of  horse,  260 
of  dog,  322 
of  ox,  303 
of  pig,  315 
surse,  of  horse,  292 
ulnaris  laterahs,  of  dog,  323 

medialis,  of  dog,  323 
unipennate,  212 
unstriped,  211 
urethral,  of  dog,  507 
of  horse,  499 
of  mare,  516 
of  ox,  504 
of  pig,  506 
vastus  externus,  of  horse,  285 
intermedins,  of  horse,  286 
of  ox,  307 


Muscle,    vastus    internus,    of 
horse,  286 
veiitricularis  et  vocalis,  446 
vocalis,  of  horse,  446 
volar,  of  pig,  315 
Wilson's,  of  dog,  509 

of  ox,  504 
zygoinatico-auricularis,  749 

of  ox,  774 
zygomaticus,  of  dog,  318 
of  horse,  215 
of  ox,  295 
of  pig,  311 
Muscular  bands  of  great  colon 
of  horse,  368 
coat  of  asophagus,  352 
layer  of  trachea  of  horse,  450 
process    of    arytenoid    car- 
tilages of  larynx,  443 
of  .temporal  bone,  57 
ring  of  ca'cum  of  horse,  365 
system,  211 
Muscularis   mucosa-   of  small 

intestine,  362 
Musculi  papillares  of  left  ven- 
tricle, 533 
of  right  ventricle,  531 
pectinati,   in   right    atrium, 
530 
Musculo-outaneous    n  e  r  v  e  s, 
696 
of  dog,  730 
of  horse,  697 
of  leg  of  horse,  708 
Musculo-spiral  groove,  77 

nerve  of  horse,  698 
Myenteric  plexus,  714 
Mj'lohyoid  nerve,  682 

of  dog,  728 
Mylo-hvoideus  muscle  of  dog, 
.319 
of  horse,  222 
of  ox,  297 
Myocardium,  534 
Myology,  211 


X.\RES,  anterior,  of  horse,  436 
posterior,  of  horse,  68,  348, 
440 
Nasal  artery,  550 
of  ox,  611 
bones  of  dog,  158 
of  horse,  61 
of  ox,  121 
of  pig,  143 
cavity  of  dog,  161,466,  467 
of  horse,  71,  4.36 

common  meatus  of,  440 
ethmoidal  meatuses,  440 
inferior  meatus  of,  439 
middle  meatus  of.  438 
parietal  cartilage,  437 
superior  meatus  of,  438 
vessels  and  ner\'es,  437 
of  ox,  125,  458 
of  pig,  145,  464 
structure  of,  436 
crest  of  horse,  71 
glands  of  horse,  440 
mucous  membrane,  440 
muscles  of  dog,  318 
nerve  of  dog,  728 
of  horse,  679 


810 


INDEX 


Nasal  process  of  horso,  GO 
region  of  horse,  66 
.septum,  71,  72,  73,  437 
vein  of  ox,  621 
of  i)ig,  630 
Naso-ciliarj'  nerve,  678 
of  ox,  717 
of  pig,  722 
Nasofrontal  suture,  o/i,  61 

of  ox,  1 19 
Naso-labial  glands  of  ox,  77") 
Naso-lacrinial  duet    of    horse, 
436,  737 
canal  for,  71 
groove  for,  71 
of  dog,  779 
of  ox,  773 
suture  of  horse,  61 
Naso-maxillary  fissure,  73,  439 
notch  of  horse,  61 
suture  of  horse,  61 
Naso-palatine  canal  of  ox,  384 
Naso-turbiiial  liones,  62 
Navicular  bone,  92,  1 1 1 

bursa  of  deep  digital  flexor 

muscle,  272 
ligaments,  inferior,  190 
suspensory,  of  horse,  189 
Neck  of  dog,  muscles  of,  324 
of  horse,  fivscia  of,  224 
fascia  propria  of,  224 
muscles  of,  224,  229 
panniculus  carnosus,  224 
transverse  spinous  muscle 
of,  231 
of  ox,  muscles  of,  298 
of  pig,  muscles  of,  311 
of  tooth,  339 
Nerve  or  nerves,  abducent,  683 
alveolar,  681,  682 

of  dog,  729 
auditory.  6S6 
auricular,  6S.3 

posterior,  69.5 
auriculopalpebral,  6S5 
of  dog,  729 
of  ox,  717 
axillary,  697 

of  horse,  697 
buccal,  685 
of  dog,  729 
of  ox,  717 
of  pig,  722 
buccinator,  of  horse,  681 
cardiac,  712 
cervical,  of  horse,  694 
chorda  tympani,  683,  684 
ciliary,  of  dog,  728 

of  horse,  679 
circumflex,  of  horse,  697 
cla.ssitication  of,  644 
coccygeal,  of  horse,  710 
cochlea,  686 
cranial,  of  dog,  728 
of  horse,  676 
of  ox,  717 
of  pig,  722 
crural,  anterior,  706 
cutaneous,  of  leg,  708 

of  neck,  69.') 
dental,  (iM,  682 
depressor,  of  dog,  730 
diga.stric,  68,5 
digital,  of  dog,  730,  732 


Nerve,  digital,  of  horse,  701 

of  ox,  718 

of  pig,  723 
eighth,  686 
eleventh,  690 
ethmoidal,  678 

of  dog,  728 
facial,  684 

of  dog,  729 

of  ox,  717 
femoral,  of  horse,  706 
fifth,  of  horse,  677 
first,  of  horse,  676 
fourth,  of  horse,  677 
frontal,  of  dog,  728 

of  horse,  678 

of  ox,  717 
glossopharyngeal,  (iSii 
ghiteal,  of  hor.se,  706 
hemorrhoidal,  of  horse,  710 
hvpoglossal,  692 
"of  dog,  730 

of  ox,  717 

of  pig,  722 
ilio-hypogastric,  704 
iUo-inguinal,  of  horse,  704 
infra-orbital,  of  dog,  728 

of  horse,  681 

of  pig,  722 
infra-trochlear,  679 

of  dog,  728 
intercostal,  of  horse,  702 
labial,  of  horse,  681 
lacrimal,  of  dog,  728 

of  horse,  678 

of  ox,  717 

of  pig,  722 
larvngeal.  of  dog,  729 

recurrent,  689 

superior,  689 
lingual,  ()S3 

of  dog,  729 
lumbar,  of  horse,  702 
mandibidar,  of  dog,  728 

of  horse,  681 

of  ox,  717 

of  pig,  722 
masseteric,  of  horse,  681 
maxillary,  of  dog,  728 

of  horse,  679 

of  pig,  722 
median,  696 

of  dog,  731 

of  horse,  699 

of  ox,  719 

of  pig,  723 
metacarpal,  of  dog,  731 

of  horse,  701 
metatarsal,  of  dog,  732 
nnisculocutaneous,  696 

of  dog,  730 

of  horse,  697,  698 

of  leg  of  horse,  708 
musculospiral,  of  horse,  098 
mvlohvoid,  t)82 

of  dog,  728 
nasal,  of  dog,  728 

of  horse,  697,  681 
nasociliary,  678 

of  ox,  717 

of  pig,  722 
ninth,  686 
oculomotor,  of  horse,  677 

of  ox,  717 


Nerve,  obturator,  of  horse,  706 
a'sophageal,  of  dog,  729 
of  adrenal  bodies,  478 
of  articulations,  171 
of  bladder  of  horse,  477 
of  cornea,  742 
of  external  ear,  752 
of  eye,  737 

of  Fallopian  tubes,  511 
of  hoof,  771 

of  mammary  glands  of  cow, 
521 
of  mare,  517 
of  ovaries  of  mare,  510 
of  penis  of  horse,  496 
of  prepuce  of  horse,  497 
of  ptervgoid  canal,  681 
of  skin^  7(i2 
of  spermatic  cord,  489 
of  tympanum,  755 
of  uterus  of  mare,  513 
of  vagina  of  mare,  514 
of  vascular  tunic  of  eye,  745 
of  veins,  525 
olfactory,  of  horse,  676 
ophthalmic,  678 

of  dog,  728 
optic,  of  horse,  676 
palatine,  of  dog,  728 

of  horse,  679,  680 
pectoral,  696 
peroneal,  deep,  of  ox,  720 

of  dog,  732 

of  horse,  708 

of  pig,  723 
petrosal,  684 
pharyngeal,  of  dog,  729 
phrenic,  695 
plantar,  of  dog,  732 

of  horse,  709 

of  ox,  720 

of  pig,  723 
pneumogastric,  687 
pterygoid,  of  horse,  681 
pudic,  of  horse,  710 
pulmonary,  of  horse,  457 
radial,  of  dog,  730 

of  horse,  696,  698 

of  ox,  718 
sacral,  of  horse,  710 
saphenous,      external,      of 
horse,  708 

of  dog.  731 

of  hnrsc.  7116 
sciatic.  i<i  liMisc,  707 
second,  of  horse,  676 
seventh,  684 
sixth,  683 

spermatic,  external,  704 
sphenopalatine,  of  dog,  728 

of  liorse,  679 
spinal  accssm-y,  690 
of  ox,  717 

of  dog,  730 

of  hor.sc,_692 

of  ox,  717 

of  pig,  723 
splanchnic,  713 
stapedial,  684 
subscapular,  696 
supply  of  eye  muscles,  739 
suprascajiular,  696 

of  horse,  697 
temporal,  682 


IXDEX 


811 


Ner\'e,  temporal,  of  dog,  72S 
of  horse,  681 
of  ox,  717 
of  pig,  722 
tenth,  687 
third,  of  horse,  677 
thoracic,  anterior,  696 

of  horse,  697,  702 
thoracodorsal,  697 
tibial,  anterior,  70S 
of  dog,  732 
of  horse,  70S 
of  ox,  720 
trifacial,  of  horse,  677 
trigeminal,  of  horse,  677 
trochlear,  of  horse,  677 
twelfth,  692 
tympanic,  686 
idnar,  of  dog,  730 
of  horse,  696,  698 
of  ox,  718 
of  pig,  723 
vagus,  687 
of  dog,  729 
of  ox,  717 
of  pig,  722 
ventral,  of  dog,  729 
vestibular,  686,  761 
Vidian.  681 
volar,  of  horse,  701 

of  ox,  718,  719 
zygomatic,  of  dog,  728 
of  horse,  679 
Xerve-ceUs,  644 
Nerve-plexus,  645 
Xervous  system.  644 
of  dog,  724 
of  horse,  724 
of  ox,  71.5 
of  pig.  720 
symphathetic,  710 
Xervus  accessorius,  690 
lacrimalis,  678 
oculomotorius,  of  horse,  677 
olfactorius  of  horse,  676 
ophthalmicus,  678 
opticus  of  horse,  676 
trigeminus,  677 
trochlearis,  677 
Neuroglia,  644 
Neurologj',  644 
Neurone,  644 
Ninth  nerve,  686 
Nippers.  339 
Nipple  of  mammary  gland  of 

mare,  .516 
Nodules,  lymph,  600 

of  spleen  of  horse,  379 
Nodulus.  660 

Nose  of  horse,  common  meatus 
of,  62 
inferior  meatus  of,  62,  72 
meatuses  of,  71 
middle  meatus  of,  62.  72 
superior  meatus  of.  62,  72 
Nostrils  of  dog,  466 
of  horse,  436 
of  ox,  458 
of  pig,  464 
Notch,  acetabular,  of  horse,  96 
cardiac,  of  lungs,  456 
carotid,  of  horse.  51 
glenoid,  of  horse.  76 
naso-maxillarj',  of  horse,  61 


Notch,    oesophageal,    of    dog, 
434 
of  tibia  of  horse,  102 
oval,  of  horse,  51 
popliteal,  of  tibia,  102 
sciatic,  lesser,  of  horse,  95 
semilunar,  of  ulna,  82 
sigmoid,  of  horse.  64 
sphenoidal,  of  horse,  55 
spinous,  of  horse,  51 
Nuchal  surface  of  skull  of  dog, 
160 
of  horse,  69 
of  ox,  124 
of  pig,  145 
Nuclei  of  origin  of  nerves,  644 
Nucleocerebellar       fasciculus, 

661 
Nucleus  als  cinerese,  690 
amygdalae,  676 
caudatus,  675 
cuneatus,  658 
dorsal  sensory,  660 
dorsalis,  651 
facial,  684 
gracilis,  658 
hypoglossal,  692 
hypothalamieus,  665 
lenticular.  675 
lentiformis,  675 
lentis,  747 

of  soUtary  tract.  690 
oUvaris  caudatis,  658 

nasalis,  660 
ruber,  665 
subthalamic,  665 
X'utrient  artery,  21 
of  femur,  580 
of  humerus,  559 
of  tibia,  .581 
foramen  of  femur,  97 
of  humerus,  78 
of  ilium.  94 
of  metacarpus,  88 
of  tibia,  100 


Obex,  663 

Oblique    extensor    muscle    of 
metacarpus  of  horse,  267 
muscle,    small,    of   head   of 
horse.  233 
Obliquus   abdominis   externus 
muscle  of  dog,  326 
of  horse.  246 
of  ox.  301 
of  pig,  313 
internus   muscle   of   dog, 
326 
of  horse,  247 
of  ox,  301 
of  pig,  313 
capitis    anterior    muscle    of 
horse,  233 
posterior  muscle  of  horse. 
233 
of  pig,  313 
ocuh  inferior,  738 
superior,  738 
Obturator  arterv,  577 
of  ox,  619 
externus    muscle    of    horse, 
283 
of  ox,  308 


Obturator  externus  muscle  of 
pig,  317 
foramen  of  dog,  1()7 
of  horse,  96,  97 
of  ox,  132 
internus  muscle  of  horse,  283 
of  ox,  308 
of  pig,  317 
membrane  of  hor.se,  191 
nerves  of  horse,  706 
vein,  .598 
Occipital  artery,  544 
of  dog,  633 
of  ox,  611 
of  pig.  627 
bone  of  dog,  154 
of  horse,  47 

development,  50 
of  ox.  115 
of  pig.  139 
condyles  of  horse,  48,  68,  69 
crest  of  horse,  .50.  69 
protuberance,  external,  50 

internal,  54 
sinus,  591 
vein,  .588 
Occipito-hvoideus  muscle,  223 

of  ox,"29S 
Ocular  muscles  of  horse,  738 

sheath  of  horse,  738 
Oculomotor  nerve  of  horse,  677 

of  ox,  717 
Odontoid  ligament,  176 
process  of  axis  of  horse,  34 
of  ox,  112 
ffidema  glottidis  of  horse,  448 
Oesophageal  arterv,  565,  567 
of  ox,  614 
of  pig,  627 
groove  of  ox,  394 

of  sheep,  408 
nerve  of  dog,  729 
notch  of  dog,  434 
opening  of  horse,  348 
plexus,  713 

of  dog,  730 
vein,  587 
Oesophagus  of  dog,  428 
of  horse.  3.50 
of  ox,  3S9 
of  pig.  417 
of  sheep.  407 
Olecranon  fossa,  80 

of  horse.  83 
Olfactory  bulb,  6.53,  671 
of  dog,  727 
of  ox,  717 
of  pig.  721 
cells,  772 

fossa  of  horse,  52,  70 
glands  of  horse,  440,  772 
nerve  of  horse,  676 
organs  of  dog,  781 

of  pig,  779 
peduncle,  671 
striae,  671 
tracts.  671 
of  pig.  721 
Olivary  eminence  of  dog,  725 
nucleus,  anterior,  660 
posterior,  658 
Olivocerebellar  fibers,  661 
Omaso-abomasal     arterj-     of 
ox,  615 


812 


INDEX 


Oniiiso-abomasal  orifice  of  ox, 

396 
Omasum  of  ox,  390,  392 

of  sheep,  408 
Omental  cavity  of  horse,  380 
Oiiientuni,  gastro-coUc,  358 
fjaslio-hepatie,  3.54,  3.58 
gastro-spleuic,  354,  358,  379 
groat,  of  horse,  354,  358 

of  ox,  396 
lesser,  of  ox,  396 
Omo-hyoideus  muscle,  224,  22() 
of  ox,  298 
of  pig,  312 
Omo-transversarius  muscle  of 
dog,  319 
of  ox,  302 
of  pig,  312,  314 
()l)hthalmic  artery,  5.53 
of  (log,  635 
of  ox,  612 
ner\e,  678 

of  dog,  728 
vein,  590 
Optic  axis,  740 
chiasm,  666 
commissure,  666 
foramen,  .50,  51,  67,  70 
groove  of  horse,  50 
nerve  of  horse,  676 
papilla,  745 
of  ox,  774 
of  pig,  778 
recess,  667 
thalamus,  664 
tract,  664,  666 
of  ox,  716 
Ora  serrata,  745 
Orbicular  muscles,  211 
Orbicularis  oculi  muscle,  218 
of  ox,  296 
oris  muscle  of  dog,  318 
of  horse,  213 
of  ox,  295 
of  pig,  311 
Orbit  of  horse,  67 
Orbital  artery,  555 
ducts  of  dog,  427 
fascia  of  horse,  738 
fissure  of  horse,  51 
foramen,  internal,  67,  70 
gland  of  dog,  427 
region  of  horse,  67 
veins  of  ox,  621 
wings  of  horse,  51 
Organ  of  ("orti,  760 
of  Jacobson,  772 
of  sense,  734 

vomero-n;isal,  of  horse,  440 
Orifice,  aortic,  of  heart,  533 
aVrio-ventricular,     left,     of 
ventricle,  530,  533 
right,    of    ventricle,    530, 
531 
ca;co-colic,  of  horse,  364 
fronto-inaxillary,  73 
ileo-ca'cal,  of  horse,  364 
laryngeal,  of  horse,  348 
of    anterior    vena    cava    of 

horse,  529 
of  coronary  sinus,  529 
of  posterior  vena  cava,  529 
omaso-abomasal,  of  ox,  396 
preputial,  of  horse,  496 


Orifice,   pulmonary,    of    right 
ventricle,  531 
reticulo-omasal,  of  ox,  394 
rumino-reticular,  of  ox,  393 
ureteral,  of  horse,  477 
urethral,    external,   of   cow, 
519 
of  horse,  499 
of  mare,  515 
of  ox,  503 
internal,  of  horse,  477 

of  male  horse,  499 
of  pig,  .505 
Os  coronae  of  horse,  89 
coxa>,  29 
of  horse,  92 
of  pig,  148 
pedis  of  dog,  506 

of  horse,  90 
rostri  of  pig,  143,  464 
sufTraginis  of  horse,  89 
uteri  externum  of  mare,  513 
internum  of  mare,  513 
Ossa  cordis  of  ox,  609 
Osseous  labyrinth,  758 
Ossicles,  auditory,  754 
Ossification,  22 
endochondral,  22 
intramembranous,  22 
of  vertebra;,  25 
Osteoblasts,  22 
Osteoclasts,  22 
Osteogenesis,  22 
Osteology,  19 

Ostium  abdominale   of   mare, 
511 
uterinum  of  mare,  51 1 
Otic  ganglion,  681,  711 

of  ox,  717 
Outlet  of  pelvis,  97,  354 
Ova  of  mare,  510 
Oval  notch  of  horse,  51 
Ovarian  artery,  571 
of  mare,  510 
ligament  of  bitch,  522 
of  mare,  509 
Ovaries  of  bitch,  .522 
of  cow,  517 
of  mare,  50S 
of  sow,  .521 
Overextended  joints,  171 
Overshot  dog,  425 
Ovulation  fossa  of  mare,  509 
in  mare,  510 


Pacchionian  liodies,  647 
Pad,  dental,  of  ox,  384 
Pads  of  dog,  780 
Palate,  hard,  of  dog,  423 

of  horse,  69,  332 

of  ox,  3S3 

of  pig,  411 

of  sheep,  405 
soft,  of  dog,  424 

of  horse,  332 

of  ox,  3S4 

of  pig,  411 
Palatine  artery,  555 

of  pig,  627 
bones  of  horse,  60 

of  ox,  120 

of  pig,  142 
canal  of  horse,  58 


Palatine  cleft  of  horse,  60,  69, 
71 
foramen,  posterior,  58,  68 
glands  of  horse,  333 
groove  of  horse,  59,  69 
nerve  of  dog,  728 

of  horse,  679,  680 
process  of  dog,  157 
of  maxilla  of  horse,  58 
of  premaxilla>  of  horse,  60 
region  of  horse,  68 
sinus  of  ox,  120,  126 
suture,  median,  69 

transverse,  of  horse,  69 
vein,  589 
Palato-labial  artery,  555 
Palato-pharvngeus  muscle,  349 
Pallium,  668 

Palmar  metacarpal  artery,  563 
Palmaris  brevis  muscle  of  dog, 
324 
longus  accessorius  muscle  of 
dog,  323 
Palpebral  fissure  of  horse,  735 
ligament,  736 
muscle  of  dog,  318 
sebum,  736 
Pampiniform  plexus  of  testi- 
cles of  horse,  487 
Pancreas  aselli  of  dog,  643 
of  dog,  434 
of  horse,  371 
of  ox,  404 
of  pig,  423 
of  sheep,  410 
Pancreatic  arteries,  569 

duct,  accessory,  of  dog,  431 
of  horse,  373 
of  dog,  431,  434 
of  horse,  372 
of  ox,  398 
of  pig,  419,  423 
lymph  glands,  605 
vein,  597 
Pancreatico-duodenal     arter\-, 

569 
Panniculus,  abdominal,  245 
adiposus  of  horse,  761 
carnosus  of  dog,  318 
of  head  of  horse,  213 
of  horse,  213,  761 
of  neck  of  horse,  224 
of  pig,  311 
facial,  of  pig,  311 
muscle  of  ox,  295 
scapulo-humeral  portion, 255 
thoracic  portion,  255 
Papilla  communis  of  kidnev, 
474 
filiform,  of  tongue,  336 
foliate,  of  tongue,  336 
fungiform,  of  tongue,  330 
hair,  763 

of  dieeks  of  ox,  382 
of  skin,  762 
of  tongue,  336 
optic,  745 

of  ox,  774 
renalis  of  ox,  480 
vallate,  of  tongue,  336 
Paramastoid  process,  48,  68. 69 
Paramero-biceps  muscle,  27S 
Paranasal    sinuses    of    horse, 
72 


Parapharvngcal  Ivmph   ghiiid 

of  ox,  &2S 
Paratliyroid  gland  of  clog,  4t)S 
of  horse,  -158 
of  ox,  -le-i 
Parenchyma  of  adrenal  bodies, 
478" 
of  liver,  377 

of  mammary  glands,  51G 
testis,  486 
Parietal  hones  of  dog,  155 
of  horse,  54 
of  ox,  117 
of  pig,  140 
cartilage  of  nasal  cavity,  437 
crest  of  ox,  117 
pleura  of  horse,  451 
region  of  skull  of  horse,  O'j 
Parieto-auricularis,  750 
of  dog,  780 
of  ox,  774 
Parieto-frontal  suture,  54,  55 
Parieto-occipital  suture,  54 
Parieto-temporal  canal,  54,  57 

suture,  56 
Parolfactory  area,  671 
Parotid  artery,  543 
of  pig,  627 
duct  of  dog,  423,  427 
of  horse,  347 
of  pig,  411,  414 
gland  of  dog,  427 
of  horse,  346 
of  ox,  388 
of  pig,  414 
lymph  gland  of  dog,  643 
of  pig,  630 
Parol  ido-auricularis,  750 
of  dog,  780 
of  ox,  774 
Pars  liasilaris  pontis,  660 
ciliaris  retinie,  745 
dorsalis  pontis,  660 
intercartilaginea  of  larvnx, 

448 
intermembranacea  of  larvnx, 

44S 
iridica  retinae,  745 
optica  retina>,  745 
Pastern  bone,  89 
joint,  188 

movements  of,  189 
Patches,  Peyer's,  of  horse,  363 
of  ox,  398 
of  pig,  419 
Patella,  29 
of  dog,  168 
of  horse,  104 
of  ox,  134 
of  pig,  149 
Patellar  ligaments,  195,  196 
Pathetic  foramen,  67 
Pectineus  muscle  of  dog,  328 
of  horse,  282 
of  ox,  307 
of  pig,  316 
Pectoral  fascia  of  horse,  252 
lymph  glands,  602 
muscle,  anterior  superficial, 
of  pig,  314 
deep,  of  dog,  320 
of  horse,  253,  254 
of  ox,  302 
of  pig,  314 


INDEX 

Pectoral   muscle,  deep,  poste- 
rior, of  pig,  314 
of  horse,  2.52 
posterior    superficial,    of 

pig,  314 
superficial,  of  dog,  320 
of  horse,  253 
of  ox,  302 
nerve,  696 
Peduncles,  cerebellar,  661 
cerebral,  664 
of  ox,  716 
of  pig,  720 
middle  cerebellar,  659 
olfactory,  671 
Pelvic    artery   of    horse,    97, 
354 
of  ox,  133,  390 
fascia  of  horse,  273 
flexure  of  horse,  366 
girdle,  29 

of  horse,  92 
limb,  bones  of,  29 

of  dog,  articulations  of, 
209 
bones  of,  165 
muscles  of,  326 
of  horse,  articulations  of, 
190 
bones  of,  92 
fascise  of,  273 
muscles  of,  274 
of   ox,    articulations   of, 
209 
bones  of,  131 
muscles  of,  306 
of   pig,   articulations  of, 
209 
bones  of,  148 
muscles  of,  316 
peritoneum  of  horse,  355 
plexus,  713,  715 
Pelvis  of  dog,  167 
inlet  of,  167 
of  horse,  96 
axis  of,  97 

conjugate  diameter,  97 
inlet  of,  96 
outlet  of,  97 

sacro-pubic  diameter,  97 
sexual,  differences  of,  97 
transverse  diameter,  97 
of  kidnev  of  horse,  473 
of  ox,  13"2 
axis  of,  133 

conjugate  diameter,  132 
inlet  of,  132 
of  pig,  148 
inlet  of,  148 
Penis,  glans,  of  dog,  506 
of  horse,  495 
of  ox,  503 
of  dog,  506 
glans,  506 
OS  of,  506 
prepuce  of,  507 
of  horse,  494 
arteries  of,  496 
Ijody  of,  494 
corona  glandis  of,  495 
corpus  cavernosum,  495 

spongiosum,  495 
fossa  glandis  of,  495 
glans,  495 


813 

Penis  of  horse,  ischio-caverno- 
sus  muscle  of,  496 
lymphatics  of,  496 
muscles  of,  496 
nerves  of,  496 
root  of,  494 
sheath  of,  496 
structure  of,  495 
suspensory        ligaments, 

494 
veins  of,  49t) 
vessels  and  nerves,  496 
of  ox,  503 

bulbo-cavernosus  muscle 

of,  503 
glans,  ,503 
ischio-cavernosus  muscle 

of,  503 
prepuce  of,  503 
retractor  muscle  of,  503 
septum  of,  .503 
of  pig,  505 

prepuce  of,  506 
Periarticular  ligaments,  171 
Pericardiac  pleura,  452 
Pericardium  of  dog,  632 
of  horse,  525 
of  ox,  608 
of  pig,  626 
Perichorioid  space,  742 
Perineal  artery,  574 
of  dog,  641 
vein  of  ox,  622 
Periople,  765 
of  ox,  775 
structure  of,  768 
Perioplic  matrix,  769 
Periorbita  of  horse,  738 
Periosteal  artery,  21 
Periosteum,  21 

alveolar,  of  teeth,  339 
Peritoneal  ring  of  horse,  490 
Peritoneum  of  horse,  353,  379 

pelvic,  355 
Permanent  teeth  of  horse,  340 
Peroneal  artery,  585 
nerve,  deep,  of  ox,  720 
of  dog,  732 
of  horse,  708 
of  pig,  723 

superficial,  of  ox,  719 
Peroneus    brevis    muscle    of 
dog,  328 
longus  muscle  of  dog,  328 

of  pig,  317 
muscle  of  horse,  288 
tertius  muscle  of  dog,  328 
of  horse,  289 
of  ox,  310 
of  pig,  317 
Perpendicular  artery,  .564 

plate  of  ethmoid,  52 
Petro-basilar   canal   of   tem- 
poral bone  of  dog,  1.56 
Petrosal  crest  of  horse,  57,  70 
nerve,  684 
sinus,  inferior,  592 
superior,  591 
Petro-tympanic  fissure,  57 
Petrous  ganglion,  ()S6 
temporal  bone,  56 
of  ox,  120 
Pever's  patches  of  horse,  363 
of  ox,  398 


814 


INDEX 


Peyer's  patches  of  pig,  419 
Phacoid  bone  of  cat,  164 
Phulanges,  29 
distal,  29 
first,  29 
of  dog,  16.5 
of  liorse,  89,  111 
of  ox,  130 
middle,  29 
of  dog,  165 
of  horse,  89    1 1 1 

ligaments  of  lateral  car- 
tilages of,  190 
of  ox,  130,  136 
of  pig,  148,  1.50 
proximal,  29 
second,  29 
of  dog,  16.5 
of  horse,  89,  111 
of  ox,  130 
tliird,  29 
of  dog,  165 
of  horse,  90,  111 
of  ox,  130 
Pharyngeal  aperture,  447 
aponeurosis,  350 
artery,  548 
of  ox,  611 
fascia  of  horse,  213 
isthmus  of  horse,  350 
lymph  glands,  602 
of  (log,  643 
of  pig,  630 
nerve  of  dog,  729 
opening  of  Eustachian  tube, 

755 
plexus  of  dog,  729 
recess,  350 
Pharynx  of  dog,  427 
of  horse,  348 
of  ox,  389 
of  pig,  416 
of  sheep,  407 
Philosophical  anatomy,  17 
Philtrum  of  horse,  331 
Phrenic  artery,  565 
of  ox,  014 
nerve,  695 
vein,  596 
Phrenieo-abdominal  artery  of 
dog,  639 
of  pig,  628 
Pia  mater,  647 
Pillar,  anterior,  of  soft  palate 
of  horse,  333 
of  fornix,  173 
of  rumen  of  ox,  393 
posterior,  of  soft  palate,  333, 
3.50 
Pilomotor  fibers,  711 
Pinchers,  339 
Pineal  body,  665 
of  ox,  716 
recess,  667 
Pinna  of  horse,  747 
Pituitary  body,  653,  664,  665 
of  (log,  726 
of  ox,  716 
fossa  of  horse,  50 
Pivot  joint,  172 
Plantar  arch,  581 
arteries,  581 
of  dog,  640 
of  ox,  619 


Plantar  cushion,  771 

artery  of,  564 
flexion  of  joints,  171 
fossa  of  femur,  99 
ligament  of  hock  joint,  201 
muscles  of  pig,  317 
nerves  of  dog,  732 

of  horse,  709 

of  ox,  720 

of  pig,  723 
venous  arch,  599 
Planum  nuchale  of  horse,  50 

parietale  of  horse,  50 
Plate,  dental,  of  ox,  384 
Pleura  of  horse,  451 

costal,  451 

diaphragmatic,  451 

mediastinal,  451 

parietal  part,  451 

pericardiac,  452 

pulmonarv,  452 

sagittal  fold  of,  452 

visceral,  452 
of  ox,  461 

of  thoracic  ca^^ty,  450 
pericardica  of  horse,  525 
Plexus,  abdominal,  713 
adrenal,  714 
annularis,  742 
aortic,  712 
basilar,  592 
brachial,  of  dog,  730 

of  horse,  696 

of  ox,  717 

of  pig,  723 
cardiac,  712 
carotid,  711 
cavernous,  711 
cervical,  694 
chorioid,  666 
coeliac,  714 
coronary,  595 
dorsal,  595 

gangliosus  ciliaris,  745 
gastric,  714 

of  dog,  729 
hepatic,  714 

of  horse,  377 
hypogastric,  715 
interosseous,  595 
lumbosacral,  of  dog,  731 

of  horse,  705 

of  ox,  719 

of  pig,  723 
mesenteric,  714 
myenteric,  714 
oesophageal,  713 

of  dog,  730 
of  ISIeissner,  714 
pampiniform,  of  testicle,  487 
pelvic,  715 

pharyngeal,  of  dog,  729 
pulmonarv,  690,  712 

of  (l(jg,  "730 
renal,  714 
solar,  713 

spermatic,  487,  714 
splenic,  714 
submucous,  714 
tympanic,  687 
utero-ovarian,  714 
venosi,  524 
venosus  sclera",  741 
venous,  of  urethra,  516 


Plexus,  volar,  595 
Plica  iridis,  744 

salpingo-pharyngea,  756 
vena'  cavje  of  horse,  452 
ventriculares  of  horse,  447 
vocalis  of  horse,  448 
Pneumogastric  nerve,  687 
Point  of  hock,  106 
Polus  lentis,  747 
Polymastia  of  cow,  520 
Polythelia  of  cow,  520 
Pons  of  dog,  725 
of  horse,  659 
of  ox,  716 
of  pig,  720 
PopUteal  artery,  581 
of  ox,  619 
of  pig,  630 
line  of  tibia,  100 
lymph  glands,  606 
of  dog,  643 
of  ox,  626 
of  pig,  632 
nerves,  external,  708 
notch  of  tibia,  102 
vein,  599 
of  dog,  642 
Popliteus  muscle  of  dog,  329 
of  horse,  294 
of  pig,  317 
Portal  fissure  of  liver  of  dog, 
434 
of  horse,  373 
of  ox,  402 
ring  of  horse,  372 
system,  524 
vein,  .596 
of  horse,  377 
of  ox,  623 
Portio  cla\ncularis,  253 
prescapularis,  253 
sternocostalis,  253 
Posterior  angle  of  ilium,  94 
of  pubis,  96 
of  scapula,  76 
annular  ligament,  263 
clinoid  process  of  dog,  156 

of  pig,  142 
cornu  of  thyroid   cartilage, 

442 
crucial   ligament   of    horse, 

198 
deep     pectoral     muscle     of 
horse,  254 
of  pig,  314 
facets  of  horse,  44 1 
ligament    of  pastern   joint, 
188 
of       temporo-mandibular 
articulation,  179 
nares  of  horse,  68,  348,  440 
obliquus  capitis  muscle,  233 
palatine  foramen,  58,  68 
pillar  of  soft  palate,  333,  350 
straight    muscle,    small,    of 

head,  234 
superficial    pectoral    muscle 
of  horse,  253 
of  pig,  314 
tibialis  muscle  of  dog,  329 
Postero-extemal       angle       of 

ischium  of  horse,  95 
Post-glenoid  fossa,  56 
process,  67 


INDEX 


815 


Pouch,    cutaneous,    of   sheep, 
777 
recto-genital,  of  horse,  350 
recto-V'e.sical,  of  horse,  356 
vesico-gonital,  of  horse,  356 
Poupart's  Ugamont,   246 
Precrural  lymph  glands,  606 
of  ox,  626 
of  pig,  632 
Premaxilla  of  dog,  157 
of  horse,  59 
of  ox,  120 
of  pig,  1-12 
Premaxillarv  region,  66 
Premolars,  33S,  342 
Prenasal  bone  of  pig,  143 
Preorbital  region  of  horse,  68 
Prepectoral   Ivmph   glands  of 
ox,  6"24 
of  pig,  631 
Preplantar  artery,  564 
Prepubic  artery,  579 

tendon  of  horse,  250 
Prepuce  of  chtoris  of  mare,  515 
of  dog,  507 
of  horse,  496 
raphe  of,  498 
structure  of,  497 
of  ox,  503 
of  pig,  506 
Preputial  diverticulum  of  pig, 
506 
frenum  of  horse,  497 
glands  of  horse,  497 
muscles  of  ox,  503 
orifice  of  horee,  496 
ring  of  horse,  497 
Prescapular  lymph  glands,  602 
of  dog,  643 
of  ox,  624 
of  pig,  631 
Presternum,  26 
Presylvian  fissure  of  dog,  727 
of  horse,  669 
of  pig,  721 
Prevertebral  artery,  545 
Process,  angular,  of  mandible 
of  dog,  159 
auditory,  external,  of  horse, 

56,  67 
basilar,  of  horse,  48 

of  third  phalanx,  91 
ciliary,  743 

clinoid,  anterior,  of  sphen- 
oid bone  of  dog,  156 
posterior,      of      sphenoid 
bone  of  dog,  156 
of  pig,  142 
coracoid,  of  horse,  77 
coronoid     of     mandible     of 
horse,  64 
of  radius  of  horse,  80 
frontal,  of  dog,  157 
hyoid,  of  horse,  57 
lacrimal,  of  dog,  158 
Ungual,  of  horse,  65 
mammillary,  25 

of  horse,  43 
mastoid,  of  horse,  67 
maxillary,  of  dog,  158 
muscular,  of  arytenoid  car- 
tilages of  horse,  443 
of  temporal  bone,  57 
nasal,  of  horse,  60 


Process,   odontoid,  of  axis  of 
horse,  34 
of  ox,  112 
of  urethra  masculina,  498 
palatine,  of  dog,  157 
of  maxilliP  of  horse,  58 
of  premaxilla;,  60 
paramastoid,  48,  68,  69 
post-glenoid,  of  horse,  67 
pterygoid,  of  horse,  51 
retrossal,  of  horse,  91 
spinous,  of  axis  of  horse,  34 
of  ox,  112 
of  cervical  vertebrae  of  ox, 

112 
of    lumbar    vertebra;    of 
horse,  39 
of  ox,  114 
of    thoracic    vertebra?    of 
horse,  36 
of  ox,  112 
of  vertebra^  of  horse,  42 
styloid,  of  horse,  48,  68,  69 
of  radius  of  dog,  161 
of  temporal  bone,  57 
of  ulna  of  horse,  82 
of  ox,  129 
supraorbital,  of  horse,  55,  56 

of  ox,  119 
temporal,  of  maxillary  bone 

of  horse,  58 
urethral,  of  horse,  495 
vocal,  of  horse,  443 
zygomatic,  of  frontal  bone, 
55 
of  maxillary  bone,  58 
of  temporal  bone,  56 
Processus  anconaeus  of  horse, 
82 
cornu  of  ox,  118 
uncinatus  of  dog,  780 
vaginalis  of  horse,  491 
Projection  fibers,  676 
Prominentia  laryngea,  442 
Promontory,  753 
Pronator  quadratus  muscle  of 
dog,  324 
teres  muscle  of  dog,  323 
of  horse,  268 
of  pig,  315 
Prostate  of  dog,  506 
of  horse,  493 
of  ox,  502 
of  pig,  505 
Prostatic  ducts  of  horse,  499 
of  ox,  502 
utricle  of  horse,  493 
Protractor  muscles  of  prepuce 

of  ox,  503 
Protuberance,     occipital,     ex- 
ternal, 50 
internal,  54 
Proximal  border  of  hoof,  765 
interphalangeal  joint,   188 
sesamoid  bones  of  horse,  92 
of  ox,  131 
Psoas  major  muscle  of  dog,  326 
of  horse,  275 
of  ox,  306 
of  pig,  316 
minor  muscle  of  dog,  326 
of  horse,  275 
of  ox,  306 
of  pig,  316 


Psoas  tubercle  of  horse,  93 
Pterygoid  artery,  552 
bones  of  dog,  158 
of  horse,  60 
of  ox,  121 
of  pig,  143 
canal  of  horse,  51,  61 
crest  of  horse,  51 
foramen  of  horse.  51,  68 
nerve  of  horse,  6.SI 
processes  of  horse,  51 
veins,  .587 
Pterygoideus  externus  muscle 
of  horse,  220 
intorniis  muscle  of  horse,  219 
lateralis  muscle  of  horse,  220 
muscle  of  ox,  297 
Pterygo-palatine  fossa,  60 

of  horse,  67 
Ptervgo-pharvngeus       muscle 

of  "horse,  349 
Pubis,  29 
of  dog,  167 
of  horse,  95 
of  ox,  131 
of  pig,  148 
Pubo-femoral      ligament      of 

horse,  193,  2,50 
Pudic  artery,  external,  580 
internal,  573 
of  ox,  619 
of  pig,  630 
nerve  of  horse,  710 
vein,  external,  598 
of  ox,  622 
Pulmonary  artery,  524,  535 
of  horse,  457 
circulation,  607 
nerves  of  horse,  457 
orifice    of    right    ventricle, 

531 
pleura  of  horse,  452 
plexus,  690,  712 

of  dog,  730 
valve  of  horse,  532 
veins,  524,  585 
of  horse,  457 

openings  of,  left  atrium, 
530 
Pulp  cavitv  of  teeth,  339 
of  teeth,  339 
spleen,  of  horse,  379 
Puncta  lacrimalia  of  horse,  737 
Punctum  lacrimale  in  pig,  778 

lacrimalis,  736 
Pupil,  744 
of  dog,  779 
of  pig,  778 
Pupillary  border  of  iris,  744 
Pyloric  artery,  569 

glands  of  stomach,  360 
sphincter  of  horse,  359 
Pyramid  or  pyramids,  of  Fer- 
rein,  473 
of  oblongata,  655 
renal,  of  horse,  473 
of  ox,  480 
Pyramidal    decussation,    655. 
658 
fasciculi,  660 
tracts,  658 

of  oblongata,  658 
Pyriform  lobe,  653,  668,  672 
of  dog,  728 


816 


INDEX 


Pyriforniis  muscle  of  ilog,  '.i'M 
of  horse,  284 
sinus  of  horse,  350 


Qiadhatis  femoris  muscle  of 
(log,  328 
of  horse,  283 
of  ox,  308 
of  pig,  317 
lumboruiii    muscle    of    dog, 
326 
of  horse,  276 
of  ox,  306 
of  pig,  316 
plauta;  muscle  of  dog,  329 
Quadriceps  femoris  muscle  of 
horse,  284 
of  ox,  307 
of  pig,  317 
Quarters,  764 


Radial  artery,  anterior,  fir^d 
of  dog,  635 
of  ox,  613 
posterior,  559 
of  ox,  612 

carpal  lione,  83 

nerve  of  dog,  730 
of  horse,  696,  698 
of  ox,  718 

veins,  595 
of  dog,  642 
Radialis  volaris  muscle  of  dog, 

323 
Radiate  ligament  of  horse,  177 
Radiatio  corporis  callosi,  672 
Radii  lentis,  747 
Radid-carpal  joint,  183 

sac  of  horse,  183 
Raiho-ulnar  articulation,  182 
Radius,  2S 

of  dog,  lli:> 

of  horse,  80 

development  of,  82 

of  ox,  127 

of  pig,  147 
Radix    pulmonalis    of    horse, 

45() 
Rami  communicantes,  711 

of  lower  jaw  of  liorse,  6:5 
Ramus  communicans,  693 
Raphe  palati  of  horse,  233 

lii'a'putii  of  horse,  406 

scroti  of  linrse,    ISS 
Rece|)lacuhnn  chyli,  600 
Recess,  pharvngeal,  350 
Reccssus  ,-(i.'lilcaris,  7.58 

elhplicus,  758 

infundil)uli,  667 

lieiialis  of  horse,  380 

opticyis,  667 

l)inealis,  667 

spha-ricus,  758 

te<-ti  s.  fastigium,  663 
Recto-genital  pouch,  356 
Recto-vesical  pouch,  356 
Rectum  of  dog,  432 

of  horse,  370 

of  ox,  400 

of  pig,  420 
Rectus     abdominis     internus 

muscle  of  pig,  313 


Rectus   abdominis   muscle    of 
dog,  326 
of  horse,  248 
of  ox,  301 
of  pig,  313 
capitis  anterior  major  mus- 
cle of  dog,  324 
of  horse,  227 
of  ox,  300 
minor  muscle  of  horse, 
227 
of  ox,  300 
dorsalis  major  muscle  of 
horse,  234 
minor  muscle  of  horse, 
234 
lateralis  of  horse,  228 

of  ox,  300 
muscle  of  pig,  313 
posterior  major  muscle  of 
horse,  234 
minor  muscle  of  horse, 
234 
femoris  muscle  of  dog,  327 

of  horse,  284 
lateralis  muscle  of  dog,  324 
minor  muscle  of  dog,  324 
ocuh,  738 

parvus  muscle  of  horse,  286 
thoracis  muscle  of  horse,  242 
of  pig,  313 
Recurrent  laryngeal  nerve,  689 
Red  nucleus,  665 
Regio  olfactoria  of  horse,  440 
Region,  cranial,  67,  68 

frontal,  of  skull  of  horse,  66 
guttural,  of  horse,  68 
maxillary,  of  horse,  68 
nasal,  of  horse,  66 
orbital,  of  horse,  67 
palatine,  of  horse,  68 
parietal,  of  skull  of  horse,  66 
premaxillary,  of  horse,  66 
preorbital,  of  horse,  68 
Renal  arteries,  571 
of  dog,  639 
of  horse,  475 
of  ox,  618 
of  pig,  628 
columns  of  horse,  473 
corpuscles  of  horse,  473,  474 
crest  of  horse,  474 
lymph  glands  of  ox,  625 
papilla  of  ox,  480 
plexus,  714 
pyramids  of  horse,  473 

of  ox,  4,80 
sinus  of  horse,  470 
tubules  of  horse,  474 
\'eins,  596 
of  ox,  621 
Respiratory  bronchioles,  457 
svstem,  436 
of  dog,  466 
of  horse,  436 
of  ox,  458 
of  pig,  464 
Restiform  bodies,  656 

of  ox,  715 
Rete  carpi  dorsale,  562 
mirabile,  524 
of  ox,  609 
testis  of  horse,  486 
Retia  vasculosa,  524 


Reticular  artery  of  ox,  615 
Reticulo-omasal  orifice  of  ox, 

394 
Reticulum  of  ox,  mucous  mem- 
brane of,  395 
of  stomach  of  ox,  390,  392 

of  sheep,  408 
splenic,  of  horse,  379 
Retina  of  dog,  779 

of  horse,  745 
Retractor  ani  muscle  of  dog, 
432 
of  horse,  371 
costiE  muscle  of  horse,  242 

of  pig,  313 
muscles  of  prepuce  of  ox,  503 
oculi,  738 

penis  muscle  of  horse.  496 
of  ox,  503 
Retrossal     process     of     third 

phalanx,  91 
Rhinencephalon,  670 
Rhombencephalon,  655 
Rhomboideus    capitis    muscle 
of  dog,  320 
cervicalis  muscle  of  dog,  320 

of  horse,  251 
muscle  of  dog,  320 
of  horse.  251 
of  ox,  302 
of  pig,  314 
thoracalis  muscle  of  dog,  320 
of  horse,  251 
Ribs,  25 
angle,  26 

anterior  borders,  26 
articulations  of ,  of  hor.se,  177 
asternal,  25 

of  horse,  43 
costal  cartilage,  25 

groove,  26 
devcloinnent,  26 
extremities.  25 
exIiTiKil  .surface,  26 

of  horse,  43 
floating,  25 
head,  26 

intercostal  spaces,  25 
internal  .surface,  26 
neck,  26 
of  dog,  1.53 
of  horse,  43 

articulations  of,  177 

de\-elopment,  44 
of  ox,  114 
of  pig,  13S 
posterior  Ijorders,  26 
shaft ,  25 
sternal,  25 

extremity,  26 

of  horse,  43 
true,  25 

of  horse,  43 
tubercle,  26 
vertebral  extremity,  26 
Ridge,cuticular,of  stomach,360 

trochanteric,  of  femur,  99 
Rima  glottidis  of  horse,  447 

of  pig,  465 
oris  of  dog,  423 

of  pig,  410 
Ring  or  rings,  fibrous,  of  heart 
of  horse,  534 


INDEX 


817 


RiiiK--^  <)i'  ring,  til  nous,  of  iiilcr- 
viTtebral    tiljiiwart Hani's, 
173 
inguinal,  external,  24G,  2ij0 

internal,  248,  249 
muscular,  of  ca-cum,  365 
of  trachea,  45',) 
peritoneal,  491) 
[jortal,  372 
preputial,  497 
subperitoneal,  490 
vaginal,  2  IS,  290 
of  ox,  500 
Ring-like  musfles,  211 
Root  of  hair,  763 
of  teeth,  339 
of  tongue  of  horse,  335 
Rostri  of  pig,  143 
Rostrum  suis,  464 
Rotation  of  joints,  172 
Rotator  muscle,  751 
Round  ligament  of  liladder  of 
horse,  47G 
of  hip  joint  of  horse,  193 
of  horse,  356 
of  Uver  of  horse,  375 
of  uterus  of  bitch,  523 
of  cow,  51S 
of  mare,  513 
Rubrospinal  tract,  661 
of  Monakow,  652 
Rugae  palatini  of  horse,  332 
Rumen  of  ox,  390,  .391 
blind  sacs  of,  392 
cardiac  orifice  of,  394 
cavity  of,  393 
coronarj'  grooves,  392 
dorsal  curvature  of,  391 
longitudinal  furrows,  391 
mucous     membrane     of, 

394,  397 
nmscular  coat  of,  30G 
pillars  of,  393 
ventral  curvature  of,  391 
of  sheep,  40S 

of  stomach,  serous  coat,  396 
Ruminal  artery  of  ox,  615 
Rumino-rcticular  fold  of  ox,393 
orifice  of  ox,  393 


Sac,  anal,  of  dog,  432 

blind,  of  rumen  of  ox,  392 
carpo-metacarpal,  183 
conjunctival,  736 
intercarpal,  of  horse,  183 
intertarsal,  first,  200 

second,  200 
radio-carpal,  of  horse,  183 
synovial,  of  hock  joint,  200 
tarso-metatarsal,  2(H) 
tibio-tarsal,  of  horse,  200 
Sacculations  of  ca-cum,  364 
Saccule,  759 

laryngeal,  of  horse,  447 
Saccus  caucus  of  horse,  357 
Sacral  angle  of  ilium,  94 
artery,  lateral,  575 
middle,  of  ox,  618 
of  ox,  619 
canal  of  horse,  41 
foramen,  inferior,  of  ox,  114 

of  horse,  40 

ganglia  of  ox,  720 

52 


Sacral  lyni|)h  glands,  604 
ncrN  cs  of  horse,  710 
vertebne,  24 
of  dog,  151 
of  hoi-se,  39 

articulations  of,  175 
development,  41 
ot  ox,  114 
of  pig,  138 
Sacro-ooccj  geus       acccssorius 
muscle  of  dog,  325 
inferior  muscle  of  horse,  240 
lateralis  muscle  of  horse,  239 
muscle  of  dog,  325 

of  pig,  314 
superior  muscle  of  horse,  238 
ventraUs    mediates    muscle 
of  horse,  240 
Sacro-iliac  joint  of  dog,  209 
of  horse,  190 
(if  ox,  209 
of  pig,  209 
ligament  of  horse,  190 
Sacro-pubic  diameter  of  pelvis 

of  horse,  97 
Sacro-sciatic  ligament,  190 
Sacrum  of  dog,  151 
of  horse,  39 

development,  41 
of  ox,  114 
of  pig,  138 
Sagittal     crest,     external,     of 
horse,  .54,  66 
internal,  of  horse,  54 
fold  of  pleura  of  horse,  452 
groove  of  horse,  54 
pole,  716 
sinus,  .591 
suture  of  horse,  54 
Salivary  glands  of  dog,  427 
of  horse,  346 
of  ox,  388 
of  sheep.  407  _ 
Santorini's  duct,  373 
Saphenous  artery,  580 
of  dog,  640 
of  ox,  619 
of  pig,  630 
nerve  of  dog,  731 

external,  of  horse,  70S 
of  horse,  706 
vein,  .59.8 
of  dog,  642 
of  ox,  622 
Sartorius  nuiscle  of  dog,  328 
of  horse,  281 
of  ox,  308 
of  pig,  316 
Satellite  vein,  524 
Scala  tympani,  759 

vestibuli,  759 
Scalenus    clorsalis    muscle     of 
dog,  324 
of  ox,  300 
of  pig,  312 
muscle  of  horse,  227 

of  pig,  312 
ventralis  muscle  of  dog,  324 
of  ox,  298 
of  pig,  312 
.'fcansorius  muscle  of  liorse,  278 
J^caiiha  of  auricle,  747 
Scaphoido-cunean  hgaments  of 
horse,  202 


scapula,  li 
of  dog,  162 
of  horse,  74 
of  ox,  127 
of  pig,  146 
Scapular  cartilage  of  horse,  75 
Scapulo-hiuiieral     portion     of 

|)anniculus,  255 
Scai)ulo  -  humcralis     posticus 

muscle,  2.58 
Scapulo-ulnaris  mas^cle,  2(i0 
Schlitz,  longitudinal  bundle  of, 

692 
Sciatic  foramen,  great,  94 
nerve  of  horse,  707 
notch,  lesser,  of  horse,  95 
Sclera  of  dog,  779 
of  horse,  740 
of  ox,  773 
Scrotum  of  dog,  500 
of  horse,  487 
of  ox,  .500 
of  pig,  504 
Scutiform  cartilage,  748 
Scutularis,  749 
cf  dog,  780 
of  ox,  774 
Scutulo-auricularis,  749,  751 
of  dog,  7.'-() 
of  ox,  774 
Sebaceous  glands,  762 
of  dog,  780 
of  ox,  775 
of  pig,  778 
Sebum  cutaneum,  762 
Second  carpal  bone,  85 
intertarsal  sac,  200 
metatarsal  bone.  111 
nerve  of  horse,  676 
phalanges  of  dog,  165 
of  horse,  ,89,  111 
of  ox,  1.30 
tarsal  bone  of  horse,  109 
of  ox,  135 
Sectorial  teeth  of  dog,  426 
Segments  of  spinal  cord,    648 
Sella  turcica  of  horse,  71 
Semicircular      canals,      mem- 
branous, 760 
osseous,  7.58 
Semilunar  canal  of  third  phal- 
anx, 91 
cartilages    of    femoro-tiliial 

articulation,  196 
crest  of  third  phalanx,  91 
ganglion,  678 
notch  of  ulna,  82 
Semimembranosus   nuiscle    of 
dog,  2.S0 
of  horse,  280 
of  ox,  306 
of  pig,  316 
Seminal  ve-sides  of  dog,  5t)t) 
of  horse,  491 
of  ox,  502 
of  pig,  505 
Seminiferous  tubules  of  testi- 
cles of  horse,  486 
Semispinalis    capitis     muscle, 
231 
colli  muscle,  231 
Semitendinosus  muscle  of  dog, 
327 
of  horse,  280 


818 


INDEX 


Semitendinosu.s  muscle  of  ox, 
300 
of  pig,  310 
Sense  organs  of  dog,  779 
of  horse,  734 
of  ox,  772 
of  pig,  777 
Sensitive,  frog,  770 

.sole,  709 
Septum,  interalvcolar,  58 
intermuscular,    212 
of  forearm,  262 
of  gluteal  region,  273,  274 
of  leg,  274 
of  shoulder,  2.35 
interventricular,  of  left  ven- 
tricle, 534 
incdiainnn  dorsale,  050 
mediastinum,  450 
nasi,  71,  72,  73,  437 
of  testicles  of  horse,  486 
of  thoracic  cavity,  450 
pelhicidum,  074 
penis  of  ox,  503 
scroti  of  horse,  488 
vertical,   of   metacarpus   of 
ox,  130 
Serous  layer  of   pericardium, 

525 
Serratus   anterior   hominis   of 
horse,  254 
anticus  muscle  of  dog,  325 
of  horse,  235 
of  ox,  300 
of  pig,  313 
cervicis  of  horse,  254 
magnus  muscle  of  dog,  320 
of  horse,  254 
of  ox,  3(32 
of  pig,  314 
posticus  muscle  of  dog,  325 
of  horse,  236 
of  ox,  300 
thoracis    muscle    of    horse, 

254 
ventralis   muscle   of   horse, 
254 
Sesamoid  bones,  29 

developing  in  tendon  tis- 
sue, 211 
distal,  29 
of  dog,  165 
of  horse,  92,  111 
of  ox,  131,  130 
of  pig,  14S 
proxitiial,  29 
Sesamoidean   ligaments,     ISO, 
273 
of  ox,  207 
Seventh  nerve,  084 
Sexual  differences  of  pelvis  of 

horse,  97 
Shaft  of  hair,  763 
Sheath,  car()al,  of  deep  digital 
flexor  muscle,  272 
of  superficial  digital  flexor 
muscle,  271 
ocular,  of  horse,  738 
of  arteries,  525 
svnovial.  See     Synoriiil 

'  shnilli. 
tarsal,  of  flexor  pedis  iier- 

forans  muscle,  294 
tendon,  211 


Short  ligament  of  hock  joint  of 
horse,  201 
muscles,  211 

sesamoidean  ligament,  188 
Shoulder  girdle.  27 

of  horse,  nuisdes  of,  250 

of  ox,  muscles  of,  302 

of  pig,  muscles  of,  314 
joint  of  dog,  205 

of  horse,  180 

of  ox,  205 

of  pig,  205 
of  horse,  fascia  of,  255 

muscles  of,  255,  257 
of  ox,  muscles  of,  302 
of  pig,  muscles  of,  314 
Sidebone  of  horse,  91 
•Sigmoid    cavity    of    vilna    of 

horse,  82 
flexure  of  ox,  503 
notch  of  horse,  04 
Sinus  or  sinuses,  cavernous, 592 
coronary,  585 

opening  of,  529 
cutis,  761 

ethmoid,  of  horse,  74 
frontal,  of  dog,  101 

of  horse,  55,  73 

of  ox,  125 

of  pig,  145 
lacrimal,  of  ox,  126 , 
lactiferous,  of  cow,  521 
longitudinal,  superior,  591 
maxillary,  inferior,  73 

of  dog,  101 

of  horse,  72  ! 

of  ox,  126  j 

of  pig,  140 

superior,  of  horse,  73 
occipital,  591 
of  aorta,  536 
of  dura  mater,  .541 
of  right  atrium  of  heart,  529  ' 
of  Valsalva,  536 
palatine,   of   maxilla  of  ox. 
120 

of  ox,  120 
paranales  of  dog,  432 
paranasal,  of  horse,  72 
petrosal,  inferior,  592 

superior,  591 
phrenico-costalis,  4.50 
pyriform,  of  horse,  3.50 
rectus,  5S1 
renal,  of  horse,  470 
sagittal,  .591 
sphenoidal,  of  horse,  50 

of  ox,  127 

of  pig,  140 
.spheno-palatine,  00 

of  horse,  50,  74 
straight,  .591 
tarsi  of  horse,  105 
tonsillaris  of  ox,  385 
transverse,  591 
urogenital,  of  mare,  514 
venosus  sclerie,  741 
Sixth  nerve,  083 
Skeletal  muscle,  211 
Skeleton,  19 

appendicidar,  19 
axial,  19 
flat  bones,  19 
irregular,  bones  19 


.Skeleton,  long  bones,  19 
medullary  cavity,  19 
number  of  bones,  19 
of  dog,  1.50 
of  horse,  31 
of  ox,  112 
of  pig,  130 
short  bones,  19 
.splanchnic,  19 
Skin,  appendages  of,  762 
of  dog,  780 
of  horse,  701,  704 
of  mammarv  glands  of  mare, 

510 
of  nostrils  of  horse,  436 
of  ox,  775 
of  pig,  778 

of  prepuce  of  horse,  497 
of  sheep.  777 
Skull,  bones  of,  27 
of  dog,  153 
of  horse,  47 
of  ox,  115 
of  pig,  139 
of  dog,  159,  160 
of  horse,  47,  05 
apex  of,  69 
articulations  of,  179 
cranial  region,  68 
frontal  region  of,  66 
guttuial  legion,  68 
middle  fossa  of,  71 
palatine  region,  68 
parietal  region  of,  06 
posterior  fossa  of,  71 
superior  curved  lines,  69 
sutures  of,  179 
synarthroses  of,  179 
synchondroses  of,  1.80 
of  ox,  115,  123 
of  pig,  144 
Smegma  prsputii  of  horse.  497 
Smell,  organ  of.  of  horse,  772 
Snout  of  pig,  404 
Soft  palate  of  dog,  424 
of  horse.  332 
of  ox,  384 
of  pig,  411 
Solar  plexus,  713 
Sole  matrix,  769 
of  horse,  765 
sensitive,  709 
Soleus  muscle  of  horse,  292 
of  ox,  311 
of  pig,  317 
Solitary  glands  of  rectum,  370 
of  small  intestine,  363 
of  pig,  420 
Space,  interalveolar,  58,  09 
intcrclenlal,  of  horse,  5S 
interosseous,  of  forearm,  80 
suliniaxillary,  of  horse,  02 
Spatia  anguli  iridis,  744 

zonularia,  747 
Spatium  perichorioideale,  742 
Special  anatomy.  17 
Spermatic  arterv,  571 
of  dog,  639 
of  horse,  487,  489 
of  ox,  618 
of  pig,  628 
cord,  lymph.atics  of,  489 
of  dog,  .506 
of  horse,  489 


INDEX 


819 


Spermatic  cord  of  ox,  500 
of  pig,  .504 
nerve,  external,  of  horse,  704 
plexus.  714 

of  horse,  487 
veins,  596 

of  horse,  487,  4.S0 
^^pheno-frontal  suture,  55 
Sphenoid  bone  of  dog,  150 
of  liorse,  50 
of  ox,  115 
of  pig,  141 
Sphenoitlal  notch  of  liorse,  55 
sinus  of  horse,  50 
of  ox,  127 
of  pig,  146 
."^pheno-occipital  crest,  51 
Sphenopalatine  artery,  555 
foramen,  58,  60,  67,  71 
ganglion,  711 
nerve  of  dog,  728 

of  horse,  679 
sinus,  60 

of  horse,  50,  74 
vein,  589 
Spheno-squamous  suture,  56 
Sphincter,  211,  213 

ani  externus  of  horse.  .371 

internus  of  horse,  371 
cardiac,  of  horse,  3.59 
of  bladder  of  horse,  476 
of  mammarv  gland  of  cow, 
521 
ot  mare.  516 
of  uterus  of  mare,  513 
pupillie.  744 

pylori  of  horse,  358,  359 
Spina  furca>  ungute,  767 

helicis  of  dog,  779 
Spinal  accessory  nerve,  690 
of  ox,  717 
araclmoidea,  647 
cord  of  dog.  724 
of  horse,  648 
of  ox,  715 
of  pig,  720 
tracts  of,  6.52 
ganglion,  692 
nerves  of  dog,  730 
of  horse,  692 
of  ox,  717 
of  pig,  723 
root  of  fifth  ner\-e,  658 
veins,  543 
Spinalis  et  semispinalis  muscle 
of  pig,  313 
muscle  of  horse,  233 
Spine,  hiemal,  25 

ischiatic,  of  horse,  94,  95 
of  hoof,  767 
of  scapula  of  horse,  74 
of  tibia  of  horse,  101 
ventral,  25 

of  cer\-ical  vertebra-  of  ox, 
112 
Spinous  muscle,  transverse,  of 
neck  of  horse,  231 
notch  of  horse,  51 
process  of  axis  of  horse,  34 
of  ox,  112 
of  cervical  vertebrae  of  ox, 

112 
of    lumbar    vertebrae    of 
horse,  39 


Spinous    process   of    lumbar 
vertebra;  of  ox,  114 
of    thoracic  vertebrae    of 
horse,  36 
of  ox.  112 
of  vertebnr  of  horse.  42 
Spiral  canal  of  cochlea,  759 

organ  of  corti,  760 
Splanchnic  nerve,  713 
Spleen,  accessory,  of  horse,  379 
of  dog,  435 
of  horse,  377 
of  ox,  404 
of  pig,  423 
of  .sheep,  410 
pul|)  of  horse,  379 
Splenial  fissure  of  dog,  727 

of  pig,  721 
Splenic  angle  of  horse,  372 
arterv,  569 
of  "dog,  638 
of  ox,  615 
of  pig.  628 
lymph  glands,  005 

of  pig,  632 
plexus,  714 
vein,  59G 
Splenium,  672 
Splenius  muscle  of  dog,  324 
of  horse,  229 
of  ox.  300 
of  pig.  312 
Spongy  substance  of  bone,  21 
Spur  \ein.  593 

Squamous    part    of    occipital 
bone  of  horse,  49 
tempKjral  bone  of  horse,  55 
of  ox,  120 
Stapedial  nerve,  684 
.Stapedius,  755 
Stapes,  754 
.Staphyline  artery,  555 
Sternal  articulations  of  horse, 
178 
flexure  of  horse,  366 
ligament  of  horse,  178 
lymph  glands  of  ox,  624 
ribs.  25 

of  horse,  43 
Sterno-cephalicus    muscle    of 
dog,  324 
of  horse,  225 
of  ox,  298 
of  pig,  312 
Stemo-mandibularis      muscle, 

225 
Sterno-maxillaris  muscle,  225 
Sterno-thyro-hvoideus   muscle 
of  dog,  319 
of  horse,  224,  226 
of  ox  298 
of  pig,  312 
Sterno-thjToideus    et    stemo- 

hyoideus  muscle,  226 
Sternum,  26 
of  dog,  1.53 
of  horse,  45 
of  ox,  115 
of  pig,  139 
Stifle  joint,  194 

movements  of,  198 
of  dog,  209 
of  ox,  209 
of  pig,  209 


Stomach  of  dog,  428 
of  horse,  357 
cardia  of,  3.58 
coats  of,  359 
fibers  of,  3.59 

greater  curvature  of,  357 
lesser  curvature  of.  357 
mucous  coat  of,  360 
muscular  coat  of,  3.59 
asopliMgcal  orifice  of,  3.58 
pyloric  extremity,  358 

orifice  of,  3.58 
serous  coat  of,  359 
structure  of,  359 
submucous  coat  of,  3.59 
ves.sels    and    nerves     of, 
360 
of  ox,  390 
of  pig,  417 
of  sheep,  408 
Stop  of  face  of  dog,  160 
Straight    mu.'^cles   of   head   of 
.  pig.  312 
sinus,  .591 
Stratum  corneum,  761 
germinativum,  761 

of  hoof.  768 
periosteale  of  hoof,  769 
\'itreum  of  body,  769 
Stria  lateralis,  671 
medullaris,  665 
terminalis,  665 
Stria-  acusticae,  662 

olfactorii,  671 
Striated  muscle,  211 
Stroma  iridis,  744 

of  kidney  of  liorse.  475 

of  ovary  of  marc,  510 

vitreuni,  746 

Stylo-glossus  muscle.  337 

Stvlo-hvoideus  muscle,  223 

of  ox,  297 
Stylohyoids  of  horse,  65 
Stvloid  process,  748 
of  horse,  68,  69 
of  radius  of  dog,  161 
of  temporal  bone,  57 
of  ulna  of  horse,  82 
of  ox,  129 
Stvlo-mandibularis    muscle, 
222 
of  ox,  297 
Stylo-mastoid  artery,  550 

foramen  of  horse,  57 
Stylo-maxillaris  muscle,  222 
Stylo-pharyngeus  muscle,  349 
Subarachnoid  cisterns.  646 

space,  646 
Subcallos.al  gjTUs,  671 
Suljcarpal  arcli.  562 

check  ligament  of  horse,  272 
ligament  of  horse,  183 
Subcostal  artery,  539 
of  dog,  6.33 
of  ox,  600 
Subcutaneous  bursa-,  761 
Subrutis.  761 
Sulxlural  space,  646 
Subiliac  lyiiipli  glands,  606 
Sul)liiiil>ic  ti^^sure.  069 
."^uljlingual  artery.  .548 
of  dog,  635 
crest  of  horse,  348 
ducts  of  dog,  427 


820 


■274 


547 


Siil)linsiial  ducts  of  horse,  348 
(jland  of  (log,  427 
of  horse,  347 
of  ox,  388 
of  pip,  41.") 
vein,  o9(1 
of  ox,  (l_n 
Sulihiinl)ar  Illu^ 
of  ox,  300 
of  pis.  316 
Siil>ni:ixillarv  artery 
duel  of  d(')K.  427 

of  hoise,  3  IS 
ghmd  of  dog,  427 
of  horse,  347 
of  ox,  388 
of  pig,  41.5 
Ivinpli  glands,  (iOl 
of  dog,  043 
of  i)ig,  630 
space  of  horse,  63 
Submental  artery,  .54f) 
Submucous  plexus,  714 
Subperitoneal  ring,  490 
Subpubic     groove     of     horse, 

9.5 
Subscapular  artery,  .5.56 
of  dog,  63.5 
of  ox,  612 
fossa  of  iiorse.  7.5 
nerve,  69(') 
Subscapularis  nuisclc    of    dog, 
.321 
of  horse,  2.57 
of  ox,  302 
of  pig,  314 
Subscapvdo-hyoideus      muscle 

of  horse,  220 
Subsphenoidal  canal,  51 

confluents,  .592 
Substantia  alba,  644 
corticalis  of  lens,  747 
gelatinosa.  644 
of  cord,  6.51 
grisea,  641 
of  corf!,  6.50 
Subtarsal  ligament,  200 
Subtiialaniic  nucleus,  66.5 

Icgmenlal  region,  06.5 
Subuielhi-al    diverticulum 
cow,  .519 
of  sow,  .522 
Sudoriferous  glands,  762 
Sulcus  aorta'  of  horse,  454 
basilaris  of  pons,  659 
callns.d,  i\'V) 
con.Mi.li^  nu-'nh:  76,5 


of 


ill-,  7(i' 


649 
■(i7 
)rsalis,  649 

f     ol)lf)ngata, 


cniio| 

dorsahs  lalcMal 
inlcn-nu.ilis,  7( 
internicdius 

of  ox,  (iOS 

ventralis 
655 

limitantcs,  6lj2 
niedianus  dorsalis,  649 
o.>;opliagus  of  horse,  4.54 
of  l)rain.  0.54 
rhinalis.  ()69 

of  dog,  727 

of  ox,  716 

of  pig,  721 
tympanicus,  753 


Superficial  digital  flexor  muscle 
of  dog,  323,  329 
of  horse,  269,  270 
of  leg  of  horse,  292 
of  ox,  30.5 
of  pig,  316,  317 
fascia,  212 

of  back  and  loins,  235 
of  forearm  of  horse,  262 
of  gluteal  region,  273 
of  head  of  horse,  213 
of  neck  of  horse,  224 
of  shoulder  of  horse,  255 
flexor  nuisclc  of  ox,  311 
gluteus  muscle  of  horse,  277 
muscl<'s  of  head  of  horse,  213 
pectoral  muscle  of  dog,  320 
of  horse,  2.53 
of  ox,  302 
sesamoidean  ligament,  188 
Superior  alveolar  arch,  69 
atlanto-axial  ligament,  176 
allanto-occipital  membrane 

of  horse,  176 
border  of  mandible,  64 
clieck  ligament  of  superficial 
digital  flexor  muscle,  270 
commissure  of  vulva,  .515 
conunon  vertebral  ligament 

coslo--iiiii,il  ligament,  178 
cost(i-ir.uis\(  Tsc  ligament  of 

horse,  177 
ciu'ved  lines  of  skull,  69 
dental  canal  of  horse,  59 
dilal.iior  ii.nis  muscle,  218 
in.-i>i\ii-  iMU-rl..,  216 
intcrdmiial  liuament  of  ox, 

206 
ischiatic  spine,  94,  95 
levator  palpebr;p  muscle,  219 
maxillaiy  sinus  of  horse,  73 
meatus  of  nasal  cavity,  438 
of  pig,  465 
of  nose  of  horse,  62,  72 
sacro-coccygeus  muscle,  238 
sesamoidean     ligament     of 

horse,  187,  273 
thyro-arytenoid  ligament  of 

horse,  444 
turbinal  bone  of  dog,  1.58 
of  horse,  62 
of  ox,  122 
crest  of  nasal  hones,  01 
fold  of  horse,  440 
Supinator  muscle  of  dog,  323 

of  jiig,  315 
Supra-ulloid  bursa,  174 
Supracondyloid    crest,    exter- 
nal, of  humerus,  SO 
of  femur,  97 
fo.ssa  of  fennir  of  horse,  99 
Supra-orbital  artery,  553 
canal  of  ox,  119 
foramen  of  liorse,  55,  66 

of  ox,  119 
groove  of  ox,  119 
process  of  horse,  55,  66 
of  ox,  119 
Suprarenal  glands,  477 
Suprascapular  artery,  550 

nerve,  696,  697 
Suprasiiinatus  muscle  of  dog. 
321 


Supraspinal  us  muscle  of  horse, 
256 
of  ox,  302 
of  pig,  31 1 
Suimispinovis  bursa,  175 
fossa  of  horse,  75 
ligament  of  horse,  174 
Suprasplenial    fissure    of    dog, 

Siipi:is\l\ian    fi.ssure    of    dog, 
720 
of  horse,  668 
of  ox,  716 
of  pig,  721 
Supratrochlear     foramen      of 

humerus  of  dog,  163 
Su-spensorv  ligament  of   penis 
of  horse,  494 
of  spleen  of  horse,  379 
navicular  ligaments,  1S9 
sesamoidean     ligament     of 
horse,  187,  273 
Sustentaculum  tali  of  fibular 

tarsal  bone,  106 
Sutura,  169 
harmonia,  169 
serrata,  169 
squamosa,  169 
Suture,  169 

cranial,  of  horse,  179 
frontal,  of  horse,  55 
fronto-lacrimal,  of  horse,  55 
interparietal,  of  horse,  54 
nasofrontal,  of  horse,  55,  61 

of  ox,  119 
na.so-lacrimal,  of  horse,  (H 
naso-maxillary,  of  horse,  61 
palatine,  median,  69 

transverse,  of  horse,  69 
parieto-frontal,  54,  55 
parieto-occipital,  54 
parieto-temporal,  50 
sagittal,  of  horse,  .54 
spheno-frontal,  of  horse,  55 
spheno-squamous,  56 
Sweat  glands,  762 
of  dog,  780 
of  ox,  775 
of  i)ig,  778 
Svmpalhetic  svsleni,  710 
of  dog,  733 
of  ox,  720 
of  pig,  724 
trunk,  711 
Sym])hysis,  109 

of  lower  jaw  of  horse,  ISO 
pelvis  of  hor.se,  191 
Synarthroses,  169 

of  .skull  of  horse,  179 
Svnchondroses  of  skull,  ISO 
Svnchondrosis,  109 
Synovia,  170 

Synovial     bursa     of    anterior 
digital  extensor  muscle 
of  horse,  265 
of  infra.spinatus  muscle  of 

hoi'se,  256 
of  lateral  digital  exten.'-'or 

muscle  of  horse,  26() 
of  teres  minor  muscle  of 
hor.se,  2.57 
fo,>isa,  170 

of  tibial  tarsal  bone,  105 
layer  of  articulations,  170 


INDEX 


821 


Synovial  membrane,  211 
bursal,  211 

of     anterior     digital     ox- 
tensor  muscle,  2()0 
of  rarpal  joints,  183 
of  elbow  joint,  181 
of  hip  joint  of  horse,  193 
of  lateral  digital  extensor 

muscle  of  horse,  265 
vaginal,  211 
sacs  of  hock  joint,  201) 
sheath  at  carpus  of  ox.  305 
of     anterior     digital     ex- 
tensor muscle,  2t)5 
of  coraco-brachialis  mus- 
cle of  horse,  258 
of  deep  digital  flexor  nuis- 

cle  of  horse,  272 
of  extensor  carpi  radialis 
of  horse,  263 
pedis  muscle,  288 
of   flexor   carpi    externus 
muscle  of  horse,  269 
pedis  perforans  muscle 
of  horse,  294 
of  lateral  digital  extensor 

muscle  of  horse,  266 

of  peroneus  muscle,  288 

of  superficial  digital  flexor 

muscle  of  horse,  271 

Systematic  anatomy,  17,  18 

Systemic  arteries,  52-1 


Tactile  hairs,  763 
Tienia  of  small  colon,  370 
semicircularis,  685 
thalami,  665 
Tail  of  dog,  miLscles  of,  325 
of  horse,  764 
fasciae  of,  238 
muscles  of,  238 
of  ox,  muscles  of,  300 
of  pig,  muscles  of.  314 
Tapetum  cellulosum,  779 
filirosum,  743 
of  ehorioid,  742 
of  ox,  774 
Tarsal  artery,  external,  5S1 
of  pig,  630 
perforating,  585 
bones,  29 

central,  of  horse,  107 

of  ox,  134 
fibular,  of  horse,  106 
Ugaments  of,  202 
of  ox,  134 
first,  of  horse,  109 

of  ox,  135 
fourth,  of  horse,  109 

of  ox,  134 
second,  of  horse,  109 

of  ox,  135 
third,  of  horse,  109 

of  ox,  135 
tibial,  of  horse,  105 
ligaments  of,  202 
of  ox,  134 
fascia  of  horse,  274 
glands,  736 
muscle,  736 

sheath  of  flexor  pedis  per- 
forans muscle,  294 
sinus  of  horse,  105 


Tarsal  vein  of  ox.  622 

recurrent,  598 
Tarso-metatarsal      hgaments, 

202 
sac  of  horse,  200 
Tarsus,  29 
of  dog,  168 
of  eye,  736 
of  horse,  105 

canal  of.  109 

development  of,  110 
of  ox,  134 
of  pig,  149 
Taste  buds,  772 

organs  of  horse,  772 
Teats  of  mammary  glands  of 
bitch,  523 
of  cow,  520 
of  mare,  516 
Teeth.  338 

alveolar  periosteum  of,  339 
canine,  338 

deciduous,  of  horse,  340 

of  dog,  425 

of  horse,  341 

of  ox,  386 

of  pig.  412 
carnassial,  of  dog,  426 
cement  of,  339 
cheek,  338 

deciduous,  of  horse,  346 

of  dog.  425 

of  horse,  342,  343,  344 

of  ox,  386 

of  pig.  412 

of  sheep,  405 
crown  of,  339 
deciduous,  of  horse,  346 
enamel  of.  339 
incisor,  338 

deciduous,  of  horse,  346 
of  ox,  386 

of  dog,  425 

of  horse,  341 

of  ox,  386 

of  pig,  412 

of  sheep,  405 
lower,  of  horse,  344 
mandibular,  of  horse,  344 
maxillary,  of  horse,  343 
milk,  of  horse,  346 
molar,  338 

of  horse,  342 
neck  of,  339 
nippers,  339 
of  dog,  424 
of  horse,  340 
of  ox,  386 
of  pig,  411,412 
of  sheep.  405 
permanent,  of  horse,  340 
pinchers,  339 
premolar,  338 

of  horse,  342 
pulp  cavitv  of,  339 
pulp  of,  339 
root  of,  339 
sectorial,  of  dog,  426 
structure  of,  339 
temporary,  of  horse,  346 
upper,  of  horse,  343 
vessels  and  nerves  of,  339 
wolf,  339 

of  horse,  58,  64 


Tegmentum,  664 

Tela  choroidea.  647.  6.57.  ()63 

of  Ihinl  ventricle,  666,  670 
Telencephalon,  (>('7 
Temporal      artery.      anterior 
deep,  553 
of  dog,  635 
of  ox,  612 
posterior  deep,  552 
superficial,  .5.50 
bone  of  dog,  156 
of  horse,  .55 
of  ox,  120 
of  pig,  141 
fascia  of  horse,  213 
foramen  of  horse.  51,  67 
fossa  of  horse,  67 
ner\'e.  682 
of  dog.  728 
of  horse,  681 
of  ox,  717 
of  pig,  722 
jirocess  of     maxillary     bone 

of  horse,  .58 
vein,  .587,  588 
wings  of  horse,  .51 
Temporalis  muscle  of  dog.  318 
of  hor.se,  219 
of  ox,  297 
Temporary  teeth  of  horse,  346 
Temporo-hyoid      articulation, 

180 
Temporo-mandibular  art  icula- 
tion  of  dog,  204 
of  horse.  179 
of  ox,  204 
of  pig.  204 
Tendinous     center      of     dia- 
phragm of  horse,  243 
Tendo    femorotarseus    muscle 

of  horse.  289 
Tendon,  prepubic.  2.50 

sheath,  211 
Tendons,  211 
Tenon,  capsule  of,  738 
Tensor   fascia;   antibracliii 
muscle  of  dog,  322 
of  horse,  260 
of  ox,  303 
of  pig,  315 
lata'  muscle  of  dog,  326 
of  horse,  276 
of  ox,  306 
of  pig,  316 
palati  muscle  of  horse,  333 
tympani,  755 
Tenth  nerve,  687 
Tentorial  area,  668 
Tentorium  cerebelli,  646 

osseum  of  horse,  70 
Teres  major  muscle  of  dog,  322 
of  horse,  258 
of  ox.  302 
of  pig.  314 
minor  muscle  of  dog,  321 
of  horse,  2.56 
of  ox,  302 
of  pig.  314 
tubercle  of  humerus,  77 
Terminal  arch   of   digital   ai- 
teries,  .564 
arteries,  524 
line  of  horse,  353 
nuclei,  658 


822 


INDEX 


Testicles  of  dog,  506 
opididyinis  of,  506 
tunica  vaginalis  of,  506 
of  luirse,  485 

appendix  of,  4S5 
delei-entiul  fold  of,  4'.ll 
descent  of,  490 
guliei'naouliim   testis,  4!tl 
hydatid  of  Morgagni,  45S 
l6l)nles  of.  486 
niediastiiuiin  testis,  486 
pampiniform  plexus,   489 
parenchyma  of,  486 
rete  testis,  486 
seminiferous  tubules,  481) 
septa  of.  486 
structure  of,  485 
tubules  of,  486 
tunica   afliuginea   of,  486 
vaginalis  propria  of,  485 
\asculosa  of,  486 
vas  deferens  of,  488 
vessels  and  nerves  of,  487 
of  ox,  500 

(•remaster  externus   mus- 
cle of,  500 
epididymis  of,  .-)(I0 
tunica  vajiiiKdis  of,  .'■>()ll 
vas  defcn-ns  of,  ."".01 
of  pig,  .51)4 

cremaster  externus  muscle 

of,  .504 
epididvmis  of,  .-|()4 
vas  d<.fenMis  of,  .-)()4 
Thalamocortical   hbers,   661 
Thalamus,  optic,  664 
Theca  folliculi  of  mare,  510 
Thigh,  29 

of    horse,    muscles  of,   '2iiK 

281,  284 
of  ox,  muscles  of,  306,  oOi, 

808 
of  pig,  mu.sdes  of,  316 
Third  carpal  bone  of  horse,  86 
eyelid,  736 
■  of  ox,  772 
of  pig,  777 
metatar.salboneof  horse,  1 10 
nerve  of  lior.se,  677 
phalanges  of  dog,   165 
of  horse,  90,  111 
of  ox,  130 
sesamoid  bone,  92,  111 
tar.sal  bone  of  hor.se,  109 

of  ox,  135 
trochanter  of  femur,  99 
ventricle,  666 
TlKjraeic  aorta,  536 
branches  of,  565 
artery  external,  541 
internal,  540 
of  dog,  633 
of  ox,  609 
of  pig,  ()27 
cavity,  27 
of  liorse,  4.50 
of  ox,  461 
duct  of  dog,  643 
of  horse,  600 
of  ox,  ()23 
of  pig,  630 
ganglia,  712 
of  ox,  720 
limb,  bones  of,  27 


I    Thoracic  liml)  of  dog,  ar(icul.-i- 
!  tions  of,  205 

bones  of,  162 
nuiseles  of,  319 
of  horse,  articulations  of, 
180 
bones  of,  74 
muscles  of,  2.50 
of  ox,  articulations  of,  205 
bones  of,  127 
muscles  of,  302 
of    pig,    articulations    of, 
205 
bones  of.  146 
muscles  of,  314 
lymph  glands  of  pig,  631 
ner\es,  anterior,  696 
of  horse,  697,  702 
portion  of  panniculus,  255 
of    sympathetic     system, 
712 
^ein,  586,  593 
vertebriE,  24 
of  dog,  1.50 
of  horse,  35,  36,  37 
of  ox,  112 
of  pig,  137 
Thoiacico-dor.sal  artery,  .5.56 
Thoraco-dorsal  nerve,  697 

\ein,  593 
Thorax,    articulations    of,    of 
dog,  204 
of  horse,  177 
of  ox.  204 
of  pig,  204 
bones  of.  27 
of  dog.  1.53 
of  hor.se,  47 
of  ox,  115 
of  pig,  139 
nuiscies  of,  of  <'og,  .325 
of  horse,  240 
of  ox,  300 
of  jiig,    313 
Thvnuis  gland  of  dog,  468 
of  horse,  458 
of  ox,  464 
of  pig,  466 
Thyro-arytenoid  ligament,  444 
Thyro-arytenoideus  muscle  of 

horse,  446 
Thyro-epiglottie  ligament,  444 
Thyro-hyoid  joints,  444 
Thyro-hyoideus  muscle,  445 
Thyrohyoiils  of  horse,  6.5 
Thyroid  artery,  accessory,  543 
■  of  ox,  610 
of  pig,  627 
cartilage  of  dog,  46)7 
of  hor.se,  442 
of  ox,  4.59 
of  pig,  465 
cornua  of  lior.se,  65 
glaiul  of  dog,  4(i8 
accessory,  4(i8 
of  liorse,  457 

accessory,  4.58 
of  ox,  464 

accessory,  464 
of  pig,  466 
vein,  .590 
Thyro-laryngeal  artery,  543 
Thvi-o-pharvngeus  muscle,  350 
Tibia,  29 


Tibia  of  dog.  167 

of  hor.se,  100,  102,  103 
of  ox,  134 
of  pig,  149 
Tibial  arterv,  anterior,  .583 
of  dog,  641 
of  ox,  620 
of  pig,  630 
posterior,  .581 
recurrent,  .581 
lioncs,  29 
crest  of  horse,  100 
nerve,  anterior,  of  horse,  70S 
of  dog,  732 
of  horse,  708 
of  ox,  720 
tansal  bone  of  horse,  105 
ligaments  of,  202 
syno\'ial  fossa  of,  105 
trochlea  of,  105 
of  ox,  134 
vein,  anterior,  .599 
of  dog,  042 
posterior.  599 
recurrent,  598 
Tibialis  ant  erior  nmscle  of  dog, 
32S 
of  horse,  290 
of  ox,  310 
of  pig,  317 
posterior  muscle  of  dog,  329 
Tibio-fibular  articulation,  199 
joints  of  dog,  210 
of  ox,  209 
of  pig,  210 
Tibio-tarsal  articulation.  199 

sac  of  horse,  200 
Toe  of  horse,  764 
Tongue  of  dog,  424 
of  horse,  335 
of  ox,  3S5 
of  pig,  411 
of  shecji,  405 
Tonsil,  faucial,  of  horse,  .'!33 
of  pig,  411 
of  sheep.  407 
Topograi)hic  anatomy.   17,   IS 
Torus  carpalis,  780 
metacarpalis,  780 
tubarius,  778 
TrabecuUe     earneip    of     right 
ventricle,  .532 
of  corpus  eavernosum  jjcnis, 

495 
of  prostate,  493 
of  thyroid  gland,  458 
splenic,  of  horse,  379 
Trachea  of  dog,  468 
of  horse,  448 
of  ox,  460 
of  i)ig,  466 
Tracheal  duets,  fi03 

of  dog,  1)43 
Tracliclo-mastoideus   nuuscle 
of  dog,  325 
of  horse,  229 
of  pig,  312 
Tract  of  spiral  cord,  6.52 
olfactory.  (;71 
optic.  666 

of  ox,  716 
pyramidal,  ()58 
Tract  us    centralis   of   thymus 
gland,  458 


823 


Tractus  olfactorins,  071 

Tnmcus  bicaroticus,  541 

rina  of  o\.  r2S 

opticus,  ()()(') 

Tuber  calcis   of  fibular  tarsal 

.of  pig,  147 

Tragicus  muscle.  751 

bone  of  horse,  106 

Ulnar  artery,  .5.59 

Tragus,  7-lS 

cinereimi,  653,  665 

of  dog,  637 

of  dog,  7.S!) 

of  dog,  72() 

of  ox,  613 

TransvcTsalis  cost  arum  muscle 

ischii  of  horse,  95 

superior  collateral,  of  ox. 

of  dog,  :ii5 

scapula'  of  horse,  77 

612 

of  horse,  2'M> 

Tubercle,  cuneate,  of  pig,  720 

carpal  bone  of  lujise,  84 

of  ox,  301) 

internal,  of  humerus,  78 

nerve  of  dog,  730 

of  pig,  313 

lacrimal,  of  horse,  61 

of  horse,  (j96,  698 

fascia  of  horse,  21i) 

of  Lower,  530 

of  ox,  718 

Transverse  arytenoid  ligament 

of  scapida  of  horse,  75 

of  pig,  723 

of  larynx;  444 

psoas,  of  horse,  93 

vein,  .595 

diameter  of  pelvis,  97 

teres,   of  humerus,  77 

of  dog,  642 

fissure,  039 

Tubcrculum  cinereum,  656 

I'lnaris  lateralis  muscle  of  dog. 

of  ox,  716 

facialc,  6.55 

323 

fossa  of  Ijrain,  667 

inter\('nosimi  of  horse,  530 

medialis  muscle  of  dog,  323 

liyoideus   muscle,  224 

olfactorium  of  pig,  721 

Umbilical  artery,  574,  606 

himina,  ethmoid  bone  of  ilo>;, 

Tuberosity,  alveolar,  69 

of  dog,  641" 

1.57 

bicipital,  of  raduis.  81 

of  ox,  619 

ligament  of  carpus,  263 

of  scapula.  77 

fissure  of  horse,  374 

of  hip  joint  of  horse,  192 

deltoid,  of  horse,  78 

ligament  of  bladder,  47() 

of     radio-ulnar     articula- 

external, of  humcius,  78 

vein,  607 

tion  of  horse,  182 

of  radius  of  horse,  81 

Undershot  dog.  425 

palatine  suture  of  horse,  69 

facial,  of  ox,  120 

Ungual  phalanx  of  hor.si'.  90 

sinuses,  591 

internal,  of  humerus,  79 

Unipcnnale  muscle.  212 

spinous  muscle  of  neck,  231 

of  radius  nf  horse.  Si 

Unstripcd  muscle,  211 

Transversus  abdominis  muscle 

in.-i\ill,-u-y,  nf  horse.  5S 

Ureters,  469 

of  dog,  326 

metacarpal,  of  hor.sc,  88 

of  bladder,  fundus  of,  47() 

of  horse,  248 

of  atlas  of  ox,  112 

of  dog,  484 

of  ox,  302 

of  1  ibia  of  horse,  102 

of  heart,  pelvic  part,  475 

of  pig,  313 

Tubules  of  testicles,  486 

of  horse,  475 

costarum   muscle,  242 

renal,  of  horse,  474 

abdominal  part,  475 

thoracis  muscle  of  horse.  2 12 

seminiferous,  of  testicles,  486 

of  ox,  480 

of  pig,  313 

uriniferous,  of  horse,  474 

of  pig,  483 

Trapezius  cervicalis  muscle, 250 

Tunic,  abdominal,  245 

Urethra,  409 

muscle  of  dog,  319 

of  pig,  313 

masculina  of  dog,  507 

of  horse,  250 

fibrous,  of  ape,  740 

of  horse,  497,  498,  499 

of  ox,  302 

Tunica  allmginea,  4.86,  495 

of  ox,  504 

of  pig,  314 

fibrosa  of  kiilney,  473 

of  pig,  506 

thoracalis  muscle,  251 

mucosa  laryngis,  448 

of  cow,  519 

Triangularis  sterni  muscle,  242 

propria  of  skin,  762 

of  mare,  515 

Triceps  brachii,  260,  261 

vaginalis  communis,  490 

of  sow,  522 

extensor  cubiti  of  hor.se,  230 

of  dog,  506 

Urethral  crest  of  horse,  499 

muscle  of  do?,  322 

of  horse,  4.89 

glands  of  horse,  499 

of  ox,  303 

of  ox,  500 

groove  of  horse,  495 

of  pig,  315 

propria  of  horse,  485,  490 

muscle  of  dog,  507 

surse  muscle  of  horse,  292 

vascuiosa  of  testicles,  486 

of  horse,  499 

Trifacial  nerve  of  horse,  677 

Turbinal  bones  of  dog,  1.58 

of  mare,  516 

Trigeminal  nerve  of  horse,  677 

of  horse,  62,  438 

of  ox,  .504 

Tiigonum  lemnisci,  634 

of  ox,  122 

of  pig,  506 

olfactorium,  653,  637,  671 

of  pig,  143,  465 

orifice,  external,  of  cow,  519 

^■esicae  of  horse,  476 

crest,  inferior,  of  horse,  58 

of  male  horse,  499 

Trochanter,  external,  of  femur 

superior,  of  nasal  bones  of 

of  mare,  515 

of  horse,  99 

horse,  61 

of  ox,  503 

great,  of  femur  of  horse,  99 

fold,  inferior,  of  horse,  440 

internal,  of  horse,  477,  499 

internal,  of  femur,  97 

superior,  of  horse,  440 

of  horse,  477 

Trochanteric  fossa  of  femur  of 

Twelfth  nerve,  692 

of  pig,  .505 

horse,  99 

Tympanic  artery,  552 

process  of  horse,  495 

ridge  of  femur  of  horse,  99 

cavity  of  dog,  780 

sinus  of  horse,  495 

Trochlea  of  femiu-  of  horse,  99 

of  horse,  7.52 

Urinary   bladder.      See   Bliid- 

of    tibial     tarsal     bone     of 

of  ox,  775 

der. 

horse.  105 

of  pig,  778 

organs,  469 

Trochlear  foramen  of  horse.  51. 

memfjrane,  753 

of  dog,  483 

67 

n(>rve,  686 

of  horse,  469 

nerve  of  horse.  677 

opening  of  Eustachian  tube, 

of  ox,  478 

origin  of,  664 

755 

of  pig,  481 

Trochoid,  172 

plexus,  687 

Uriniferous   tubules,  474 

True  joints,  170 

Urogenital  fold  of  horse,  355 

ribs,  25 

sinus  of  mare,  514 

of  horse,  43 

Udder  of  cow,  519 

system,  469 

vertebrie,  24 

Ulna,  28 

Uterine  artery,  571 

vocal  cords  of  dog,  468 

of  dog,  163 

middle,  578 

of  horse,  448 

of  horse,  82 

of  dog,  641 

824 


INDEX 


Uterine  artery  of  ox,  019 

posterior,  57-1 
cotyledons  of  cow,  518 
glands  of  cow,  518 

of  niaro,  513 
tubes  of  bitch,  522 

of  cow,  517 

of  inaro,  511 

of  sow,  522 
Utero-ovarian  artcrv,  571 

of  dos,  639 

of  ox,  618 
plexus,  714 
veins,  596 
Uterus  inasculinus  of  dog  oO:! 

of  horse,  493 

of  ox,  503 

of  pig,  505 
of  l)itch,  522 
of  cow,  517,  5)8 
of  horse,  Ijroad  ligaments,356 
of  mare,  511,  512,  513 
of  sow,  522 
Utricle,  759 

prostatic,  of  horse,  493 
Uvula  of  pig,  411 

V.\(ii.\A  of  l)itch,  523 
of  cow,  518 
of  mare,  514 
of  sow,  522 
tendinis,  211 
\aginal  ligaments,  212 
ring  of  horse,  248,  490 

of  ox,  500 
svnovial  membrane,  211 
Vagus,  687 
of  dog,  729 
of  ox,  717 
of  pig,  722 
Vallate  papillc  of  tongue,  33(> 
Vallecula  of  Sylvius,  W>7 
Valve,  bicusi>i<l,  of  liorse,  533 
ileo-ca^cal,  of  dog,  431 

of  horse,  362,  364 
mitral,  of  horse,  533 
of  vein,  525 
of  Vieussens,  663 
imlmonary,  of  horse,  532 
\'alvula  foraminis  ovalis,  607 
Valvvdar  fold  of  ciecum,  3()5 
\'as  dc-ferens  of  horse,  488 
of  ox,  501 
of  pig,  504 

of  spermatic  cord,  4S9 
vasorum  of  veins,  525 
V;iscular  system,  524 
l)lood-,  524 
of  horee,  525 
tunic,  742 
Vastus  externus  muscle,  285 
intermedins  muscle,  286 

of  ox,  307 
intern  us  muscle  of  horse,  280 
\'eins  or  vein,  524,  585 
abdominal,  598 
alveolar,  5S9 

inferior,  587 
auricular,  588 
azygos,  586 
brachial.  593 
of  dog,  042 
brachiocephalic,  of  dog.  04  1 


Veins,  bronchial,  587 
buccinator,  590 

of  pig,  630 
cardiac,  586 
cephalic,  591,  593 

of  dog,  642 

of  ox,  622 
cerebellar,  592 
cerebral,  588,  592 

of  ox,  621 
cervical,  deep,  586 

inferior.  .591 
circuiiilicx,  cxlcrnal,  .59  ■ 
condvloid,  .")SS 
coronarv.  535,  5s0 
dental.  .587 
digilal.  .595 

of  dog,  642,  643 

of  ox,  621,  623 
diploic,  .593 
dorsal,  586 
emissary,  .591 
esophageal,  587 
facial,  588 

of  pig,  630 
femoral,  598 

of  dog,  642 
femoropopUteal,  598 
frontal,  of  ox,  621 
giustric,  597 
gastro-duodcnal,  597 
hepatic,  .596 

of  horse,  377 
liypogaslric,  .597 
ilitic.  common.  597 

ilin-l.-iiioial.  .V.IS 
ili(.-liMiil.ar.  .V.I7 
infni-orbital.  5S9 
intercostal,  5S7 
interosseous,  595 
intima  of,  525 
jngular.  .587 

of  dog,  642 

of  ox,  621 

of  pig,  630 
labial,  589 

of  ox.  021 
lingual.  .590 

dorsal.  .587 
luinliar,  .590,  .597 
iiiainniarv.  of  ox.  622 
inaxilliuy.  .58S 

inlernal.  .587 

of  dog.  t)42 
maxillo-muscular,  58S 
mrniiisical,  .592 

lur^ru\rnr.   .V.I7 
ni,'l;ir;,l|,;,l.  .V.I5 

of  .log.  t,42 

of  ox,  621 
metatarsal,  599 

of  dog,  643 

of  ox,  622 
middle  coat  of,  .525 
milk,  301 

of  cow,  .521 
nasal,  of  ox,  621 

of  pig,  630 
nerves  of,  525 
obturator,  598 
occipital,  588 
of  adrenal  bodies,  478 
of  articulations,  171 


Veins  of  bladder  of  horse.  477 
of  brain,  592 
of  dog,  641 

of  Fallopian  tubes,  511 
of  Galen,  .592 
of  heart,  .585 
of  horse,  585 
of  internal  ear,  761 
of  kidney  of  horse,  475 
of  mammarv  glands  of  cow, 
.521 
of  mare,  510 
of  ovaries  of  mare,  510 
of  ox,  621 

of  penis  of  horse,  490 
of  pig,  ()30 

of  prepuce  of  horse,  497 
of  uterus  of  mare,  513 
of  vagina  of  mare,  514 
ophthalmic,  590 
orbital,  of  ox,  621 
palatine,  .589 
pancreatic,  597 
perineal,  of  ox.  622 
plirenie.  .590 
popliteal,  .599 

of  dog,  042 
portal,  596 

of  horse,  377 

of  ox,  623 
pterygoid,  587 
pudic,  external,  598 

of  ox,  622 
pidmonary,  524,  585 

of  horse,  457 

openings  of,  left   .atrium, 
.530 
radial,  595 

of  dog,  012 
renal,  .590 

of  ox,  022 
saphenous,  598 

of  dog,  (i42 

of  ox,  622 
satellite,  524 
spermatic,  596 

of  horse,  487,  489 
sphenopalatine,  589 
spinal,  59:) 
splenic.  .590 
spur,  593 
struct\n-e  of,  .525 
sublingual,  590 

of  ox,  021 
tarsal,  of  ox,  022 

recurrent,  598 
temporal,  5S7 

SU])rlliri:il,   5S8 
thon. r.r.  ."I'.i:;,  ."iSO 
thyroid.  .">'..'!) 
tibial,  anterior,  .599 

of  dog,  642 

posterior,  599 

reciu'rent,  .598 
ulnar,  .595 

of  dog,  642 
umbilical,  007 
utero-ovarian,  596 
valves  of,  .525 
vas  vasorum  of.  525 
vertebral,  580 
Velum   interpositum   of   (lord 

ventricle.  060 
medullarv.  000,  603 


825 


Vena  azygos.  5S6 
of  (log,  642 

of  horse,  oponiiig  of,   529 
cava.  .524 
anterior.  .580 

opening  of.  529 
of  (log.  641.  642 
of  ox.  622 
posterior,  595 
opening  of,  529 
coraitans,  .524 
hemiazygos.  5.S7 
of  (log,  642 
of  ox,  621 
jugularis  of  ox,  621 
reflexa,  589 
of  ox,  621 
Vena^  vorticosa",  745 
\'enous  arch,  595 

plexus  of  lu'ethra  of  mare, 
516 
Venter   of   scapula   of    horse, 

75 
^"entral  columns  of  spinal  cord, 
651 
muscles  of  neck  of  horse,  224 
nerve  of  dog.  729 
sacral  foramina  of  horse,  40 
sacro-iliac  ligament.  190 
spine.  25 

of  cervical  vertebne  of  ox. 
112 
Ventricle,  fourth,  of  horse,  662 
lateral.  674 

of  larynx  of  horse.  447 
of  ox.  4.59 
middle,  of  larynx.  447 
of  heart  of  horse,  k^ft,  533 

right,  .530 
third,  666 
\'entricular  ligament  of  larynx 

of  hor.se.  444 
Ventricularis  et  vocahs  muscle 

of  horse,  446 
Ventriculus    bulbi     olfactorii, 
671 
larvngis  medianus  of  horse, 

447 
lateralis,  674 

larjTigis  of  horse.  447 
quartus.  662 
tertius,  666 
Vermis,  660 

of  dog,  725 
^'ertebra;,  24 

accessory  processes,  25 
anticlinal,  of  horse,  42 
arch.  24 

articular  processes,  25 
body.  24 
caudal.  24.  25 
centrimi.  24 
cervical,  24 
of  dog.  1.50 
of  horse,  32 
of  ox.  112 
of  pig,  1.36 
coccygeal,  24 
of  dog,  1.52 
of  horse.  41 
of  ox,  114 
of  pig.  138 
development.  25 
diaphragmatic,  of  horse,  42 


\'erlcl)ne.  false.  24 
tixed,  24 
foramen,  25 
ha-mal  spine.  25 
ligaments  of.  of  dog,  204 

of  horse,  172 

of  ox.  203 

of  pig,  204 
lumbar.  24 

of  dog.  151 

of  horse,  38 

of  0.x,  112 

of  pig,  138 
mammillary  processes,  25 
movable,  24 
notches,  25 

of  horse,  intercentral  articu- 
lations of,  173 

interneural     articulations 
of,  173 
ossification  of,  25 
primary  centers  of  ossifica- 
tion, 25 
sacral,  24 

of  dog,  151 

of  horse,  39 

articulations  of,  175 
development,  41 

of  ox,  114 

of  pig,  138 
secondary  centers  of  ossifi- 
cation, 25 
spinous  process,  25 
thoracic,  24 

of  dog,  150 

of  horse,  35,  36,  37 

of  ox,  112 

of  pig.  137 
transverse  processes,  25 
true,  24 

ventral  spine,  25 
^'ertebral  artery,  540 

of  dog.  633 

of  ox.  609 

of  pig.  627 
canal,  25 

of  horse.  42 
cohmm.  24 

of  d(jg.  l.'iO 

of  horse.  31 

of  ox,  112 

of  pig,  136 
foramen,  25 
formula,  24 
groove  of  horse,  42 
ligaments  of  dog,  204 

of  horse,  172 

of  ox,  203 

of  pig,  204 
notches,  25 
vein,  586 
Vertex  comesp,  741 
Vertical  septum  of  metacarpus 

of  ox,  130 
Vesical  artery,  574 
Vesicles,  seminal,  of  dog,  506 

of  horse,  491 

of  ox,  502 

of  pig,  505 
Vesico-genital  pouch,  3.56 
Vesico-prostatic  artery.  574 
Vestibular  ganglion.  686 

ner\-e.  686.  761 
Vestibule  of  ear,  758 


Vestibule  of  larvnx  of  horse, 
447 
of  omental  cavity,  380 
Veterinary  anatomy,  17 
Vibriss;!',  763 
Vidian  canal  of  horse.  51.  61 

nerve,  6.81 
Villi  of  articulations,  170 
Visceral  layer  of  pericardium, 
525 
pleura  of  horse.  4.52 
Vitreous  body.  74() 

of  ox,  774 
^'ocal  cords,  false,  of  dog,  467 
of  horse,  447 
of  ox,  459 
of  pig.  465 
true,  of  dog,  468 
of  horse.  44S 
ligament  of  horse,  444 
process  of  horse.  443 
^"ocalis  muscle  of  horse,  446 
Volar  arch,  .562 
artery,  deep.  .562 

of  .second  phalanx.  564 
common  digital  arter\'  of  ox, 

614 
digital  nerves  of  (log.  731 
flexion  of  joints.  171 
foramen  of  third  phalanx.  91 
ligament  of  carpal  joints,  183 

of  pastern  joint.  188 
muscle  of  pig,  315 
nerve  of  horse.  701 

of  ox,  718.  719 
plexus,  .595 
sesamoids  of  dog,  165 
\"omer  of  dog,  1-58 
of  horse.  ()3.  431 
of  ox,  122 
of  pig,  143 
Vomero-nasal  organ.  772 

of  horse.  440 
Vortex  cordis  of  horse.  534 
V-shaped  ligament.  188 
\'ulva  of  bitch.  523 
of  cow,  519 
of  mare,  514 
of  sow,  522 
A"ulvar  cleft  of  mare,  514 


Wall  of  horse's  hoof,  764 
White  commissure  of  cord,  650 
line  of  hoof,  765 
matter  of  nervous  system, 

644 
Wilson's  muscle  of  dog,  507 

of  ox,  504 
Win.slow's   foramen.  379 

of  ox,  396 
Wirsung's  duct  of  hor.se,  372 
Wolf  tooth.  .3.39 

of  horse.  oS.  64 
Wool,  777 


Xiphoid  cartilage.  26 
of  horse.  46 


Y-.sH.\rKD   ligament,  188 


826 


Zone,     epigastric,    of     horse, 
353 

hypogastrii-,         of        liorse, 

353 
intermeilialc.      of      kidney, 

473 
inesogastric,  of  horse,  353 
Zonula  ciliaris,  743,  747 
of  Zinn,  747 


Zygoniatii-  arcli   of  liorse,  .56, 

07 
hones  of  horse,  62 
erest  of  horse,  58,  62 
gland  of  dog,  427 
nerv'e  of  dog,  72S 

of  liorse,  67(1 
proee.ss  of  frontal  hone,  55 

of  maxillary  hone,  58 


Zygomatic  process  of  t(m[  oral 

hone,  56 
Zygomatico-auricularis.  74'.» 

of  ox,  747 
Zvgomaticus    muscle    of   dog, 
318 
of  horse,  215 
of  ox,  295 
of  pig,  311 


/ 


